netchan: allow client to send as well as receive.

much rewriting and improving, but it's still experimental.

R=rsc
CC=golang-dev
https://golang.org/cl/875045

src/pkg/netchan/common.go

-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -6,12 +6,12 @@ package netchan
 
 import (
 	"gob"
-	"log"
 	"net"
 	"os"
 	"sync"
 )
 
+// The direction of a connection from the client's perspective.
 type Dir int
 
 const (
@@ -19,8 +19,34 @@ const (
 	Send
 )
 
-// Mutex-protected encoder and decoder pair
+// Payload types
+const (
+	payRequest = iota // request structure follows
+	payError          // error structure follows
+	payData           // user payload follows
+)
+
+// A header is sent as a prefix to every transmission.  It will be followed by
+// a request structure, an error structure, or an arbitrary user payload structure.
+type header struct {
+	name        string
+	payloadType int
+}
+
+// Sent with a header once per channel from importer to exporter to report
+// that it wants to bind to a channel with the specified direction for count
+// messages.  If count is zero, it means unlimited.
+type request struct {
+	count int
+	dir   Dir
+}
 
+// Sent with a header to report an error.
+type error struct {
+	error string
+}
+
+// Mutex-protected encoder and decoder pair.
 type encDec struct {
 	decLock sync.Mutex
 	dec     *gob.Decoder
@@ -35,29 +61,27 @@ func newEncDec(conn net.Conn) *encDec {
 	}
 }
 
+// Decode an item from the connection.
 func (ed *encDec) decode(e interface{}) os.Error {
 	ed.decLock.Lock()
-	defer ed.decLock.Unlock()
 	err := ed.dec.Decode(e)
 	if err != nil {
-		log.Stderr("exporter decode:", err)
-		// TODO: tear down connection
-		return err
+		// TODO: tear down connection?
 	}
-	return nil
+	ed.decLock.Unlock()
+	return err
 }
 
-func (ed *encDec) encode(e0, e1 interface{}) os.Error {
+// Encode a header and payload onto the connection.
+func (ed *encDec) encode(hdr *header, payloadType int, payload interface{}) os.Error {
 	ed.encLock.Lock()
-	defer ed.encLock.Unlock()
-	err := ed.enc.Encode(e0)
-	if err == nil && e1 != nil {
-		err = ed.enc.Encode(e1)
-	}
-	if err != nil {
-		log.Stderr("exporter encode:", err)
-		// TODO: tear down connection?
-		return err
+	hdr.payloadType = payloadType
+	err := ed.enc.Encode(hdr)
+	if err == nil {
+		err = ed.enc.Encode(payload)
+	} else {
+		// TODO: tear down connection if there is an error?
 	}
-	return nil
+	ed.encLock.Unlock()
+	return err
 }

src/pkg/netchan/export.go

-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -17,10 +17,6 @@
 	Networked channels are not synchronized; they always behave
 	as if there is a buffer of at least one element between the
 	two machines.
-
-	TODO: at the moment, the exporting machine must send and
-	the importing machine must receive.  This restriction will
-	be lifted soon.
 */
 package netchan
 
@@ -34,10 +30,12 @@ import (
 
 // Export
 
-// A channel and its associated information: a direction
+// A channel and its associated information: a direction plus
+// a handy marshaling place for its data.
 type exportChan struct {
 	ch  *reflect.ChanValue
 	dir Dir
+	ptr *reflect.PtrValue // a pointer value we can point at each new received item
 }
 
 // An Exporter allows a set of channels to be published on a single
@@ -62,21 +60,6 @@ func newClient(exp *Exporter, conn net.Conn) *expClient {
 
 }
 
-// TODO: ASSUMES EXPORT MEANS SEND
-
-// Sent once per channel from importer to exporter to report that it's listening to a channel
-type request struct {
-	name  string
-	dir   Dir
-	count int
-}
-
-// Reply to request, sent from exporter to importer on each send.
-type response struct {
-	name  string
-	error string
-}
-
 // Wait for incoming connections, start a new runner for each
 func (exp *Exporter) listen() {
 	for {
@@ -85,70 +68,112 @@ func (exp *Exporter) listen() {
 			log.Stderr("exporter.listen:", err)
 			break
 		}
-		log.Stderr("accepted call from", conn.RemoteAddr())
 		client := newClient(exp, conn)
 		go client.run()
 	}
 }
 
