Imported Upstream version 60upstream/60

9 files changed, 1955 insertions, 0 deletions

diff --git a/src/pkg/rpc/Makefile b/src/pkg/rpc/Makefile
new file mode 100644
index 000000000..191b10d05
--- /dev/null
+++ b/src/pkg/rpc/Makefile
@@ -0,0 +1,13 @@
+# Copyright 2009 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.
+
+include ../../Make.inc
+
+TARG=rpc
+GOFILES=\
+	client.go\
+	debug.go\
+	server.go\
+
+include ../../Make.pkg
diff --git a/src/pkg/rpc/client.go b/src/pkg/rpc/client.go
new file mode 100644
index 000000000..4acfdf6d9
--- /dev/null
+++ b/src/pkg/rpc/client.go
@@ -0,0 +1,286 @@
+// Copyright 2009 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.
+
+package rpc
+
+import (
+	"bufio"
+	"gob"
+	"http"
+	"io"
+	"log"
+	"net"
+	"os"
+	"sync"
+)
+
+// ServerError represents an error that has been returned from
+// the remote side of the RPC connection.
+type ServerError string
+
+func (e ServerError) String() string {
+	return string(e)
+}
+
+var ErrShutdown = os.NewError("connection is shut down")
+
+// Call represents an active RPC.
+type Call struct {
+	ServiceMethod string      // The name of the service and method to call.
+	Args          interface{} // The argument to the function (*struct).
+	Reply         interface{} // The reply from the function (*struct).
+	Error         os.Error    // After completion, the error status.
+	Done          chan *Call  // Strobes when call is complete; value is the error status.
+	seq           uint64
+}
+
+// Client represents an RPC Client.
+// There may be multiple outstanding Calls associated
+// with a single Client.
+type Client struct {
+	mutex    sync.Mutex // protects pending, seq, request
+	sending  sync.Mutex
+	request  Request
+	seq      uint64
+	codec    ClientCodec
+	pending  map[uint64]*Call
+	closing  bool
+	shutdown bool
+}
+
+// A ClientCodec implements writing of RPC requests and
+// reading of RPC responses for the client side of an RPC session.
+// The client calls WriteRequest to write a request to the connection
+// and calls ReadResponseHeader and ReadResponseBody in pairs
+// to read responses.  The client calls Close when finished with the
+// connection. ReadResponseBody may be called with a nil
+// argument to force the body of the response to be read and then
+// discarded.
+type ClientCodec interface {
+	WriteRequest(*Request, interface{}) os.Error
+	ReadResponseHeader(*Response) os.Error
+	ReadResponseBody(interface{}) os.Error
+
+	Close() os.Error
+}
+
+func (client *Client) send(c *Call) {
+	// Register this call.
+	client.mutex.Lock()
+	if client.shutdown {
+		c.Error = ErrShutdown
+		client.mutex.Unlock()
+		c.done()
+		return
+	}
+	c.seq = client.seq
+	client.seq++
+	client.pending[c.seq] = c
+	client.mutex.Unlock()
+
+	// Encode and send the request.
+	client.sending.Lock()
+	defer client.sending.Unlock()
+	client.request.Seq = c.seq
+	client.request.ServiceMethod = c.ServiceMethod
+	if err := client.codec.WriteRequest(&client.request, c.Args); err != nil {
+		panic("rpc: client encode error: " + err.String())
+	}
+}
+
+func (client *Client) input() {
+	var err os.Error
+	var response Response
+	for err == nil {
+		response = Response{}
+		err = client.codec.ReadResponseHeader(&response)
+		if err != nil {
+			if err == os.EOF && !client.closing {
+				err = io.ErrUnexpectedEOF
+			}
+			break
+		}
+		seq := response.Seq
+		client.mutex.Lock()
+		c := client.pending[seq]
+		client.pending[seq] = c, false
+		client.mutex.Unlock()
+
+		if response.Error == "" {
+			err = client.codec.ReadResponseBody(c.Reply)
+			if err != nil {
+				c.Error = os.NewError("reading body " + err.String())
+			}
+		} else {
+			// We've got an error response. Give this to the request;
+			// any subsequent requests will get the ReadResponseBody
+			// error if there is one.
+			c.Error = ServerError(response.Error)
+			err = client.codec.ReadResponseBody(nil)
+			if err != nil {
+				err = os.NewError("reading error body: " + err.String())
+			}
+		}
+		c.done()
+	}
+	// Terminate pending calls.
+	client.mutex.Lock()
+	client.shutdown = true
+	for _, call := range client.pending {
+		call.Error = err
+		call.done()
+	}
+	client.mutex.Unlock()
+	if err != os.EOF || !client.closing {
+		log.Println("rpc: client protocol error:", err)
+	}
+}
+
+func (call *Call) done() {
+	select {
+	case call.Done <- call:
+		// ok
+	default:
+		// We don't want to block here.  It is the caller's responsibility to make
+		// sure the channel has enough buffer space. See comment in Go().
+	}
+}
+
+// NewClient returns a new Client to handle requests to the
+// set of services at the other end of the connection.
+// It adds a buffer to the write side of the connection so
+// the header and payload are sent as a unit.
+func NewClient(conn io.ReadWriteCloser) *Client {
+	encBuf := bufio.NewWriter(conn)
+	client := &gobClientCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(encBuf), encBuf}
+	return NewClientWithCodec(client)
+}
+
+// NewClientWithCodec is like NewClient but uses the specified
+// codec to encode requests and decode responses.
+func NewClientWithCodec(codec ClientCodec) *Client {
+	client := &Client{
+		codec:   codec,
+		pending: make(map[uint64]*Call),
+	}
+	go client.input()
+	return client
+}
+
+type gobClientCodec struct {
+	rwc    io.ReadWriteCloser
+	dec    *gob.Decoder
+	enc    *gob.Encoder
+	encBuf *bufio.Writer
+}
+
+func (c *gobClientCodec) WriteRequest(r *Request, body interface{}) (err os.Error) {
+	if err = c.enc.Encode(r); err != nil {
+		return
+	}
+	if err = c.enc.Encode(body); err != nil {
+		return
+	}
+	return c.encBuf.Flush()
+}
+
+func (c *gobClientCodec) ReadResponseHeader(r *Response) os.Error {
+	return c.dec.Decode(r)
+}
+
+func (c *gobClientCodec) ReadResponseBody(body interface{}) os.Error {
+	return c.dec.Decode(body)
+}
+
+func (c *gobClientCodec) Close() os.Error {
+	return c.rwc.Close()
+}
+
+// DialHTTP connects to an HTTP RPC server at the specified network address
+// listening on the default HTTP RPC path.
+func DialHTTP(network, address string) (*Client, os.Error) {
+	return DialHTTPPath(network, address, DefaultRPCPath)
+}
+
+// DialHTTPPath connects to an HTTP RPC server 
+// at the specified network address and path.
+func DialHTTPPath(network, address, path string) (*Client, os.Error) {
+	var err os.Error
+	conn, err := net.Dial(network, address)
+	if err != nil {
+		return nil, err
+	}
+	io.WriteString(conn, "CONNECT "+path+" HTTP/1.0\n\n")
+
+	// Require successful HTTP response
+	// before switching to RPC protocol.
+	resp, err := http.ReadResponse(bufio.NewReader(conn), &http.Request{Method: "CONNECT"})
+	if err == nil && resp.Status == connected {
+		return NewClient(conn), nil
+	}
+	if err == nil {
+		err = os.NewError("unexpected HTTP response: " + resp.Status)
+	}
+	conn.Close()
+	return nil, &net.OpError{"dial-http", network + " " + address, nil, err}
+}
+
+// Dial connects to an RPC server at the specified network address.
