Handle Execute limit correctly by sending PortalSuspended

cache.go

@@ -2,12 +2,21 @@ package wire
 
 import (
 	"context"
+	"errors"
 	"fmt"
+	"iter"
 	"sync"
 
 	"github.com/jeroenrinzema/psql-wire/pkg/buffer"
+	"github.com/jeroenrinzema/psql-wire/pkg/types"
 )
 
+// Limit represents the maximum number of rows to be written.
+// Zero denotes "no limit".
+type Limit uint32
+
+const NoLimit Limit = 0
+
 type Statement struct {
 	fn         PreparedStatementFn
 	parameters []uint32
@@ -77,15 +86,126 @@ type Portal struct {
 	statement  *Statement
 	parameters []Parameter
 	formats    []FormatCode
+
+	// The iterator state (created by iter.Pull)
+	next func() (struct{}, bool)
+	stop func()
+	// Filled in by dataWriter.Complete when the handler finishes. Used to
+	// return the tag when re-executing a completed portal.
+	tag string
+	err error
+	// Set to true when execution of the portal has finished.
+	done bool
+
+	// pending is closed when the most recently launched async goroutine
+	// finishes. A new goroutine for the same portal waits on this channel
+	// before starting, so same-portal executes serialize while different
+	// portals run in parallel.
+	pending chan struct{}
+}
+
+// Close tears down the portal from outside the execution goroutine (e.g.
+// explicit Close message or portal re-bind). If an async goroutine is still
+// running, cleanup is deferred to a background goroutine that waits for it.
+func (p *Portal) Close() {
+	if p.pending != nil {
+		pending := p.pending
+		go func() {
+			<-pending
+			p.close()
+		}()
+		return
+	}
+	p.close()
+}
+
+// close tears down the iterator inline. Used from within execute where we
+// are already inside the execution context and don't need to wait on pending.
+func (p *Portal) close() {
+	if p.stop != nil {
+		p.stop()
+		p.next = nil
+		p.stop = nil
+	}
+}
+
+func portalSuspended(writer *buffer.Writer) error {
+	writer.Start(types.ServerPortalSuspended)
+	return writer.End()
+}
+
+func (p *Portal) execute(ctx context.Context, limit Limit, reader *buffer.Reader, writer *buffer.Writer) error {
+	if p.done {
+		// Re-executing an already completed portal simply returns the tag or
+		// error again.
+		if p.err != nil {
+			return p.err
+		}
+		return commandComplete(writer, p.tag)
+	}
+
+	if p.next == nil {
+		// This is the first execute call on this portal. So let's start the
+		// execution. Otherwise we continue from where we left off.
+		session, _ := GetSession(ctx)
+		// Create a simple push-style iterator (iter.Seq) around the
+		// statement.fn.
+		seq := func(yield func(struct{}) bool) {
+			dw := &dataWriter{
+				ctx:     ctx,
+				session: session,
+				columns: p.statement.columns,
+				formats: p.formats,
+				reader:  reader,
+				client:  writer,
+				yield:   yield,
+				tag:     &p.tag,
+			}
+			err := p.statement.fn(ctx, dw, p.parameters)
+			if err != nil && !errors.Is(err, ErrSuspendedHandlerClosed) {
+				p.err = err
+			}
+		}
+
+		// Then we convert that push-style iterator into a pull-style iterator,
+		// so we can suspend the iterator when we reach the row limit.
+		p.next, p.stop = iter.Pull(seq)
+	}
+
+	var count Limit
+	for {
+		if limit != NoLimit && count >= limit {
+			// We've reached the row limit. Suspend the portal and let the
+			// client know, so it can either issue a new Execute to continue or
+			// close the portal.
+			return portalSuspended(writer)
+		}
+
+		// Run the handler until it has produced the next row or finishes. The
+		// dataWriter inside the handler will call yield to "teleport" back
+		// here.
+		_, ok := p.next()
+		if !ok {
+			// The handler has finished. CommandComplete was already written
+			// by dataWriter.Complete.
+			p.close()
+			p.done = true
+			return p.err
+		}
+
+		count++
+	}
 }
 
 func DefaultPortalCacheFn() PortalCache {
 	return &DefaultPortalCache{}
 }
 
 type DefaultPortalCache struct {
-	portals map[string]*Portal
-	mu      sync.RWMutex
+	portals      map[string]*Portal
+	executing    *Portal
+	closePending bool
+	mu           sync.RWMutex
 }
 
 func (cache *DefaultPortalCache) Bind(ctx context.Context, name string, stmt *Statement, parameters []Parameter, formats []FormatCode) error {
@@ -96,6 +216,10 @@ func (cache *DefaultPortalCache) Bind(ctx context.Context, name string, stmt *St
 		cache.portals = map[string]*Portal{}
 	}
 
