rpc: Avoid using Pool since it conflicts with http2 (#7467)

A race is detected between a bytes.Buffer generated with cmd/rpc.Pool
and http2 module. An issue is raised in golang (https://github.com/golang/go/issues/31192).

Meanwhile, this commit disables Pool in RPC code and it generates a
new 1kb of bytes.Buffer for each RPC call.

cmd/rpc/client.go

@@ -17,6 +17,7 @@
 package rpc
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"encoding/gob"
@@ -49,8 +50,7 @@ func (client *Client) Call(serviceMethod string, args, reply interface{}) error
 		return fmt.Errorf("rpc reply must be a pointer type, but found %v", replyKind)
 	}
 
-	argBuf := bufPool.Get()
-	defer bufPool.Put(argBuf)
+	argBuf := bytes.NewBuffer(make([]byte, 0, 1024))
 
 	if err := gobEncodeBuf(args, argBuf); err != nil {
 		return err
@@ -61,8 +61,7 @@ func (client *Client) Call(serviceMethod string, args, reply interface{}) error
 		ArgBytes: argBuf.Bytes(),
 	}
 
-	reqBuf := bufPool.Get()
-	defer bufPool.Put(reqBuf)
+	reqBuf := bytes.NewBuffer(make([]byte, 0, 1024))
 	if err := gob.NewEncoder(reqBuf).Encode(callRequest); err != nil {
 		return err
 	}

cmd/rpc/server.go

@@ -40,8 +40,6 @@ var errorType = reflect.TypeOf((*error)(nil)).Elem()
 // reflect.Type of Authenticator interface.
 var authenticatorType = reflect.TypeOf((*Authenticator)(nil)).Elem()
 
-var bufPool = NewPool()
-
 func gobEncodeBuf(e interface{}, buf *bytes.Buffer) error {
 	return gob.NewEncoder(buf).Encode(e)
 }
@@ -239,8 +237,8 @@ func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	}
 
 	callResponse := CallResponse{}
-	buf := bufPool.Get()
-	defer bufPool.Put(buf)
+
+	buf := bytes.NewBuffer(make([]byte, 0, 1024))
 
 	if err := server.call(callRequest.Method, callRequest.ArgBytes, buf); err != nil {
 		callResponse.Error = err.Error()

cmd/rpc/server_test.go

@@ -253,8 +253,7 @@ func TestServerCall(t *testing.T) {
 	}
 
 	for i, testCase := range testCases {
-		buf := bufPool.Get()
-		defer bufPool.Put(buf)
+		buf := bytes.NewBuffer([]byte{})
 
 		err := testCase.server.call(testCase.serviceMethod, testCase.argBytes, buf)
 		expectErr := (err != nil)