-// Send a single client all its data.  For each request, this will launch
-// a serveRecv goroutine to deliver the data for that channel.
+func (client *expClient) sendError(hdr *header, err string) {
+	error := &error{err}
+	log.Stderr("export:", error.error)
+	client.encode(hdr, payError, error) // ignore any encode error, hope client gets it
+}
+
+func (client *expClient) getChan(hdr *header, dir Dir) *exportChan {
+	exp := client.exp
+	exp.chanLock.Lock()
+	ech, ok := exp.chans[hdr.name]
+	exp.chanLock.Unlock()
+	if !ok {
+		client.sendError(hdr, "no such channel: "+hdr.name)
+		return nil
+	}
+	if ech.dir != dir {
+		client.sendError(hdr, "wrong direction for channel: "+hdr.name)
+		return nil
+	}
+	return ech
+}
+
+// Manage sends and receives for a single client.  For each (client Recv) request,
+// this will launch a serveRecv goroutine to deliver the data for that channel,
+// while (client Send) requests are handled as data arrives from the client.
 func (client *expClient) run() {
+	hdr := new(header)
 	req := new(request)
+	error := new(error)
 	for {
-		if err := client.decode(req); err != nil {
-			log.Stderr("error decoding client request:", err)
+		if err := client.decode(hdr); err != nil {
+			log.Stderr("error decoding client header:", err)
 			// TODO: tear down connection
-			break
+			return
 		}
-		log.Stderrf("export request: %+v", req)
-		if req.dir == Recv {
-			go client.serveRecv(req)
-		} else {
-			log.Stderr("export request: can't handle channel direction", req.dir)
-			resp := new(response)
-			resp.name = req.name
-			resp.error = "export request: can't handle channel direction"
-			client.encode(resp, nil)
-			break
+		switch hdr.payloadType {
+		case payRequest:
+			if err := client.decode(req); err != nil {
+				log.Stderr("error decoding client request:", err)
+				// TODO: tear down connection
+				return
+			}
+			switch req.dir {
+			case Recv:
+				go client.serveRecv(*hdr, req.count)
+			case Send:
+				// Request to send is clear as a matter of protocol
+				// but not actually used by the implementation.
+				// The actual sends will have payload type payData.
+				// TODO: manage the count?
+			default:
+				error.error = "export request: can't handle channel direction"
+				log.Stderr(error.error, req.dir)
+				client.encode(hdr, payError, error)
+			}
+		case payData:
+			client.serveSend(*hdr)
 		}
 	}
 }
 
-// Send all the data on a single channel to a client asking for a Recv
-func (client *expClient) serveRecv(req *request) {
-	exp := client.exp
-	resp := new(response)
-	resp.name = req.name
-	var ok bool
-	exp.chanLock.Lock()
-	ech, ok := exp.chans[req.name]
-	exp.chanLock.Unlock()
-	if !ok {
-		resp.error = "no such channel: " + req.name
-		log.Stderr("export:", resp.error)
-		client.encode(resp, nil) // ignore any encode error, hope client gets it
+// Send all the data on a single channel to a client asking for a Recv.
+// The header is passed by value to avoid issues of overwriting.
+func (client *expClient) serveRecv(hdr header, count int) {
+	ech := client.getChan(&hdr, Send)
+	if ech == nil {
 		return
 	}
 	for {
-		if ech.dir != Send {
-			log.Stderr("TODO: recv export unimplemented")
-			break
-		}
 		val := ech.ch.Recv()
-		if err := client.encode(resp, val.Interface()); err != nil {
+		if err := client.encode(&hdr, payData, val.Interface()); err != nil {
 			log.Stderr("error encoding client response:", err)
+			client.sendError(&hdr, err.String())
 			break
 		}
-		if req.count > 0 {
-			req.count--
-			if req.count == 0 {
+		if count > 0 {
+			if count--; count == 0 {
 				break
 			}
 		}
 	}
 }
 
+// Receive and deliver locally one item from a client asking for a Send
+// The header is passed by value to avoid issues of overwriting.
+func (client *expClient) serveSend(hdr header) {
+	ech := client.getChan(&hdr, Recv)
+	if ech == nil {
+		return
+	}
+	// Create a new value for each received item.
+	val := reflect.MakeZero(ech.ptr.Type().(*reflect.PtrType).Elem())
+	ech.ptr.PointTo(val)
+	if err := client.decode(ech.ptr.Interface()); err != nil {
+		log.Stderr("exporter value decode:", err)
+		return
+	}
+	ech.ch.Send(val)
+	// TODO count
+}
+
 // NewExporter creates a new Exporter to export channels
 // on the network and local address defined as in net.Listen.
 func NewExporter(network, localaddr string) (*Exporter, os.Error) {
@@ -195,7 +220,8 @@ func checkChan(chT interface{}, dir Dir) (*reflect.ChanValue, os.Error) {
 // Despite the literal signature, the effective signature is
 //	Export(name string, chT chan T, dir Dir)
 // where T must be a struct, pointer to struct, etc.
-func (exp *Exporter) Export(name string, chT interface{}, dir Dir) os.Error {
+// TODO: fix gob interface so we can eliminate the need for pT, and for structs.
+func (exp *Exporter) Export(name string, chT interface{}, dir Dir, pT interface{}) os.Error {
 	ch, err := checkChan(chT, dir)
 	if err != nil {
 		return err
@@ -206,6 +232,7 @@ func (exp *Exporter) Export(name string, chT interface{}, dir Dir) os.Error {
 	if present {
 		return os.ErrorString("channel name already being exported:" + name)
 	}
-	exp.chans[name] = &exportChan{ch, dir}
+	ptr := reflect.MakeZero(reflect.Typeof(pT)).(*reflect.PtrValue)
+	exp.chans[name] = &exportChan{ch, dir, ptr}
 	return nil
 }

