pgconn.go

package pgconn

import (
	"container/list"
	"context"
	"crypto/md5"
	"crypto/tls"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"maps"
	"math"
	"net"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/jackc/pgx/v5/internal/iobufpool"
	"github.com/jackc/pgx/v5/internal/pgio"
	"github.com/jackc/pgx/v5/pgconn/ctxwatch"
	"github.com/jackc/pgx/v5/pgconn/internal/bgreader"
	"github.com/jackc/pgx/v5/pgproto3"
	"github.com/jackc/pgx/v5/pgtype"
)

const (
	connStatusUninitialized = iota
	connStatusConnecting
	connStatusClosed
	connStatusIdle
	connStatusBusy
)

// Notice represents a notice response message reported by the PostgreSQL server. Be aware that this is distinct from
// LISTEN/NOTIFY notification.
type Notice PgError

// Notification is a message received from the PostgreSQL LISTEN/NOTIFY system
type Notification struct {
	PID     uint32 // backend pid that sent the notification
	Channel string // channel from which notification was received
	Payload string
}

// DialFunc is a function that can be used to connect to a PostgreSQL server.
type DialFunc func(ctx context.Context, network, addr string) (net.Conn, error)

// LookupFunc is a function that can be used to lookup IPs addrs from host. Optionally an ip:port combination can be
// returned in order to override the connection string's port.
type LookupFunc func(ctx context.Context, host string) (addrs []string, err error)

// BuildFrontendFunc is a function that can be used to create Frontend implementation for connection.
type BuildFrontendFunc func(r io.Reader, w io.Writer) *pgproto3.Frontend

// PgErrorHandler is a function that handles errors returned from Postgres. This function must return true to keep
// the connection open. Returning false will cause the connection to be closed immediately. You should return
// false on any FATAL-severity errors. This will not receive network errors. The *PgConn is provided so the handler is
// aware of the origin of the error, but it must not invoke any query method.
type PgErrorHandler func(*PgConn, *PgError) bool

// NoticeHandler is a function that can handle notices received from the PostgreSQL server. Notices can be received at
// any time, usually during handling of a query response. The *PgConn is provided so the handler is aware of the origin
// of the notice, but it must not invoke any query method. Be aware that this is distinct from LISTEN/NOTIFY
// notification.
type NoticeHandler func(*PgConn, *Notice)

// NotificationHandler is a function that can handle notifications received from the PostgreSQL server. Notifications
// can be received at any time, usually during handling of a query response. The *PgConn is provided so the handler is
// aware of the origin of the notice, but it must not invoke any query method. Be aware that this is distinct from a
// notice event.
type NotificationHandler func(*PgConn, *Notification)

// PgConn is a low-level PostgreSQL connection handle. It is not safe for concurrent usage.
type PgConn struct {
	conn              net.Conn
	tlsConfig         *tls.Config       // tls.Config that conn was negotiated with; nil if conn is not TLS
	pid               uint32            // backend pid
	secretKey         []byte            // key to use to send a cancel query message to the server
	parameterStatuses map[string]string // parameters that have been reported by the server
	txStatus          byte
	frontend          *pgproto3.Frontend
	bgReader          *bgreader.BGReader
	slowWriteTimer    *time.Timer
	bgReaderStarted   chan struct{}

	customData map[string]any

	config *Config

	status byte // One of connStatus* constants

	bufferingReceive    bool
	bufferingReceiveMux sync.Mutex
	bufferingReceiveMsg pgproto3.BackendMessage
	bufferingReceiveErr error

	peekedMsg pgproto3.BackendMessage

	// Reusable / preallocated resources
	resultReader      ResultReader
	multiResultReader MultiResultReader
	pipeline          Pipeline
	contextWatcher    *ctxwatch.ContextWatcher
	fieldDescriptions [16]FieldDescription

	cleanupDone chan struct{}
}

// Connect establishes a connection to a PostgreSQL server using the environment and connString (in URL or keyword/value
// format) to provide configuration. See documentation for [ParseConfig] for details. ctx can be used to cancel a
// connect attempt.
func Connect(ctx context.Context, connString string) (*PgConn, error) {
	config, err := ParseConfig(connString)
	if err != nil {
		return nil, err
	}

	return ConnectConfig(ctx, config)
}

// Connect establishes a connection to a PostgreSQL server using the environment and connString (in URL or keyword/value
// format) and ParseConfigOptions to provide additional configuration. See documentation for [ParseConfig] for details.
// ctx can be used to cancel a connect attempt.
func ConnectWithOptions(ctx context.Context, connString string, parseConfigOptions ParseConfigOptions) (*PgConn, error) {
	config, err := ParseConfigWithOptions(connString, parseConfigOptions)
	if err != nil {
		return nil, err
	}

	return ConnectConfig(ctx, config)
}

// Connect establishes a connection to a PostgreSQL server using config. config must have been constructed with
// [ParseConfig]. ctx can be used to cancel a connect attempt.
//
// If config.Fallbacks are present they will sequentially be tried in case of error establishing network connection. An
// authentication error will terminate the chain of attempts (like libpq:
// https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS) and be returned as the error.
func ConnectConfig(ctx context.Context, config *Config) (*PgConn, error) {
	// Default values are set in ParseConfig. Enforce initial creation by ParseConfig rather than setting defaults from
	// zero values.
	if !config.createdByParseConfig {
		panic("config must be created by ParseConfig")
	}

	var allErrors []error

	connectConfigs, errs := buildConnectOneConfigs(ctx, config)
	if len(errs) > 0 {
		allErrors = append(allErrors, errs...)
	}

	if len(connectConfigs) == 0 {
		return nil, &ConnectError{Config: config, err: fmt.Errorf("hostname resolving error: %w", errors.Join(allErrors...))}
	}

	pgConn, errs := connectPreferred(ctx, config, connectConfigs)
	if len(errs) > 0 {
		allErrors = append(allErrors, errs...)
		return nil, &ConnectError{Config: config, err: errors.Join(allErrors...)}
	}

	if config.AfterConnect != nil {
		err := config.AfterConnect(ctx, pgConn)
		if err != nil {
			pgConn.conn.Close()
			return nil, &ConnectError{Config: config, err: fmt.Errorf("AfterConnect error: %w", err)}
		}
	}

	return pgConn, nil
}

// buildConnectOneConfigs resolves hostnames and builds a list of connectOneConfigs to try connecting to. It returns a
// slice of successfully resolved connectOneConfigs and a slice of errors. It is possible for both slices to contain
// values if some hosts were successfully resolved and others were not.
func buildConnectOneConfigs(ctx context.Context, config *Config) ([]*connectOneConfig, []error) {
	// Simplify usage by treating primary config and fallbacks the same.
	fallbackConfigs := []*FallbackConfig{
		{
			Host:      config.Host,
			Port:      config.Port,
			TLSConfig: config.TLSConfig,
		},
	}
	fallbackConfigs = append(fallbackConfigs, config.Fallbacks...)

	var configs []*connectOneConfig

	var allErrors []error

	for _, fb := range fallbackConfigs {
		// skip resolve for unix sockets
		if isAbsolutePath(fb.Host) {
			network, address := NetworkAddress(fb.Host, fb.Port)
			configs = append(configs, &connectOneConfig{
				network:          network,
				address:          address,
				originalHostname: fb.Host,
				tlsConfig:        fb.TLSConfig,
			})

			continue
		}

		ips, err := config.LookupFunc(ctx, fb.Host)
		if err != nil {
			allErrors = append(allErrors, err)
			continue
		}

		for _, ip := range ips {
			splitIP, splitPort, err := net.SplitHostPort(ip)
			if err == nil {
				port, err := strconv.ParseUint(splitPort, 10, 16)
				if err != nil {
					return nil, []error{fmt.Errorf("error parsing port (%s) from lookup: %w", splitPort, err)}
				}
				network, address := NetworkAddress(splitIP, uint16(port))
				configs = append(configs, &connectOneConfig{
					network:          network,
					address:          address,
					originalHostname: fb.Host,
					tlsConfig:        fb.TLSConfig,
				})
			} else {
				network, address := NetworkAddress(ip, fb.Port)
				configs = append(configs, &connectOneConfig{
					network:          network,
					address:          address,
					originalHostname: fb.Host,
					tlsConfig:        fb.TLSConfig,
				})
			}
		}
	}

	return configs, allErrors
}

// connectPreferred attempts to connect to the preferred host from connectOneConfigs. The connections are attempted in
// order. If a connection is successful it is returned. If no connection is successful then all errors are returned. If
// a connection attempt returns a [NotPreferredError], then that host will be used if no other hosts are successful.
func connectPreferred(ctx context.Context, config *Config, connectOneConfigs []*connectOneConfig) (*PgConn, []error) {
	octx := ctx
	var allErrors []error

	var fallbackConnectOneConfig *connectOneConfig
	for i, c := range connectOneConfigs {
		// ConnectTimeout restricts the whole connection process.
		if config.ConnectTimeout != 0 {
			// create new context first time or when previous host was different
			if i == 0 || (connectOneConfigs[i].address != connectOneConfigs[i-1].address) {
				var cancel context.CancelFunc
				ctx, cancel = context.WithTimeout(octx, config.ConnectTimeout)
				defer cancel()
			}
		} else {
			ctx = octx
		}

		pgConn, err := connectOne(ctx, config, c, false)
		if pgConn != nil {
			return pgConn, nil
		}

		allErrors = append(allErrors, err)

		var pgErr *PgError
		if errors.As(err, &pgErr) {
			// pgx will try next host even if libpq does not in certain cases (see #2246)
			// consider change for the next major version

			const ERRCODE_INVALID_PASSWORD = "28P01"
			const ERRCODE_INVALID_CATALOG_NAME = "3D000"   // db does not exist
			const ERRCODE_INSUFFICIENT_PRIVILEGE = "42501" // missing connect privilege

			// auth failed due to invalid password, db does not exist or user has no permission
			if pgErr.Code == ERRCODE_INVALID_PASSWORD ||
				pgErr.Code == ERRCODE_INVALID_CATALOG_NAME ||
				pgErr.Code == ERRCODE_INSUFFICIENT_PRIVILEGE {
				return nil, allErrors
			}
		}

		var npErr *NotPreferredError
		if errors.As(err, &npErr) {
			fallbackConnectOneConfig = c
		}
	}

	if fallbackConnectOneConfig != nil {
		fallbackCtx := octx
		if config.ConnectTimeout != 0 {
			var cancel context.CancelFunc
			fallbackCtx, cancel = context.WithTimeout(octx, config.ConnectTimeout)
			defer cancel()
		}
		pgConn, err := connectOne(fallbackCtx, config, fallbackConnectOneConfig, true)
		if err == nil {
			return pgConn, nil
		}
		allErrors = append(allErrors, err)
	}

	return nil, allErrors
}

// connectOne makes one connection attempt to a single host.
func connectOne(ctx context.Context, config *Config, connectConfig *connectOneConfig,
	ignoreNotPreferredErr bool,
) (*PgConn, error) {
	pgConn := new(PgConn)
	pgConn.config = config
	pgConn.cleanupDone = make(chan struct{})
	pgConn.customData = make(map[string]any)

	var err error

	newPerDialConnectError := func(msg string, err error) *perDialConnectError {
		err = normalizeTimeoutError(ctx, err)
		e := &perDialConnectError{address: connectConfig.address, originalHostname: connectConfig.originalHostname, err: fmt.Errorf("%s: %w", msg, err)}
		return e
	}

	maxProtocolVersion, err := parseProtocolVersion(config.MaxProtocolVersion)
	if err != nil {
		return nil, newPerDialConnectError("invalid max_protocol_version", err)
	}
	minProtocolVersion, err := parseProtocolVersion(config.MinProtocolVersion)
	if err != nil {
		return nil, newPerDialConnectError("invalid min_protocol_version", err)
	}

	pgConn.conn, err = config.DialFunc(ctx, connectConfig.network, connectConfig.address)
	if err != nil {
		return nil, newPerDialConnectError("dial error", err)
	}

	if connectConfig.tlsConfig != nil {
		pgConn.contextWatcher = ctxwatch.NewContextWatcher(&DeadlineContextWatcherHandler{Conn: pgConn.conn})
		pgConn.contextWatcher.Watch(ctx)
		var (
			tlsConn net.Conn
			err     error
		)
		if config.SSLNegotiation == "direct" {
			tlsConn = tls.Client(pgConn.conn, connectConfig.tlsConfig)
		} else {
			tlsConn, err = startTLS(pgConn.conn, connectConfig.tlsConfig)
		}
		pgConn.contextWatcher.Unwatch() // Always unwatch `netConn` after TLS.
		if err != nil {
			pgConn.conn.Close()
			return nil, newPerDialConnectError("tls error", err)
		}

		pgConn.conn = tlsConn
		pgConn.tlsConfig = connectConfig.tlsConfig
	}

	if config.AfterNetConnect != nil {
		pgConn.conn, err = config.AfterNetConnect(ctx, config, pgConn.conn)
		if err != nil {
			pgConn.conn.Close()
			return nil, newPerDialConnectError("AfterNetConnect failed", err)
		}
	}