+func Dial(network, address string) (*Client, os.Error) {
+	conn, err := net.Dial(network, address)
+	if err != nil {
+		return nil, err
+	}
+	return NewClient(conn), nil
+}
+
+func (client *Client) Close() os.Error {
+	client.mutex.Lock()
+	if client.shutdown || client.closing {
+		client.mutex.Unlock()
+		return ErrShutdown
+	}
+	client.closing = true
+	client.mutex.Unlock()
+	return client.codec.Close()
+}
+
+// Go invokes the function asynchronously.  It returns the Call structure representing
+// the invocation.  The done channel will signal when the call is complete by returning
+// the same Call object.  If done is nil, Go will allocate a new channel.
+// If non-nil, done must be buffered or Go will deliberately crash.
+func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call {
+	c := new(Call)
+	c.ServiceMethod = serviceMethod
+	c.Args = args
+	c.Reply = reply
+	if done == nil {
+		done = make(chan *Call, 10) // buffered.
+	} else {
+		// If caller passes done != nil, it must arrange that
+		// done has enough buffer for the number of simultaneous
+		// RPCs that will be using that channel.  If the channel
+		// is totally unbuffered, it's best not to run at all.
+		if cap(done) == 0 {
+			log.Panic("rpc: done channel is unbuffered")
+		}
+	}
+	c.Done = done
+	if client.shutdown {
+		c.Error = ErrShutdown
+		c.done()
+		return c
+	}
+	client.send(c)
+	return c
+}
+
+// Call invokes the named function, waits for it to complete, and returns its error status.
+func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) os.Error {
+	if client.shutdown {
+		return ErrShutdown
+	}
+	call := <-client.Go(serviceMethod, args, reply, make(chan *Call, 1)).Done
+	return call.Error
+}
diff --git a/src/pkg/rpc/debug.go b/src/pkg/rpc/debug.go
new file mode 100644
index 000000000..7e3e6f6e5
--- /dev/null
+++ b/src/pkg/rpc/debug.go
@@ -0,0 +1,90 @@
+// Copyright 2009 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.
+
+package rpc
+
+/*
+	Some HTML presented at http://machine:port/debug/rpc
+	Lists services, their methods, and some statistics, still rudimentary.
+*/
+
+import (
+	"fmt"
+	"http"
+	"sort"
+	"template"
+)
+
+const debugText = `<html>
+	<body>
+	<title>Services</title>
+	{{range .}}
+	<hr>
+	Service {{.Name}}
+	<hr>
+		<table>
+		<th align=center>Method</th><th align=center>Calls</th>
+		{{range .Method}}
+			<tr>
+			<td align=left font=fixed>{{.Name}}({{.Type.ArgType}}, {{.Type.ReplyType}}) os.Error</td>
+			<td align=center>{{.Type.NumCalls}}</td>
+			</tr>
+		{{end}}
+		</table>
+	{{end}}
+	</body>
+	</html>`
+
+var debug = template.Must(template.New("RPC debug").Parse(debugText))
+
+type debugMethod struct {
+	Type *methodType
+	Name string
+}
+
+type methodArray []debugMethod
+
+type debugService struct {
+	Service *service
+	Name    string
+	Method  methodArray
+}
+
+type serviceArray []debugService
+
+func (s serviceArray) Len() int           { return len(s) }
+func (s serviceArray) Less(i, j int) bool { return s[i].Name < s[j].Name }
+func (s serviceArray) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+func (m methodArray) Len() int           { return len(m) }
+func (m methodArray) Less(i, j int) bool { return m[i].Name < m[j].Name }
+func (m methodArray) Swap(i, j int)      { m[i], m[j] = m[j], m[i] }
+
+type debugHTTP struct {
+	*Server
+}
+
+// Runs at /debug/rpc
+func (server debugHTTP) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	// Build a sorted version of the data.
+	var services = make(serviceArray, len(server.serviceMap))
+	i := 0
+	server.mu.Lock()
+	for sname, service := range server.serviceMap {
+		services[i] = debugService{service, sname, make(methodArray, len(service.method))}
+		j := 0
+		for mname, method := range service.method {
+			services[i].Method[j] = debugMethod{method, mname}
+			j++
+		}
+		sort.Sort(services[i].Method)
+		i++
+	}
+	server.mu.Unlock()
+	sort.Sort(services)
+	err := debug.Execute(w, services)
+	if err != nil {
+		fmt.Fprintln(w, "rpc: error executing template:", err.String())
+	}
+}
diff --git a/src/pkg/rpc/jsonrpc/Makefile b/src/pkg/rpc/jsonrpc/Makefile
new file mode 100644
index 000000000..b9a1ac2f7
--- /dev/null
+++ b/src/pkg/rpc/jsonrpc/Makefile
@@ -0,0 +1,12 @@
+# 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.
+
+include ../../../Make.inc
+
+TARG=rpc/jsonrpc
+GOFILES=\
+	client.go\
+	server.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/rpc/jsonrpc/all_test.go b/src/pkg/rpc/jsonrpc/all_test.go
new file mode 100644
index 000000000..c1a9e8ecb
--- /dev/null
+++ b/src/pkg/rpc/jsonrpc/all_test.go
@@ -0,0 +1,156 @@
+// 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.
+
+package jsonrpc
+
+import (
+	"fmt"
+	"json"
+	"net"
+	"os"
+	"rpc"
+	"testing"
+)
+
+type Args struct {
+	A, B int
+}
+
+type Reply struct {
+	C int
+}
+
+type Arith int
+
+func (t *Arith) Add(args *Args, reply *Reply) os.Error {
+	reply.C = args.A + args.B
+	return nil
+}
+
+func (t *Arith) Mul(args *Args, reply *Reply) os.Error {
+	reply.C = args.A * args.B
+	return nil
+}
+
+func (t *Arith) Div(args *Args, reply *Reply) os.Error {
+	if args.B == 0 {
+		return os.NewError("divide by zero")
+	}
+	reply.C = args.A / args.B
+	return nil
+}
+
+func (t *Arith) Error(args *Args, reply *Reply) os.Error {
+	panic("ERROR")
+}
+
+func init() {
+	rpc.Register(new(Arith))
+}
+
+func TestServer(t *testing.T) {
+	type addResp struct {
+		Id     interface{} `json:"id"`
+		Result Reply       `json:"result"`
+		Error  interface{} `json:"error"`
+	}
+
+	cli, srv := net.Pipe()
+	defer cli.Close()
+	go ServeConn(srv)
+	dec := json.NewDecoder(cli)
+
+	// Send hand-coded requests to server, parse responses.
+	for i := 0; i < 10; i++ {
+		fmt.Fprintf(cli, `{"method": "Arith.Add", "id": "\u%04d", "params": [{"A": %d, "B": %d}]}`, i, i, i+1)
+		var resp addResp
+		err := dec.Decode(&resp)
+		if err != nil {
+			t.Fatalf("Decode: %s", err)
+		}
+		if resp.Error != nil {
+			t.Fatalf("resp.Error: %s", resp.Error)
+		}
+		if resp.Id.(string) != string(i) {
+			t.Fatalf("resp: bad id %q want %q", resp.Id.(string), string(i))
+		}
+		if resp.Result.C != 2*i+1 {
+			t.Fatalf("resp: bad result: %d+%d=%d", i, i+1, resp.Result.C)
+		}
+	}
+
+	fmt.Fprintf(cli, "{}\n")
+	var resp addResp
+	if err := dec.Decode(&resp); err != nil {
+		t.Fatalf("Decode after empty: %s", err)
+	}
+	if resp.Error == nil {
+		t.Fatalf("Expected error, got nil")
+	}
+}
+
+func TestClient(t *testing.T) {
+	// Assume server is okay (TestServer is above).
+	// Test client against server.
