path: root/rpc/client.go

// 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"
    "context"
    "encoding/json"
    "errors"
    "fmt"
    "net/url"
    "reflect"
    "strconv"
    "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")
    errClientReconnected         = errors.New("client reconnected")
    errDead                      = errors.New("connection lost")
)

const (
    // Timeouts
    tcpKeepAliveInterval = 30 * time.Second
    defaultDialTimeout   = 10 * time.Second // used if 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 = 20000
)

// 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
}

// Client represents a connection to an RPC server.
type Client struct {
    idgen    func() ID // for subscriptions
    isHTTP   bool
    services *serviceRegistry

    idCounter uint32

    // This function, if non-nil, is called when the connection is lost.
    reconnectFunc reconnectFunc

    // writeConn is used for writing to the connection on the caller's goroutine. It should
    // only be accessed outside of dispatch, with the write lock held. The write lock is
    // taken by sending on requestOp and released by sending on sendDone.
    writeConn jsonWriter

    // for dispatch
    close       chan struct{}
    closing     chan struct{}    // closed when client is quitting
    didClose    chan struct{}    // closed when client quits
    reconnected chan ServerCodec // where write/reconnect sends the new connection
    readOp      chan readOp      // read messages
    readErr     chan error       // errors from read
    reqInit     chan *requestOp  // register response IDs, takes write lock
    reqSent     chan error       // signals write completion, releases write lock
    reqTimeout  chan *requestOp  // removes response IDs when call timeout expires
}

type reconnectFunc func(ctx context.Context) (ServerCodec, error)

type clientContextKey struct{}

type clientConn struct {
    codec   ServerCodec
    handler *handler
}

func (c *Client) newClientConn(conn ServerCodec) *clientConn {
    ctx := context.WithValue(context.Background(), clientContextKey{}, c)
    handler := newHandler(ctx, conn, c.idgen, c.services)
    return &clientConn{conn, handler}
}

func (cc *clientConn) close(err error, inflightReq *requestOp) {
    cc.handler.close(err, inflightReq)
    cc.codec.Close()
}

type readOp struct {
    msgs  []*jsonrpcMessage
    batch bool
}

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, c *Client) (*jsonrpcMessage, error) {
    select {
    case <-ctx.Done():
        // Send the timeout to dispatch so it can remove the request IDs.
        select {
        case c.reqTimeout <- op:
        case <-c.closing:
        }
        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 "stdio":
        return DialStdIO(ctx)
    case "":
        return DialIPC(ctx, rawurl)
    default:
        return nil, fmt.Errorf("no known transport for URL scheme %q", u.Scheme)
    }
}

// Client retrieves the client from the context, if any. This can be used to perform
// 'reverse calls' in a handler method.
func ClientFromContext(ctx context.Context) (*Client, bool) {
    client, ok := ctx.Value(clientContextKey{}).(*Client)
    return client, ok
}

func newClient(initctx context.Context, connect reconnectFunc) (*Client, error) {
    conn, err := connect(initctx)
    if err != nil {
        return nil, err
    }
    c := initClient(conn, randomIDGenerator(), new(serviceRegistry))
    c.reconnectFunc = connect
    return c, nil
}

func initClient(conn ServerCodec, idgen func() ID, services *serviceRegistry) *Client {
    _, isHTTP := conn.(*httpConn)
    c := &Client{
        idgen:       idgen,
        isHTTP:      isHTTP,
        services:    services,
        writeConn:   conn,
        close:       make(chan struct{}),
        closing:     make(chan struct{}),
        didClose:    make(chan struct{}),
        reconnected: make(chan ServerCodec),
        readOp:      make(chan readOp),
        readErr:     make(chan error),
        reqInit:     make(chan *requestOp),
        reqSent:     make(chan error, 1),
        reqTimeout:  make(chan *requestOp),
    }
    if !isHTTP {
        go c.dispatch(conn)
    }
    return c
}

// RegisterName creates a service for the given receiver type under the given name. When no
// methods on the given receiver match the criteria to be either a RPC method or a
// subscription an error is returned. Otherwise a new service is created and added to the
// service collection this client provides to the server.
func (c *Client) RegisterName(name string, receiver interface{}) error {
    return c.services.registerName(name, receiver)
}

func (c *Client) nextID() json.RawMessage {
    id := atomic.AddUint32(&c.idCounter, 1)
    return strconv.AppendUint(nil, 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.didClose
    case <-c.didClose:
    }
}

// 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 when it quits.
    switch resp, err := op.wait(ctx, c); {
    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, c)
        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
}

// Notify sends a notification, i.e. a method call that doesn't expect a response.
func (c *Client) Notify(ctx context.Context, method string, args ...interface{}) error {
    op := new(requestOp)
    msg, err := c.newMessage(method, args...)
    if err != nil {
        return err
    }
    msg.ID = nil

    if c.isHTTP {
        return c.sendHTTP(ctx, op, msg)
    } else {
        return c.send(ctx, op, msg)
    }
}

// EthSubscribe registers a subscripion under the "eth" namespace.
func (c *Client) EthSubscribe(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error) {
    return c.Subscribe(ctx, "eth", channel, args...)
}