	// Use a deadline-only watcher during connect. The application-supplied
	// BuildContextWatcherHandler may read *PgConn fields (e.g.
	// CancelRequestContextWatcherHandler reads pgConn.pid and
	// pgConn.secretKey), which would race with this function's writes to
	// those fields when handling BackendKeyData. The application handler is
	// installed below, after the connection reaches connStatusIdle.
	pgConn.contextWatcher = ctxwatch.NewContextWatcher(&DeadlineContextWatcherHandler{Conn: pgConn.conn})
	pgConn.contextWatcher.Watch(ctx)
	defer pgConn.contextWatcher.Unwatch()

	pgConn.parameterStatuses = make(map[string]string)
	pgConn.status = connStatusConnecting
	pgConn.bgReader = bgreader.New(pgConn.conn)
	pgConn.slowWriteTimer = time.AfterFunc(time.Duration(math.MaxInt64),
		func() {
			pgConn.bgReader.Start()
			pgConn.bgReaderStarted <- struct{}{}
		},
	)
	pgConn.slowWriteTimer.Stop()
	pgConn.bgReaderStarted = make(chan struct{})
	pgConn.frontend = config.BuildFrontend(pgConn.bgReader, pgConn.conn)

	startupMsg := pgproto3.StartupMessage{
		ProtocolVersion: maxProtocolVersion,
		Parameters:      make(map[string]string),
	}

	// Copy default run-time params
	maps.Copy(startupMsg.Parameters, config.RuntimeParams)

	startupMsg.Parameters["user"] = config.User
	if config.Database != "" {
		startupMsg.Parameters["database"] = config.Database
	}

	pgConn.frontend.Send(&startupMsg)
	if err := pgConn.flushWithPotentialWriteReadDeadlock(); err != nil {
		pgConn.conn.Close()
		return nil, newPerDialConnectError("failed to write startup message", err)
	}

	// Parse require_auth on each connect so that callers who mutate
	// Config.RequireAuth after ParseConfig see their change take effect.
	// The parser is pure and cheap; ParseConfigWithOptions validates the
	// value up front so any parse error here indicates post-parse mutation.
	requireAuthPolicy, err := parseRequireAuth(config.RequireAuth)
	if err != nil {
		pgConn.conn.Close()
		return nil, newPerDialConnectError("invalid require_auth", err)
	}
	requireAuthFail := func(err error) (*PgConn, error) {
		pgConn.conn.Close()
		return nil, newPerDialConnectError("require_auth check failed", err)
	}
	clientFinishedAuth := false

	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			pgConn.conn.Close()
			if err, ok := err.(*PgError); ok {
				return nil, newPerDialConnectError("server error", err)
			}
			return nil, newPerDialConnectError("failed to receive message", err)
		}

		switch msg := msg.(type) {
		case *pgproto3.BackendKeyData:
			pgConn.pid = msg.ProcessID
			pgConn.secretKey = msg.SecretKey

		case *pgproto3.AuthenticationOk:
			if requireAuthPolicy.authRequired && !clientFinishedAuth {
				return requireAuthFail(requireAuthPolicy.check(authMethodNone))
			}
		case *pgproto3.AuthenticationCleartextPassword:
			if err := requireAuthPolicy.check(authMethodPassword); err != nil {
				return requireAuthFail(err)
			}
			err = pgConn.txPasswordMessage(pgConn.config.Password)
			if err != nil {
				pgConn.conn.Close()
				return nil, newPerDialConnectError("failed to write password message", err)
			}
			clientFinishedAuth = true
		case *pgproto3.AuthenticationMD5Password:
			if err := requireAuthPolicy.check(authMethodMD5); err != nil {
				return requireAuthFail(err)
			}
			digestedPassword := "md5" + hexMD5(hexMD5(pgConn.config.Password+pgConn.config.User)+string(msg.Salt[:]))
			err = pgConn.txPasswordMessage(digestedPassword)
			if err != nil {
				pgConn.conn.Close()
				return nil, newPerDialConnectError("failed to write password message", err)
			}
			clientFinishedAuth = true
		case *pgproto3.AuthenticationSASL:
			// Check if OAUTHBEARER is supported
			serverSupportsOAuthBearer := false
			for _, mech := range msg.AuthMechanisms {
				if mech == "OAUTHBEARER" {
					serverSupportsOAuthBearer = true
					break
				}
			}

			if serverSupportsOAuthBearer && pgConn.config.OAuthTokenProvider != nil {
				if err := requireAuthPolicy.check(authMethodOAuth); err != nil {
					return requireAuthFail(err)
				}
				err = pgConn.oauthAuth(ctx)
			} else {
				if err := requireAuthPolicy.check(authMethodSCRAMSHA256); err != nil {
					return requireAuthFail(err)
				}
				err = pgConn.scramAuth(msg.AuthMechanisms)
			}
			if err != nil {
				pgConn.conn.Close()
				return nil, newPerDialConnectError("failed SASL auth", err)
			}
			clientFinishedAuth = true
		case *pgproto3.AuthenticationGSS:
			if err := requireAuthPolicy.check(authMethodGSS); err != nil {
				return requireAuthFail(err)
			}
			err = pgConn.gssAuth()
			if err != nil {
				pgConn.conn.Close()
				return nil, newPerDialConnectError("failed GSS auth", err)
			}
			clientFinishedAuth = true
		case *pgproto3.ReadyForQuery:
			pgConn.status = connStatusIdle
			// The connect-phase deadline-only watcher is no longer needed; replace
			// it with the application-supplied watcher so subsequent operations
			// (including any queries run by ValidateConnect) use it.
			pgConn.contextWatcher.Unwatch()
			pgConn.contextWatcher = ctxwatch.NewContextWatcher(config.BuildContextWatcherHandler(pgConn))

			if config.ValidateConnect != nil {
				err := config.ValidateConnect(ctx, pgConn)
				if err != nil {
					if _, ok := err.(*NotPreferredError); ignoreNotPreferredErr && ok {
						return pgConn, nil
					}
					pgConn.conn.Close()
					return nil, newPerDialConnectError("ValidateConnect failed", err)
				}
			}
			return pgConn, nil
		case *pgproto3.ParameterStatus, *pgproto3.NoticeResponse:
			// handled by ReceiveMessage
		case *pgproto3.NegotiateProtocolVersion:
			serverVersion := pgproto3.ProtocolVersion30&0xFFFF0000 | msg.NewestMinorProtocol
			if serverVersion < minProtocolVersion {
				pgConn.conn.Close()
				return nil, newPerDialConnectError("server protocol version too low", nil)
			}
		case *pgproto3.ErrorResponse:
			pgConn.conn.Close()
			return nil, newPerDialConnectError("server error", ErrorResponseToPgError(msg))
		default:
			pgConn.conn.Close()
			return nil, newPerDialConnectError("received unexpected message", err)
		}
	}
}

func startTLS(conn net.Conn, tlsConfig *tls.Config) (net.Conn, error) {
	err := binary.Write(conn, binary.BigEndian, []int32{8, 80877103})
	if err != nil {
		return nil, err
	}

	response := make([]byte, 1)
	if _, err = io.ReadFull(conn, response); err != nil {
		return nil, err
	}

	if response[0] != 'S' {
		return nil, errors.New("server refused TLS connection")
	}

	return tls.Client(conn, tlsConfig), nil
}

func (pgConn *PgConn) txPasswordMessage(password string) (err error) {
	pgConn.frontend.Send(&pgproto3.PasswordMessage{Password: password})
	return pgConn.flushWithPotentialWriteReadDeadlock()
}

func hexMD5(s string) string {
	hash := md5.New()
	io.WriteString(hash, s)
	return hex.EncodeToString(hash.Sum(nil))
}

func (pgConn *PgConn) signalMessage() chan struct{} {
	if pgConn.bufferingReceive {
		panic("BUG: signalMessage when already in progress")
	}

	pgConn.bufferingReceive = true
	pgConn.bufferingReceiveMux.Lock()

	ch := make(chan struct{})
	go func() {
		pgConn.bufferingReceiveMsg, pgConn.bufferingReceiveErr = pgConn.frontend.Receive()
		pgConn.bufferingReceiveMux.Unlock()
		close(ch)
	}()

	return ch
}

// ReceiveMessage receives one wire protocol message from the PostgreSQL server. It must only be used when the
// connection is not busy. e.g. It is an error to call [PgConn.ReceiveMessage] while reading the result of a query. The messages
// are still handled by the core pgconn message handling system so receiving a NotificationResponse will still trigger
// the OnNotification callback.
//
// This is a very low level method that requires deep understanding of the PostgreSQL wire protocol to use correctly.
// See https://www.postgresql.org/docs/current/protocol.html.
func (pgConn *PgConn) ReceiveMessage(ctx context.Context) (pgproto3.BackendMessage, error) {
	if err := pgConn.lock(); err != nil {
		return nil, err
	}
	defer pgConn.unlock()

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			return nil, newContextAlreadyDoneError(ctx)
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	msg, err := pgConn.receiveMessage()
	if err != nil {
		err = &pgconnError{
			msg:         "receive message failed",
			err:         normalizeTimeoutError(ctx, err),
			safeToRetry: true,
		}
	}
	return msg, err
}

// peekMessage peeks at the next message without setting up context cancellation.
func (pgConn *PgConn) peekMessage() (pgproto3.BackendMessage, error) {
	if pgConn.peekedMsg != nil {
		return pgConn.peekedMsg, nil
	}

	var msg pgproto3.BackendMessage
	var err error
	if pgConn.bufferingReceive {
		pgConn.bufferingReceiveMux.Lock()
		msg = pgConn.bufferingReceiveMsg
		err = pgConn.bufferingReceiveErr
		pgConn.bufferingReceiveMux.Unlock()
		pgConn.bufferingReceive = false

		// If a timeout error happened in the background try the read again.
		var netErr net.Error
		if errors.As(err, &netErr) && netErr.Timeout() {
			msg, err = pgConn.frontend.Receive()
		}
	} else {
		msg, err = pgConn.frontend.Receive()
	}

	if err != nil {
		// Close on anything other than timeout error - everything else is fatal
		var netErr net.Error
		isNetErr := errors.As(err, &netErr)
		if !(isNetErr && netErr.Timeout()) {
			pgConn.asyncClose()
		}

		return nil, err
	}

	pgConn.peekedMsg = msg
	return msg, nil
}

// receiveMessage receives a message without setting up context cancellation
func (pgConn *PgConn) receiveMessage() (pgproto3.BackendMessage, error) {
	if pgConn.status == connStatusClosed {
		return nil, &connLockError{status: "conn closed"}
	}

	msg, err := pgConn.peekMessage()
	if err != nil {
		return nil, err
	}
	pgConn.peekedMsg = nil

	switch msg := msg.(type) {
	case *pgproto3.ReadyForQuery:
		pgConn.txStatus = msg.TxStatus
	case *pgproto3.ParameterStatus:
		pgConn.parameterStatuses[msg.Name] = msg.Value
	case *pgproto3.ErrorResponse:
		err := ErrorResponseToPgError(msg)
		if pgConn.config.OnPgError != nil && !pgConn.config.OnPgError(pgConn, err) {
			pgConn.status = connStatusClosed
			pgConn.conn.Close() // Ignore error as the connection is already broken and there is already an error to return.
			close(pgConn.cleanupDone)
			return nil, err
		}
	case *pgproto3.NoticeResponse:
		if pgConn.config.OnNotice != nil {
			pgConn.config.OnNotice(pgConn, noticeResponseToNotice(msg))
		}
	case *pgproto3.NotificationResponse:
		if pgConn.config.OnNotification != nil {
			pgConn.config.OnNotification(pgConn, &Notification{PID: msg.PID, Channel: msg.Channel, Payload: msg.Payload})
		}
	}

	return msg, nil
}

// Conn returns the underlying net.Conn. This rarely necessary. If the connection will be directly used for reading or
// writing then SyncConn should usually be called before Conn.
func (pgConn *PgConn) Conn() net.Conn {
	return pgConn.conn
}