+	cli, srv := net.Pipe()
+	go ServeConn(srv)
+
+	client := NewClient(cli)
+	defer client.Close()
+
+	// Synchronous calls
+	args := &Args{7, 8}
+	reply := new(Reply)
+	err := client.Call("Arith.Add", args, reply)
+	if err != nil {
+		t.Errorf("Add: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", reply.C, args.A+args.B)
+	}
+
+	args = &Args{7, 8}
+	reply = new(Reply)
+	err = client.Call("Arith.Mul", args, reply)
+	if err != nil {
+		t.Errorf("Mul: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A*args.B {
+		t.Errorf("Mul: expected %d got %d", reply.C, args.A*args.B)
+	}
+
+	// Out of order.
+	args = &Args{7, 8}
+	mulReply := new(Reply)
+	mulCall := client.Go("Arith.Mul", args, mulReply, nil)
+	addReply := new(Reply)
+	addCall := client.Go("Arith.Add", args, addReply, nil)
+
+	addCall = <-addCall.Done
+	if addCall.Error != nil {
+		t.Errorf("Add: expected no error but got string %q", addCall.Error.String())
+	}
+	if addReply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", addReply.C, args.A+args.B)
+	}
+
+	mulCall = <-mulCall.Done
+	if mulCall.Error != nil {
+		t.Errorf("Mul: expected no error but got string %q", mulCall.Error.String())
+	}
+	if mulReply.C != args.A*args.B {
+		t.Errorf("Mul: expected %d got %d", mulReply.C, args.A*args.B)
+	}
+
+	// Error test
+	args = &Args{7, 0}
+	reply = new(Reply)
+	err = client.Call("Arith.Div", args, reply)
+	// expect an error: zero divide
+	if err == nil {
+		t.Error("Div: expected error")
+	} else if err.String() != "divide by zero" {
+		t.Error("Div: expected divide by zero error; got", err)
+	}
+}
diff --git a/src/pkg/rpc/jsonrpc/client.go b/src/pkg/rpc/jsonrpc/client.go
new file mode 100644
index 000000000..577d0ce42
--- /dev/null
+++ b/src/pkg/rpc/jsonrpc/client.go
@@ -0,0 +1,124 @@
+// 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.
+
+// Package jsonrpc implements a JSON-RPC ClientCodec and ServerCodec
+// for the rpc package.
+package jsonrpc
+
+import (
+	"fmt"
+	"io"
+	"json"
+	"net"
+	"os"
+	"rpc"
+	"sync"
+)
+
+type clientCodec struct {
+	dec *json.Decoder // for reading JSON values
+	enc *json.Encoder // for writing JSON values
+	c   io.Closer
+
+	// temporary work space
+	req  clientRequest
+	resp clientResponse
+
+	// JSON-RPC responses include the request id but not the request method.
+	// Package rpc expects both.
+	// We save the request method in pending when sending a request
+	// and then look it up by request ID when filling out the rpc Response.
+	mutex   sync.Mutex        // protects pending
+	pending map[uint64]string // map request id to method name
+}
+
+// NewClientCodec returns a new rpc.ClientCodec using JSON-RPC on conn.
+func NewClientCodec(conn io.ReadWriteCloser) rpc.ClientCodec {
+	return &clientCodec{
+		dec:     json.NewDecoder(conn),
+		enc:     json.NewEncoder(conn),
+		c:       conn,
+		pending: make(map[uint64]string),
+	}
+}
+
+type clientRequest struct {
+	Method string         `json:"method"`
+	Params [1]interface{} `json:"params"`
+	Id     uint64         `json:"id"`
+}
+
+func (c *clientCodec) WriteRequest(r *rpc.Request, param interface{}) os.Error {
+	c.mutex.Lock()
+	c.pending[r.Seq] = r.ServiceMethod
+	c.mutex.Unlock()
+	c.req.Method = r.ServiceMethod
+	c.req.Params[0] = param
+	c.req.Id = r.Seq
+	return c.enc.Encode(&c.req)
+}
+
+type clientResponse struct {
+	Id     uint64           `json:"id"`
+	Result *json.RawMessage `json:"result"`
+	Error  interface{}      `json:"error"`
+}
+
+func (r *clientResponse) reset() {
+	r.Id = 0
+	r.Result = nil
+	r.Error = nil
+}
+
+func (c *clientCodec) ReadResponseHeader(r *rpc.Response) os.Error {
+	c.resp.reset()
+	if err := c.dec.Decode(&c.resp); err != nil {
+		return err
+	}
+
+	c.mutex.Lock()
+	r.ServiceMethod = c.pending[c.resp.Id]
+	c.pending[c.resp.Id] = "", false
+	c.mutex.Unlock()
+
+	r.Error = ""
+	r.Seq = c.resp.Id
+	if c.resp.Error != nil {
+		x, ok := c.resp.Error.(string)
+		if !ok {
+			return fmt.Errorf("invalid error %v", c.resp.Error)
+		}
+		if x == "" {
+			x = "unspecified error"
+		}
+		r.Error = x
+	}
+	return nil
+}
+
+func (c *clientCodec) ReadResponseBody(x interface{}) os.Error {
+	if x == nil {
+		return nil
+	}
+	return json.Unmarshal(*c.resp.Result, x)
+}
+
+func (c *clientCodec) Close() os.Error {
+	return c.c.Close()
+}
+
+// NewClient returns a new rpc.Client to handle requests to the
+// set of services at the other end of the connection.
+func NewClient(conn io.ReadWriteCloser) *rpc.Client {
+	return rpc.NewClientWithCodec(NewClientCodec(conn))
+}
+
+// Dial connects to a JSON-RPC server at the specified network address.
+func Dial(network, address string) (*rpc.Client, os.Error) {
+	conn, err := net.Dial(network, address)
+	if err != nil {
+		return nil, err
+	}
+	return NewClient(conn), err
+}
diff --git a/src/pkg/rpc/jsonrpc/server.go b/src/pkg/rpc/jsonrpc/server.go
new file mode 100644
index 000000000..9801fdf22
--- /dev/null
+++ b/src/pkg/rpc/jsonrpc/server.go
@@ -0,0 +1,136 @@
+// 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.
+
+package jsonrpc
+
+import (
+	"io"
+	"json"
+	"os"
+	"rpc"
+	"sync"
+)
+
+type serverCodec struct {
+	dec *json.Decoder // for reading JSON values
+	enc *json.Encoder // for writing JSON values
+	c   io.Closer
+
+	// temporary work space
+	req  serverRequest
+	resp serverResponse
+
+	// JSON-RPC clients can use arbitrary json values as request IDs.
+	// Package rpc expects uint64 request IDs.
+	// We assign uint64 sequence numbers to incoming requests
+	// but save the original request ID in the pending map.
+	// When rpc responds, we use the sequence number in
+	// the response to find the original request ID.
+	mutex   sync.Mutex // protects seq, pending
+	seq     uint64
+	pending map[uint64]*json.RawMessage
+}
+
+// NewServerCodec returns a new rpc.ServerCodec using JSON-RPC on conn.
+func NewServerCodec(conn io.ReadWriteCloser) rpc.ServerCodec {
+	return &serverCodec{
+		dec:     json.NewDecoder(conn),
+		enc:     json.NewEncoder(conn),
+		c:       conn,
+		pending: make(map[uint64]*json.RawMessage),
+	}
+}
+
+type serverRequest struct {
+	Method string           `json:"method"`
+	Params *json.RawMessage `json:"params"`
+	Id     *json.RawMessage `json:"id"`
+}
+
+func (r *serverRequest) reset() {
+	r.Method = ""
+	if r.Params != nil {
+		*r.Params = (*r.Params)[0:0]
+	}
+	if r.Id != nil {
+		*r.Id = (*r.Id)[0:0]
+	}
+}
+
+type serverResponse struct {
+	Id     *json.RawMessage `json:"id"`
+	Result interface{}      `json:"result"`
+	Error  interface{}      `json:"error"`
+}
+
+func (c *serverCodec) ReadRequestHeader(r *rpc.Request) os.Error {
+	c.req.reset()
+	if err := c.dec.Decode(&c.req); err != nil {
+		return err
+	}
+	r.ServiceMethod = c.req.Method
+
+	// JSON request id can be any JSON value;
+	// RPC package expects uint64.  Translate to
+	// internal uint64 and save JSON on the side.
