netchan: use gob DecodeValue to eliminate the need for a pointer value

in Import and Export.

R=rsc
CC=golang-dev
https://golang.org/cl/1707047

src/pkg/netchan/common.go

@@ -8,6 +8,7 @@ import (
 	"gob"
 	"net"
 	"os"
+	"reflect"
 	"sync"
 )
 
@@ -62,9 +63,9 @@ func newEncDec(conn net.Conn) *encDec {
 }
 
 // Decode an item from the connection.
-func (ed *encDec) decode(e interface{}) os.Error {
+func (ed *encDec) decode(value reflect.Value) os.Error {
 	ed.decLock.Lock()
-	err := ed.dec.Decode(e)
+	err := ed.dec.DecodeValue(value)
 	if err != nil {
 		// TODO: tear down connection?
 	}

src/pkg/netchan/export.go

@@ -36,7 +36,6 @@ import (
 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
@@ -101,17 +100,19 @@ func (client *expClient) getChan(hdr *header, dir Dir) *exportChan {
 // while (client Send) requests are handled as data arrives from the client.
 func (client *expClient) run() {
 	hdr := new(header)
+	hdrValue := reflect.NewValue(hdr)
 	req := new(request)
+	reqValue := reflect.NewValue(req)
 	error := new(error)
 	for {
-		if err := client.decode(hdr); err != nil {
+		if err := client.decode(hdrValue); err != nil {
 			log.Stderr("error decoding client header:", err)
 			// TODO: tear down connection
 			return
 		}
 		switch hdr.payloadType {
 		case payRequest:
-			if err := client.decode(req); err != nil {
+			if err := client.decode(reqValue); err != nil {
 				log.Stderr("error decoding client request:", err)
 				// TODO: tear down connection
 				return
@@ -169,9 +170,8 @@ func (client *expClient) serveSend(hdr header) {
 		return
 	}
 	// Create a new value for each received item.
-	val := reflect.MakeZero(ech.ptr.Type().(*reflect.PtrType).Elem())
+	val := reflect.MakeZero(ech.ch.Type().(*reflect.ChanType).Elem())
-	ech.ptr.PointTo(val)
+	if err := client.decode(val); err != nil {
-	if err := client.decode(ech.ptr.Interface()); err != nil {
 		log.Stderr("exporter value decode:", err)
 		return
 	}
@@ -224,9 +224,7 @@ func checkChan(chT interface{}, dir Dir) (*reflect.ChanValue, os.Error) {
 // channel type.
 // 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 reflection so we can eliminate the need for pT.
-func (exp *Exporter) Export(name string, chT interface{}, dir Dir, pT interface{}) os.Error {
 	ch, err := checkChan(chT, dir)
 	if err != nil {
 		return err
@@ -237,7 +235,6 @@ func (exp *Exporter) Export(name string, chT interface{}, dir Dir, pT interface{
 	if present {
 		return os.ErrorString("channel name already being exported:" + name)
 	}
-	ptr := reflect.MakeZero(reflect.Typeof(pT)).(*reflect.PtrValue)
+	exp.chans[name] = &exportChan{ch, dir}
-	exp.chans[name] = &exportChan{ch, dir, ptr}
 	return nil
 }

src/pkg/netchan/import.go

@@ -19,7 +19,6 @@ import (
 type importChan struct {
 	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
@@ -67,9 +66,11 @@ func (imp *Importer) shutdown() {
 func (imp *Importer) run() {
 	// Loop on responses; requests are sent by ImportNValues()
 	hdr := new(header)
+	hdrValue := reflect.NewValue(hdr)
 	err := new(error)
+	errValue := reflect.NewValue(err)
 	for {
-		if e := imp.decode(hdr); e != nil {
+		if e := imp.decode(hdrValue); e != nil {
 			log.Stderr("importer header:", e)
 			imp.shutdown()
 			return
@@ -78,7 +79,7 @@ func (imp *Importer) run() {
 		case payData:
 			// done lower in loop
 		case payError:
-			if e := imp.decode(err); e != nil {
+			if e := imp.decode(errValue); e != nil {
 				log.Stderr("importer error:", e)
 				return
 			}
@@ -103,20 +104,19 @@ func (imp *Importer) run() {
 			return
 		}
 		// Create a new value for each received item.
-		val := reflect.MakeZero(ich.ptr.Type().(*reflect.PtrType).Elem())
+		value := reflect.MakeZero(ich.ch.Type().(*reflect.ChanType).Elem())
-		ich.ptr.PointTo(val)
+		if e := imp.decode(value); e != nil {
-		if e := imp.decode(ich.ptr.Interface()); e != nil {
 			log.Stderr("importer value decode:", e)
 			return
 		}
-		ich.ch.Send(val)
+		ich.ch.Send(value)
 	}
 }
 