src/pkg/netchan/import.go

-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -14,12 +14,12 @@ import (
 
 // Import
 
-// A channel and its associated information: a template value, direction and a count
+// A channel and its associated information: a template value and direction,
+// plus a handy marshaling place for its data.
 type importChan struct {
-	ch    *reflect.ChanValue
-	dir   Dir
-	ptr   *reflect.PtrValue // a pointer value we can point at each new item
-	count int
+	ch  *reflect.ChanValue
+	dir Dir
+	ptr *reflect.PtrValue // a pointer value we can point at each new received item
 }
 
 // An Importer allows a set of channels to be imported from a single
@@ -32,8 +32,6 @@ type Importer struct {
 	chans    map[string]*importChan
 }
 
-// TODO: ASSUMES IMPORT MEANS RECEIVE
-
 // NewImporter creates a new Importer object to import channels
 // from an Exporter at the network and remote address as defined in net.Dial.
 // The Exporter must be available and serving when the Importer is
@@ -54,37 +52,49 @@ func NewImporter(network, remoteaddr string) (*Importer, os.Error) {
 // Handle the data from a single imported data stream, which will
 // have the form
 //	(response, data)*
-// The response identifies by name which channel is receiving data.
-// TODO: allow an importer to send.
+// The response identifies by name which channel is transmitting data.
 func (imp *Importer) run() {
 	// Loop on responses; requests are sent by ImportNValues()
-	resp := new(response)
+	hdr := new(header)
+	err := new(error)
 	for {
-		if err := imp.decode(resp); err != nil {
-			log.Stderr("importer response decode:", err)
-			break
+		if e := imp.decode(hdr); e != nil {
+			log.Stderr("importer header:", e)
+			return
 		}
-		if resp.error != "" {
-			log.Stderr("importer response error:", resp.error)
-			// TODO: tear down connection
-			break
+		switch hdr.payloadType {
+		case payData:
+			// done lower in loop
+		case payError:
+			if e := imp.decode(err); e != nil {
+				log.Stderr("importer error:", e)
+				return
+			}
+			if err.error != "" {
+				log.Stderr("importer response error:", err.error)
+				// TODO: tear down connection
+				return
+			}
+		default:
+			log.Stderr("unexpected payload type:", hdr.payloadType)
+			return
 		}
 		imp.chanLock.Lock()
-		ich, ok := imp.chans[resp.name]
+		ich, ok := imp.chans[hdr.name]
 		imp.chanLock.Unlock()
 		if !ok {
-			log.Stderr("unknown name in request:", resp.name)
-			break
+			log.Stderr("unknown name in request:", hdr.name)
+			return
 		}
 		if ich.dir != Recv {
-			log.Stderr("TODO: import send unimplemented")
-			break
+			log.Stderr("cannot happen: receive from non-Recv channel")
+			return
 		}
 		// Create a new value for each received item.
 		val := reflect.MakeZero(ich.ptr.Type().(*reflect.PtrType).Elem())
 		ich.ptr.PointTo(val)
-		if err := imp.decode(ich.ptr.Interface()); err != nil {
-			log.Stderr("importer value decode:", err)
+		if e := imp.decode(ich.ptr.Interface()); e != nil {
+			log.Stderr("importer value decode:", e)
 			return
 		}
 		ich.ch.Send(val)
@@ -103,7 +113,7 @@ func (imp *Importer) Import(name string, chT interface{}, dir Dir, pT interface{
 // the remote site's channel is provided in the call and may be of arbitrary
 // channel type.
 // Despite the literal signature, the effective signature is
-//	ImportNValues(name string, chT chan T, dir Dir, pT T)
+//	ImportNValues(name string, chT chan T, dir Dir, pT T, n int) os.Error
 // where T must be a struct, pointer to struct, etc.  pT may be more indirect
 // than the value type of the channel (e.g.  chan T, pT *T) but it must be a
 // pointer.
@@ -114,7 +124,7 @@ func (imp *Importer) Import(name string, chT interface{}, dir Dir, pT interface{
 //	err := imp.ImportNValues("name", ch, Recv, new(myType), 1)
 //	if err != nil { log.Exit(err) }
 //	fmt.Printf("%+v\n", <-ch)
-// (TODO: Can we eliminate the need for pT?)
+// TODO: fix gob interface so we can eliminate the need for pT, and for structs.
 func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, pT interface{}, n int) os.Error {
 	ch, err := checkChan(chT, dir)
 	if err != nil {
@@ -135,15 +145,28 @@ func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, pT int
 		return os.ErrorString("channel name already being imported:" + name)
 	}
 	ptr := reflect.MakeZero(reflect.Typeof(pT)).(*reflect.PtrValue)
-	imp.chans[name] = &importChan{ch, dir, ptr, n}
+	imp.chans[name] = &importChan{ch, dir, ptr}
 	// Tell the other side about this channel.
+	hdr := new(header)
+	hdr.name = name
+	hdr.payloadType = payRequest
 	req := new(request)
-	req.name = name
 	req.dir = dir
 	req.count = n
-	if err := imp.encode(req, nil); err != nil {
+	if err := imp.encode(hdr, payRequest, req); err != nil {
 		log.Stderr("importer request encode:", err)
 		return err
 	}
+	if dir == Send {
+		go func() {
+			for i := 0; n == 0 || i < n; i++ {
+				val := ch.Recv()
+				if err := imp.encode(hdr, payData, val.Interface()); err != nil {
+					log.Stderr("error encoding client response:", err)
+					return
+				}
+			}
+		}()
+	}
 	return nil
 }

