// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package rpc
import (
"bytes"
"container/list"
"context"
"encoding/json"
"errors"
"fmt"
"net"
"net/url"
"reflect"
"strconv"
"strings"
"sync"
"sync/atomic"
"time"
"github.com/ethereum/go-ethereum/log"
)
var (
ErrClientQuit = errors.New("client is closed")
ErrNoResult = errors.New("no result in JSON-RPC response")
ErrSubscriptionQueueOverflow = errors.New("subscription queue overflow")
)
const (
// Timeouts
tcpKeepAliveInterval = 30 * time.Second
defaultDialTimeout = 10 * time.Second // used when dialing if the context has no deadline
defaultWriteTimeout = 10 * time.Second // used for calls if the context has no deadline
subscribeTimeout = 5 * time.Second // overall timeout eth_subscribe, rpc_modules calls
)
const (
// Subscriptions are removed when the subscriber cannot keep up.
//
// This can be worked around by supplying a channel with sufficiently sized buffer,
// but this can be inconvenient and hard to explain in the docs. Another issue with
// buffered channels is that the buffer is static even though it might not be needed
// most of the time.
//
// The approach taken here is to maintain a per-subscription linked list buffer
// shrinks on demand. If the buffer reaches the size below, the subscription is
// dropped.
maxClientSubscriptionBuffer = 8000
)
// BatchElem is an element in a batch request.
type BatchElem struct {
Method string
Args []interface{}
// The result is unmarshaled into this field. Result must be set to a
// non-nil pointer value of the desired type, otherwise the response will be
// discarded.
Result interface{}
// Error is set if the server returns an error for this request, or if
// unmarshaling into Result fails. It is not set for I/O errors.
Error error
}
// A value of this type can a JSON-RPC request, notification, successful response or
// error response. Which one it is depends on the fields.
type jsonrpcMessage struct {
Version string `json:"jsonrpc"`
ID json.RawMessage `json:"id,omitempty"`
Method string `json:"method,omitempty"`
Params json.RawMessage `json:"params,omitempty"`
Error *jsonError `json:"error,omitempty"`
Result json.RawMessage `json:"result,omitempty"`
}
func (msg *jsonrpcMessage) isNotification() bool {
return msg.ID == nil && msg.Method != ""
}
func (msg *jsonrpcMessage) isResponse() bool {
return msg.hasValidID() && msg.Method == "" && len(msg.Params) == 0
}
func (msg *jsonrpcMessage) hasValidID() bool {
return len(msg.ID) > 0 && msg.ID[0] != '{' && msg.ID[0] != '['
}
func (msg *jsonrpcMessage) String() string {
b, _ := json.Marshal(msg)
return string(b)
}
// Client represents a connection to an RPC server.
type Client struct {
idCounter uint32
connectFunc func(ctx context.Context) (net.Conn, error)
isHTTP bool
// writeConn is only safe to access outside dispatch, with the
// write lock held. The write lock is taken by sending on
// requestOp and released by sending on sendDone.
writeConn net.Conn
// for dispatch
close chan struct{}
didQuit chan struct{} // closed when client quits
reconnected chan net.Conn // where write/reconnect sends the new connection
readErr chan error // errors from read
readResp chan []*jsonrpcMessage // valid messages from read
requestOp chan *requestOp // for registering response IDs
sendDone chan error // signals write completion, releases write lock
respWait map[string]*requestOp // active requests
subs map[string]*ClientSubscription // active subscriptions
}
type requestOp struct {
ids []json.RawMessage
err error
resp chan *jsonrpcMessage // receives up to len(ids) responses
sub *ClientSubscription // only set for EthSubscribe requests
}
func (op *requestOp) wait(ctx context.Context) (*jsonrpcMessage, error) {
select {
case <-ctx.Done():
return nil, ctx.Err()
case resp := <-op.resp:
return resp, op.err
}
}
// Dial creates a new client for the given URL.
//
// The currently supported URL schemes are "http", "https", "ws" and "wss". If rawurl is a
// file name with no URL scheme, a local socket connection is established using UNIX
// domain sockets on supported platforms and named pipes on Windows. If you want to
// configure transport options, use DialHTTP, DialWebsocket or DialIPC instead.
//
// For websocket connections, the origin is set to the local host name.
//
// The client reconnects automatically if the connection is lost.
func Dial(rawurl string) (*Client, error) {
return DialContext(context.Background(), rawurl)
}
// DialContext creates a new RPC client, just like Dial.