+	c.mutex.Lock()
+	c.seq++
+	c.pending[c.seq] = c.req.Id
+	c.req.Id = nil
+	r.Seq = c.seq
+	c.mutex.Unlock()
+
+	return nil
+}
+
+func (c *serverCodec) ReadRequestBody(x interface{}) os.Error {
+	if x == nil {
+		return nil
+	}
+	// JSON params is array value.
+	// RPC params is struct.
+	// Unmarshal into array containing struct for now.
+	// Should think about making RPC more general.
+	var params [1]interface{}
+	params[0] = x
+	return json.Unmarshal(*c.req.Params, &params)
+}
+
+var null = json.RawMessage([]byte("null"))
+
+func (c *serverCodec) WriteResponse(r *rpc.Response, x interface{}) os.Error {
+	var resp serverResponse
+	c.mutex.Lock()
+	b, ok := c.pending[r.Seq]
+	if !ok {
+		c.mutex.Unlock()
+		return os.NewError("invalid sequence number in response")
+	}
+	c.pending[r.Seq] = nil, false
+	c.mutex.Unlock()
+
+	if b == nil {
+		// Invalid request so no id.  Use JSON null.
+		b = &null
+	}
+	resp.Id = b
+	resp.Result = x
+	if r.Error == "" {
+		resp.Error = nil
+	} else {
+		resp.Error = r.Error
+	}
+	return c.enc.Encode(resp)
+}
+
+func (c *serverCodec) Close() os.Error {
+	return c.c.Close()
+}
+
+// ServeConn runs the JSON-RPC server on a single connection.
+// ServeConn blocks, serving the connection until the client hangs up.
+// The caller typically invokes ServeConn in a go statement.
+func ServeConn(conn io.ReadWriteCloser) {
+	rpc.ServeCodec(NewServerCodec(conn))
+}
diff --git a/src/pkg/rpc/server.go b/src/pkg/rpc/server.go
new file mode 100644
index 000000000..745074428
--- /dev/null
+++ b/src/pkg/rpc/server.go
@@ -0,0 +1,637 @@
+// Copyright 2009 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.
+
+/*
+	Package rpc provides access to the exported methods of an object across a
+	network or other I/O connection.  A server registers an object, making it visible
+	as a service with the name of the type of the object.  After registration, exported
+	methods of the object will be accessible remotely.  A server may register multiple
+	objects (services) of different types but it is an error to register multiple
+	objects of the same type.
+
+	Only methods that satisfy these criteria will be made available for remote access;
+	other methods will be ignored:
+
+		- the method name is exported, that is, begins with an upper case letter.
+		- the method receiver is exported or local (defined in the package
+		  registering the service).
+		- the method has two arguments, both exported or local types.
+		- the method's second argument is a pointer.
+		- the method has return type os.Error.
+
+	The method's first argument represents the arguments provided by the caller; the
+	second argument represents the result parameters to be returned to the caller.
+	The method's return value, if non-nil, is passed back as a string that the client
+	sees as an os.ErrorString.
+
+	The server may handle requests on a single connection by calling ServeConn.  More
+	typically it will create a network listener and call Accept or, for an HTTP
+	listener, HandleHTTP and http.Serve.
+
+	A client wishing to use the service establishes a connection and then invokes
+	NewClient on the connection.  The convenience function Dial (DialHTTP) performs
+	both steps for a raw network connection (an HTTP connection).  The resulting
+	Client object has two methods, Call and Go, that specify the service and method to
+	call, a pointer containing the arguments, and a pointer to receive the result
+	parameters.
+
+	Call waits for the remote call to complete; Go launches the call asynchronously
+	and returns a channel that will signal completion.
+
+	Package "gob" is used to transport the data.
+
+	Here is a simple example.  A server wishes to export an object of type Arith:
+
+		package server
+
+		type Args struct {
+			A, B int
+		}
+
+		type Quotient struct {
+			Quo, Rem int
+		}
+
+		type Arith int
+
+		func (t *Arith) Multiply(args *Args, reply *int) os.Error {
+			*reply = args.A * args.B
+			return nil
+		}
+
+		func (t *Arith) Divide(args *Args, quo *Quotient) os.Error {
+			if args.B == 0 {
+				return os.ErrorString("divide by zero")
+			}
+			quo.Quo = args.A / args.B
+			quo.Rem = args.A % args.B
+			return nil
+		}
+
+	The server calls (for HTTP service):
+
+		arith := new(Arith)
+		rpc.Register(arith)
+		rpc.HandleHTTP()
+		l, e := net.Listen("tcp", ":1234")
+		if e != nil {
+			log.Fatal("listen error:", e)
+		}
+		go http.Serve(l, nil)
+
+	At this point, clients can see a service "Arith" with methods "Arith.Multiply" and
+	"Arith.Divide".  To invoke one, a client first dials the server:
+
+		client, err := rpc.DialHTTP("tcp", serverAddress + ":1234")
+		if err != nil {
+			log.Fatal("dialing:", err)
+		}
+
+	Then it can make a remote call:
+
+		// Synchronous call
+		args := &server.Args{7,8}
+		var reply int
+		err = client.Call("Arith.Multiply", args, &reply)
+		if err != nil {
+			log.Fatal("arith error:", err)
+		}
+		fmt.Printf("Arith: %d*%d=%d", args.A, args.B, *reply)
+
+	or
+
+		// Asynchronous call
+		quotient := new(Quotient)
+		divCall := client.Go("Arith.Divide", args, &quotient, nil)
+		replyCall := <-divCall.Done	// will be equal to divCall
+		// check errors, print, etc.
+
+	A server implementation will often provide a simple, type-safe wrapper for the
+	client.
+*/
+package rpc
+
+import (
+	"bufio"
+	"gob"
+	"http"
+	"log"
+	"io"
+	"net"
+	"os"
+	"reflect"
+	"strings"
+	"sync"
+	"unicode"
+	"utf8"
+)
+
+const (
+	// Defaults used by HandleHTTP
+	DefaultRPCPath   = "/_goRPC_"
+	DefaultDebugPath = "/debug/rpc"
+)
+
+// Precompute the reflect type for os.Error.  Can't use os.Error directly
+// because Typeof takes an empty interface value.  This is annoying.
+var unusedError *os.Error
+var typeOfOsError = reflect.TypeOf(unusedError).Elem()
+
+type methodType struct {
+	sync.Mutex // protects counters
+	method     reflect.Method
+	ArgType    reflect.Type
+	ReplyType  reflect.Type
+	numCalls   uint
+}
+
+type service struct {
+	name   string                 // name of service
+	rcvr   reflect.Value          // receiver of methods for the service
+	typ    reflect.Type           // type of the receiver
+	method map[string]*methodType // registered methods
+}
+
+// Request is a header written before every RPC call.  It is used internally
+// but documented here as an aid to debugging, such as when analyzing
+// network traffic.
+type Request struct {
+	ServiceMethod string   // format: "Service.Method"
+	Seq           uint64   // sequence number chosen by client
+	next          *Request // for free list in Server
+}
+
+// Response is a header written before every RPC return.  It is used internally
+// but documented here as an aid to debugging, such as when analyzing
+// network traffic.
+type Response struct {
+	ServiceMethod string    // echoes that of the Request
+	Seq           uint64    // echoes that of the request
+	Error         string    // error, if any.