src/pkg/netchan/netchan_test.go

-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -14,37 +14,82 @@ type value struct {
 	s string
 }
 
+const count = 10
+
 func exportSend(exp *Exporter, t *testing.T) {
-	c := make(chan value)
-	err := exp.Export("name", c, Send)
+	ch := make(chan value)
+	err := exp.Export("exportedSend", ch, Send, new(value))
+	if err != nil {
+		t.Fatal("exportSend:", err)
+	}
+	for i := 0; i < count; i++ {
+		ch <- value{23 + i, "hello"}
+	}
+}
+
+func exportReceive(exp *Exporter, t *testing.T) {
+	ch := make(chan value)
+	err := exp.Export("exportedRecv", ch, Recv, new(value))
 	if err != nil {
-		t.Fatal("export:", err)
+		t.Fatal("exportReceive:", err)
+	}
+	for i := 0; i < count; i++ {
+		v := <-ch
+		fmt.Printf("%v\n", v)
+		if v.i != 45+i || v.s != "hello" {
+			t.Errorf("export Receive: bad value: expected 4%d, hello; got %+v", 45+i, v)
+		}
 	}
-	c <- value{23, "hello"}
 }
 
 func importReceive(imp *Importer, t *testing.T) {
 	ch := make(chan value)
-	err := imp.ImportNValues("name", ch, Recv, new(value), 1)
+	err := imp.ImportNValues("exportedSend", ch, Recv, new(value), count)
 	if err != nil {
-		t.Fatal("import:", err)
+		t.Fatal("importReceive:", err)
 	}
-	v := <-ch
-	fmt.Printf("%v\n", v)
-	if v.i != 23 || v.s != "hello" {
-		t.Errorf("bad value: expected 23, hello; got %+v\n", v)
+	for i := 0; i < count; i++ {
+		v := <-ch
+		fmt.Printf("%v\n", v)
+		if v.i != 23+i || v.s != "hello" {
+			t.Errorf("importReceive: bad value: expected %d, hello; got %+v", 23+i, v)
+		}
 	}
 }
 
-func TestBabyStep(t *testing.T) {
+func importSend(imp *Importer, t *testing.T) {
+	ch := make(chan value)
+	err := imp.ImportNValues("exportedRecv", ch, Send, new(value), count)
+	if err != nil {
+		t.Fatal("importSend:", err)
+	}
+	for i := 0; i < count; i++ {
+		ch <- value{45 + i, "hello"}
+	}
+}
+
+func TestExportSendImportReceive(t *testing.T) {
 	exp, err := NewExporter("tcp", ":0")
 	if err != nil {
 		t.Fatal("new exporter:", err)
 	}
-	go exportSend(exp, t)
 	imp, err := NewImporter("tcp", exp.Addr().String())
 	if err != nil {
 		t.Fatal("new importer:", err)
 	}
+	go exportSend(exp, t)
 	importReceive(imp, t)
 }
+
+func TestExportReceiveImportSend(t *testing.T) {
+	exp, err := NewExporter("tcp", ":0")
+	if err != nil {
+		t.Fatal("new exporter:", err)
+	}
+	imp, err := NewImporter("tcp", exp.Addr().String())
+	if err != nil {
+		t.Fatal("new importer:", err)
+	}
+	go importSend(imp, t)
+	exportReceive(exp, t)
+}