// PID returns the backend PID.
func (pgConn *PgConn) PID() uint32 {
	return pgConn.pid
}

// TxStatus returns the current TxStatus as reported by the server in the ReadyForQuery message.
//
// Possible return values:
//
//	'I' - idle / not in transaction
//	'T' - in a transaction
//	'E' - in a failed transaction
//
// See https://www.postgresql.org/docs/current/protocol-message-formats.html.
func (pgConn *PgConn) TxStatus() byte {
	return pgConn.txStatus
}

// SecretKey returns the backend secret key used to send a cancel query message to the server.
func (pgConn *PgConn) SecretKey() []byte {
	return pgConn.secretKey
}

// Frontend returns the underlying *pgproto3.Frontend. This rarely necessary.
func (pgConn *PgConn) Frontend() *pgproto3.Frontend {
	return pgConn.frontend
}

// Close closes a connection. It is safe to call Close on an already closed connection. Close attempts a clean close by
// sending the exit message to PostgreSQL. However, this could block so ctx is available to limit the time to wait. The
// underlying net.Conn.Close() will always be called regardless of any other errors.
func (pgConn *PgConn) Close(ctx context.Context) error {
	if pgConn.status == connStatusClosed {
		return nil
	}
	pgConn.status = connStatusClosed

	defer close(pgConn.cleanupDone)
	defer pgConn.conn.Close()

	if ctx != context.Background() {
		// Close may be called while a cancellable query is in progress. This will most often be triggered by panic when
		// a defer closes the connection (possibly indirectly via a transaction or a connection pool). Unwatch to end any
		// previous watch. It is safe to Unwatch regardless of whether a watch is already is progress.
		//
		// See https://github.com/jackc/pgconn/issues/29
		pgConn.contextWatcher.Unwatch()

		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	// Ignore any errors sending Terminate message and waiting for server to close connection.
	// This mimics the behavior of libpq PQfinish. It calls closePGconn which calls sendTerminateConn which purposefully
	// ignores errors.
	//
	// See https://github.com/jackc/pgx/issues/637
	pgConn.frontend.Send(&pgproto3.Terminate{})
	pgConn.flushWithPotentialWriteReadDeadlock()

	return pgConn.conn.Close()
}

// asyncClose marks the connection as closed and asynchronously sends a cancel query message and closes the underlying
// connection.
func (pgConn *PgConn) asyncClose() {
	if pgConn.status == connStatusClosed {
		return
	}
	pgConn.status = connStatusClosed

	go func() {
		defer close(pgConn.cleanupDone)
		defer pgConn.conn.Close()

		deadline := time.Now().Add(time.Second * 15)

		ctx, cancel := context.WithDeadline(context.Background(), deadline)
		defer cancel()

		pgConn.CancelRequest(ctx)

		pgConn.conn.SetDeadline(deadline)

		pgConn.frontend.Send(&pgproto3.Terminate{})
		pgConn.flushWithPotentialWriteReadDeadlock()

		// Drain any data already in flight from the server (DataRows that were sent before the
		// CancelRequest landed, the resulting ErrorResponse, ReadyForQuery, and finally the server's
		// own close after it processes Terminate). Closing a TCP socket while unread data remains in
		// the kernel receive buffer causes the OS to send RST instead of FIN, which surfaces on the
		// server or proxy as "connection reset by peer". The deadline set above bounds how long this
		// will block; on timeout we fall through to Close() and accept the abortive close.
		//
		// See https://github.com/jackc/pgx/issues/2584
		io.Copy(io.Discard, pgConn.conn)
	}()
}

// CleanupDone returns a channel that will be closed after all underlying resources have been cleaned up. A closed
// connection is no longer usable, but underlying resources, in particular the net.Conn, may not have finished closing
// yet. This is because certain errors such as a context cancellation require that the interrupted function call return
// immediately, but the error may also cause the connection to be closed. In these cases the underlying resources are
// closed asynchronously.
//
// This is only likely to be useful to connection pools. It gives them a way avoid establishing a new connection while
// an old connection is still being cleaned up and thereby exceeding the maximum pool size.
func (pgConn *PgConn) CleanupDone() chan (struct{}) {
	return pgConn.cleanupDone
}

// IsClosed reports if the connection has been closed.
//
// CleanupDone() can be used to determine if all cleanup has been completed.
func (pgConn *PgConn) IsClosed() bool {
	return pgConn.status < connStatusIdle
}

// IsBusy reports if the connection is busy.
func (pgConn *PgConn) IsBusy() bool {
	return pgConn.status == connStatusBusy
}

// lock locks the connection.
func (pgConn *PgConn) lock() error {
	switch pgConn.status {
	case connStatusBusy:
		return &connLockError{status: "conn busy"} // This only should be possible in case of an application bug.
	case connStatusClosed:
		return &connLockError{status: "conn closed"}
	case connStatusUninitialized:
		return &connLockError{status: "conn uninitialized"}
	}
	pgConn.status = connStatusBusy
	return nil
}

func (pgConn *PgConn) unlock() {
	switch pgConn.status {
	case connStatusBusy:
		pgConn.status = connStatusIdle
	case connStatusClosed:
	default:
		panic("BUG: cannot unlock unlocked connection") // This should only be possible if there is a bug in this package.
	}
}

// ParameterStatus returns the value of a parameter reported by the server (e.g.
// server_version). Returns an empty string for unknown parameters.
func (pgConn *PgConn) ParameterStatus(key string) string {
	return pgConn.parameterStatuses[key]
}

// CommandTag is the status text returned by PostgreSQL for a query.
type CommandTag struct {
	s string
}

// NewCommandTag makes a CommandTag from s.
func NewCommandTag(s string) CommandTag {
	return CommandTag{s: s}
}

// RowsAffected returns the number of rows affected. If the CommandTag was not
// for a row affecting command (e.g. "CREATE TABLE") then it returns 0.
func (ct CommandTag) RowsAffected() int64 {
	// Parse the number from the end in a single pass.
	var n int64
	var mult int64 = 1

	for i := len(ct.s) - 1; i >= 0; i-- {
		c := ct.s[i]
		if c >= '0' && c <= '9' {
			n += int64(c-'0') * mult
			mult *= 10
		} else {
			break
		}
	}

	return n
}

func (ct CommandTag) String() string {
	return ct.s
}

// Insert is true if the command tag starts with "INSERT".
func (ct CommandTag) Insert() bool {
	return strings.HasPrefix(ct.s, "INSERT")
}

// Update is true if the command tag starts with "UPDATE".
func (ct CommandTag) Update() bool {
	return strings.HasPrefix(ct.s, "UPDATE")
}

// Delete is true if the command tag starts with "DELETE".
func (ct CommandTag) Delete() bool {
	return strings.HasPrefix(ct.s, "DELETE")
}

// Select is true if the command tag starts with "SELECT".
func (ct CommandTag) Select() bool {
	return strings.HasPrefix(ct.s, "SELECT")
}

type FieldDescription struct {
	Name                 string
	TableOID             uint32
	TableAttributeNumber uint16
	DataTypeOID          uint32
	DataTypeSize         int16
	TypeModifier         int32
	Format               int16
}

func (pgConn *PgConn) getFieldDescriptionSlice(n int) []FieldDescription {
	if cap(pgConn.fieldDescriptions) >= n {
		return pgConn.fieldDescriptions[:n:n]
	} else {
		return make([]FieldDescription, n)
	}
}

func convertRowDescription(dst []FieldDescription, rd *pgproto3.RowDescription) {
	for i := range rd.Fields {
		dst[i].Name = string(rd.Fields[i].Name)
		dst[i].TableOID = rd.Fields[i].TableOID
		dst[i].TableAttributeNumber = rd.Fields[i].TableAttributeNumber
		dst[i].DataTypeOID = rd.Fields[i].DataTypeOID
		dst[i].DataTypeSize = rd.Fields[i].DataTypeSize
		dst[i].TypeModifier = rd.Fields[i].TypeModifier
		dst[i].Format = rd.Fields[i].Format
	}
}

type StatementDescription struct {
	Name      string
	SQL       string
	ParamOIDs []uint32
	Fields    []FieldDescription
}

// Prepare creates a prepared statement. If the name is empty, the anonymous prepared statement will be used. This
// allows Prepare to also to describe statements without creating a server-side prepared statement.
//
// Prepare does not send a PREPARE statement to the server. It uses the PostgreSQL Parse and Describe protocol messages
// directly.
//
// In extremely rare cases, Prepare may fail after the Parse is successful, but before the Describe is complete. In this
// case, the returned error will be an error where errors.As with a *PrepareError succeeds and the *PrepareError has
// ParseComplete set to true.
func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs []uint32) (*StatementDescription, error) {
	if err := pgConn.lock(); err != nil {
		return nil, err
	}
	defer pgConn.unlock()

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			return nil, newContextAlreadyDoneError(ctx)
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	pgConn.frontend.SendParse(&pgproto3.Parse{Name: name, Query: sql, ParameterOIDs: paramOIDs})
	pgConn.frontend.SendDescribe(&pgproto3.Describe{ObjectType: 'S', Name: name})
	pgConn.frontend.SendSync(&pgproto3.Sync{})
	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		return nil, err
	}

	psd := &StatementDescription{Name: name, SQL: sql}

	var ParseComplete bool
	var pgErr *PgError

readloop:
	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			pgConn.asyncClose()
			return nil, normalizeTimeoutError(ctx, err)
		}

		switch msg := msg.(type) {
		case *pgproto3.ParseComplete:
			ParseComplete = true
		case *pgproto3.ParameterDescription:
			psd.ParamOIDs = make([]uint32, len(msg.ParameterOIDs))
			copy(psd.ParamOIDs, msg.ParameterOIDs)
		case *pgproto3.RowDescription:
			psd.Fields = make([]FieldDescription, len(msg.Fields))
			convertRowDescription(psd.Fields, msg)
		case *pgproto3.ErrorResponse:
			pgErr = ErrorResponseToPgError(msg)
		case *pgproto3.ReadyForQuery:
			break readloop
		}
	}

	if pgErr != nil {
		return nil, &PrepareError{err: pgErr, ParseComplete: ParseComplete}
	}
	return psd, nil
}

// Deallocate deallocates a prepared statement.
//
// Deallocate does not send a DEALLOCATE statement to the server. It uses the PostgreSQL Close protocol message
// directly. This has slightly different behavior than executing DEALLOCATE statement.
//   - Deallocate can succeed in an aborted transaction.
//   - Deallocating a non-existent prepared statement is not an error.
func (pgConn *PgConn) Deallocate(ctx context.Context, name string) error {
	if err := pgConn.lock(); err != nil {
		return err
	}
	defer pgConn.unlock()

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			return newContextAlreadyDoneError(ctx)
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	pgConn.frontend.SendClose(&pgproto3.Close{ObjectType: 'S', Name: name})
	pgConn.frontend.SendSync(&pgproto3.Sync{})
	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		return err
	}

	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			pgConn.asyncClose()
			return normalizeTimeoutError(ctx, err)
		}

		switch msg := msg.(type) {
		case *pgproto3.ErrorResponse:
			return ErrorResponseToPgError(msg)
		case *pgproto3.ReadyForQuery:
			return nil
		}
	}
}

// ErrorResponseToPgError converts a wire protocol error message to a *PgError.
func ErrorResponseToPgError(msg *pgproto3.ErrorResponse) *PgError {
	return &PgError{
		Severity:            msg.Severity,
		SeverityUnlocalized: msg.SeverityUnlocalized,
		Code:                msg.Code,
		Message:             msg.Message,
		Detail:              msg.Detail,
		Hint:                msg.Hint,
		Position:            msg.Position,
		InternalPosition:    msg.InternalPosition,
		InternalQuery:       msg.InternalQuery,
		Where:               msg.Where,
		SchemaName:          msg.SchemaName,
		TableName:           msg.TableName,
		ColumnName:          msg.ColumnName,
		DataTypeName:        msg.DataTypeName,
		ConstraintName:      msg.ConstraintName,
		File:                msg.File,
		Line:                msg.Line,
		Routine:             msg.Routine,
	}
}

func noticeResponseToNotice(msg *pgproto3.NoticeResponse) *Notice {
	pgerr := ErrorResponseToPgError((*pgproto3.ErrorResponse)(msg))
	return (*Notice)(pgerr)
}