//
// The context is used to cancel or time out the initial connection establishment. It does
// not affect subsequent interactions with the client.
func DialContext(ctx context.Context, rawurl string) (*Client, error) {
u, err := url.Parse(rawurl)
if err != nil {
return nil, err
}
switch u.Scheme {
case "http", "https":
return DialHTTP(rawurl)
case "ws", "wss":
return DialWebsocket(ctx, rawurl, "")
case "":
return DialIPC(ctx, rawurl)
default:
return nil, fmt.Errorf("no known transport for URL scheme %q", u.Scheme)
}
}
func newClient(initctx context.Context, connectFunc func(context.Context) (net.Conn, error)) (*Client, error) {
conn, err := connectFunc(initctx)
if err != nil {
return nil, err
}
_, isHTTP := conn.(*httpConn)
c := &Client{
writeConn: conn,
isHTTP: isHTTP,
connectFunc: connectFunc,
close: make(chan struct{}),
didQuit: make(chan struct{}),
reconnected: make(chan net.Conn),
readErr: make(chan error),
readResp: make(chan []*jsonrpcMessage),
requestOp: make(chan *requestOp),
sendDone: make(chan error, 1),
respWait: make(map[string]*requestOp),
subs: make(map[string]*ClientSubscription),
}
if !isHTTP {
go c.dispatch(conn)
}
return c, nil
}
func (c *Client) nextID() json.RawMessage {
id := atomic.AddUint32(&c.idCounter, 1)
return []byte(strconv.FormatUint(uint64(id), 10))
}
// SupportedModules calls the rpc_modules method, retrieving the list of
// APIs that are available on the server.
func (c *Client) SupportedModules() (map[string]string, error) {
var result map[string]string
ctx, cancel := context.WithTimeout(context.Background(), subscribeTimeout)
defer cancel()
err := c.CallContext(ctx, &result, "rpc_modules")
return result, err
}
// Close closes the client, aborting any in-flight requests.
func (c *Client) Close() {
if c.isHTTP {
return
}
select {
case c.close <- struct{}{}:
<-c.didQuit
case <-c.didQuit:
}
}
// Call performs a JSON-RPC call with the given arguments and unmarshals into
// result if no error occurred.
//
// The result must be a pointer so that package json can unmarshal into it. You
// can also pass nil, in which case the result is ignored.
func (c *Client) Call(result interface{}, method string, args ...interface{}) error {
ctx := context.Background()
return c.CallContext(ctx, result, method, args...)
}
// CallContext performs a JSON-RPC call with the given arguments. If the context is
// canceled before the call has successfully returned, CallContext returns immediately.
//
// The result must be a pointer so that package json can unmarshal into it. You
// can also pass nil, in which case the result is ignored.
func (c *Client) CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error {
msg, err := c.newMessage(method, args...)
if err != nil {
return err
}
op := &requestOp{ids: []json.RawMessage{msg.ID}, resp: make(chan *jsonrpcMessage, 1)}
if c.isHTTP {
err = c.sendHTTP(ctx, op, msg)
} else {
err = c.send(ctx, op, msg)
}
if err != nil {
return err
}
// dispatch has accepted the request and will close the channel it when it quits.
switch resp, err := op.wait(ctx); {
case err != nil:
return err
case resp.Error != nil:
return resp.Error
case len(resp.Result) == 0:
return ErrNoResult
default:
return json.Unmarshal(resp.Result, &result)
}
}
// BatchCall sends all given requests as a single batch and waits for the server
// to return a response for all of them.
//
// In contrast to Call, BatchCall only returns I/O errors. Any error specific to
// a request is reported through the Error field of the corresponding BatchElem.
//
// Note that batch calls may not be executed atomically on the server side.
func (c *Client) BatchCall(b []BatchElem) error {
ctx := context.Background()
return c.BatchCallContext(ctx, b)
}
// BatchCall sends all given requests as a single batch and waits for the server
// to return a response for all of them. The wait duration is bounded by the
// context's deadline.
//
// In contrast to CallContext, BatchCallContext only returns errors that have occurred
// while sending the request. Any error specific to a request is reported through the
// Error field of the corresponding BatchElem.