 // Import imports a channel of the given type and specified direction.
 // It is equivalent to ImportNValues with a count of 0, meaning unbounded.
-func (imp *Importer) Import(name string, chT interface{}, dir Dir, pT interface{}) os.Error {
+func (imp *Importer) Import(name string, chT interface{}, dir Dir) os.Error {
-	return imp.ImportNValues(name, chT, dir, pT, 0)
+	return imp.ImportNValues(name, chT, dir, 0)
 }
 
 // ImportNValues imports a channel of the given type and specified direction
@@ -125,36 +125,26 @@ 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, n int) os.Error
+//	ImportNValues(name string, chT chan T, dir Dir, 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.
 // Example usage:
 //	imp, err := NewImporter("tcp", "netchanserver.mydomain.com:1234")
 //	if err != nil { log.Exit(err) }
 //	ch := make(chan myType)
-//	err := imp.ImportNValues("name", ch, Recv, new(myType), 1)
+//	err := imp.ImportNValues("name", ch, Recv, 1)
 //	if err != nil { log.Exit(err) }
 //	fmt.Printf("%+v\n", <-ch)
-// TODO: fix reflection so we can eliminate the need for pT.
+func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, n int) os.Error {
-func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, pT interface{}, n int) os.Error {
 	ch, err := checkChan(chT, dir)
 	if err != nil {
 		return err
 	}
-	// Make sure pT is a pointer (to a pointer...) to a struct.
-	rt := reflect.Typeof(pT)
-	if _, ok := rt.(*reflect.PtrType); !ok {
-		return os.ErrorString("not a pointer:" + rt.String())
-	}
 	imp.chanLock.Lock()
 	defer imp.chanLock.Unlock()
 	_, present := imp.chans[name]
 	if present {
 		return os.ErrorString("channel name already being imported:" + name)
 	}
-	ptr := reflect.MakeZero(reflect.Typeof(pT)).(*reflect.PtrValue)
+	imp.chans[name] = &importChan{ch, dir}
-	imp.chans[name] = &importChan{ch, dir, ptr}
 	// Tell the other side about this channel.
 	hdr := new(header)
 	hdr.name = name

src/pkg/netchan/netchan_test.go

@@ -11,7 +11,7 @@ const closeCount = 5 // number of items when sender closes early
 
 func exportSend(exp *Exporter, n int, t *testing.T) {
 	ch := make(chan int)
-	err := exp.Export("exportedSend", ch, Send, new(int))
+	err := exp.Export("exportedSend", ch, Send)
 	if err != nil {
 		t.Fatal("exportSend:", err)
 	}
@@ -23,7 +23,7 @@ func exportSend(exp *Exporter, n int, t *testing.T) {
 
 func exportReceive(exp *Exporter, t *testing.T) {
 	ch := make(chan int)
-	err := exp.Export("exportedRecv", ch, Recv, new(int))
+	err := exp.Export("exportedRecv", ch, Recv)
 	if err != nil {
 		t.Fatal("exportReceive:", err)
 	}
@@ -37,7 +37,7 @@ func exportReceive(exp *Exporter, t *testing.T) {
 
 func importReceive(imp *Importer, t *testing.T) {
 	ch := make(chan int)
-	err := imp.ImportNValues("exportedSend", ch, Recv, new(int), count)
+	err := imp.ImportNValues("exportedSend", ch, Recv, count)
 	if err != nil {
 		t.Fatal("importReceive:", err)
 	}
@@ -57,7 +57,7 @@ func importReceive(imp *Importer, t *testing.T) {
 
 func importSend(imp *Importer, t *testing.T) {
 	ch := make(chan int)
-	err := imp.ImportNValues("exportedRecv", ch, Send, new(int), count)
+	err := imp.ImportNValues("exportedRecv", ch, Send, count)
 	if err != nil {
 		t.Fatal("importSend:", err)
 	}