// CancelRequest sends a cancel request to the PostgreSQL server. It returns an error if unable to deliver the cancel
// request, but lack of an error does not ensure that the query was canceled. As specified in the documentation, there
// is no way to be sure a query was canceled.
// See https://www.postgresql.org/docs/current/protocol-flow.html#PROTOCOL-FLOW-CANCELING-REQUESTS
func (pgConn *PgConn) CancelRequest(ctx context.Context) error {
	// Open a cancellation request to the same server. The address is taken from the net.Conn directly instead of reusing
	// the connection config. This is important in high availability configurations where fallback connections may be
	// specified or DNS may be used to load balance.
	serverAddr := pgConn.conn.RemoteAddr()
	var serverNetwork string
	var serverAddress string
	if serverAddr.Network() == "unix" {
		// for unix sockets, RemoteAddr() calls getpeername() which returns the name the
		// server passed to bind(). For Postgres, this is always a relative path "./.s.PGSQL.5432"
		// so connecting to it will fail. Fall back to the config's value
		serverNetwork, serverAddress = NetworkAddress(pgConn.config.Host, pgConn.config.Port)
	} else {
		serverNetwork, serverAddress = serverAddr.Network(), serverAddr.String()
	}
	cancelConn, err := pgConn.config.DialFunc(ctx, serverNetwork, serverAddress)
	if err != nil {
		// In case of unix sockets, RemoteAddr() returns only the file part of the path. If the
		// first connect failed, try the config.
		if serverAddr.Network() != "unix" {
			return err
		}
		serverNetwork, serverAddr := NetworkAddress(pgConn.config.Host, pgConn.config.Port)
		cancelConn, err = pgConn.config.DialFunc(ctx, serverNetwork, serverAddr)
		if err != nil {
			return err
		}
	}
	defer cancelConn.Close()

	if ctx != context.Background() {
		contextWatcher := ctxwatch.NewContextWatcher(&DeadlineContextWatcherHandler{Conn: cancelConn})
		contextWatcher.Watch(ctx)
		defer contextWatcher.Unwatch()
	}

	// If the primary connection is encrypted, encrypt the cancel connection the same way so the
	// backend pid and secret key are not exposed to a passive network observer. This mirrors libpq's
	// PQcancelCreate (PG17+), which reuses the original connection's sslmode/gssencmode for the
	// cancel connection. The legacy unencrypted path is still used when the primary connection is
	// plaintext (e.g. unix sockets or sslmode=disable).
	if pgConn.tlsConfig != nil {
		var tlsCancelConn net.Conn
		if pgConn.config.SSLNegotiation == "direct" {
			tlsCancelConn = tls.Client(cancelConn, pgConn.tlsConfig)
		} else {
			tlsCancelConn, err = startTLS(cancelConn, pgConn.tlsConfig)
			if err != nil {
				return fmt.Errorf("tls error on cancel connection: %w", err)
			}
		}
		cancelConn = tlsCancelConn
		defer cancelConn.Close()
	}

	buf := make([]byte, 12+len(pgConn.secretKey))
	binary.BigEndian.PutUint32(buf[0:4], uint32(len(buf)))
	binary.BigEndian.PutUint32(buf[4:8], 80877102)
	binary.BigEndian.PutUint32(buf[8:12], pgConn.pid)
	copy(buf[12:], pgConn.secretKey)

	if _, err := cancelConn.Write(buf); err != nil {
		return fmt.Errorf("write to connection for cancellation: %w", err)
	}

	// Wait for the cancel request to be acknowledged by the server.
	// It copies the behavior of the libpq: https://github.com/postgres/postgres/blob/REL_16_0/src/interfaces/libpq/fe-connect.c#L4946-L4960
	_, _ = cancelConn.Read(buf)

	return nil
}

// WaitForNotification waits for a LISTEN/NOTIFY message to be received. It returns an error if a notification was not
// received.
func (pgConn *PgConn) WaitForNotification(ctx context.Context) error {
	if err := pgConn.lock(); err != nil {
		return err
	}
	defer pgConn.unlock()

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			return newContextAlreadyDoneError(ctx)
		default:
		}

		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			return normalizeTimeoutError(ctx, err)
		}

		if _, ok := msg.(*pgproto3.NotificationResponse); ok {
			return nil
		}
	}
}

// Exec executes SQL via the PostgreSQL simple query protocol. SQL may contain multiple queries. Execution is
// implicitly wrapped in a transaction unless a transaction is already in progress or SQL contains transaction control
// statements.
//
// Prefer [PgConn.ExecParams] unless executing arbitrary SQL that may contain multiple queries.
func (pgConn *PgConn) Exec(ctx context.Context, sql string) *MultiResultReader {
	if err := pgConn.lock(); err != nil {
		return &MultiResultReader{
			closed: true,
			err:    err,
		}
	}

	pgConn.multiResultReader = MultiResultReader{
		pgConn: pgConn,
		ctx:    ctx,
	}
	multiResult := &pgConn.multiResultReader
	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			multiResult.closed = true
			multiResult.err = newContextAlreadyDoneError(ctx)
			pgConn.unlock()
			return multiResult
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
	}

	pgConn.frontend.SendQuery(&pgproto3.Query{String: sql})
	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		pgConn.contextWatcher.Unwatch()
		multiResult.closed = true
		multiResult.err = err
		pgConn.unlock()
		return multiResult
	}

	return multiResult
}

// ExecParams executes a command via the PostgreSQL extended query protocol.
//
// sql is a SQL command string. It may only contain one query. Parameter substitution is positional using $1, $2, $3,
// etc.
//
// paramValues are the parameter values. It must be encoded in the format given by paramFormats.
//
// paramOIDs is a slice of data type OIDs for paramValues. If paramOIDs is nil, the server will infer the data type for
// all parameters. Any paramOID element that is 0 that will cause the server to infer the data type for that parameter.
// ExecParams will panic if len(paramOIDs) is not 0, 1, or len(paramValues).
//
// paramFormats is a slice of format codes determining for each paramValue column whether it is encoded in text or
// binary format. If paramFormats is nil all params are text format. ExecParams will panic if
// len(paramFormats) is not 0, 1, or len(paramValues).
//
// resultFormats is a slice of format codes determining for each result column whether it is encoded in text or
// binary format. If resultFormats is nil all results will be in text format.
//
// [ResultReader] must be closed before [PgConn] can be used again.
func (pgConn *PgConn) ExecParams(ctx context.Context, sql string, paramValues [][]byte, paramOIDs []uint32, paramFormats, resultFormats []int16) *ResultReader {
	result := pgConn.execExtendedPrefix(ctx, paramValues)
	if result.closed {
		return result
	}

	pgConn.frontend.SendParse(&pgproto3.Parse{Query: sql, ParameterOIDs: paramOIDs})
	pgConn.frontend.SendBind(&pgproto3.Bind{ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})

	pgConn.execExtendedSuffix(result, nil, nil)

	return result
}

// ExecPrepared enqueues the execution of a prepared statement via the PostgreSQL extended query protocol.
//
// paramValues are the parameter values. It must be encoded in the format given by paramFormats.
//
// paramFormats is a slice of format codes determining for each paramValue column whether it is encoded in text or
// binary format. If paramFormats is nil all params are text format. ExecPrepared will panic if
// len(paramFormats) is not 0, 1, or len(paramValues).
//
// resultFormats is a slice of format codes determining for each result column whether it is encoded in text or
// binary format. If resultFormats is nil all results will be in text format.
//
// [ResultReader] must be closed before [PgConn] can be used again.
func (pgConn *PgConn) ExecPrepared(ctx context.Context, stmtName string, paramValues [][]byte, paramFormats, resultFormats []int16) *ResultReader {
	result := pgConn.execExtendedPrefix(ctx, paramValues)
	if result.closed {
		return result
	}

	pgConn.frontend.SendBind(&pgproto3.Bind{PreparedStatement: stmtName, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})

	pgConn.execExtendedSuffix(result, nil, nil)

	return result
}

// ExecStatement enqueues the execution of a prepared statement via the PostgreSQL extended query protocol.
//
// This differs from [PgConn.ExecPrepared] in that it takes a [*StatementDescription] instead of the prepared statement name.
// Because it has the [*StatementDescription] it can avoid the Describe Portal message that [PgConn.ExecPrepared] must send to get
// the result column descriptions.
//
// paramValues are the parameter values. It must be encoded in the format given by paramFormats.
//
// paramFormats is a slice of format codes determining for each paramValue column whether it is encoded in text or
// binary format. If paramFormats is nil all params are text format. ExecStatement will panic if len(paramFormats) is not
// 0, 1, or len(paramValues).
//
// resultFormats is a slice of format codes determining for each result column whether it is encoded in text or binary
// format. If resultFormats is nil all results will be in text format.
//
// [ResultReader] must be closed before [PgConn] can be used again.
func (pgConn *PgConn) ExecStatement(ctx context.Context, statementDescription *StatementDescription, paramValues [][]byte, paramFormats, resultFormats []int16) *ResultReader {
	result := pgConn.execExtendedPrefix(ctx, paramValues)
	if result.closed {
		return result
	}

	pgConn.frontend.SendBind(&pgproto3.Bind{PreparedStatement: statementDescription.Name, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})

	pgConn.execExtendedSuffix(result, statementDescription, resultFormats)

	return result
}

func (pgConn *PgConn) execExtendedPrefix(ctx context.Context, paramValues [][]byte) *ResultReader {
	pgConn.resultReader = ResultReader{
		pgConn: pgConn,
		ctx:    ctx,
	}
	result := &pgConn.resultReader

	if err := pgConn.lock(); err != nil {
		result.concludeCommand(CommandTag{}, err)
		result.closed = true
		return result
	}

	if len(paramValues) > math.MaxUint16 {
		result.concludeCommand(CommandTag{}, fmt.Errorf("extended protocol limited to %v parameters", math.MaxUint16))
		result.closed = true
		pgConn.unlock()
		return result
	}

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			result.concludeCommand(CommandTag{}, newContextAlreadyDoneError(ctx))
			result.closed = true
			pgConn.unlock()
			return result
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
	}

	return result
}

func (pgConn *PgConn) execExtendedSuffix(result *ResultReader, statementDescription *StatementDescription, resultFormats []int16) {
	if statementDescription == nil {
		pgConn.frontend.SendDescribe(&pgproto3.Describe{ObjectType: 'P'})
	}
	pgConn.frontend.SendExecute(&pgproto3.Execute{})
	pgConn.frontend.SendSync(&pgproto3.Sync{})

	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		result.concludeCommand(CommandTag{}, err)
		pgConn.contextWatcher.Unwatch()
		result.closed = true
		pgConn.unlock()
		return
	}

	result.readUntilRowDescription(statementDescription, resultFormats)
}

// CopyTo executes the copy command sql and copies the results to w.
func (pgConn *PgConn) CopyTo(ctx context.Context, w io.Writer, sql string) (CommandTag, error) {
	if err := pgConn.lock(); err != nil {
		return CommandTag{}, err
	}

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			pgConn.unlock()
			return CommandTag{}, newContextAlreadyDoneError(ctx)
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	// Send copy to command
	pgConn.frontend.SendQuery(&pgproto3.Query{String: sql})

	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		pgConn.unlock()
		return CommandTag{}, err
	}

	// Read results
	var commandTag CommandTag
	var pgErr error
	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			pgConn.asyncClose()
			return CommandTag{}, normalizeTimeoutError(ctx, err)
		}

		switch msg := msg.(type) {
		case *pgproto3.CopyDone:
		case *pgproto3.CopyData:
			_, err := w.Write(msg.Data)
			if err != nil {
				pgConn.asyncClose()
				return CommandTag{}, err
			}
		case *pgproto3.ReadyForQuery:
			pgConn.unlock()
			return commandTag, pgErr
		case *pgproto3.CommandComplete:
			commandTag = pgConn.makeCommandTag(msg.CommandTag)
		case *pgproto3.ErrorResponse:
			pgErr = ErrorResponseToPgError(msg)
		}
	}
}

// CopyFrom executes the copy command sql and copies all of r to the PostgreSQL server.
//
// Note: context cancellation will only interrupt operations on the underlying PostgreSQL network connection. Reads on r
// could still block.
func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (CommandTag, error) {
	if err := pgConn.lock(); err != nil {
		return CommandTag{}, err
	}
	defer pgConn.unlock()

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			return CommandTag{}, newContextAlreadyDoneError(ctx)
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
		defer pgConn.contextWatcher.Unwatch()
	}

	// Send copy from query
	pgConn.frontend.SendQuery(&pgproto3.Query{String: sql})
	err := pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		return CommandTag{}, err
	}

