internal/jsonrpc2: remove unused code (#910)

Remove code inherited from x/tools/internal/jsonrpc2_v2 that is not used
by MCP transports. MCP transports implement their own framing and
connection management, using only the Connection engine and message
encode/decode from this package.

Removed files:
- serve.go: Server, Listener, Dialer, idleListener, Dial, NewServer
- net.go: NetListener, NetDialer, NetPipeListener
- serve_test.go, jsonrpc2_test.go: tests for removed infrastructure

Removed from remaining files:
- frame.go: Framer interface, RawFramer, HeaderFramer implementations
- conn.go: Binder, BinderFunc, ConnectionOptions, bindConnection
- jsonrpc2.go: ErrIdleTimeout, PreempterFunc, defaultHandler, async
helper
- wire.go: ErrServerOverloaded
- conn.go: AsyncCall.IsReady (unused method)

Author: maciej-kisiel

internal/jsonrpc2/conn.go

@@ -16,45 +16,6 @@ import (
 	"github.com/modelcontextprotocol/go-sdk/internal/json"
 )
 
-// Binder builds a connection configuration.
-// This may be used in servers to generate a new configuration per connection.
-// ConnectionOptions itself implements Binder returning itself unmodified, to
-// allow for the simple cases where no per connection information is needed.
-type Binder interface {
-	// Bind returns the ConnectionOptions to use when establishing the passed-in
-	// Connection.
-	//
-	// The connection is not ready to use when Bind is called,
-	// but Bind may close it without reading or writing to it.
-	Bind(context.Context, *Connection) ConnectionOptions
-}
-
-// A BinderFunc implements the Binder interface for a standalone Bind function.
-type BinderFunc func(context.Context, *Connection) ConnectionOptions
-
-func (f BinderFunc) Bind(ctx context.Context, c *Connection) ConnectionOptions {
-	return f(ctx, c)
-}
-
-var _ Binder = BinderFunc(nil)
-
-// ConnectionOptions holds the options for new connections.
-type ConnectionOptions struct {
-	// Framer allows control over the message framing and encoding.
-	// If nil, HeaderFramer will be used.
-	Framer Framer
-	// Preempter allows registration of a pre-queue message handler.
-	// If nil, no messages will be preempted.
-	Preempter Preempter
-	// Handler is used as the queued message handler for inbound messages.
-	// If nil, all responses will be ErrNotHandled.
-	Handler Handler
-	// OnInternalError, if non-nil, is called with any internal errors that occur
-	// while serving the connection, such as protocol errors or invariant
-	// violations. (If nil, internal errors result in panics.)
-	OnInternalError func(error)
-}
-
 // Connection manages the jsonrpc2 protocol, connecting responses back to their
 // calls. Connection is bidirectional; it does not have a designated server or
 // client end.
@@ -197,9 +158,28 @@ type incomingRequest struct {
 	cancel   context.CancelFunc
 }
 
-// Bind returns the options unmodified.
-func (o ConnectionOptions) Bind(context.Context, *Connection) ConnectionOptions {
-	return o
+// Reader abstracts the transport mechanics from the JSON RPC protocol.
+// A Connection reads messages from the reader it was provided on construction,
+// and assumes that each call to Read fully transfers a single message,
+// or returns an error.
+//
+// A reader is not safe for concurrent use, it is expected it will be used by
+// a single Connection in a safe manner.
+type Reader interface {
+	// Read gets the next message from the stream.
+	Read(context.Context) (Message, error)
+}
+
+// Writer abstracts the transport mechanics from the JSON RPC protocol.
+// A Connection writes messages using the writer it was provided on construction,
+// and assumes that each call to Write fully transfers a single message,
+// or returns an error.
+//
+// A writer must be safe for concurrent use, as writes may occur concurrently
+// in practice: libraries may make calls or respond to requests asynchronously.
+type Writer interface {
+	// Write sends a message to the stream.
+	Write(context.Context, Message) error
 }
 
 // A ConnectionConfig configures a bidirectional jsonrpc2 connection.
@@ -230,59 +210,16 @@ func NewConnection(ctx context.Context, cfg ConnectionConfig) *Connection {
 	return c
 }
 
-// bindConnection creates a new connection and runs it.
-//
-// This is used by the Dial and Serve functions to build the actual connection.
-//
-// The connection is closed automatically (and its resources cleaned up) when
-// the last request has completed after the underlying ReadWriteCloser breaks,
-// but it may be stopped earlier by calling Close (for a clean shutdown).
-func bindConnection(bindCtx context.Context, rwc io.ReadWriteCloser, binder Binder, onDone func()) *Connection {
-	// TODO: Should we create a new event span here?
-	// This will propagate cancellation from ctx; should it?
-	ctx := notDone{bindCtx}
-
-	c := &Connection{
-		state:  inFlightState{closer: rwc},
-		done:   make(chan struct{}),
-		onDone: onDone,
-	}
-	// It's tempting to set a finalizer on c to verify that the state has gone
-	// idle when the connection becomes unreachable. Unfortunately, the Binder
-	// interface makes that unsafe: it allows the Handler to close over the
-	// Connection, which could create a reference cycle that would cause the
-	// Connection to become uncollectable.
-
-	options := binder.Bind(bindCtx, c)
-	framer := options.Framer
-	if framer == nil {
-		framer = HeaderFramer()
-	}
-	c.handler = options.Handler
-	if c.handler == nil {
-		c.handler = defaultHandler{}
-	}
-	c.onInternalError = options.OnInternalError
-
-	c.writer = framer.Writer(rwc)
-	reader := framer.Reader(rwc)
-	c.start(ctx, reader, options.Preempter)
-	return c
-}
-
 func (c *Connection) start(ctx context.Context, reader Reader, preempter Preempter) {
 	c.updateInFlight(func(s *inFlightState) {
 		select {
 		case <-c.done:
-			// Bind already closed the connection; don't start a goroutine to read it.
+			// The connection was already closed; don't start a goroutine to read it.
 			return
 		default:
 		}
 
 		// The goroutine started here will continue until the underlying stream is closed.
-		//
-		// (If the Binder closed the Connection already, this should error out and
-		// return almost immediately.)
 		s.reading = true
 		go c.readIncoming(ctx, reader, preempter)
 	})
@@ -439,18 +376,6 @@ type AsyncCall struct {
 // This can be used to cancel the call if needed.
 func (ac *AsyncCall) ID() ID { return ac.id }
 
-// IsReady can be used to check if the result is already prepared.
-// This is guaranteed to return true on a result for which Await has already
-// returned, or a call that failed to send in the first place.
-func (ac *AsyncCall) IsReady() bool {
-	select {
-	case <-ac.ready:
-		return true
-	default:
-		return false
-	}
-}
-
 // retire processes the response to the call.
 //
 // It is an error to call retire more than once: retire is guarded by the