Fix 271

answer.go

@@ -2,6 +2,7 @@ package capnp
 
 import (
 	"context"
+	"fmt"
 	"strconv"
 	"sync"
 
@@ -128,9 +129,7 @@ func (p *Promise) resolution() resolution {
 func (p *Promise) Fulfill(result Ptr) {
 	defer p.mu.Unlock()
 	p.mu.Lock()
-	if !p.isUnresolved() {
-		panic("Promise.Fulfill called after Fulfill or Reject")
-	}
+	p.requireUnresolved("Fulfill")
 	p.resolve(result, nil)
 }
 
@@ -145,9 +144,7 @@ func (p *Promise) Reject(e error) {
 	}
 	defer p.mu.Unlock()
 	p.mu.Lock()
-	if !p.isUnresolved() {
-		panic("Promise.Reject called after Fulfill or Reject")
-	}
+	p.requireUnresolved("Reject")
 	p.resolve(Ptr{}, e)
 }
 
@@ -163,6 +160,28 @@ func (p *Promise) Resolve(r Ptr, e error) {
 	}
 }
 
+// requireUnresolved is a helper method for checking for duplicate
+// calls to Fulfill() or Reject(); panics if the promise is not in
+// the unresolved state.
+//
+// The callerMethod argument should be the name of the method which
+// is invoking requireUnresolved. The panic message will report this
+// value as well as the method that originally resolved the promise,
+// and which method (Fulfill or Reject) was used to resolve it.
+func (p *Promise) requireUnresolved(callerMethod string) {
+	if !p.isUnresolved() {
+		var prevMethod string
+		if p.err == nil {
+			prevMethod = "Fulfill"
+		} else {
+			prevMethod = fmt.Sprintf("Reject (error = %q)", p.err)
+		}
+
+		panic("Promise." + callerMethod +
+			" called after previous call to " + prevMethod)
+	}
+}
+
 // resolve moves p into the resolved state from unresolved.  The caller
 // must be holding onto p.mu.
 func (p *Promise) resolve(r Ptr, e error) {

rpc/level0_test.go

@@ -15,6 +15,7 @@ import (
 	"capnproto.org/go/capnp/v3/exc"
 	"capnproto.org/go/capnp/v3/pogs"
 	"capnproto.org/go/capnp/v3/rpc"
+	testcp "capnproto.org/go/capnp/v3/rpc/internal/testcapnp"
 	"capnproto.org/go/capnp/v3/rpc/transport"
 	"capnproto.org/go/capnp/v3/server"
 	rpccp "capnproto.org/go/capnp/v3/std/capnp/rpc"
@@ -1768,6 +1769,58 @@ func TestSendCancel(t *testing.T) {
 	}
 }
 
+func TestHandleReturn_regression(t *testing.T) {
+	t.Parallel()
+
+	p1, p2 := transport.NewPipe(1)
+
+	srv := testcp.PingPong_ServerToClient(pingPongServer{})
+	conn1 := rpc.NewConn(rpc.NewTransport(p2), &rpc.Options{
+		BootstrapClient: capnp.Client(srv),
+	})
+	defer conn1.Close()
+
+	conn2 := rpc.NewConn(rpc.NewTransport(p1), nil)
+	defer conn2.Close()
+
+	t.Run("MethodCallWithExpiredContext", func(t *testing.T) {
+		pp := testcp.PingPong(conn2.Bootstrap(context.Background()))
+		defer pp.Release()
+
+		// create an EXPIRED context
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+
+		f, release := pp.EchoNum(ctx, func(ps testcp.PingPong_echoNum_Params) error {
+			ps.SetN(42)
+			return nil
+		})
+		defer release()
+
+		_, err := f.Struct()
+		assert.ErrorIs(t, err, ctx.Err())
+	})
+
+	t.Run("BootstrapWithExpiredContext", func(t *testing.T) {
+		// create an EXPIRED context
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+
+		// NOTE: bootstrap with expired context
+		pp := testcp.PingPong(conn2.Bootstrap(ctx))
+		defer pp.Release()
+
+		f, release := pp.EchoNum(ctx, func(ps testcp.PingPong_echoNum_Params) error {
+			ps.SetN(42)
+			return nil
+		})
+		defer release()
+
+		_, err := f.Struct()
+		assert.ErrorIs(t, err, ctx.Err())
+	})
+}
+
 // finishTest drains both sides of a pipe and reports any errors to t.
 func finishTest(t errorfer, conn *rpc.Conn, p2 rpc.Transport) {
 	ctx, cancel := context.WithCancel(context.Background())

rpc/question.go

@@ -157,9 +157,11 @@ func (q *question) PipelineSend(ctx context.Context, transform []capnp.PipelineO
 			return q.c.newPipelineCallMessage(m, q.id, transform, q2.id, s)
 		}, func(err error) {
 			if err != nil {
-				q.c.questions[q2.id] = nil
-				q.c.questionID.remove(uint32(q2.id))
-				q.p.Reject(rpcerr.Failedf("send message: %w", err))
+				syncutil.With(&q.c.mu, func() {
+					q.c.questions[q2.id] = nil
+					q.c.questionID.remove(uint32(q2.id))
+				})
+				q2.p.Reject(rpcerr.Failedf("send message: %w", err))
 				return
 			}