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// Copyright 2018 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 jsonrpc2 is a minimal implementation of the JSON RPC 2 spec.
// https://www.jsonrpc.org/specification
// It is intended to be compatible with other implementations at the wire level.
package jsonrpc2
import (
"context"
"encoding/json"
"fmt"
"sync"
"sync/atomic"
)
// Conn is a JSON RPC 2 client server connection.
// Conn is bidirectional; it does not have a designated server or client end.
type Conn struct {
seq int64 // must only be accessed using atomic operations
handlers []Handler
stream Stream
err error
pendingMu sync.Mutex // protects the pending map
pending map[ID]chan *WireResponse
handlingMu sync.Mutex // protects the handling map
handling map[ID]*Request
}
type requestState int
const (
requestWaiting = requestState(iota)
requestSerial
requestParallel
requestReplied
requestDone
)
// Request is sent to a server to represent a Call or Notify operaton.
type Request struct {
conn *Conn
cancel context.CancelFunc
state requestState
nextRequest chan struct{}
// The Wire values of the request.
WireRequest
}
// NewErrorf builds a Error struct for the supplied message and code.
// If args is not empty, message and args will be passed to Sprintf.
func NewErrorf(code int64, format string, args ...interface{}) *Error {
return &Error{
Code: code,
Message: fmt.Sprintf(format, args...),
}
}
// NewConn creates a new connection object around the supplied stream.
// You must call Run for the connection to be active.
func NewConn(s Stream) *Conn {
conn := &Conn{
handlers: []Handler{defaultHandler{}},
stream: s,
pending: make(map[ID]chan *WireResponse),
handling: make(map[ID]*Request),
}
return conn
}
// AddHandler adds a new handler to the set the connection will invoke.
// Handlers are invoked in the reverse order of how they were added, this
// allows the most recent addition to be the first one to attempt to handle a
// message.
func (c *Conn) AddHandler(handler Handler) {
// prepend the new handlers so we use them first
c.handlers = append([]Handler{handler}, c.handlers...)
}
// Cancel cancels a pending Call on the server side.
// The call is identified by its id.
// JSON RPC 2 does not specify a cancel message, so cancellation support is not
// directly wired in. This method allows a higher level protocol to choose how
// to propagate the cancel.
func (c *Conn) Cancel(id ID) {
c.handlingMu.Lock()
handling, found := c.handling[id]
c.handlingMu.Unlock()
if found {
handling.cancel()
}
}
// Notify is called to send a notification request over the connection.
// It will return as soon as the notification has been sent, as no response is
// possible.
func (c *Conn) Notify(ctx context.Context, method string, params interface{}) (err error) {
jsonParams, err := marshalToRaw(params)
if err != nil {
return fmt.Errorf("marshalling notify parameters: %v", err)
}
request := &WireRequest{
Method: method,
Params: jsonParams,
}
data, err := json.Marshal(request)
if err != nil {
return fmt.Errorf("marshalling notify request: %v", err)
}
for _, h := range c.handlers {
ctx = h.Request(ctx, Send, request)
}
defer func() {
for _, h := range c.handlers {
h.Done(ctx, err)
}
}()
n, err := c.stream.Write(ctx, data)
for _, h := range c.handlers {
ctx = h.Wrote(ctx, n)
}
return err
}
// Call sends a request over the connection and then waits for a response.
// If the response is not an error, it will be decoded into result.
// result must be of a type you an pass to json.Unmarshal.
func (c *Conn) Call(ctx context.Context, method string, params, result interface{}) (err error) {
// generate a new request identifier
id := ID{Number: atomic.AddInt64(&c.seq, 1)}
jsonParams, err := marshalToRaw(params)
if err != nil {
return fmt.Errorf("marshalling call parameters: %v", err)
}
request := &WireRequest{
ID: &id,
Method: method,
Params: jsonParams,
}
// marshal the request now it is complete
data, err := json.Marshal(request)
if err != nil {
return fmt.Errorf("marshalling call request: %v", err)
}
for _, h := range c.handlers {
ctx = h.Request(ctx, Send, request)
}
// we have to add ourselves to the pending map before we send, otherwise we
// are racing the response
rchan := make(chan *WireResponse)
c.pendingMu.Lock()
c.pending[id] = rchan
c.pendingMu.Unlock()
defer func() {
// clean up the pending response handler on the way out
c.pendingMu.Lock()
delete(c.pending, id)
c.pendingMu.Unlock()
for _, h := range c.handlers {
h.Done(ctx, err)
}
}()
// now we are ready to send
n, err := c.stream.Write(ctx, data)
for _, h := range c.handlers {
ctx = h.Wrote(ctx, n)
}
if err != nil {
// sending failed, we will never get a response, so don't leave it pending
return err
}
// now wait for the response
select {
case response := <-rchan:
for _, h := range c.handlers {
ctx = h.Response(ctx, Receive, response)
}
// is it an error response?
if response.Error != nil {
return response.Error
}
if result == nil || response.Result == nil {
return nil
}
if err := json.Unmarshal(*response.Result, result); err != nil {
return fmt.Errorf("unmarshalling result: %v", err)
}
return nil
case <-ctx.Done():
// allow the handler to propagate the cancel
cancelled := false
for _, h := range c.handlers {
if h.Cancel(ctx, c, id, cancelled) {
cancelled = true
}
}
return ctx.Err()
}
}
// Conn returns the connection that created this request.
func (r *Request) Conn() *Conn { return r.conn }
// IsNotify returns true if this request is a notification.
func (r *Request) IsNotify() bool {
return r.ID == nil
}
// Parallel indicates that the system is now allowed to process other requests
// in parallel with this one.