+	next          *Response // for free list in Server
+}
+
+// Server represents an RPC Server.
+type Server struct {
+	mu         sync.Mutex // protects the serviceMap
+	serviceMap map[string]*service
+	reqLock    sync.Mutex // protects freeReq
+	freeReq    *Request
+	respLock   sync.Mutex // protects freeResp
+	freeResp   *Response
+}
+
+// NewServer returns a new Server.
+func NewServer() *Server {
+	return &Server{serviceMap: make(map[string]*service)}
+}
+
+// DefaultServer is the default instance of *Server.
+var DefaultServer = NewServer()
+
+// Is this an exported - upper case - name?
+func isExported(name string) bool {
+	rune, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(rune)
+}
+
+// Is this type exported or a builtin?
+func isExportedOrBuiltinType(t reflect.Type) bool {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	// PkgPath will be non-empty even for an exported type,
+	// so we need to check the type name as well.
+	return isExported(t.Name()) || t.PkgPath() == ""
+}
+
+// Register publishes in the server the set of methods of the
+// receiver value that satisfy the following conditions:
+//	- exported method
+//	- two arguments, both pointers to exported structs
+//	- one return value, of type os.Error
+// It returns an error if the receiver is not an exported type or has no
+// suitable methods.
+// The client accesses each method using a string of the form "Type.Method",
+// where Type is the receiver's concrete type.
+func (server *Server) Register(rcvr interface{}) os.Error {
+	return server.register(rcvr, "", false)
+}
+
+// RegisterName is like Register but uses the provided name for the type 
+// instead of the receiver's concrete type.
+func (server *Server) RegisterName(name string, rcvr interface{}) os.Error {
+	return server.register(rcvr, name, true)
+}
+
+func (server *Server) register(rcvr interface{}, name string, useName bool) os.Error {
+	server.mu.Lock()
+	defer server.mu.Unlock()
+	if server.serviceMap == nil {
+		server.serviceMap = make(map[string]*service)
+	}
+	s := new(service)
+	s.typ = reflect.TypeOf(rcvr)
+	s.rcvr = reflect.ValueOf(rcvr)
+	sname := reflect.Indirect(s.rcvr).Type().Name()
+	if useName {
+		sname = name
+	}
+	if sname == "" {
+		log.Fatal("rpc: no service name for type", s.typ.String())
+	}
+	if !isExported(sname) && !useName {
+		s := "rpc Register: type " + sname + " is not exported"
+		log.Print(s)
+		return os.NewError(s)
+	}
+	if _, present := server.serviceMap[sname]; present {
+		return os.NewError("rpc: service already defined: " + sname)
+	}
+	s.name = sname
+	s.method = make(map[string]*methodType)
+
+	// Install the methods
+	for m := 0; m < s.typ.NumMethod(); m++ {
+		method := s.typ.Method(m)
+		mtype := method.Type
+		mname := method.Name
+		if method.PkgPath != "" {
+			continue
+		}
+		// Method needs three ins: receiver, *args, *reply.
+		if mtype.NumIn() != 3 {
+			log.Println("method", mname, "has wrong number of ins:", mtype.NumIn())
+			continue
+		}
+		// First arg need not be a pointer.
+		argType := mtype.In(1)
+		if !isExportedOrBuiltinType(argType) {
+			log.Println(mname, "argument type not exported or local:", argType)
+			continue
+		}
+		// Second arg must be a pointer.
+		replyType := mtype.In(2)
+		if replyType.Kind() != reflect.Ptr {
+			log.Println("method", mname, "reply type not a pointer:", replyType)
+			continue
+		}
+		if !isExportedOrBuiltinType(replyType) {
+			log.Println("method", mname, "reply type not exported or local:", replyType)
+			continue
+		}
+		// Method needs one out: os.Error.
+		if mtype.NumOut() != 1 {
+			log.Println("method", mname, "has wrong number of outs:", mtype.NumOut())
+			continue
+		}
+		if returnType := mtype.Out(0); returnType != typeOfOsError {
+			log.Println("method", mname, "returns", returnType.String(), "not os.Error")
+			continue
+		}
+		s.method[mname] = &methodType{method: method, ArgType: argType, ReplyType: replyType}
+	}
+
+	if len(s.method) == 0 {
+		s := "rpc Register: type " + sname + " has no exported methods of suitable type"
+		log.Print(s)
+		return os.NewError(s)
+	}
+	server.serviceMap[s.name] = s
+	return nil
+}
+
+// A value sent as a placeholder for the response when the server receives an invalid request.
+type InvalidRequest struct{}
+
+var invalidRequest = InvalidRequest{}
+
+func (server *Server) sendResponse(sending *sync.Mutex, req *Request, reply interface{}, codec ServerCodec, errmsg string) {
+	resp := server.getResponse()
+	// Encode the response header
+	resp.ServiceMethod = req.ServiceMethod
+	if errmsg != "" {
+		resp.Error = errmsg
+		reply = invalidRequest
+	}
+	resp.Seq = req.Seq
+	sending.Lock()
+	err := codec.WriteResponse(resp, reply)
+	if err != nil {
+		log.Println("rpc: writing response:", err)
+	}
+	sending.Unlock()
+	server.freeResponse(resp)
+}
+
+func (m *methodType) NumCalls() (n uint) {
+	m.Lock()
+	n = m.numCalls
+	m.Unlock()
+	return n
+}
+
+func (s *service) call(server *Server, sending *sync.Mutex, mtype *methodType, req *Request, argv, replyv reflect.Value, codec ServerCodec) {
+	mtype.Lock()
+	mtype.numCalls++
+	mtype.Unlock()
+	function := mtype.method.Func
+	// Invoke the method, providing a new value for the reply.
+	returnValues := function.Call([]reflect.Value{s.rcvr, argv, replyv})
+	// The return value for the method is an os.Error.
+	errInter := returnValues[0].Interface()
+	errmsg := ""
+	if errInter != nil {
+		errmsg = errInter.(os.Error).String()
+	}
+	server.sendResponse(sending, req, replyv.Interface(), codec, errmsg)
+	server.freeRequest(req)
+}
+
+type gobServerCodec struct {
+	rwc    io.ReadWriteCloser
+	dec    *gob.Decoder
+	enc    *gob.Encoder
+	encBuf *bufio.Writer
+}
+
+func (c *gobServerCodec) ReadRequestHeader(r *Request) os.Error {
+	return c.dec.Decode(r)
+}
+
+func (c *gobServerCodec) ReadRequestBody(body interface{}) os.Error {
+	return c.dec.Decode(body)
+}
+
+func (c *gobServerCodec) WriteResponse(r *Response, body interface{}) (err os.Error) {
+	if err = c.enc.Encode(r); err != nil {
+		return
+	}
+	if err = c.enc.Encode(body); err != nil {
+		return
+	}
+	return c.encBuf.Flush()
+}
+
+func (c *gobServerCodec) Close() os.Error {
+	return c.rwc.Close()
+}
+
+// ServeConn runs the server on a single connection.
+// ServeConn blocks, serving the connection until the client hangs up.
+// The caller typically invokes ServeConn in a go statement.
+// ServeConn uses the gob wire format (see package gob) on the
+// connection.  To use an alternate codec, use ServeCodec.
+func (server *Server) ServeConn(conn io.ReadWriteCloser) {
+	buf := bufio.NewWriter(conn)
+	srv := &gobServerCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(buf), buf}
+	server.ServeCodec(srv)
+}
+
+// ServeCodec is like ServeConn but uses the specified codec to
+// decode requests and encode responses.
+func (server *Server) ServeCodec(codec ServerCodec) {
+	sending := new(sync.Mutex)
+	for {
+		service, mtype, req, argv, replyv, err := server.readRequest(codec)
+		if err != nil {
+			if err != os.EOF {
+				log.Println("rpc:", err)
+			}
+			if err == os.EOF || err == io.ErrUnexpectedEOF {
+				break
+			}
+			// send a response if we actually managed to read a header.
