rpc

package
v1.9.1 Latest Latest
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 Go to latest Published: Jul 24, 2019 License: GPL-3.0 Imports: 37 Imported by: 18

Documentation

Overview

Package rpc implements bi-directional JSON-RPC 2.0 on multiple transports.

It provides access to the exported methods of an object across a network or other I/O connection. After creating a server or client instance, objects can be registered to make them visible as 'services'. Exported methods that follow specific conventions can be called remotely. It also has support for the publish/subscribe pattern.

RPC Methods

Methods that satisfy the following criteria are made available for remote access:

  • method must be exported
  • method returns 0, 1 (response or error) or 2 (response and error) values
  • method argument(s) must be exported or builtin types
  • method returned value(s) must be exported or builtin types

An example method: 

func (s *CalcService) Add(a, b int) (int, error)

When the returned error isn't nil the returned integer is ignored and the error is sent back to the client. Otherwise the returned integer is sent back to the client.

Optional arguments are supported by accepting pointer values as arguments. E.g. if we want to do the addition in an optional finite field we can accept a mod argument as pointer value. 

func (s *CalcService) Add(a, b int, mod *int) (int, error)

This RPC method can be called with 2 integers and a null value as third argument. In that case the mod argument will be nil. Or it can be called with 3 integers, in that case mod will be pointing to the given third argument. Since the optional argument is the last argument the RPC package will also accept 2 integers as arguments. It will pass the mod argument as nil to the RPC method.

The server offers the ServeCodec method which accepts a ServerCodec instance. It will read requests from the codec, process the request and sends the response back to the client using the codec. The server can execute requests concurrently. Responses can be sent back to the client out of order.

An example server which uses the JSON codec: 

 type CalculatorService struct {}

 func (s *CalculatorService) Add(a, b int) int {
	return a + b
 }

 func (s *CalculatorService) Div(a, b int) (int, error) {
	if b == 0 {
		return 0, errors.New("divide by zero")
	}
	return a/b, nil
 }

 calculator := new(CalculatorService)
 server := NewServer()
 server.RegisterName("calculator", calculator")

 l, _ := net.ListenUnix("unix", &net.UnixAddr{Net: "unix", Name: "/tmp/calculator.sock"})
 for {
	c, _ := l.AcceptUnix()
	codec := v2.NewJSONCodec(c)
	go server.ServeCodec(codec, 0)
 }

Subscriptions

The package also supports the publish subscribe pattern through the use of subscriptions. A method that is considered eligible for notifications must satisfy the following criteria:

  • method must be exported
  • first method argument type must be context.Context
  • method argument(s) must be exported or builtin types
  • method must have return types (rpc.Subscription, error)

An example method: 

func (s *BlockChainService) NewBlocks(ctx context.Context) (rpc.Subscription, error) {
	...
}

When the service containing the subscription method is registered to the server, for example under the "blockchain" namespace, a subscription is created by calling the "blockchain_subscribe" method.

Subscriptions are deleted when the user sends an unsubscribe request or when the connection which was used to create the subscription is closed. This can be initiated by the client and server. The server will close the connection for any write error.

For more information about subscriptions, see https://github.com/ethereum/go-ethereum/wiki/RPC-PUB-SUB.

Reverse Calls

In any method handler, an instance of rpc.Client can be accessed through the ClientFromContext method. Using this client instance, server-to-client method calls can be performed on the RPC connection.

Index

Examples

Constants

View Source 
const (
	PendingBlockNumber  = BlockNumber(-2)
	LatestBlockNumber   = BlockNumber(-1)
	EarliestBlockNumber = BlockNumber(0)
)
View Source 
const MetadataApi = "rpc"

Variables

View Source 
var (
	ErrClientQuit                = errors.New("client is closed")
	ErrNoResult                  = errors.New("no result in JSON-RPC response")
	ErrSubscriptionQueueOverflow = errors.New("subscription queue overflow")
)
View Source 
var (
	// ErrNotificationsUnsupported is returned when the connection doesn't support notifications
	ErrNotificationsUnsupported = errors.New("notifications not supported")
	// ErrNotificationNotFound is returned when the notification for the given id is not found
	ErrSubscriptionNotFound = errors.New("subscription not found")
)
View Source 
var DefaultHTTPTimeouts = HTTPTimeouts{
	ReadTimeout:  30 * time.Second,
	WriteTimeout: 30 * time.Second,
	IdleTimeout:  120 * time.Second,
}

DefaultHTTPTimeouts represents the default timeout values used if further configuration is not provided.