+	if existing, ok := cache.portals[name]; ok {
+		existing.Close()
+	}
+
 	cache.portals[name] = &Portal{
 		statement:  stmt,
 		parameters: parameters,
@@ -145,13 +269,41 @@ func (cache *DefaultPortalCache) Execute(ctx context.Context, name string, limit
 		return nil
 	}
 
-	session, _ := GetSession(ctx)
-	return portal.statement.fn(ctx, NewDataWriter(ctx, session, portal.statement.columns, portal.formats, limit, reader, writer), portal.parameters)
+	cache.mu.Lock()
+	cache.executing = portal
+	cache.mu.Unlock()
+
+	err = portal.execute(ctx, limit, reader, writer)
+
+	cache.mu.Lock()
+	cache.executing = nil
+	needsClose := cache.closePending
+	cache.closePending = false
+	cache.mu.Unlock()
+	if needsClose {
+		portal.close()
+	}
+
+	return err
+}
+
+// closePortal closes the portal immediately, unless it is the currently
+// executing portal, in which case it marks the portal for deferred closing
+// after the current Execute call returns.
+func (cache *DefaultPortalCache) closePortal(portal *Portal) {
+	if portal == cache.executing {
+		cache.closePending = true
+	} else {
+		portal.Close()
+	}
 }
 
 func (cache *DefaultPortalCache) Delete(ctx context.Context, name string) error {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
+	if portal, ok := cache.portals[name]; ok {
+		cache.closePortal(portal)
+	}
 	delete(cache.portals, name)
 	return nil
 }
@@ -161,6 +313,7 @@ func (cache *DefaultPortalCache) DeleteByStatement(ctx context.Context, stmt *St
 	defer cache.mu.Unlock()
 	for name, portal := range cache.portals {
 		if portal.statement == stmt {
+			cache.closePortal(portal)
 			delete(cache.portals, name)
 		}
 	}
@@ -170,5 +323,8 @@ func (cache *DefaultPortalCache) DeleteByStatement(ctx context.Context, stmt *St
 func (cache *DefaultPortalCache) Close() {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
+	for _, portal := range cache.portals {
+		cache.closePortal(portal)
+	}
 	clear(cache.portals)
 }

cache_test.go

@@ -0,0 +1,66 @@
+package wire
+
+import (
+	"bytes"
+	"context"
+	"log/slog"
+	"testing"
+
+	"github.com/jeroenrinzema/psql-wire/pkg/buffer"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func newDiscardWriter() *buffer.Writer {
+	return buffer.NewWriter(slog.Default(), &bytes.Buffer{})
+}
+
+// TestCloseFromHandler verifies that calling Close from within a handler does
+// not deadlock. The currently executing portal is automatically deferred and
+// closed after Execute returns.
+func TestCloseFromHandler(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	cache := &DefaultPortalCache{}
+
+	stmt := &Statement{
+		fn: func(ctx context.Context, writer DataWriter, _ []Parameter) error {
+			cache.Close()
+			return writer.Complete("OK")
+		},
+	}
+
+	require.NoError(t, cache.Bind(ctx, "", stmt, nil, nil))
+	err := cache.Execute(ctx, "", NoLimit, nil, newDiscardWriter())
+	require.NoError(t, err)
+
+	portal, err := cache.Get(ctx, "")
+	require.NoError(t, err)
+	assert.Nil(t, portal)
+}
+
+// TestDeleteByStatementFromHandler verifies that calling DeleteByStatement
+// from within a handler does not deadlock when the currently executing portal
+// is bound to the deleted statement.
+func TestDeleteByStatementFromHandler(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	cache := &DefaultPortalCache{}
+
+	var selfStmt *Statement
+	selfStmt = &Statement{
+		fn: func(ctx context.Context, writer DataWriter, _ []Parameter) error {
+			err := cache.DeleteByStatement(ctx, selfStmt)
+			require.NoError(t, err)
+			return writer.Complete("OK")
+		},
+	}
+
+	require.NoError(t, cache.Bind(ctx, "portal", selfStmt, nil, nil))
+	err := cache.Execute(ctx, "portal", NoLimit, nil, newDiscardWriter())
+	require.NoError(t, err)
+
+	portal, err := cache.Get(ctx, "portal")
+	require.NoError(t, err)
+	assert.Nil(t, portal)
+}