//
// Note that batch calls may not be executed atomically on the server side.
func (c *Client) BatchCallContext(ctx context.Context, b []BatchElem) error {
msgs := make([]*jsonrpcMessage, len(b))
op := &requestOp{
ids: make([]json.RawMessage, len(b)),
resp: make(chan *jsonrpcMessage, len(b)),
}
for i, elem := range b {
msg, err := c.newMessage(elem.Method, elem.Args...)
if err != nil {
return err
}
msgs[i] = msg
op.ids[i] = msg.ID
}
var err error
if c.isHTTP {
err = c.sendBatchHTTP(ctx, op, msgs)
} else {
err = c.send(ctx, op, msgs)
}
// Wait for all responses to come back.
for n := 0; n < len(b) && err == nil; n++ {
var resp *jsonrpcMessage
resp, err = op.wait(ctx)
if err != nil {
break
}
// Find the element corresponding to this response.
// The element is guaranteed to be present because dispatch
// only sends valid IDs to our channel.
var elem *BatchElem
for i := range msgs {
if bytes.Equal(msgs[i].ID, resp.ID) {
elem = &b[i]
break
}
}
if resp.Error != nil {
elem.Error = resp.Error
continue
}
if len(resp.Result) == 0 {
elem.Error = ErrNoResult
continue
}
elem.Error = json.Unmarshal(resp.Result, elem.Result)
}
return err
}
// EthSubscribe calls the "eth_subscribe" method with the given arguments,
// registering a subscription. Server notifications for the subscription are
// sent to the given channel. The element type of the channel must match the
// expected type of content returned by the subscription.
//
// The context argument cancels the RPC request that sets up the subscription but has no
// effect on the subscription after EthSubscribe has returned.
//
// Slow subscribers will be dropped eventually. Client buffers up to 8000 notifications
// before considering the subscriber dead. The subscription Err channel will receive
// ErrSubscriptionQueueOverflow. Use a sufficiently large buffer on the channel or ensure
// that the channel usually has at least one reader to prevent this issue.
func (c *Client) EthSubscribe(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error) {
// Check type of channel first.
chanVal := reflect.ValueOf(channel)
if chanVal.Kind() != reflect.Chan || chanVal.Type().ChanDir()&reflect.SendDir == 0 {
panic("first argument to EthSubscribe must be a writable channel")
}
if chanVal.IsNil() {
panic("channel given to EthSubscribe must not be nil")
}
if c.isHTTP {
return nil, ErrNotificationsUnsupported
}
msg, err := c.newMessage("eth"+subscribeMethodSuffix, args...)
if err != nil {
return nil, err
}
op := &requestOp{
ids: []json.RawMessage{msg.ID},
resp: make(chan *jsonrpcMessage),
sub: newClientSubscription(c, "eth", chanVal),
}
// Send the subscription request.
// The arrival and validity of the response is signaled on sub.quit.
if err := c.send(ctx, op, msg); err != nil {
return nil, err
}
if _, err := op.wait(ctx); err != nil {
return nil, err
}
return op.sub, nil
}
func (c *Client) newMessage(method string, paramsIn ...interface{}) (*jsonrpcMessage, error) {
params, err := json.Marshal(paramsIn)
if err != nil {
return nil, err
}
return &jsonrpcMessage{Version: "2.0", ID: c.nextID(), Method: method, Params: params}, nil
}
// send registers op with the dispatch loop, then sends msg on the connection.
// if sending fails, op is deregistered.
func (c *Client) send(ctx context.Context, op *requestOp, msg interface{}) error {
select {
case c.requestOp <- op:
log.Trace("", "msg", log.Lazy{Fn: func() string {
return fmt.Sprint("sending ", msg)
}})
err := c.write(ctx, msg)
c.sendDone <- err
return err
case <-ctx.Done():
// This can happen if the client is overloaded or unable to keep up with
// subscription notifications.
return ctx.Err()
case <-c.didQuit:
return ErrClientQuit
}
}
func (c *Client) write(ctx context.Context, msg interface{}) error {
deadline, ok := ctx.Deadline()
if !ok {
deadline = time.Now().Add(defaultWriteTimeout)
}
// The previous write failed. Try to establish a new connection.
if c.writeConn == nil {
if err := c.reconnect(ctx); err != nil {
return err
}
}
c.writeConn.SetWriteDeadline(deadline)
err := json.NewEncoder(c.writeConn).Encode(msg)
if err != nil {
c.writeConn = nil
}
return err
}
func (c *Client) reconnect(ctx context.Context) error {
newconn, err := c.connectFunc(ctx)
if err != nil {
log.Trace(fmt.Sprintf("reconnect failed: %v", err))
return err
}
select {
case c.reconnected <- newconn:
c.writeConn = newconn
return nil
case <-c.didQuit:
newconn.Close()
return ErrClientQuit
}
}
// dispatch is the main loop of the client.