Functions

func NewHTTPServer deprecated added in v1.4.0 

func NewHTTPServer(cors []string, vhosts []string, timeouts HTTPTimeouts, srv http.Handler) *http.Server

NewHTTPServer creates a new HTTP RPC server around an API provider.

Deprecated: Server implements http.Handler

func NewWSServer deprecated added in v1.4.0 

func NewWSServer(allowedOrigins []string, srv *Server) *http.Server

NewWSServer creates a new websocket RPC server around an API provider.

Deprecated: use Server.WebsocketHandler

Types

type API added in v1.4.0 

type API struct {
	Namespace string      // namespace under which the rpc methods of Service are exposed
	Version   string      // api version for DApp's
	Service   interface{} // receiver instance which holds the methods
	Public    bool        // indication if the methods must be considered safe for public use
}

API describes the set of methods offered over the RPC interface

type BatchElem added in v1.5.0 

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
}

BatchElem is an element in a batch request.

type BlockNumber added in v1.4.0 

type BlockNumber int64

func (BlockNumber) Int64 added in v1.4.0 

func (bn BlockNumber) Int64() int64

func (*BlockNumber) UnmarshalJSON added in v1.4.0 

func (bn *BlockNumber) UnmarshalJSON(data []byte) error

UnmarshalJSON parses the given JSON fragment into a BlockNumber. It supports: - "latest", "earliest" or "pending" as string arguments - the block number Returned errors: - an invalid block number error when the given argument isn't a known strings - an out of range error when the given block number is either too little or too large

type Client added in v1.4.0 

type Client struct {
	// contains filtered or unexported fields
}

Client represents a connection to an RPC server.

func ClientFromContext added in v1.9.0 

func ClientFromContext(ctx context.Context) (*Client, bool)

Client retrieves the client from the context, if any. This can be used to perform 'reverse calls' in a handler method.

func Dial added in v1.5.0 

func Dial(rawurl string) (*Client, error)

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 DialContext added in v1.5.0 

func DialContext(ctx context.Context, rawurl string) (*Client, error)

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 DialHTTP added in v1.5.0 

func DialHTTP(endpoint string) (*Client, error)

DialHTTP creates a new RPC client that connects to an RPC server over HTTP.

func DialHTTPWithClient added in v1.8.0 

func DialHTTPWithClient(endpoint string, client *http.Client) (*Client, error)

DialHTTPWithClient creates a new RPC client that connects to an RPC server over HTTP using the provided HTTP Client.

func DialIO added in v1.9.0 

func DialIO(ctx context.Context, in io.Reader, out io.Writer) (*Client, error)

DialIO creates a client which uses the given IO channels

func DialIPC added in v1.5.0 

func DialIPC(ctx context.Context, endpoint string) (*Client, error)

DialIPC create a new IPC client that connects to the given endpoint. On Unix it assumes the endpoint is the full path to a unix socket, and Windows the endpoint is an identifier for a named pipe.

The context is used for the initial connection establishment. It does not affect subsequent interactions with the client.

func DialInProc added in v1.5.0 

func DialInProc(handler *Server) *Client

DialInProc attaches an in-process connection to the given RPC server.

func DialStdIO added in v1.8.4 

func DialStdIO(ctx context.Context) (*Client, error)

DialStdIO creates a client on stdin/stdout.

func DialWebsocket added in v1.5.0 

func DialWebsocket(ctx context.Context, endpoint, origin string) (*Client, error)

DialWebsocket creates a new RPC client that communicates with a JSON-RPC server that is listening on the given endpoint.