// It is safe to call any number of times, but must only be called from the
// request handling go routine.
// It is implied by both reply and by the handler returning.
func (r *Request) Parallel() {
if r.state >= requestParallel {
return
}
r.state = requestParallel
close(r.nextRequest)
}
// Reply sends a reply to the given request.
// It is an error to call this if request was not a call.
// You must call this exactly once for any given request.
// It should only be called from the handler go routine.
// If err is set then result will be ignored.
// If the request has not yet dropped into parallel mode
// it will be before this function returns.
func (r *Request) Reply(ctx context.Context, result interface{}, err error) error {
if r.state >= requestReplied {
return fmt.Errorf("reply invoked more than once")
}
if r.IsNotify() {
return fmt.Errorf("reply not invoked with a valid call")
}
// reply ends the handling phase of a call, so if we are not yet
// parallel we should be now. The go routine is allowed to continue
// to do work after replying, which is why it is important to unlock
// the rpc system at this point.
r.Parallel()
r.state = requestReplied
var raw *json.RawMessage
if err == nil {
raw, err = marshalToRaw(result)
}
response := &WireResponse{
Result: raw,
ID: r.ID,
}
if err != nil {
if callErr, ok := err.(*Error); ok {
response.Error = callErr
} else {
response.Error = NewErrorf(0, "%s", err)
}
}
data, err := json.Marshal(response)
if err != nil {
return err
}
for _, h := range r.conn.handlers {
ctx = h.Response(ctx, Send, response)
}
n, err := r.conn.stream.Write(ctx, data)
for _, h := range r.conn.handlers {
ctx = h.Wrote(ctx, n)
}
if err != nil {
// TODO(iancottrell): if a stream write fails, we really need to shut down
// the whole stream
return err
}
return nil
}
func (c *Conn) setHandling(r *Request, active bool) {
if r.ID == nil {
return
}
r.conn.handlingMu.Lock()
defer r.conn.handlingMu.Unlock()
if active {
r.conn.handling[*r.ID] = r
} else {
delete(r.conn.handling, *r.ID)
}
}
// combined has all the fields of both Request and Response.
// We can decode this and then work out which it is.
type combined struct {
VersionTag VersionTag `json:"jsonrpc"`
ID *ID `json:"id,omitempty"`
Method string `json:"method"`
Params *json.RawMessage `json:"params,omitempty"`
Result *json.RawMessage `json:"result,omitempty"`
Error *Error `json:"error,omitempty"`
}
// Run blocks until the connection is terminated, and returns any error that
// caused the termination.
// It must be called exactly once for each Conn.
// It returns only when the reader is closed or there is an error in the stream.
func (c *Conn) Run(runCtx context.Context) error {
// we need to make the next request "lock" in an unlocked state to allow
// the first incoming request to proceed. All later requests are unlocked
// by the preceding request going to parallel mode.
nextRequest := make(chan struct{})
close(nextRequest)
for {
// get the data for a message
data, n, err := c.stream.Read(runCtx)
if err != nil {
// the stream failed, we cannot continue
return err
}
// read a combined message
msg := &combined{}
if err := json.Unmarshal(data, msg); err != nil {
// a badly formed message arrived, log it and continue
// we trust the stream to have isolated the error to just this message
for _, h := range c.handlers {
h.Error(runCtx, fmt.Errorf("unmarshal failed: %v", err))
}
continue
}
// work out which kind of message we have
switch {
case msg.Method != "":
// if method is set it must be a request
reqCtx, cancelReq := context.WithCancel(runCtx)
thisRequest := nextRequest
nextRequest = make(chan struct{})
req := &Request{
conn: c,
cancel: cancelReq,
nextRequest: nextRequest,
WireRequest: WireRequest{
VersionTag: msg.VersionTag,
Method: msg.Method,
Params: msg.Params,
ID: msg.ID,
},
}
for _, h := range c.handlers {
reqCtx = h.Request(reqCtx, Receive, &req.WireRequest)
reqCtx = h.Read(reqCtx, n)
}
c.setHandling(req, true)
go func() {
<-thisRequest
req.state = requestSerial
defer func() {
c.setHandling(req, false)
if !req.IsNotify() && req.state < requestReplied {
req.Reply(reqCtx, nil, NewErrorf(CodeInternalError, "method %q did not reply", req.Method))
}
req.Parallel()
for _, h := range c.handlers {
h.Done(reqCtx, err)
}
cancelReq()
}()
delivered := false
for _, h := range c.handlers {
if h.Deliver(reqCtx, req, delivered) {
delivered = true
}
}
}()
case msg.ID != nil:
// we have a response, get the pending entry from the map
c.pendingMu.Lock()
rchan := c.pending[*msg.ID]
if rchan != nil {
delete(c.pending, *msg.ID)
}
c.pendingMu.Unlock()
// and send the reply to the channel
response := &WireResponse{
Result: msg.Result,
Error: msg.Error,
ID: msg.ID,
}
rchan <- response
close(rchan)
default:
for _, h := range c.handlers {
h.Error(runCtx, fmt.Errorf("message not a call, notify or response, ignoring"))
}
}
}
}
func marshalToRaw(obj interface{}) (*json.RawMessage, error) {
data, err := json.Marshal(obj)
if err != nil {
return nil, err
}
raw := json.RawMessage(data)
return &raw, nil
}