	// Send copy data
	abortCopyChan := make(chan struct{})
	copyErrChan := make(chan error, 1)
	signalMessageChan := pgConn.signalMessage()
	var wg sync.WaitGroup
	wg.Go(func() {
		buf := iobufpool.Get(65536)
		defer iobufpool.Put(buf)
		(*buf)[0] = 'd'

		for {
			n, readErr := r.Read((*buf)[5:cap(*buf)])
			if n > 0 {
				*buf = (*buf)[0 : n+5]
				pgio.SetInt32((*buf)[1:], int32(n+4))

				writeErr := pgConn.frontend.SendUnbufferedEncodedCopyData(*buf)
				if writeErr != nil {
					// Write errors are always fatal, but we can't use asyncClose because we are in a different goroutine. Not
					// setting pgConn.status or closing pgConn.cleanupDone for the same reason.
					pgConn.conn.Close()

					copyErrChan <- writeErr
					return
				}
			}
			if readErr != nil {
				copyErrChan <- readErr
				return
			}

			select {
			case <-abortCopyChan:
				return
			default:
			}
		}
	})

	var pgErr error
	var copyErr error
	for copyErr == nil && pgErr == nil {
		select {
		case copyErr = <-copyErrChan:
		case <-signalMessageChan:
			// If pgConn.receiveMessage encounters an error it will call pgConn.asyncClose. But that is a race condition with
			// the goroutine. So instead check pgConn.bufferingReceiveErr which will have been set by the signalMessage. If an
			// error is found then forcibly close the connection without sending the Terminate message.
			if err := pgConn.bufferingReceiveErr; err != nil {
				pgConn.status = connStatusClosed
				pgConn.conn.Close()
				close(pgConn.cleanupDone)
				return CommandTag{}, normalizeTimeoutError(ctx, err)
			}
			// peekMessage never returns err in the bufferingReceive mode - it only forwards the bufferingReceive variables.
			// Therefore, the only case for receiveMessage to return err is during handling of the ErrorResponse message type
			// and using pgOnError handler to determine the connection is no longer valid (and thus closing the conn).
			msg, serverError := pgConn.receiveMessage()
			if serverError != nil {
				close(abortCopyChan)
				return CommandTag{}, serverError
			}

			switch msg := msg.(type) {
			case *pgproto3.ErrorResponse:
				pgErr = ErrorResponseToPgError(msg)
			default:
				signalMessageChan = pgConn.signalMessage()
			}
		}
	}
	close(abortCopyChan)
	// Make sure io goroutine finishes before writing.
	wg.Wait()

	if copyErr == io.EOF || pgErr != nil {
		pgConn.frontend.Send(&pgproto3.CopyDone{})
	} else {
		pgConn.frontend.Send(&pgproto3.CopyFail{Message: copyErr.Error()})
	}
	err = pgConn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		pgConn.asyncClose()
		return CommandTag{}, err
	}

	// Read results
	var commandTag CommandTag
	for {
		msg, err := pgConn.receiveMessage()
		if err != nil {
			pgConn.asyncClose()
			return CommandTag{}, normalizeTimeoutError(ctx, err)
		}

		switch msg := msg.(type) {
		case *pgproto3.ReadyForQuery:
			return commandTag, pgErr
		case *pgproto3.CommandComplete:
			commandTag = pgConn.makeCommandTag(msg.CommandTag)
		case *pgproto3.ErrorResponse:
			pgErr = ErrorResponseToPgError(msg)
		}
	}
}

// MultiResultReader is a reader for a command that could return multiple results such as Exec or ExecBatch.
type MultiResultReader struct {
	pgConn *PgConn
	ctx    context.Context

	rr *ResultReader

	// Data from when the batch was queued.
	statementDescriptions []*StatementDescription
	resultFormats         [][]int16

	closed bool
	err    error
}

// ReadAll reads all available results. Calling ReadAll is mutually exclusive with all other MultiResultReader methods.
func (mrr *MultiResultReader) ReadAll() ([]*Result, error) {
	var results []*Result

	for mrr.NextResult() {
		results = append(results, mrr.ResultReader().Read())
	}
	err := mrr.Close()

	return results, err
}

func (mrr *MultiResultReader) receiveMessage() (pgproto3.BackendMessage, error) {
	msg, err := mrr.pgConn.receiveMessage()
	if err != nil {
		mrr.pgConn.contextWatcher.Unwatch()
		mrr.err = normalizeTimeoutError(mrr.ctx, err)
		mrr.closed = true
		mrr.pgConn.asyncClose()
		return nil, mrr.err
	}

	switch msg := msg.(type) {
	case *pgproto3.ReadyForQuery:
		mrr.closed = true
		mrr.pgConn.contextWatcher.Unwatch()
		mrr.pgConn.unlock()
	case *pgproto3.ErrorResponse:
		mrr.err = ErrorResponseToPgError(msg)
	}

	return msg, nil
}

// NextResult returns advances the MultiResultReader to the next result and returns true if a result is available.
func (mrr *MultiResultReader) NextResult() bool {
	for !mrr.closed && mrr.err == nil {
		msg, _ := mrr.pgConn.peekMessage()
		if _, ok := msg.(*pgproto3.DataRow); ok {
			if len(mrr.statementDescriptions) > 0 {
				rr := ResultReader{
					pgConn:            mrr.pgConn,
					multiResultReader: mrr,
					ctx:               mrr.ctx,
				}

				// This result corresponds to a prepared statement description that was provided when queuing the batch.
				sd := mrr.statementDescriptions[0]
				mrr.statementDescriptions = mrr.statementDescriptions[1:]

				resultFormats := mrr.resultFormats[0]
				mrr.resultFormats = mrr.resultFormats[1:]

				sdFields := sd.Fields
				rr.fieldDescriptions = rr.pgConn.getFieldDescriptionSlice(len(sdFields))

				err := combineFieldDescriptionsAndResultFormats(rr.fieldDescriptions, sdFields, resultFormats)
				if err != nil {
					rr.concludeCommand(CommandTag{}, err)
				}

				mrr.pgConn.resultReader = rr
				mrr.rr = &mrr.pgConn.resultReader
				return true
			}

			mrr.err = fmt.Errorf("unexpected DataRow message without preceding RowDescription")
			return false
		}

		msg, err := mrr.receiveMessage()
		if err != nil {
			return false
		}

		switch msg := msg.(type) {
		case *pgproto3.RowDescription:
			mrr.pgConn.resultReader = ResultReader{
				pgConn:            mrr.pgConn,
				multiResultReader: mrr,
				ctx:               mrr.ctx,
				fieldDescriptions: mrr.pgConn.getFieldDescriptionSlice(len(msg.Fields)),
			}
			convertRowDescription(mrr.pgConn.resultReader.fieldDescriptions, msg)

			mrr.rr = &mrr.pgConn.resultReader
			return true
		case *pgproto3.CommandComplete:
			mrr.pgConn.resultReader = ResultReader{
				commandTag:       mrr.pgConn.makeCommandTag(msg.CommandTag),
				commandConcluded: true,
				closed:           true,
			}
			mrr.rr = &mrr.pgConn.resultReader
			return true
		case *pgproto3.EmptyQueryResponse:
			mrr.pgConn.resultReader = ResultReader{
				commandConcluded: true,
				closed:           true,
			}
			mrr.rr = &mrr.pgConn.resultReader
			return true
		}
	}

	return false
}

// ResultReader returns the current ResultReader.
func (mrr *MultiResultReader) ResultReader() *ResultReader {
	return mrr.rr
}

// Close closes the MultiResultReader and returns the first error that occurred during the MultiResultReader's use.
func (mrr *MultiResultReader) Close() error {
	for !mrr.closed {
		_, err := mrr.receiveMessage()
		if err != nil {
			return mrr.err
		}
	}

	return mrr.err
}

// ResultReader is a reader for the result of a single query.
type ResultReader struct {
	pgConn            *PgConn
	multiResultReader *MultiResultReader
	pipeline          *Pipeline
	ctx               context.Context

	fieldDescriptions []FieldDescription
	rowValues         [][]byte
	commandTag        CommandTag
	preloaded         bool
	commandConcluded  bool
	closed            bool
	err               error
}

// Result is the saved query response that is returned by calling Read on a ResultReader.
type Result struct {
	FieldDescriptions []FieldDescription
	Rows              [][][]byte
	CommandTag        CommandTag
	Err               error
}

// Read saves the query response to a Result.
func (rr *ResultReader) Read() *Result {
	br := &Result{}

	for rr.NextRow() {
		if br.FieldDescriptions == nil {
			br.FieldDescriptions = make([]FieldDescription, len(rr.FieldDescriptions()))
			copy(br.FieldDescriptions, rr.FieldDescriptions())
		}

		values := rr.Values()
		row := make([][]byte, len(values))
		for i := range row {
			if values[i] != nil {
				row[i] = make([]byte, len(values[i]))
				copy(row[i], values[i])
			}
		}
		br.Rows = append(br.Rows, row)
	}

	br.CommandTag, br.Err = rr.Close()

	return br
}

// NextRow advances the ResultReader to the next row and returns true if a row is available.
func (rr *ResultReader) NextRow() bool {
	if rr.preloaded {
		rr.preloaded = false
		return true
	}

	for !rr.commandConcluded {
		msg, err := rr.receiveMessage()
		if err != nil {
			return false
		}

		if msg, ok := msg.(*pgproto3.DataRow); ok {
			rr.rowValues = msg.Values
			return true
		}
	}

	return false
}

func (rr *ResultReader) preloadRowValues(values [][]byte) {
	rr.rowValues = values
	rr.preloaded = true
}

// FieldDescriptions returns the field descriptions for the current result set. The returned slice is only valid until
// the ResultReader is closed. It may return nil (for example, if the query did not return a result set or an error was
// encountered.)
func (rr *ResultReader) FieldDescriptions() []FieldDescription {
	return rr.fieldDescriptions
}

// Values returns the current row data. NextRow must have been previously been called. The returned [][]byte is only
// valid until the next NextRow call or the ResultReader is closed.
func (rr *ResultReader) Values() [][]byte {
	return rr.rowValues
}

// Close consumes any remaining result data and returns the command tag or
// error.
func (rr *ResultReader) Close() (CommandTag, error) {
	if rr.closed {
		return rr.commandTag, rr.err
	}
	rr.closed = true

	for !rr.commandConcluded {
		_, err := rr.receiveMessage()
		if err != nil {
			return CommandTag{}, rr.err
		}
	}

	if rr.multiResultReader == nil && rr.pipeline == nil {
		for {
			msg, err := rr.receiveMessage()
			if err != nil {
				return CommandTag{}, rr.err
			}

			switch msg := msg.(type) {
			// Detect a deferred constraint violation where the ErrorResponse is sent after CommandComplete.
			case *pgproto3.ErrorResponse:
				rr.err = ErrorResponseToPgError(msg)
			case *pgproto3.ReadyForQuery:
				rr.pgConn.contextWatcher.Unwatch()
				rr.pgConn.unlock()
				return rr.commandTag, rr.err
			}
		}
	}

	return rr.commandTag, rr.err
}

// readUntilRowDescription ensures the ResultReader's fieldDescriptions are loaded. It does not return an error as any
// error will be stored in the ResultReader.
func (rr *ResultReader) readUntilRowDescription(statementDescription *StatementDescription, resultFormats []int16) {
	for !rr.commandConcluded {
		msg, _ := rr.receiveMessage()
		switch msg := msg.(type) {
		case *pgproto3.RowDescription:
			return
		case *pgproto3.DataRow:
			rr.preloadRowValues(msg.Values)
			if statementDescription != nil {
				sdFields := statementDescription.Fields
				rr.fieldDescriptions = rr.pgConn.getFieldDescriptionSlice(len(sdFields))

				err := combineFieldDescriptionsAndResultFormats(rr.fieldDescriptions, sdFields, resultFormats)
				if err != nil {
					rr.concludeCommand(CommandTag{}, err)
				}
			}
			return
		case *pgproto3.CommandComplete:
			if statementDescription != nil {
				sdFields := statementDescription.Fields
				rr.fieldDescriptions = rr.pgConn.getFieldDescriptionSlice(len(sdFields))

				err := combineFieldDescriptionsAndResultFormats(rr.fieldDescriptions, sdFields, resultFormats)
				if err != nil {
					rr.concludeCommand(CommandTag{}, err)
				}
			}
			return
		}
	}
}

func (rr *ResultReader) receiveMessage() (msg pgproto3.BackendMessage, err error) {
	if rr.multiResultReader == nil {
		msg, err = rr.pgConn.receiveMessage()
	} else {
		msg, err = rr.multiResultReader.receiveMessage()
	}

	if err != nil {
		err = normalizeTimeoutError(rr.ctx, err)
		rr.concludeCommand(CommandTag{}, err)
		rr.pgConn.contextWatcher.Unwatch()
		rr.closed = true
		if rr.multiResultReader == nil {
			rr.pgConn.asyncClose()
		}

		return nil, rr.err
	}

	switch msg := msg.(type) {
	case *pgproto3.RowDescription:
		rr.fieldDescriptions = rr.pgConn.getFieldDescriptionSlice(len(msg.Fields))
		convertRowDescription(rr.fieldDescriptions, msg)
	case *pgproto3.CommandComplete:
		rr.concludeCommand(rr.pgConn.makeCommandTag(msg.CommandTag), nil)
	case *pgproto3.EmptyQueryResponse:
		rr.concludeCommand(CommandTag{}, nil)
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		if rr.pipeline != nil {
			rr.pipeline.state.HandleError(pgErr)
		}
		rr.concludeCommand(CommandTag{}, pgErr)
	}

	return msg, nil
}

func (rr *ResultReader) concludeCommand(commandTag CommandTag, err error) {
	// Keep the first error that is recorded. Store the error before checking if the command is already concluded to
	// allow for receiving an error after CommandComplete but before ReadyForQuery.
	if err != nil && rr.err == nil {
		rr.err = err
	}

	if rr.commandConcluded {
		return
	}

	rr.commandTag = commandTag
	rr.rowValues = nil
	rr.commandConcluded = true
}

// Batch is a collection of queries that can be sent to the PostgreSQL server in a single round-trip.
type Batch struct {
	buf                   []byte
	statementDescriptions []*StatementDescription
	resultFormats         [][]int16
	err                   error
}