+			if req != nil {
+				server.sendResponse(sending, req, invalidRequest, codec, err.String())
+				server.freeRequest(req)
+			}
+			continue
+		}
+		go service.call(server, sending, mtype, req, argv, replyv, codec)
+	}
+	codec.Close()
+}
+
+// ServeRequest is like ServeCodec but synchronously serves a single request.
+// It does not close the codec upon completion.
+func (server *Server) ServeRequest(codec ServerCodec) os.Error {
+	sending := new(sync.Mutex)
+	service, mtype, req, argv, replyv, err := server.readRequest(codec)
+	if err != nil {
+		if err == os.EOF || err == io.ErrUnexpectedEOF {
+			return err
+		}
+		// send a response if we actually managed to read a header.
+		if req != nil {
+			server.sendResponse(sending, req, invalidRequest, codec, err.String())
+			server.freeRequest(req)
+		}
+		return err
+	}
+	service.call(server, sending, mtype, req, argv, replyv, codec)
+	return nil
+}
+
+func (server *Server) getRequest() *Request {
+	server.reqLock.Lock()
+	req := server.freeReq
+	if req == nil {
+		req = new(Request)
+	} else {
+		server.freeReq = req.next
+		*req = Request{}
+	}
+	server.reqLock.Unlock()
+	return req
+}
+
+func (server *Server) freeRequest(req *Request) {
+	server.reqLock.Lock()
+	req.next = server.freeReq
+	server.freeReq = req
+	server.reqLock.Unlock()
+}
+
+func (server *Server) getResponse() *Response {
+	server.respLock.Lock()
+	resp := server.freeResp
+	if resp == nil {
+		resp = new(Response)
+	} else {
+		server.freeResp = resp.next
+		*resp = Response{}
+	}
+	server.respLock.Unlock()
+	return resp
+}
+
+func (server *Server) freeResponse(resp *Response) {
+	server.respLock.Lock()
+	resp.next = server.freeResp
+	server.freeResp = resp
+	server.respLock.Unlock()
+}
+
+func (server *Server) readRequest(codec ServerCodec) (service *service, mtype *methodType, req *Request, argv, replyv reflect.Value, err os.Error) {
+	service, mtype, req, err = server.readRequestHeader(codec)
+	if err != nil {
+		if err == os.EOF || err == io.ErrUnexpectedEOF {
+			return
+		}
+		// discard body
+		codec.ReadRequestBody(nil)
+		return
+	}
+
+	// Decode the argument value.
+	argIsValue := false // if true, need to indirect before calling.
+	if mtype.ArgType.Kind() == reflect.Ptr {
+		argv = reflect.New(mtype.ArgType.Elem())
+	} else {
+		argv = reflect.New(mtype.ArgType)
+		argIsValue = true
+	}
+	// argv guaranteed to be a pointer now.
+	if err = codec.ReadRequestBody(argv.Interface()); err != nil {
+		return
+	}
+	if argIsValue {
+		argv = argv.Elem()
+	}
+
+	replyv = reflect.New(mtype.ReplyType.Elem())
+	return
+}
+
+func (server *Server) readRequestHeader(codec ServerCodec) (service *service, mtype *methodType, req *Request, err os.Error) {
+	// Grab the request header.
+	req = server.getRequest()
+	err = codec.ReadRequestHeader(req)
+	if err != nil {
+		req = nil
+		if err == os.EOF || err == io.ErrUnexpectedEOF {
+			return
+		}
+		err = os.NewError("rpc: server cannot decode request: " + err.String())
+		return
+	}
+
+	serviceMethod := strings.Split(req.ServiceMethod, ".")
+	if len(serviceMethod) != 2 {
+		err = os.NewError("rpc: service/method request ill-formed: " + req.ServiceMethod)
+		return
+	}
+	// Look up the request.
+	server.mu.Lock()
+	service = server.serviceMap[serviceMethod[0]]
+	server.mu.Unlock()
+	if service == nil {
+		err = os.NewError("rpc: can't find service " + req.ServiceMethod)
+		return
+	}
+	mtype = service.method[serviceMethod[1]]
+	if mtype == nil {
+		err = os.NewError("rpc: can't find method " + req.ServiceMethod)
+	}
+	return
+}
+
+// Accept accepts connections on the listener and serves requests
+// for each incoming connection.  Accept blocks; the caller typically
+// invokes it in a go statement.
+func (server *Server) Accept(lis net.Listener) {
+	for {
+		conn, err := lis.Accept()
+		if err != nil {
+			log.Fatal("rpc.Serve: accept:", err.String()) // TODO(r): exit?
+		}
+		go server.ServeConn(conn)
+	}
+}
+
+// Register publishes the receiver's methods in the DefaultServer.
+func Register(rcvr interface{}) os.Error { return DefaultServer.Register(rcvr) }
+
+// RegisterName is like Register but uses the provided name for the type 
+// instead of the receiver's concrete type.
+func RegisterName(name string, rcvr interface{}) os.Error {
+	return DefaultServer.RegisterName(name, rcvr)
+}
+
+// A ServerCodec implements reading of RPC requests and writing of
+// RPC responses for the server side of an RPC session.
+// The server calls ReadRequestHeader and ReadRequestBody in pairs
+// to read requests from the connection, and it calls WriteResponse to
+// write a response back.  The server calls Close when finished with the
+// connection. ReadRequestBody may be called with a nil
+// argument to force the body of the request to be read and discarded.
+type ServerCodec interface {
+	ReadRequestHeader(*Request) os.Error
+	ReadRequestBody(interface{}) os.Error
+	WriteResponse(*Response, interface{}) os.Error
+
+	Close() os.Error
+}
+
+// ServeConn runs the DefaultServer on a single connection.
+// ServeConn blocks, serving the connection until the client hangs up.
+// The caller typically invokes ServeConn in a go statement.
+// ServeConn uses the gob wire format (see package gob) on the
+// connection.  To use an alternate codec, use ServeCodec.
+func ServeConn(conn io.ReadWriteCloser) {
+	DefaultServer.ServeConn(conn)
+}
+
+// ServeCodec is like ServeConn but uses the specified codec to
+// decode requests and encode responses.
+func ServeCodec(codec ServerCodec) {
+	DefaultServer.ServeCodec(codec)
+}
+
+// ServeRequest is like ServeCodec but synchronously serves a single request.
+// It does not close the codec upon completion.
+func ServeRequest(codec ServerCodec) os.Error {
+	return DefaultServer.ServeRequest(codec)
+}
+
+// Accept accepts connections on the listener and serves requests
+// to DefaultServer for each incoming connection.  
+// Accept blocks; the caller typically invokes it in a go statement.
+func Accept(lis net.Listener) { DefaultServer.Accept(lis) }
+
+// Can connect to RPC service using HTTP CONNECT to rpcPath.
+var connected = "200 Connected to Go RPC"
+
+// ServeHTTP implements an http.Handler that answers RPC requests.
+func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	if req.Method != "CONNECT" {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		io.WriteString(w, "405 must CONNECT\n")
+		return
+	}
+	conn, _, err := w.(http.Hijacker).Hijack()
+	if err != nil {
+		log.Print("rpc hijacking ", req.RemoteAddr, ": ", err.String())
+		return
+	}
+	io.WriteString(conn, "HTTP/1.0 "+connected+"\n\n")
+	server.ServeConn(conn)
+}
+
+// HandleHTTP registers an HTTP handler for RPC messages on rpcPath,
+// and a debugging handler on debugPath.
+// It is still necessary to invoke http.Serve(), typically in a go statement.
