netchan: add new method Hangup to terminate transmission on a channel

Fixes #1151.

R=rsc
CC=golang-dev
https://golang.org/cl/2469043

src/pkg/netchan/export.go

@@ -346,3 +346,19 @@ func (exp *Exporter) Export(name string, chT interface{}, dir Dir) os.Error {
 	exp.chans[name] = &chanDir{ch, dir}
 	return nil
 }
+
+// Hangup disassociates the named channel from the Exporter and closes
+// the channel.  Messages in flight for the channel may be dropped.
+func (exp *Exporter) Hangup(name string) os.Error {
+	exp.mu.Lock()
+	chDir, ok := exp.chans[name]
+	if ok {
+		exp.chans[name] = nil, false
+	}
+	exp.mu.Unlock()
+	if !ok {
+		return os.ErrorString("netchan export: hangup: no such channel: " + name)
+	}
+	chDir.ch.Close()
+	return nil
+}

src/pkg/netchan/import.go

@@ -203,3 +203,19 @@ func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, n int)
 	}
 	return nil
 }
+
+// Hangup disassociates the named channel from the Importer and closes
+// the channel.  Messages in flight for the channel may be dropped.
+func (imp *Importer) Hangup(name string) os.Error {
+	imp.chanLock.Lock()
+	chDir, ok := imp.chans[name]
+	if ok {
+		imp.chans[name] = nil, false
+	}
+	imp.chanLock.Unlock()
+	if !ok {
+		return os.ErrorString("netchan import: hangup: no such channel: " + name)
+	}
+	chDir.ch.Close()
+	return nil
+}

src/pkg/netchan/netchan_test.go

@@ -230,12 +230,86 @@ func TestExportSync(t *testing.T) {
 	<-done
 }
 
+// Test hanging up the send side of an export.
+// TODO: test hanging up the receive side of an export.
+func TestExportHangup(t *testing.T) {
+	exp, err := NewExporter("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal("new exporter:", err)
+	}
+	imp, err := NewImporter("tcp", exp.Addr().String())
+	if err != nil {
+		t.Fatal("new importer:", err)
+	}
+	ech := make(chan int)
+	err = exp.Export("exportedSend", ech, Send)
+	if err != nil {
+		t.Fatal("export:", err)
+	}
+	// Prepare to receive two values. We'll actually deliver only one.
+	ich := make(chan int)
+	err = imp.ImportNValues("exportedSend", ich, Recv, 2)
+	if err != nil {
+		t.Fatal("import exportedSend:", err)
+	}
+	// Send one value, receive it.
+	const Value = 1234
+	ech <- Value
+	v := <-ich
+	if v != Value {
+		t.Fatal("expected", Value, "got", v)
+	}
+	// Now hang up the channel.  Importer should see it close.
+	exp.Hangup("exportedSend")
+	v = <-ich
+	if !closed(ich) {
+		t.Fatal("expected channel to be closed; got value", v)
+	}
+}
+
+// Test hanging up the send side of an import.
+// TODO: test hanging up the receive side of an import.
+func TestImportHangup(t *testing.T) {
+	exp, err := NewExporter("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal("new exporter:", err)
+	}
+	imp, err := NewImporter("tcp", exp.Addr().String())
+	if err != nil {
+		t.Fatal("new importer:", err)
+	}
+	ech := make(chan int)
+	err = exp.Export("exportedRecv", ech, Recv)
+	if err != nil {
+		t.Fatal("export:", err)
+	}
+	// Prepare to Send two values. We'll actually deliver only one.
+	ich := make(chan int)
+	err = imp.ImportNValues("exportedRecv", ich, Send, 2)
+	if err != nil {
+		t.Fatal("import exportedRecv:", err)
+	}
+	// Send one value, receive it.
+	const Value = 1234
+	ich <- Value
+	v := <-ech
+	if v != Value {
+		t.Fatal("expected", Value, "got", v)
+	}
+	// Now hang up the channel.  Exporter should see it close.
+	imp.Hangup("exportedRecv")
+	v = <-ech
+	if !closed(ech) {
+		t.Fatal("expected channel to be closed; got value", v)
+	}
+}
+
+// This test cross-connects a pair of exporter/importer pairs.
 type value struct {
 	i      int
 	source string
 }
 
-// This test cross-connects a pair of exporter/importer pairs.
 func TestCrossConnect(t *testing.T) {
 	e1, err := NewExporter("tcp", "127.0.0.1:0")
 	if err != nil {