// ExecParams appends an ExecParams command to the batch. See PgConn.ExecParams for parameter descriptions.
func (batch *Batch) ExecParams(sql string, paramValues [][]byte, paramOIDs []uint32, paramFormats, resultFormats []int16) {
	if batch.err != nil {
		return
	}

	batch.buf, batch.err = (&pgproto3.Parse{Query: sql, ParameterOIDs: paramOIDs}).Encode(batch.buf)
	if batch.err != nil {
		return
	}
	batch.ExecPrepared("", paramValues, paramFormats, resultFormats)
}

// ExecPrepared appends an ExecPrepared e command to the batch. See PgConn.ExecPrepared for parameter descriptions.
func (batch *Batch) ExecPrepared(stmtName string, paramValues [][]byte, paramFormats, resultFormats []int16) {
	if batch.err != nil {
		return
	}

	batch.buf, batch.err = (&pgproto3.Bind{PreparedStatement: stmtName, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats}).Encode(batch.buf)
	if batch.err != nil {
		return
	}

	batch.buf, batch.err = (&pgproto3.Describe{ObjectType: 'P'}).Encode(batch.buf)
	if batch.err != nil {
		return
	}

	batch.buf, batch.err = (&pgproto3.Execute{}).Encode(batch.buf)
	if batch.err != nil {
		return
	}
}

// ExecStatement appends an ExecStatement command to the batch. See PgConn.ExecPrepared for parameter descriptions.
//
// This differs from ExecPrepared in that it takes a *StatementDescription instead of just the prepared statement name.
// Because it has the *StatementDescription it can avoid the Describe Portal message that ExecPrepared must send to get
// the result column descriptions.
func (batch *Batch) ExecStatement(statementDescription *StatementDescription, paramValues [][]byte, paramFormats, resultFormats []int16) {
	if batch.err != nil {
		return
	}

	batch.buf, batch.err = (&pgproto3.Bind{PreparedStatement: statementDescription.Name, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats}).Encode(batch.buf)
	if batch.err != nil {
		return
	}

	batch.statementDescriptions = append(batch.statementDescriptions, statementDescription)
	batch.resultFormats = append(batch.resultFormats, resultFormats)

	batch.buf, batch.err = (&pgproto3.Execute{}).Encode(batch.buf)
	if batch.err != nil {
		return
	}
}

// ExecBatch executes all the queries in batch in a single round-trip. Execution is implicitly transactional unless a
// transaction is already in progress or SQL contains transaction control statements. This is a simpler way of executing
// multiple queries in a single round trip than using pipeline mode.
func (pgConn *PgConn) ExecBatch(ctx context.Context, batch *Batch) *MultiResultReader {
	if batch.err != nil {
		return &MultiResultReader{
			closed: true,
			err:    batch.err,
		}
	}

	if err := pgConn.lock(); err != nil {
		return &MultiResultReader{
			closed: true,
			err:    err,
		}
	}

	pgConn.multiResultReader = MultiResultReader{
		pgConn:                pgConn,
		ctx:                   ctx,
		statementDescriptions: batch.statementDescriptions,
		resultFormats:         batch.resultFormats,
	}
	multiResult := &pgConn.multiResultReader

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			multiResult.closed = true
			multiResult.err = newContextAlreadyDoneError(ctx)
			pgConn.unlock()
			return multiResult
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
	}

	batch.buf, batch.err = (&pgproto3.Sync{}).Encode(batch.buf)
	if batch.err != nil {
		pgConn.contextWatcher.Unwatch()
		multiResult.err = normalizeTimeoutError(multiResult.ctx, batch.err)
		multiResult.closed = true
		pgConn.asyncClose()
		return multiResult
	}

	_, err := func(buf []byte) (int, error) {
		pgConn.enterPotentialWriteReadDeadlock()
		defer pgConn.exitPotentialWriteReadDeadlock()
		return pgConn.conn.Write(buf)
	}(batch.buf)
	if err != nil {
		pgConn.contextWatcher.Unwatch()
		multiResult.err = normalizeTimeoutError(multiResult.ctx, err)
		multiResult.closed = true
		pgConn.asyncClose()
		return multiResult
	}

	return multiResult
}

// EscapeString escapes a string such that it can safely be interpolated into a SQL command string. It does not include
// the surrounding single quotes.
//
// The current implementation requires that standard_conforming_strings=on and client_encoding="UTF8". If these
// conditions are not met an error will be returned. It is possible these restrictions will be lifted in the future.
func (pgConn *PgConn) EscapeString(s string) (string, error) {
	if pgConn.ParameterStatus("standard_conforming_strings") != "on" {
		return "", errors.New("EscapeString must be run with standard_conforming_strings=on")
	}

	if pgConn.ParameterStatus("client_encoding") != "UTF8" {
		return "", errors.New("EscapeString must be run with client_encoding=UTF8")
	}

	return strings.ReplaceAll(s, "'", "''"), nil
}

// CheckConn checks the underlying connection without writing any bytes. This is currently implemented by doing a read
// with a very short deadline. This can be useful because a TCP connection can be broken such that a write will appear
// to succeed even though it will never actually reach the server. Reading immediately before a write will detect this
// condition. If this is done immediately before sending a query it reduces the chances a query will be sent that fails
// without the client knowing whether the server received it or not.
//
// Deprecated: CheckConn is deprecated in favor of Ping. CheckConn cannot detect all types of broken connections where
// the write would still appear to succeed. Prefer Ping unless on a high latency connection.
func (pgConn *PgConn) CheckConn() error {
	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
	defer cancel()

	_, err := pgConn.ReceiveMessage(ctx)
	if err != nil {
		if !Timeout(err) {
			return err
		}
	}

	return nil
}

// Ping pings the server. This can be useful because a TCP connection can be broken such that a write will appear to
// succeed even though it will never actually reach the server. Pinging immediately before sending a query reduces the
// chances a query will be sent that fails without the client knowing whether the server received it or not.
func (pgConn *PgConn) Ping(ctx context.Context) error {
	return pgConn.Exec(ctx, "-- ping").Close()
}

// makeCommandTag makes a CommandTag. It does not retain a reference to buf or buf's underlying memory.
func (pgConn *PgConn) makeCommandTag(buf []byte) CommandTag {
	return CommandTag{s: string(buf)}
}

// enterPotentialWriteReadDeadlock must be called before a write that could deadlock if the server is simultaneously
// blocked writing to us.
func (pgConn *PgConn) enterPotentialWriteReadDeadlock() {
	// The time to wait is somewhat arbitrary. A Write should only take as long as the syscall and memcpy to the OS
	// outbound network buffer unless the buffer is full (which potentially is a block). It needs to be long enough for
	// the normal case, but short enough not to kill performance if a block occurs.
	//
	// In addition, on Windows the default timer resolution is 15.6ms. So setting the timer to less than that is
	// ineffective.
	if pgConn.slowWriteTimer.Reset(15 * time.Millisecond) {
		panic("BUG: slow write timer already active")
	}
}

// exitPotentialWriteReadDeadlock must be called after a call to enterPotentialWriteReadDeadlock.
func (pgConn *PgConn) exitPotentialWriteReadDeadlock() {
	if !pgConn.slowWriteTimer.Stop() {
		// The timer starts its function in a separate goroutine. It is necessary to ensure the background reader has
		// started before calling Stop. Otherwise, the background reader may not be stopped. That on its own is not a
		// serious problem. But what is a serious problem is that the background reader may start at an inopportune time in
		// a subsequent query. For example, if a subsequent query was canceled then a deadline may be set on the net.Conn to
		// interrupt an in-progress read. After the read is interrupted, but before the deadline is cleared, the background
		// reader could start and read a deadline error. Then the next query would receive the an unexpected deadline error.
		<-pgConn.bgReaderStarted
		pgConn.bgReader.Stop()
	}
}

func (pgConn *PgConn) flushWithPotentialWriteReadDeadlock() error {
	pgConn.enterPotentialWriteReadDeadlock()
	defer pgConn.exitPotentialWriteReadDeadlock()
	err := pgConn.frontend.Flush()
	return err
}

// SyncConn prepares the underlying net.Conn for direct use. PgConn may internally buffer reads or use goroutines for
// background IO. This means that any direct use of the underlying net.Conn may be corrupted if a read is already
// buffered or a read is in progress. SyncConn drains read buffers and stops background IO. In some cases this may
// require sending a ping to the server. ctx can be used to cancel this operation. This should be called before any
// operation that will use the underlying net.Conn directly. e.g. Before Conn() or Hijack().
//
// This should not be confused with the PostgreSQL protocol Sync message.
func (pgConn *PgConn) SyncConn(ctx context.Context) error {
	for range 10 {
		if pgConn.bgReader.Status() == bgreader.StatusStopped && pgConn.frontend.ReadBufferLen() == 0 {
			return nil
		}

		err := pgConn.Ping(ctx)
		if err != nil {
			return fmt.Errorf("SyncConn: Ping failed while syncing conn: %w", err)
		}
	}

	// This should never happen. Only way I can imagine this occurring is if the server is constantly sending data such as
	// LISTEN/NOTIFY or log notifications such that we never can get an empty buffer.
	return errors.New("SyncConn: conn never synchronized")
}

// CustomData returns a map that can be used to associate custom data with the connection.
func (pgConn *PgConn) CustomData() map[string]any {
	return pgConn.customData
}

// HijackedConn is the result of hijacking a connection.
//
// Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning
// compatibility.
type HijackedConn struct {
	Conn              net.Conn
	TLSConfig         *tls.Config       // tls.Config that Conn was negotiated with; nil if Conn is not TLS
	PID               uint32            // backend pid
	SecretKey         []byte            // key to use to send a cancel query message to the server
	ParameterStatuses map[string]string // parameters that have been reported by the server
	TxStatus          byte
	Frontend          *pgproto3.Frontend
	Config            *Config
	CustomData        map[string]any
}

// Hijack extracts the internal connection data. pgConn must be in an idle state. SyncConn should be called immediately
// before Hijack. pgConn is unusable after hijacking. Hijacking is typically only useful when using pgconn to establish
// a connection, but taking complete control of the raw connection after that (e.g. a load balancer or proxy).
//
// Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning
// compatibility.
func (pgConn *PgConn) Hijack() (*HijackedConn, error) {
	if err := pgConn.lock(); err != nil {
		return nil, err
	}
	pgConn.status = connStatusClosed

	return &HijackedConn{
		Conn:              pgConn.conn,
		TLSConfig:         pgConn.tlsConfig,
		PID:               pgConn.pid,
		SecretKey:         pgConn.secretKey,
		ParameterStatuses: pgConn.parameterStatuses,
		TxStatus:          pgConn.txStatus,
		Frontend:          pgConn.frontend,
		Config:            pgConn.config,
		CustomData:        pgConn.customData,
	}, nil
}

