path: root/rpc/handler.go

// Copyright 2019 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 (
	"context"
	"encoding/json"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/log"
)

// handler handles JSON-RPC messages. There is one handler per connection. Note that
// handler is not safe for concurrent use. Message handling never blocks indefinitely
// because RPCs are processed on background goroutines launched by handler.
//
// The entry points for incoming messages are:
//
//    h.handleMsg(message)
//    h.handleBatch(message)
//
// Outgoing calls use the requestOp struct. Register the request before sending it
// on the connection:
//
//    op := &requestOp{ids: ...}
//    h.addRequestOp(op)
//
// Now send the request, then wait for the reply to be delivered through handleMsg:
//
//    if err := op.wait(...); err != nil {
//        h.removeRequestOp(op) // timeout, etc.
//    }
//
type handler struct {
	reg            *serviceRegistry
	unsubscribeCb  *callback
	idgen          func() ID                      // subscription ID generator
	respWait       map[string]*requestOp          // active client requests
	clientSubs     map[string]*ClientSubscription // active client subscriptions
	callWG         sync.WaitGroup                 // pending call goroutines
	rootCtx        context.Context                // canceled by close()
	cancelRoot     func()                         // cancel function for rootCtx
	conn           jsonWriter                     // where responses will be sent
	log            log.Logger
	allowSubscribe bool

	subLock    sync.Mutex
	serverSubs map[ID]*Subscription
}

type callProc struct {
	ctx       context.Context
	notifiers []*Notifier
}

func newHandler(connCtx context.Context, conn jsonWriter, idgen func() ID, reg *serviceRegistry) *handler {
	rootCtx, cancelRoot := context.WithCancel(connCtx)
	h := &handler{
		reg:            reg,
		idgen:          idgen,
		conn:           conn,
		respWait:       make(map[string]*requestOp),
		clientSubs:     make(map[string]*ClientSubscription),
		rootCtx:        rootCtx,
		cancelRoot:     cancelRoot,
		allowSubscribe: true,
		serverSubs:     make(map[ID]*Subscription),
		log:            log.Root(),
	}
	if conn.remoteAddr() != "" {
		h.log = h.log.New("conn", conn.remoteAddr())
	}
	h.unsubscribeCb = newCallback(reflect.Value{}, reflect.ValueOf(h.unsubscribe))
	return h
}

// handleBatch executes all messages in a batch and returns the responses.
func (h *handler) handleBatch(msgs []*jsonrpcMessage) {
	// Emit error response for empty batches:
	if len(msgs) == 0 {
		h.startCallProc(func(cp *callProc) {
			h.conn.writeJSON(cp.ctx, errorMessage(&invalidRequestError{"empty batch"}))
		})
		return
	}

	// Handle non-call messages first:
	calls := make([]*jsonrpcMessage, 0, len(msgs))
	for _, msg := range msgs {
		if handled := h.handleImmediate(msg); !handled {
			calls = append(calls, msg)
		}
	}
	if len(calls) == 0 {
		return
	}
	// Process calls on a goroutine because they may block indefinitely:
	h.startCallProc(func(cp *callProc) {
		answers := make([]*jsonrpcMessage, 0, len(msgs))
		for _, msg := range calls {
			if answer := h.handleCallMsg(cp, msg); answer != nil {
				answers = append(answers, answer)
			}
		}
		h.addSubscriptions(cp.notifiers)
		if len(answers) > 0 {
			h.conn.writeJSON(cp.ctx, answers)
		}
		for _, n := range cp.notifiers {
			n.activate()
		}
	})
}

// handleMsg handles a single message.
func (h *handler) handleMsg(msg *jsonrpcMessage) {
	if ok := h.handleImmediate(msg); ok {
		return
	}
	h.startCallProc(func(cp *callProc) {
		answer := h.handleCallMsg(cp, msg)
		h.addSubscriptions(cp.notifiers)
		if answer != nil {
			h.conn.writeJSON(cp.ctx, answer)
		}
		for _, n := range cp.notifiers {
			n.activate()
		}
	})
}

// close cancels all requests except for inflightReq and waits for
// call goroutines to shut down.
func (h *handler) close(err error, inflightReq *requestOp) {
	h.cancelAllRequests(err, inflightReq)
	h.callWG.Wait()
	h.cancelRoot()
	h.cancelServerSubscriptions(err)
}

// addRequestOp registers a request operation.
func (h *handler) addRequestOp(op *requestOp) {
	for _, id := range op.ids {
		h.respWait[string(id)] = op
	}
}

// removeRequestOps stops waiting for the given request IDs.
func (h *handler) removeRequestOp(op *requestOp) {
	for _, id := range op.ids {
		delete(h.respWait, string(id))
	}
}

// cancelAllRequests unblocks and removes pending requests and active subscriptions.
func (h *handler) cancelAllRequests(err error, inflightReq *requestOp) {
	didClose := make(map[*requestOp]bool)
	if inflightReq != nil {
		didClose[inflightReq] = true
	}

	for id, op := range h.respWait {
		// Remove the op so that later calls will not close op.resp again.
		delete(h.respWait, id)

		if !didClose[op] {
			op.err = err
			close(op.resp)
			didClose[op] = true
		}
	}
	for id, sub := range h.clientSubs {
		delete(h.clientSubs, id)
		sub.quitWithError(false, err)
	}
}

func (h *handler) addSubscriptions(nn []*Notifier) {
	h.subLock.Lock()
	defer h.subLock.Unlock()

	for _, n := range nn {
		if sub := n.takeSubscription(); sub != nil {
			h.serverSubs[sub.ID] = sub
		}
	}
}

// cancelServerSubscriptions removes all subscriptions and closes their error channels.
func (h *handler) cancelServerSubscriptions(err error) {
	h.subLock.Lock()
	defer h.subLock.Unlock()

	for id, s := range h.serverSubs {
		s.err <- err
		close(s.err)
		delete(h.serverSubs, id)
	}
}

// startCallProc runs fn in a new goroutine and starts tracking it in the h.calls wait group.
func (h *handler) startCallProc(fn func(*callProc)) {
	h.callWG.Add(1)
	go func() {
		ctx, cancel := context.WithCancel(h.rootCtx)
		defer h.callWG.Done()
		defer cancel()
		fn(&callProc{ctx: ctx})
	}()
}

// handleImmediate executes non-call messages. It returns false if the message is a
// call or requires a reply.
func (h *handler) handleImmediate(msg *jsonrpcMessage) bool {
	start := time.Now()
	switch {
	case msg.isNotification():
		if strings.HasSuffix(msg.Method, notificationMethodSuffix) {
			h.handleSubscriptionResult(msg)
			return true
		}
		return false
	case msg.isResponse():
		h.handleResponse(msg)
		h.log.Trace("Handled RPC response", "reqid", idForLog{msg.ID}, "t", time.Since(start))
		return true
	default:
		return false
	}
}

// handleSubscriptionResult processes subscription notifications.
func (h *handler) handleSubscriptionResult(msg *jsonrpcMessage) {
	var result subscriptionResult
	if err := json.Unmarshal(msg.Params, &result); err != nil {
		h.log.Debug("Dropping invalid subscription message")
		return
	}
	if h.clientSubs[result.ID] != nil {
		h.clientSubs[result.ID].deliver(result.Result)
	}
}

// handleResponse processes method call responses.
func (h *handler) handleResponse(msg *jsonrpcMessage) {
	op := h.respWait[string(msg.ID)]
	if op