+func (server *Server) HandleHTTP(rpcPath, debugPath string) {
+	http.Handle(rpcPath, server)
+	http.Handle(debugPath, debugHTTP{server})
+}
+
+// HandleHTTP registers an HTTP handler for RPC messages to DefaultServer
+// on DefaultRPCPath and a debugging handler on DefaultDebugPath.
+// It is still necessary to invoke http.Serve(), typically in a go statement.
+func HandleHTTP() {
+	DefaultServer.HandleHTTP(DefaultRPCPath, DefaultDebugPath)
+}
diff --git a/src/pkg/rpc/server_test.go b/src/pkg/rpc/server_test.go
new file mode 100644
index 000000000..e7bbfbe97
--- /dev/null
+++ b/src/pkg/rpc/server_test.go
@@ -0,0 +1,501 @@
+// Copyright 2009 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.
+
+package rpc
+
+import (
+	"fmt"
+	"http/httptest"
+	"io"
+	"log"
+	"net"
+	"os"
+	"runtime"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+var (
+	newServer                 *Server
+	serverAddr, newServerAddr string
+	httpServerAddr            string
+	once, newOnce, httpOnce   sync.Once
+)
+
+const (
+	second      = 1e9
+	newHttpPath = "/foo"
+)
+
+type Args struct {
+	A, B int
+}
+
+type Reply struct {
+	C int
+}
+
+type Arith int
+
+// Some of Arith's methods have value args, some have pointer args. That's deliberate.
+
+func (t *Arith) Add(args Args, reply *Reply) os.Error {
+	reply.C = args.A + args.B
+	return nil
+}
+
+func (t *Arith) Mul(args *Args, reply *Reply) os.Error {
+	reply.C = args.A * args.B
+	return nil
+}
+
+func (t *Arith) Div(args Args, reply *Reply) os.Error {
+	if args.B == 0 {
+		return os.NewError("divide by zero")
+	}
+	reply.C = args.A / args.B
+	return nil
+}
+
+func (t *Arith) String(args *Args, reply *string) os.Error {
+	*reply = fmt.Sprintf("%d+%d=%d", args.A, args.B, args.A+args.B)
+	return nil
+}
+
+func (t *Arith) Scan(args string, reply *Reply) (err os.Error) {
+	_, err = fmt.Sscan(args, &reply.C)
+	return
+}
+
+func (t *Arith) Error(args *Args, reply *Reply) os.Error {
+	panic("ERROR")
+}
+
+func listenTCP() (net.Listener, string) {
+	l, e := net.Listen("tcp", "127.0.0.1:0") // any available address
+	if e != nil {
+		log.Fatalf("net.Listen tcp :0: %v", e)
+	}
+	return l, l.Addr().String()
+}
+
+func startServer() {
+	Register(new(Arith))
+
+	var l net.Listener
+	l, serverAddr = listenTCP()
+	log.Println("Test RPC server listening on", serverAddr)
+	go Accept(l)
+
+	HandleHTTP()
+	httpOnce.Do(startHttpServer)
+}
+
+func startNewServer() {
+	newServer = NewServer()
+	newServer.Register(new(Arith))
+
+	var l net.Listener
+	l, newServerAddr = listenTCP()
+	log.Println("NewServer test RPC server listening on", newServerAddr)
+	go Accept(l)
+
+	newServer.HandleHTTP(newHttpPath, "/bar")
+	httpOnce.Do(startHttpServer)
+}
+
+func startHttpServer() {
+	server := httptest.NewServer(nil)
+	httpServerAddr = server.Listener.Addr().String()
+	log.Println("Test HTTP RPC server listening on", httpServerAddr)
+}
+
+func TestRPC(t *testing.T) {
+	once.Do(startServer)
+	testRPC(t, serverAddr)
+	newOnce.Do(startNewServer)
+	testRPC(t, newServerAddr)
+}
+
+func testRPC(t *testing.T, addr string) {
+	client, err := Dial("tcp", addr)
+	if err != nil {
+		t.Fatal("dialing", err)
+	}
+
+	// Synchronous calls
+	args := &Args{7, 8}
+	reply := new(Reply)
+	err = client.Call("Arith.Add", args, reply)
+	if err != nil {
+		t.Errorf("Add: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", reply.C, args.A+args.B)
+	}
+
+	// Nonexistent method
+	args = &Args{7, 0}
+	reply = new(Reply)
+	err = client.Call("Arith.BadOperation", args, reply)
+	// expect an error
+	if err == nil {
+		t.Error("BadOperation: expected error")
+	} else if !strings.HasPrefix(err.String(), "rpc: can't find method ") {
+		t.Errorf("BadOperation: expected can't find method error; got %q", err)
+	}
+
+	// Unknown service
+	args = &Args{7, 8}
+	reply = new(Reply)
+	err = client.Call("Arith.Unknown", args, reply)
+	if err == nil {
+		t.Error("expected error calling unknown service")
+	} else if strings.Index(err.String(), "method") < 0 {
+		t.Error("expected error about method; got", err)
+	}
+
+	// Out of order.
+	args = &Args{7, 8}
+	mulReply := new(Reply)
+	mulCall := client.Go("Arith.Mul", args, mulReply, nil)
+	addReply := new(Reply)
+	addCall := client.Go("Arith.Add", args, addReply, nil)
+
+	addCall = <-addCall.Done
+	if addCall.Error != nil {
+		t.Errorf("Add: expected no error but got string %q", addCall.Error.String())
+	}
+	if addReply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", addReply.C, args.A+args.B)
+	}
+
+	mulCall = <-mulCall.Done
+	if mulCall.Error != nil {
+		t.Errorf("Mul: expected no error but got string %q", mulCall.Error.String())
+	}
+	if mulReply.C != args.A*args.B {
+		t.Errorf("Mul: expected %d got %d", mulReply.C, args.A*args.B)
+	}
+
+	// Error test
+	args = &Args{7, 0}
+	reply = new(Reply)
+	err = client.Call("Arith.Div", args, reply)
+	// expect an error: zero divide
+	if err == nil {
+		t.Error("Div: expected error")
+	} else if err.String() != "divide by zero" {
+		t.Error("Div: expected divide by zero error; got", err)
+	}
+
+	// Bad type.
+	reply = new(Reply)
+	err = client.Call("Arith.Add", reply, reply) // args, reply would be the correct thing to use
+	if err == nil {
+		t.Error("expected error calling Arith.Add with wrong arg type")
+	} else if strings.Index(err.String(), "type") < 0 {
+		t.Error("expected error about type; got", err)
+	}
+
+	// Non-struct argument
+	const Val = 12345
+	str := fmt.Sprint(Val)
+	reply = new(Reply)
+	err = client.Call("Arith.Scan", &str, reply)
+	if err != nil {
+		t.Errorf("Scan: expected no error but got string %q", err.String())
+	} else if reply.C != Val {
+		t.Errorf("Scan: expected %d got %d", Val, reply.C)
+	}
+
+	// Non-struct reply
+	args = &Args{27, 35}
+	str = ""
+	err = client.Call("Arith.String", args, &str)
+	if err != nil {
+		t.Errorf("String: expected no error but got string %q", err.String())
+	}
+	expect := fmt.Sprintf("%d+%d=%d", args.A, args.B, args.A+args.B)
+	if str != expect {
+		t.Errorf("String: expected %s got %s", expect, str)
+	}
+
+	args = &Args{7, 8}
+	reply = new(Reply)
+	err = client.Call("Arith.Mul", args, reply)
+	if err != nil {
+		t.Errorf("Mul: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A*args.B {
+		t.Errorf("Mul: expected %d got %d", reply.C, args.A*args.B)
+	}
+}
+
+func TestHTTP(t *testing.T) {
+	once.Do(startServer)
+	testHTTPRPC(t, "")
+	newOnce.Do(startNewServer)
+	testHTTPRPC(t, newHttpPath)
+}
+
+func testHTTPRPC(t *testing.T, path string) {
+	var client *Client
+	var err os.Error
+	if path == "" {
+		client, err = DialHTTP("tcp", httpServerAddr)
+	} else {
+		client, err = DialHTTPPath("tcp", httpServerAddr, path)
+	}
+	if err != nil {
+		t.Fatal("dialing", err)
+	}
+
+	// Synchronous calls
+	args := &Args{7, 8}
+	reply := new(Reply)
+	err = client.Call("Arith.Add", args, reply)
+	if err != nil {
+		t.Errorf("Add: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", reply.C, args.A+args.B)
+	}
+}
+
+// CodecEmulator provides a client-like api and a ServerCodec interface.