// Construct created a PgConn from an already established connection to a PostgreSQL server. This is the inverse of
// PgConn.Hijack. The connection must be in an idle state.
//
// hc.Frontend is replaced by a new pgproto3.Frontend built by hc.Config.BuildFrontend.
//
// Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning
// compatibility.
func Construct(hc *HijackedConn) (*PgConn, error) {
	pgConn := &PgConn{
		conn:              hc.Conn,
		tlsConfig:         hc.TLSConfig,
		pid:               hc.PID,
		secretKey:         hc.SecretKey,
		parameterStatuses: hc.ParameterStatuses,
		txStatus:          hc.TxStatus,
		frontend:          hc.Frontend,
		config:            hc.Config,
		customData:        hc.CustomData,

		status: connStatusIdle,

		cleanupDone: make(chan struct{}),
	}

	pgConn.contextWatcher = ctxwatch.NewContextWatcher(hc.Config.BuildContextWatcherHandler(pgConn))
	pgConn.bgReader = bgreader.New(pgConn.conn)
	pgConn.slowWriteTimer = time.AfterFunc(time.Duration(math.MaxInt64),
		func() {
			pgConn.bgReader.Start()
			pgConn.bgReaderStarted <- struct{}{}
		},
	)
	pgConn.slowWriteTimer.Stop()
	pgConn.bgReaderStarted = make(chan struct{})
	pgConn.frontend = hc.Config.BuildFrontend(pgConn.bgReader, pgConn.conn)

	return pgConn, nil
}

// Pipeline represents a connection in pipeline mode.
//
// SendPrepare, SendQueryParams, SendQueryPrepared, and SendQueryStatement queue requests to the server. These requests
// are not written until pipeline is flushed by Flush or Sync. Sync must be called after the last request is queued.
// Requests between synchronization points are implicitly transactional unless explicit transaction control statements
// have been issued.
//
// The context the pipeline was started with is in effect for the entire life of the Pipeline.
//
// For a deeper understanding of pipeline mode see the PostgreSQL documentation for the extended query protocol
// (https://www.postgresql.org/docs/current/protocol-flow.html#PROTOCOL-FLOW-EXT-QUERY) and the libpq pipeline mode
// (https://www.postgresql.org/docs/current/libpq-pipeline-mode.html).
type Pipeline struct {
	conn *PgConn
	ctx  context.Context

	state  pipelineState
	err    error
	closed bool
}

// PipelineSync is returned by GetResults when a ReadyForQuery message is received.
type PipelineSync struct{}

// CloseComplete is returned by GetResults when a CloseComplete message is received.
type CloseComplete struct{}

type pipelineRequestType int

const (
	pipelineNil pipelineRequestType = iota
	pipelinePrepare
	pipelineQueryParams
	pipelineQueryPrepared
	pipelineQueryStatement
	pipelineDeallocate
	pipelineSyncRequest
	pipelineFlushRequest
)

type pipelineRequestEvent struct {
	RequestType       pipelineRequestType
	WasSentToServer   bool
	BeforeFlushOrSync bool
}

type pipelineState struct {
	requestEventQueue          list.List
	statementDescriptionsQueue list.List
	resultFormatsQueue         list.List
	lastRequestType            pipelineRequestType
	pgErr                      *PgError
	expectedReadyForQueryCount int
}

func (s *pipelineState) Init() {
	s.requestEventQueue.Init()
	s.statementDescriptionsQueue.Init()
	s.resultFormatsQueue.Init()
	s.lastRequestType = pipelineNil
}

func (s *pipelineState) RegisterSendingToServer() {
	for elem := s.requestEventQueue.Back(); elem != nil; elem = elem.Prev() {
		val := elem.Value.(pipelineRequestEvent)
		if val.WasSentToServer {
			return
		}
		val.WasSentToServer = true
		elem.Value = val
	}
}

func (s *pipelineState) registerFlushingBufferOnServer() {
	for elem := s.requestEventQueue.Back(); elem != nil; elem = elem.Prev() {
		val := elem.Value.(pipelineRequestEvent)
		if val.BeforeFlushOrSync {
			return
		}
		val.BeforeFlushOrSync = true
		elem.Value = val
	}
}

func (s *pipelineState) PushBackRequestType(req pipelineRequestType) {
	if req == pipelineNil {
		return
	}

	if req != pipelineFlushRequest {
		s.requestEventQueue.PushBack(pipelineRequestEvent{RequestType: req})
	}
	if req == pipelineFlushRequest || req == pipelineSyncRequest {
		s.registerFlushingBufferOnServer()
	}
	s.lastRequestType = req

	if req == pipelineSyncRequest {
		s.expectedReadyForQueryCount++
	}
}

func (s *pipelineState) ExtractFrontRequestType() pipelineRequestType {
	for {
		elem := s.requestEventQueue.Front()
		if elem == nil {
			return pipelineNil
		}
		val := elem.Value.(pipelineRequestEvent)
		if !(val.WasSentToServer && val.BeforeFlushOrSync) {
			return pipelineNil
		}

		s.requestEventQueue.Remove(elem)
		if val.RequestType == pipelineSyncRequest {
			s.pgErr = nil
		}
		if s.pgErr == nil {
			return val.RequestType
		}
	}
}

func (s *pipelineState) PushBackStatementData(sd *StatementDescription, resultFormats []int16) {
	s.statementDescriptionsQueue.PushBack(sd)
	s.resultFormatsQueue.PushBack(resultFormats)
}

func (s *pipelineState) ExtractFrontStatementData() (*StatementDescription, []int16) {
	sdElem := s.statementDescriptionsQueue.Front()
	var sd *StatementDescription
	if sdElem != nil {
		s.statementDescriptionsQueue.Remove(sdElem)
		sd = sdElem.Value.(*StatementDescription)
	}

	rfElem := s.resultFormatsQueue.Front()
	var resultFormats []int16
	if rfElem != nil {
		s.resultFormatsQueue.Remove(rfElem)
		resultFormats = rfElem.Value.([]int16)
	}

	return sd, resultFormats
}

func (s *pipelineState) HandleError(err *PgError) {
	s.pgErr = err
}

func (s *pipelineState) HandleReadyForQuery() {
	s.expectedReadyForQueryCount--
}

func (s *pipelineState) PendingSync() bool {
	var notPendingSync bool

	if elem := s.requestEventQueue.Back(); elem != nil {
		val := elem.Value.(pipelineRequestEvent)
		notPendingSync = (val.RequestType == pipelineSyncRequest) && val.WasSentToServer
	} else {
		notPendingSync = (s.lastRequestType == pipelineSyncRequest) || (s.lastRequestType == pipelineNil)
	}

	return !notPendingSync
}

func (s *pipelineState) ExpectedReadyForQuery() int {
	return s.expectedReadyForQueryCount
}

// StartPipeline switches the connection to pipeline mode and returns a *Pipeline. In pipeline mode requests can be sent
// to the server without waiting for a response. Close must be called on the returned *Pipeline to return the connection
// to normal mode. While in pipeline mode, no methods that communicate with the server may be called except
// CancelRequest and Close. ctx is in effect for entire life of the *Pipeline.
//
// Prefer ExecBatch when only sending one group of queries at once.
func (pgConn *PgConn) StartPipeline(ctx context.Context) *Pipeline {
	if err := pgConn.lock(); err != nil {
		pipeline := &Pipeline{
			closed: true,
			err:    err,
		}
		pipeline.state.Init()

		return pipeline
	}

	pgConn.resultReader = ResultReader{closed: true}

	pgConn.pipeline = Pipeline{
		conn: pgConn,
		ctx:  ctx,
	}
	pgConn.pipeline.state.Init()

	pipeline := &pgConn.pipeline

	if ctx != context.Background() {
		select {
		case <-ctx.Done():
			pipeline.closed = true
			pipeline.err = newContextAlreadyDoneError(ctx)
			pgConn.unlock()
			return pipeline
		default:
		}
		pgConn.contextWatcher.Watch(ctx)
	}

	return pipeline
}

// SendPrepare is the pipeline version of *PgConn.Prepare.
func (p *Pipeline) SendPrepare(name, sql string, paramOIDs []uint32) {
	if p.closed {
		return
	}

	p.conn.frontend.SendParse(&pgproto3.Parse{Name: name, Query: sql, ParameterOIDs: paramOIDs})
	p.conn.frontend.SendDescribe(&pgproto3.Describe{ObjectType: 'S', Name: name})
	p.state.PushBackRequestType(pipelinePrepare)
}

// SendDeallocate deallocates a prepared statement.
func (p *Pipeline) SendDeallocate(name string) {
	if p.closed {
		return
	}

	p.conn.frontend.SendClose(&pgproto3.Close{ObjectType: 'S', Name: name})
	p.state.PushBackRequestType(pipelineDeallocate)
}

// SendQueryParams is the pipeline version of *PgConn.ExecParams.
func (p *Pipeline) SendQueryParams(sql string, paramValues [][]byte, paramOIDs []uint32, paramFormats, resultFormats []int16) {
	if p.closed {
		return
	}

	p.conn.frontend.SendParse(&pgproto3.Parse{Query: sql, ParameterOIDs: paramOIDs})
	p.conn.frontend.SendBind(&pgproto3.Bind{ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})
	p.conn.frontend.SendDescribe(&pgproto3.Describe{ObjectType: 'P'})
	p.conn.frontend.SendExecute(&pgproto3.Execute{})
	p.state.PushBackRequestType(pipelineQueryParams)
}

// SendQueryPrepared is the pipeline version of *PgConn.ExecPrepared.
func (p *Pipeline) SendQueryPrepared(stmtName string, paramValues [][]byte, paramFormats, resultFormats []int16) {
	if p.closed {
		return
	}

	p.conn.frontend.SendBind(&pgproto3.Bind{PreparedStatement: stmtName, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})
	p.conn.frontend.SendDescribe(&pgproto3.Describe{ObjectType: 'P'})
	p.conn.frontend.SendExecute(&pgproto3.Execute{})
	p.state.PushBackRequestType(pipelineQueryPrepared)
}

// SendQueryStatement is the pipeline version of *PgConn.ExecStatement.
func (p *Pipeline) SendQueryStatement(statementDescription *StatementDescription, paramValues [][]byte, paramFormats, resultFormats []int16) {
	if p.closed {
		return
	}

	p.conn.frontend.SendBind(&pgproto3.Bind{PreparedStatement: statementDescription.Name, ParameterFormatCodes: paramFormats, Parameters: paramValues, ResultFormatCodes: resultFormats})
	p.conn.frontend.SendExecute(&pgproto3.Execute{})
	p.state.PushBackRequestType(pipelineQueryStatement)
	p.state.PushBackStatementData(statementDescription, resultFormats)
}

// SendFlushRequest sends a request for the server to flush its output buffer.
//
// The server flushes its output buffer automatically as a result of Sync being called,
// or on any request when not in pipeline mode; this function is useful to cause the server
// to flush its output buffer in pipeline mode without establishing a synchronization point.
// Note that the request is not itself flushed to the server automatically; use Flush if
// necessary. This copies the behavior of libpq PQsendFlushRequest.
func (p *Pipeline) SendFlushRequest() {
	if p.closed {
		return
	}

	p.conn.frontend.Send(&pgproto3.Flush{})
	p.state.PushBackRequestType(pipelineFlushRequest)
}

// SendPipelineSync marks a synchronization point in a pipeline by sending a sync message
// without flushing the send buffer. This serves as the delimiter of an implicit
// transaction and an error recovery point.
//
// Note that the request is not itself flushed to the server automatically; use Flush if
// necessary. This copies the behavior of libpq PQsendPipelineSync.
func (p *Pipeline) SendPipelineSync() {
	if p.closed {
		return
	}

	p.conn.frontend.SendSync(&pgproto3.Sync{})
	p.state.PushBackRequestType(pipelineSyncRequest)
}

// Flush flushes the queued requests without establishing a synchronization point.
func (p *Pipeline) Flush() error {
	if p.closed {
		if p.err != nil {
			return p.err
		}
		return errors.New("pipeline closed")
	}

	err := p.conn.flushWithPotentialWriteReadDeadlock()
	if err != nil {
		err = normalizeTimeoutError(p.ctx, err)

		p.conn.asyncClose()

		p.conn.contextWatcher.Unwatch()
		p.conn.unlock()
		p.closed = true
		p.err = err
		return err
	}

	p.state.RegisterSendingToServer()
	return nil
}

// Sync establishes a synchronization point and flushes the queued requests.
func (p *Pipeline) Sync() error {
	p.SendPipelineSync()
	return p.Flush()
}

