net/rpc/jsonrpc: handles missing "params" in jsonrpc.

A crash happens in the first request in a connection
if "params" field is missing because c.req.Params is Nil.

Fixes #3848.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6446051

src/pkg/net/rpc/jsonrpc/all_test.go

@@ -24,6 +24,12 @@ type Reply struct {
 
 type Arith int
 
+type ArithAddResp struct {
+	Id     interface{} `json:"id"`
+	Result Reply       `json:"result"`
+	Error  interface{} `json:"error"`
+}
+
 func (t *Arith) Add(args *Args, reply *Reply) error {
 	reply.C = args.A + args.B
 	return nil
@@ -50,13 +56,39 @@ 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"`
+func TestServerNoParams(t *testing.T) {
+	cli, srv := net.Pipe()
+	defer cli.Close()
+	go ServeConn(srv)
+	dec := json.NewDecoder(cli)
+
+	fmt.Fprintf(cli, `{"method": "Arith.Add", "id": "123"}`)
+	var resp ArithAddResp
+	if err := dec.Decode(&resp); err != nil {
+		t.Fatalf("Decode after no params: %s", err)
+	}
+	if resp.Error == nil {
+		t.Fatalf("Expected error, got nil")
+	}
+}
+
+func TestServerEmptyMessage(t *testing.T) {
+	cli, srv := net.Pipe()
+	defer cli.Close()
+	go ServeConn(srv)
+	dec := json.NewDecoder(cli)
+
+	fmt.Fprintf(cli, "{}")
+	var resp ArithAddResp
+	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 TestServer(t *testing.T) {
 	cli, srv := net.Pipe()
 	defer cli.Close()
 	go ServeConn(srv)
@@ -65,7 +97,7 @@ func TestServer(t *testing.T) {
 	// 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
+		var resp ArithAddResp
 		err := dec.Decode(&resp)
 		if err != nil {
 			t.Fatalf("Decode: %s", err)
@@ -80,15 +112,6 @@ func TestServer(t *testing.T) {
 			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) {

src/pkg/net/rpc/jsonrpc/server.go

@@ -12,6 +12,8 @@ import (
 	"sync"
 )
 
+var errMissingParams = errors.New("jsonrpc: request body missing params")
+
 type serverCodec struct {
 	dec *json.Decoder // for reading JSON values
 	enc *json.Encoder // for writing JSON values
@@ -50,12 +52,8 @@ type serverRequest struct {
 
 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]
-	}
+	r.Params = nil
+	r.Id = nil
 }
 
 type serverResponse struct {
@@ -88,6 +86,9 @@ func (c *serverCodec) ReadRequestBody(x interface{}) error {
 	if x == nil {
 		return nil
 	}
+	if c.req.Params == nil {
+		return errMissingParams
+	}
 	// JSON params is array value.
 	// RPC params is struct.
 	// Unmarshal into array containing struct for now.