// It sends read messages to waiting calls to Call and BatchCall
// and subscription notifications to registered subscriptions.
func (c *Client) dispatch(conn net.Conn) {
// Spawn the initial read loop.
go c.read(conn)
var (
lastOp *requestOp // tracks last send operation
requestOpLock = c.requestOp // nil while the send lock is held
reading = true // if true, a read loop is running
)
defer close(c.didQuit)
defer func() {
c.closeRequestOps(ErrClientQuit)
conn.Close()
if reading {
// Empty read channels until read is dead.
for {
select {
case <-c.readResp:
case <-c.readErr:
return
}
}
}
}()
for {
select {
case <-c.close:
return
// Read path.
case batch := <-c.readResp:
for _, msg := range batch {
switch {
case msg.isNotification():
log.Trace("", "msg", log.Lazy{Fn: func() string {
return fmt.Sprint("<-readResp: notification ", msg)
}})
c.handleNotification(msg)
case msg.isResponse():
log.Trace("", "msg", log.Lazy{Fn: func() string {
return fmt.Sprint("<-readResp: response ", msg)
}})
c.handleResponse(msg)
default:
log.Debug("", "msg", log.Lazy{Fn: func() string {
return fmt.Sprint("<-readResp: dropping weird message", msg)
}})
// TODO: maybe close
}
}
case err := <-c.readErr:
log.Debug(fmt.Sprintf("<-readErr: %v", err))
c.closeRequestOps(err)
conn.Close()
reading = false
case newconn := <-c.reconnected:
log.Debug(fmt.Sprintf("<-reconnected: (reading=%t) %v", reading, conn.RemoteAddr()))
if reading {
// Wait for the previous read loop to exit. This is a rare case.
conn.Close()
<-c.readErr
}
go c.read(newconn)
reading = true
conn = newconn
// Send path.
case op := <-requestOpLock:
// Stop listening for further send ops until the current one is done.
requestOpLock = nil
lastOp = op
for _, id := range op.ids {
c.respWait[string(id)] = op
}
case err := <-c.sendDone:
if err != nil {
// Remove response handlers for the last send. We remove those here
// because the error is already handled in Call or BatchCall. When the
// read loop goes down, it will signal all other current operations.
for _, id := range lastOp.ids {
delete(c.respWait, string(id))
}
}
// Listen for send ops again.
requestOpLock = c.requestOp
lastOp = nil
}
}
}
// closeRequestOps unblocks pending send ops and active subscriptions.
func (c *Client) closeRequestOps(err error) {
didClose := make(map[*requestOp]bool)
for id, op := range c.respWait {
// Remove the op so that later calls will not close op.resp again.
delete(c.respWait, id)
if !didClose[op] {
op.err = err
close(op.resp)
didClose[op] = true
}
}
for id, sub := range c.subs {
delete(c.subs, id)
sub.quitWithError(err, false)
}
}
func (c *Client) handleNotification(msg *jsonrpcMessage) {
if !strings.HasSuffix(msg.Method, notificationMethodSuffix) {
log.Debug(fmt.Sprint("dropping non-subscription message: ", msg))
return
}
var subResult struct {
ID string `json:"subscription"`
Result json.RawMessage `json:"result"`
}
if err := json.Unmarshal(msg.Params, &subResult); err != nil {
log.Debug(fmt.Sprint("dropping invalid subscription message: ", msg))
return
}
if c.subs[subResult.ID] != nil {
c.subs[subResult.ID].deliver(subResult.Result)
}
}
func (c *Client) handleResponse(msg *jsonrpcMessage) {
op := c.respWait[string(msg.ID)]
if op == nil {
log.Debug(fmt.Sprintf("unsolicited response %v", msg))
return
}
delete(c.respWait, string(msg.ID))
// For normal responses, just forward the reply to Call/BatchCall.
if op.sub == nil {
op.resp <- msg
return
}
// For subscription responses, start the subscription if the server
// indicates success. EthSubscribe gets unblocked in either case through
// the op.resp channel.
defer close(op.resp)
if msg.Error != nil {
op.err = msg.Error
return
}
if op.err = json.Unmarshal(msg.Result, &op.sub.subid); op.err == nil {
go op.sub.start()
c.subs[op.sub.subid] = op.sub
}
}
// Reading happens on a dedicated goroutine.