// ShhSubscribe registers a subscripion under the "shh" namespace.
func (c *Client) ShhSubscribe(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error) {
    return c.Subscribe(ctx, "shh", channel, args...)
}

// Subscribe calls the "<namespace>_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 Subscribe 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) Subscribe(ctx context.Context, namespace string, 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 Subscribe must be a writable channel")
    }
    if chanVal.IsNil() {
        panic("channel given to Subscribe must not be nil")
    }
    if c.isHTTP {
        return nil, ErrNotificationsUnsupported
    }

    msg, err := c.newMessage(namespace+subscribeMethodSuffix, args...)
    if err != nil {
        return nil, err
    }
    op := &requestOp{
        ids:  []json.RawMessage{msg.ID},
        resp: make(chan *jsonrpcMessage),
        sub:  newClientSubscription(c, namespace, 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, c); err != nil {
        return nil, err
    }
    return op.sub, nil
}

func (c *Client) newMessage(method string, paramsIn ...interface{}) (*jsonrpcMessage, error) {
    msg := &jsonrpcMessage{Version: vsn, ID: c.nextID(), Method: method}
    if paramsIn != nil { // prevent sending "params":null
        var err error
        if msg.Params, err = json.Marshal(paramsIn); err != nil {
            return nil, err
        }
    }
    return msg, 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.reqInit <- op:
        err := c.write(ctx, msg)
        c.reqSent <- 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.closing:
        return ErrClientQuit
    }
}

func (c *Client) write(ctx context.Context, msg interface{}) error {
    // The previous write failed. Try to establish a new connection.
    if c.writeConn == nil {
        if err := c.reconnect(ctx); err != nil {
            return err
        }
    }
    err := c.writeConn.Write(ctx, msg)
    if err != nil {
        c.writeConn = nil
    }
    return err
}

func (c *Client) reconnect(ctx context.Context) error {
    if c.reconnectFunc == nil {
        return errDead
    }

    if _, ok := ctx.Deadline(); !ok {
        var cancel func()
        ctx, cancel = context.WithTimeout(ctx, defaultDialTimeout)
        defer cancel()
    }
    newconn, err := c.reconnectFunc(ctx)
    if err != nil {
        log.Trace("RPC client reconnect failed", "err", err)
        return err
    }
    select {
    case c.reconnected <- newconn:
        c.writeConn = newconn
        return nil
    case <-c.didClose:
        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(codec ServerCodec) {
    var (
        lastOp      *requestOp  // tracks last send operation
        reqInitLock = c.reqInit // nil while the send lock is held
        conn        = c.newClientConn(codec)
        reading     = true
    )
    defer func() {
        close(c.closing)
        if reading {
            conn.close(ErrClientQuit, nil)
            c.drainRead()
        }
        close(c.didClose)
    }()

    // Spawn the initial read loop.
    go c.read(codec)

    for {
        select {
        case <-c.close:
            return

        // Read path:
        case op := <-c.readOp:
            if op.batch {
                conn.handler.handleBatch(op.msgs)
            } else {
                conn.handler.handleMsg(op.msgs[0])
            }

        case err := <-c.readErr:
            conn.handler.log.Debug("RPC connection read error", "err", err)
            conn.close(err, lastOp)
            reading = false

        // Reconnect:
        case newcodec := <-c.reconnected:
            log.Debug("RPC client reconnected", "reading", reading, "conn", newcodec.RemoteAddr())
            if reading {
                // Wait for the previous read loop to exit. This is a rare case which
                // happens if this loop isn't notified in time after the connection breaks.
                // In those cases the caller will notice first and reconnect. Closing the
                // handler terminates all waiting requests (closing op.resp) except for
                // lastOp, which will be transferred to the new handler.
                conn.close(errClientReconnected, lastOp)
                c.drainRead()
            }
            go c.read(newcodec)
            reading = true
            conn = c.newClientConn(newcodec)
            // Re-register the in-flight request on the new handler
            // because that's where it will be sent.
            conn.handler.addRequestOp(lastOp)

        // Send path:
        case op := <-reqInitLock:
            // Stop listening for further requests until the current one has been sent.
            reqInitLock = nil
            lastOp = op
            conn.handler.addRequestOp(op)

        case err := <-c.reqSent:
            if err != nil {
                // Remove response handlers for the last send. When the read loop
                // goes down, it will signal all other current operations.
                conn.handler.removeRequestOp(lastOp)
            }
            // Let the next request in.
            reqInitLock = c.reqInit
            lastOp = nil

        case op := <-c.reqTimeout:
            conn.handler.removeRequestOp(op)
        }
    }
}

// drainRead drops read messages until an error occurs.
func (c *Client) drainRead() {
    for {
        select {
        case <-c.readOp:
        case <-c.readErr:
            return
        }
    }
}

// read decodes RPC messages from a codec, feeding them into dispatch.
func (c *Client) read(codec ServerCodec) {
    for {
        msgs, batch, err := codec.Read()
        if _, ok := err.(*json.SyntaxError); ok {
            codec.Write(context.Background(), errorMessage(&parseError{err.Error()}))
        }
        if err != nil {
            c.readErr <- err
            return
        }
        c.readOp <- readOp{msgs, batch}
    }
}