// GetResults gets the next results. If results are present, results may be a *ResultReader, *StatementDescription, or
// *PipelineSync. If an ErrorResponse is received from the server, results will be nil and err will be a *PgError. If no
// results are available, results and err will both be nil.
func (p *Pipeline) GetResults() (results any, err error) {
	if p.closed {
		if p.err != nil {
			return nil, p.err
		}
		return nil, errors.New("pipeline closed")
	}

	return p.getResults()
}

func (p *Pipeline) getResults() (results any, err error) {
	if !p.conn.resultReader.closed {
		_, err := p.conn.resultReader.Close()
		if err != nil {
			return nil, err
		}
	}

	currentRequestType := p.state.ExtractFrontRequestType()
	switch currentRequestType {
	case pipelineNil:
		return nil, nil
	case pipelinePrepare:
		return p.getResultsPrepare()
	case pipelineQueryParams:
		return p.getResultsQueryParams()
	case pipelineQueryPrepared:
		return p.getResultsQueryPrepared()
	case pipelineQueryStatement:
		return p.getResultsQueryStatement()
	case pipelineDeallocate:
		return p.getResultsDeallocate()
	case pipelineSyncRequest:
		return p.getResultsSync()
	case pipelineFlushRequest:
		return nil, errors.New("BUG: pipelineFlushRequest should not be in request queue")
	default:
		return nil, errors.New("BUG: unknown pipeline request type")
	}
}

func (p *Pipeline) getResultsPrepare() (*StatementDescription, error) {
	err := p.receiveParseComplete("Prepare")
	if err != nil {
		return nil, err
	}

	psd := &StatementDescription{}

	msg, err := p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.ParameterDescription:
		psd.ParamOIDs = make([]uint32, len(msg.ParameterOIDs))
		copy(psd.ParamOIDs, msg.ParameterOIDs)
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage("Prepare ParameterDescription", msg)
	}

	msg, err = p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.RowDescription:
		psd.Fields = make([]FieldDescription, len(msg.Fields))
		convertRowDescription(psd.Fields, msg)
		return psd, nil

	// NoData is returned instead of RowDescription when there is no expected result. e.g. An INSERT without a RETURNING
	// clause.
	case *pgproto3.NoData:
		return psd, nil

	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage("Prepare RowDescription", msg)
	}
}

func (p *Pipeline) getResultsQueryParams() (*ResultReader, error) {
	err := p.receiveParseComplete("QueryParams")
	if err != nil {
		return nil, err
	}

	err = p.receiveBindComplete("QueryParams")
	if err != nil {
		return nil, err
	}

	return p.receiveDescribedResultReader("QueryParams")
}

func (p *Pipeline) getResultsQueryPrepared() (*ResultReader, error) {
	err := p.receiveBindComplete("QueryPrepared")
	if err != nil {
		return nil, err
	}

	return p.receiveDescribedResultReader("QueryPrepared")
}

func (p *Pipeline) getResultsQueryStatement() (*ResultReader, error) {
	err := p.receiveBindComplete("QueryStatement")
	if err != nil {
		return nil, err
	}

	msg, err := p.receiveMessage()
	if err != nil {
		return nil, err
	}

	sd, resultFormats := p.state.ExtractFrontStatementData()
	if sd == nil {
		return nil, errors.New("BUG: missing statement description or result formats for QueryStatement")
	}
	sdFields := sd.Fields
	fieldDescriptions := p.conn.getFieldDescriptionSlice(len(sdFields))
	err = combineFieldDescriptionsAndResultFormats(fieldDescriptions, sdFields, resultFormats)
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.DataRow:
		rr := ResultReader{
			pgConn:            p.conn,
			pipeline:          p,
			ctx:               p.ctx,
			fieldDescriptions: fieldDescriptions,
		}
		rr.preloadRowValues(msg.Values)
		p.conn.resultReader = rr
		return &p.conn.resultReader, nil
	case *pgproto3.CommandComplete:
		p.conn.resultReader = ResultReader{
			commandTag:        p.conn.makeCommandTag(msg.CommandTag),
			commandConcluded:  true,
			closed:            true,
			fieldDescriptions: fieldDescriptions,
		}
		return &p.conn.resultReader, nil
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		p.conn.resultReader.closed = true
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage("QueryStatement", msg)
	}
}

func (p *Pipeline) getResultsDeallocate() (*CloseComplete, error) {
	msg, err := p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.CloseComplete:
		return &CloseComplete{}, nil
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		p.conn.resultReader.closed = true
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage("Deallocate", msg)
	}
}

func (p *Pipeline) getResultsSync() (*PipelineSync, error) {
	msg, err := p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.ReadyForQuery:
		p.state.HandleReadyForQuery()
		return &PipelineSync{}, nil
	case *pgproto3.ErrorResponse:
		// Error message that is received while expecting a Sync message still consumes the expected Sync. Put it back.
		p.state.requestEventQueue.PushFront(pipelineRequestEvent{RequestType: pipelineSyncRequest, WasSentToServer: true, BeforeFlushOrSync: true})

		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		p.conn.resultReader.closed = true
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage("Sync", msg)
	}
}

func (p *Pipeline) receiveParseComplete(errStr string) error {
	msg, err := p.receiveMessage()
	if err != nil {
		return err
	}

	switch msg := msg.(type) {
	case *pgproto3.ParseComplete:
		return nil
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		return pgErr
	default:
		return p.handleUnexpectedMessage(fmt.Sprintf("%s Parse", errStr), msg)
	}
}

func (p *Pipeline) receiveBindComplete(errStr string) error {
	msg, err := p.receiveMessage()
	if err != nil {
		return err
	}

	switch msg := msg.(type) {
	case *pgproto3.BindComplete:
		return nil
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		return pgErr
	default:
		return p.handleUnexpectedMessage(fmt.Sprintf("%s Bind", errStr), msg)
	}
}

func (p *Pipeline) receiveDescribedResultReader(errStr string) (*ResultReader, error) {
	msg, err := p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.RowDescription:
		p.conn.resultReader = ResultReader{
			pgConn:            p.conn,
			pipeline:          p,
			ctx:               p.ctx,
			fieldDescriptions: p.conn.getFieldDescriptionSlice(len(msg.Fields)),
		}
		convertRowDescription(p.conn.resultReader.fieldDescriptions, msg)
		return &p.conn.resultReader, nil
	case *pgproto3.NoData:
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		p.conn.resultReader.closed = true
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage(fmt.Sprintf("%s RowDescription or NoData", errStr), msg)
	}

	msg, err = p.receiveMessage()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.CommandComplete:
		p.conn.resultReader = ResultReader{
			commandTag:       p.conn.makeCommandTag(msg.CommandTag),
			commandConcluded: true,
			closed:           true,
		}
		return &p.conn.resultReader, nil
	case *pgproto3.ErrorResponse:
		pgErr := ErrorResponseToPgError(msg)
		p.state.HandleError(pgErr)
		p.conn.resultReader.closed = true
		return nil, pgErr
	default:
		return nil, p.handleUnexpectedMessage(fmt.Sprintf("%s CommandComplete", errStr), msg)
	}
}

func (p *Pipeline) receiveMessage() (pgproto3.BackendMessage, error) {
	for {
		msg, err := p.conn.receiveMessage()
		if err != nil {
			p.err = err
			p.conn.asyncClose()
			return nil, normalizeTimeoutError(p.ctx, err)
		}

		switch msg := msg.(type) {
		case *pgproto3.ParameterStatus, *pgproto3.NoticeResponse, *pgproto3.NotificationResponse:
			// Filter these message types out in pipeline mode. The normal processing is handled by PgConn.receiveMessage.
		default:
			return msg, nil
		}
	}
}

func (p *Pipeline) handleUnexpectedMessage(errStr string, msg pgproto3.BackendMessage) error {
	p.err = fmt.Errorf("pipeline: %s: received unexpected message type %T", errStr, msg)
	p.conn.asyncClose()
	return p.err
}

// Close closes the pipeline and returns the connection to normal mode.
func (p *Pipeline) Close() error {
	if p.closed {
		return p.err
	}

	p.closed = true

	if p.state.PendingSync() {
		p.conn.asyncClose()
		p.err = errors.New("pipeline has unsynced requests")
		p.conn.contextWatcher.Unwatch()
		p.conn.unlock()

		return p.err
	}

	for p.state.ExpectedReadyForQuery() > 0 {
		results, err := p.getResults()
		if err != nil {
			p.err = err
			var pgErr *PgError
			if !errors.As(err, &pgErr) {
				p.conn.asyncClose()
				break
			}
		} else if results == nil {
			// getResults returns (nil, nil) when the request queue is exhausted but
			// ExpectedReadyForQuery is still > 0. This can happen when FATAL errors consume
			// queued request slots without the server ever sending ReadyForQuery.
			p.conn.asyncClose()
			if p.err == nil {
				p.err = errors.New("pipeline: no more results but expected ReadyForQuery")
			}
			break
		}
	}

	p.conn.contextWatcher.Unwatch()
	p.conn.unlock()

	return p.err
}

// DeadlineContextWatcherHandler handles canceled contexts by setting a deadline on a net.Conn.
type DeadlineContextWatcherHandler struct {
	Conn net.Conn

	// DeadlineDelay is the delay to set on the deadline set on net.Conn when the context is canceled.
	DeadlineDelay time.Duration
}

func (h *DeadlineContextWatcherHandler) HandleCancel(ctx context.Context) {
	h.Conn.SetDeadline(time.Now().Add(h.DeadlineDelay))
}

func (h *DeadlineContextWatcherHandler) HandleUnwatchAfterCancel() {
	h.Conn.SetDeadline(time.Time{})
}

// CancelRequestContextWatcherHandler handles canceled contexts by sending a cancel request to the server. It also sets
// a deadline on a net.Conn as a fallback.
type CancelRequestContextWatcherHandler struct {
	Conn *PgConn

	// CancelRequestDelay is the delay before sending the cancel request to the server.
	CancelRequestDelay time.Duration

	// DeadlineDelay is the delay to set on the deadline set on net.Conn when the context is canceled.
	DeadlineDelay time.Duration

	cancelFinishedChan             chan struct{}
	handleUnwatchAfterCancelCalled func()
}

func (h *CancelRequestContextWatcherHandler) HandleCancel(context.Context) {
	h.cancelFinishedChan = make(chan struct{})
	var handleUnwatchedAfterCancelCalledCtx context.Context
	handleUnwatchedAfterCancelCalledCtx, h.handleUnwatchAfterCancelCalled = context.WithCancel(context.Background())

	deadline := time.Now().Add(h.DeadlineDelay)
	h.Conn.conn.SetDeadline(deadline)

	go func() {
		defer close(h.cancelFinishedChan)

		select {
		case <-handleUnwatchedAfterCancelCalledCtx.Done():
			return
		case <-time.After(h.CancelRequestDelay):
		}

		cancelRequestCtx, cancel := context.WithDeadline(handleUnwatchedAfterCancelCalledCtx, deadline)
		defer cancel()
		h.Conn.CancelRequest(cancelRequestCtx)

		// CancelRequest is inherently racy. Even though the cancel request has been received by the server at this point,
		// it hasn't necessarily been delivered to the other connection. If we immediately return and the connection is
		// immediately used then it is possible the CancelRequest will actually cancel our next query. The
		// TestCancelRequestContextWatcherHandler Stress test can produce this error without the sleep below. The sleep time
		// is arbitrary, but should be sufficient to prevent this error case.
		time.Sleep(100 * time.Millisecond)
	}()
}

func (h *CancelRequestContextWatcherHandler) HandleUnwatchAfterCancel() {
	h.handleUnwatchAfterCancelCalled()
	<-h.cancelFinishedChan

	h.Conn.conn.SetDeadline(time.Time{})
}

func combineFieldDescriptionsAndResultFormats(outputFields, inputFields []FieldDescription, resultFormats []int16) error {
	switch {
	case len(resultFormats) == 0:
		// No format codes provided means text format for all columns.
		for i := range inputFields {
			outputFields[i] = inputFields[i]
			outputFields[i].Format = pgtype.TextFormatCode
		}
	case len(resultFormats) == 1:
		// Single format code applies to all columns.
		format := resultFormats[0]
		for i := range inputFields {
			outputFields[i] = inputFields[i]
			outputFields[i].Format = format
		}
	case len(resultFormats) == len(inputFields):
		// One format code per column.
		for i := range inputFields {
			outputFields[i] = inputFields[i]
			outputFields[i].Format = resultFormats[i]
		}
	default:
		// This should not occur if Bind validation is correct, but handle gracefully
		return fmt.Errorf("result format codes length %d does not match field count %d", len(resultFormats), len(inputFields))
	}

	return nil
}