+// Can be used to test ServeRequest.
+type CodecEmulator struct {
+	server        *Server
+	serviceMethod string
+	args          *Args
+	reply         *Reply
+	err           os.Error
+}
+
+func (codec *CodecEmulator) Call(serviceMethod string, args *Args, reply *Reply) os.Error {
+	codec.serviceMethod = serviceMethod
+	codec.args = args
+	codec.reply = reply
+	codec.err = nil
+	var serverError os.Error
+	if codec.server == nil {
+		serverError = ServeRequest(codec)
+	} else {
+		serverError = codec.server.ServeRequest(codec)
+	}
+	if codec.err == nil && serverError != nil {
+		codec.err = serverError
+	}
+	return codec.err
+}
+
+func (codec *CodecEmulator) ReadRequestHeader(req *Request) os.Error {
+	req.ServiceMethod = codec.serviceMethod
+	req.Seq = 0
+	return nil
+}
+
+func (codec *CodecEmulator) ReadRequestBody(argv interface{}) os.Error {
+	if codec.args == nil {
+		return io.ErrUnexpectedEOF
+	}
+	*(argv.(*Args)) = *codec.args
+	return nil
+}
+
+func (codec *CodecEmulator) WriteResponse(resp *Response, reply interface{}) os.Error {
+	if resp.Error != "" {
+		codec.err = os.NewError(resp.Error)
+	}
+	*codec.reply = *(reply.(*Reply))
+	return nil
+}
+
+func (codec *CodecEmulator) Close() os.Error {
+	return nil
+}
+
+func TestServeRequest(t *testing.T) {
+	once.Do(startServer)
+	testServeRequest(t, nil)
+	newOnce.Do(startNewServer)
+	testServeRequest(t, newServer)
+}
+
+func testServeRequest(t *testing.T, server *Server) {
+	client := CodecEmulator{server: server}
+
+	args := &Args{7, 8}
+	reply := new(Reply)
+	err := client.Call("Arith.Add", args, reply)
+	if err != nil {
+		t.Errorf("Add: expected no error but got string %q", err.String())
+	}
+	if reply.C != args.A+args.B {
+		t.Errorf("Add: expected %d got %d", reply.C, args.A+args.B)
+	}
+
+	err = client.Call("Arith.Add", nil, reply)
+	if err == nil {
+		t.Errorf("expected error calling Arith.Add with nil arg")
+	}
+}
+
+type ReplyNotPointer int
+type ArgNotPublic int
+type ReplyNotPublic int
+type local struct{}
+
+func (t *ReplyNotPointer) ReplyNotPointer(args *Args, reply Reply) os.Error {
+	return nil
+}
+
+func (t *ArgNotPublic) ArgNotPublic(args *local, reply *Reply) os.Error {
+	return nil
+}
+
+func (t *ReplyNotPublic) ReplyNotPublic(args *Args, reply *local) os.Error {
+	return nil
+}
+
+// Check that registration handles lots of bad methods and a type with no suitable methods.
+func TestRegistrationError(t *testing.T) {
+	err := Register(new(ReplyNotPointer))
+	if err == nil {
+		t.Errorf("expected error registering ReplyNotPointer")
+	}
+	err = Register(new(ArgNotPublic))
+	if err == nil {
+		t.Errorf("expected error registering ArgNotPublic")
+	}
+	err = Register(new(ReplyNotPublic))
+	if err == nil {
+		t.Errorf("expected error registering ReplyNotPublic")
+	}
+}
+
+type WriteFailCodec int
+
+func (WriteFailCodec) WriteRequest(*Request, interface{}) os.Error {
+	// the panic caused by this error used to not unlock a lock.
+	return os.NewError("fail")
+}
+
+func (WriteFailCodec) ReadResponseHeader(*Response) os.Error {
+	time.Sleep(120e9)
+	panic("unreachable")
+}
+
+func (WriteFailCodec) ReadResponseBody(interface{}) os.Error {
+	time.Sleep(120e9)
+	panic("unreachable")
+}
+
+func (WriteFailCodec) Close() os.Error {
+	return nil
+}
+
+func TestSendDeadlock(t *testing.T) {
+	client := NewClientWithCodec(WriteFailCodec(0))
+
+	done := make(chan bool)
+	go func() {
+		testSendDeadlock(client)
+		testSendDeadlock(client)
+		done <- true
+	}()
+	select {
+	case <-done:
+		return
+	case <-time.After(5e9):
+		t.Fatal("deadlock")
+	}
+}
+
+func testSendDeadlock(client *Client) {
+	defer func() {
+		recover()
+	}()
+	args := &Args{7, 8}
+	reply := new(Reply)
+	client.Call("Arith.Add", args, reply)
+}
+
+func dialDirect() (*Client, os.Error) {
+	return Dial("tcp", serverAddr)
+}
+
+func dialHTTP() (*Client, os.Error) {
+	return DialHTTP("tcp", httpServerAddr)
+}
+
+func countMallocs(dial func() (*Client, os.Error), t *testing.T) uint64 {
+	once.Do(startServer)
+	client, err := dial()
+	if err != nil {
+		t.Fatal("error dialing", err)
+	}
+	args := &Args{7, 8}
+	reply := new(Reply)
+	runtime.UpdateMemStats()
+	mallocs := 0 - runtime.MemStats.Mallocs
+	const count = 100
+	for i := 0; i < count; i++ {
+		err := client.Call("Arith.Add", args, reply)
+		if err != nil {
+			t.Errorf("Add: expected no error but got string %q", err.String())
+		}
+		if reply.C != args.A+args.B {
+			t.Errorf("Add: expected %d got %d", reply.C, args.A+args.B)
+		}
+	}
+	runtime.UpdateMemStats()
+	mallocs += runtime.MemStats.Mallocs
+	return mallocs / count
+}
+
+func TestCountMallocs(t *testing.T) {
+	fmt.Printf("mallocs per rpc round trip: %d\n", countMallocs(dialDirect, t))
+}
+
+func TestCountMallocsOverHTTP(t *testing.T) {
+	fmt.Printf("mallocs per HTTP rpc round trip: %d\n", countMallocs(dialHTTP, t))
+}
+
+func benchmarkEndToEnd(dial func() (*Client, os.Error), b *testing.B) {
+	b.StopTimer()
+	once.Do(startServer)
+	client, err := dial()
+	if err != nil {
+		fmt.Println("error dialing", err)
+		return
+	}
+
+	// Synchronous calls
+	args := &Args{7, 8}
+	reply := new(Reply)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		err = client.Call("Arith.Add", args, reply)
+		if err != nil {
+			fmt.Printf("Add: expected no error but got string %q", err.String())
+			break
+		}
+		if reply.C != args.A+args.B {
+			fmt.Printf("Add: expected %d got %d", reply.C, args.A+args.B)
+			break
+		}
+	}
+}
+
+func BenchmarkEndToEnd(b *testing.B) {
+	benchmarkEndToEnd(dialDirect, b)
+}
+
+func BenchmarkEndToEndHTTP(b *testing.B) {
+	benchmarkEndToEnd(dialHTTP, b)
+}