drpcmanager: expose error from transport failures

A cancel can sometimes only be performed by closing the underlying
transport because that is the only way to interrupt a read/write
syscall. But, rather than assume that every error from the transport
failing is due to a cancel, only assume that an io.EOF means that.
This can help with debugging when the remote side dies due things
besides a "clean" close of the underlying transport.

Closes #31

Change-Id: Ia655d07984f6abe0492e7f9300d2638a1c82b4d4

drpcmanager/manager.go

@@ -5,7 +5,9 @@ package drpcmanager
 
 import (
 	"context"
+	"errors"
 	"fmt"
+	"io"
 	"time"
 
 	"github.com/zeebo/errs"
@@ -294,7 +296,11 @@ func (m *Manager) manageStream(ctx context.Context, stream *drpcstream.Stream) {
 
 	select {
 	case <-m.sigs.term.Signal():
-		stream.Cancel(context.Canceled)
+		err := m.sigs.term.Err()
+		if errors.Is(err, io.EOF) {
+			err = context.Canceled
+		}
+		stream.Cancel(err)
 		<-m.sterm
 		return
 

internal/integration/transport_test.go

@@ -5,6 +5,8 @@ package integration
 
 import (
 	"context"
+	"errors"
+	"io"
 	"testing"
 
 	"github.com/zeebo/assert"
@@ -80,13 +82,14 @@ func TestTransport_ErrorCausesCancel(t *testing.T) {
 
 	// create a channel to signal when the rpc has started
 	started := make(chan struct{})
-	errs := make(chan error, 2)
+	serr := make(chan error, 1)
+	cerr := make(chan error, 1)
 
 	// create a server that signals then waits for the context to die
 	cli, close := createConnection(impl{
 		Method2Fn: func(stream DRPCService_Method2Stream) error {
 			started <- struct{}{}
-			errs <- stream.MsgRecv(nil, Encoding)
+			serr <- stream.MsgRecv(nil, Encoding)
 			return nil
 		},
 	})
@@ -96,7 +99,7 @@ func TestTransport_ErrorCausesCancel(t *testing.T) {
 	ctx.Run(func(ctx context.Context) {
 		stream, _ := cli.Method2(ctx)
 		started <- struct{}{}
-		errs <- stream.MsgRecv(nil, Encoding)
+		cerr <- stream.MsgRecv(nil, Encoding)
 	})
 
 	// wait for it to be started. it is important to wait for
@@ -111,6 +114,6 @@ func TestTransport_ErrorCausesCancel(t *testing.T) {
 	assert.NoError(t, cli.DRPCConn().(*drpcconn.Conn).Transport().Close())
 
 	// ensure both of the errors we sent are canceled
-	assert.Equal(t, <-errs, context.Canceled)
-	assert.Equal(t, <-errs, context.Canceled)
+	assert.That(t, errors.Is(<-serr, context.Canceled))
+	assert.That(t, errors.Is(<-cerr, io.ErrClosedPipe))
 }