func (c *Client) read(conn net.Conn) error {
var (
buf json.RawMessage
dec = json.NewDecoder(conn)
)
readMessage := func() (rs []*jsonrpcMessage, err error) {
buf = buf[:0]
if err = dec.Decode(&buf); err != nil {
return nil, err
}
if isBatch(buf) {
err = json.Unmarshal(buf, &rs)
} else {
rs = make([]*jsonrpcMessage, 1)
err = json.Unmarshal(buf, &rs[0])
}
return rs, err
}
for {
resp, err := readMessage()
if err != nil {
c.readErr <- err
return err
}
c.readResp <- resp
}
}
// Subscriptions.
// A ClientSubscription represents a subscription established through EthSubscribe.
type ClientSubscription struct {
client *Client
etype reflect.Type
channel reflect.Value
namespace string
subid string
in chan json.RawMessage
quitOnce sync.Once // ensures quit is closed once
quit chan struct{} // quit is closed when the subscription exits
errOnce sync.Once // ensures err is closed once
err chan error
}
func newClientSubscription(c *Client, namespace string, channel reflect.Value) *ClientSubscription {
sub := &ClientSubscription{
client: c,
namespace: namespace,
etype: channel.Type().Elem(),
channel: channel,
quit: make(chan struct{}),
err: make(chan error, 1),
in: make(chan json.RawMessage),
}
return sub
}
// Err returns the subscription error channel. The intended use of Err is to schedule
// resubscription when the client connection is closed unexpectedly.
//
// The error channel receives a value when the subscription has ended due
// to an error. The received error is nil if Close has been called
// on the underlying client and no other error has occurred.
//
// The error channel is closed when Unsubscribe is called on the subscription.
func (sub *ClientSubscription) Err() <-chan error {
return sub.err
}
// Unsubscribe unsubscribes the notification and closes the error channel.
// It can safely be called more than once.
func (sub *ClientSubscription) Unsubscribe() {
sub.quitWithError(nil, true)
sub.errOnce.Do(func() { close(sub.err) })
}
func (sub *ClientSubscription) quitWithError(err error, unsubscribeServer bool) {
sub.quitOnce.Do(func() {
// The dispatch loop won't be able to execute the unsubscribe call
// if it is blocked on deliver. Close sub.quit first because it
// unblocks deliver.
close(sub.quit)
if unsubscribeServer {
sub.requestUnsubscribe()
}
if err != nil {
if err == ErrClientQuit {
err = nil // Adhere to subscription semantics.
}
sub.err <- err
}
})
}
func (sub *ClientSubscription) deliver(result json.RawMessage) (ok bool) {
select {
case sub.in <- result:
return true
case <-sub.quit:
return false
}
}
func (sub *ClientSubscription) start() {
sub.quitWithError(sub.forward())
}
func (sub *ClientSubscription) forward() (err error, unsubscribeServer bool) {
cases := []reflect.SelectCase{
{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sub.quit)},
{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sub.in)},
{Dir: reflect.SelectSend, Chan: sub.channel},
}
buffer := list.New()
defer buffer.Init()
for {
var chosen int
var recv reflect.Value
if buffer.Len() == 0 {
// Idle, omit send case.
chosen, recv, _ = reflect.Select(cases[:2])
} else {
// Non-empty buffer, send the first queued item.
cases[2].Send = reflect.ValueOf(buffer.Front().Value)
chosen, recv, _ = reflect.Select(cases)
}
switch chosen {
case 0: // <-sub.quit
return nil, false
case 1: // <-sub.in
val, err := sub.unmarshal(recv.Interface().(json.RawMessage))
if err != nil {
return err, true
}
if buffer.Len() == maxClientSubscriptionBuffer {
return ErrSubscriptionQueueOverflow, true
}
buffer.PushBack(val)
case 2: // sub.channel<-
cases[2].Send = reflect.Value{} // Don't hold onto the value.
buffer.Remove(buffer.Front())
}
}
}
func (sub *ClientSubscription) unmarshal(result json.RawMessage) (interface{}, error) {
val := reflect.New(sub.etype)
err := json.Unmarshal(result, val.Interface())
return val.Elem().Interface(), err
}
func (sub *ClientSubscription) requestUnsubscribe() error {
var result interface{}
return sub.client.Call(&result, sub.namespace+unsubscribeMethodSuffix, sub.subid)
}