The context is used for the initial connection establishment. It does not affect subsequent interactions with the client.

func (*Client) BatchCall added in v1.5.0 

func (c *Client) BatchCall(b []BatchElem) error

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 (*Client) BatchCallContext added in v1.5.0 

func (c *Client) BatchCallContext(ctx context.Context, b []BatchElem) error

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 (*Client) Call added in v1.5.0 

func (c *Client) Call(result interface{}, method string, args ...interface{}) error

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 (*Client) CallContext added in v1.5.0 

func (c *Client) CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error

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 (*Client) Close added in v1.4.0 

func (c *Client) Close()

Close closes the client, aborting any in-flight requests.

func (*Client) EthSubscribe added in v1.5.0 

func (c *Client) EthSubscribe(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error)

EthSubscribe registers a subscripion under the "eth" namespace.

func (*Client) Notify added in v1.9.0 

func (c *Client) Notify(ctx context.Context, method string, args ...interface{}) error

Notify sends a notification, i.e. a method call that doesn't expect a response.

func (*Client) RegisterName added in v1.9.0 

func (c *Client) RegisterName(name string, receiver interface{}) error

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 (*Client) ShhSubscribe added in v1.6.7 

func (c *Client) ShhSubscribe(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error)

ShhSubscribe registers a subscripion under the "shh" namespace.

func (*Client) Subscribe added in v1.7.1 

func (c *Client) Subscribe(ctx context.Context, namespace string, channel interface{}, args ...interface{}) (*ClientSubscription, error)

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 20000 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 (*Client) SupportedModules added in v1.4.0 

func (c *Client) SupportedModules() (map[string]string, error)

SupportedModules calls the rpc_modules method, retrieving the list of APIs that are available on the server.

type ClientSubscription added in v1.5.0 

type ClientSubscription struct {
	// contains filtered or unexported fields
}

ClientSubscription is a subscription established through the Client's Subscribe or EthSubscribe methods.

Example 
package main

import (
	"context"
	"fmt"
	"math/big"
	"time"

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

// In this example, our client wishes to track the latest 'block number'
// known to the server. The server supports two methods:
//
// eth_getBlockByNumber("latest", {})
//    returns the latest block object.
//
// eth_subscribe("newBlocks")
//    creates a subscription which fires block objects when new blocks arrive.

type Block struct {
	Number *big.Int
}

func main() {
	// Connect the client.
	client, _ := rpc.Dial("ws://127.0.0.1:8485")
	subch := make(chan Block)

	// Ensure that subch receives the latest block.
	go func() {
		for i := 0; ; i++ {
			if i > 0 {
				time.Sleep(2 * time.Second)
			}
			subscribeBlocks(client, subch)
		}
	}()

	// Print events from the subscription as they arrive.
	for block := range subch {
		fmt.Println("latest block:", block.Number)
	}
}

// subscribeBlocks runs in its own goroutine and maintains
// a subscription for new blocks.
func subscribeBlocks(client *rpc.Client, subch chan Block) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	// Subscribe to new blocks.
	sub, err := client.EthSubscribe(ctx, subch, "newHeads")
	if err != nil {
		fmt.Println("subscribe error:", err)
		return
	}

	// The connection is established now.
	// Update the channel with the current block.
	var lastBlock Block
	if err := client.CallContext(ctx, &lastBlock, "eth_getBlockByNumber", "latest"); err != nil {
		fmt.Println("can't get latest block:", err)
		return
	}
	subch <- lastBlock

	// The subscription will deliver events to the channel. Wait for the
	// subscription to end for any reason, then loop around to re-establish
	// the connection.
	fmt.Println("connection lost: ", <-sub.Err())
}

Output:

func (*ClientSubscription) Err added in v1.5.0 

func (sub *ClientSubscription) Err() <-chan error

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 (*ClientSubscription) Unsubscribe added in v1.5.0 

func (sub *ClientSubscription) Unsubscribe()

Unsubscribe unsubscribes the notification and closes the error channel. It can safely be called more than once.

type CodecOption deprecated added in v1.4.0 

type CodecOption int

CodecOption specifies which type of messages a codec supports.

Deprecated: this option is no longer honored by Server. 

const (
	// OptionMethodInvocation is an indication that the codec supports RPC method calls
	OptionMethodInvocation CodecOption = 1 << iota

	// OptionSubscriptions is an indication that the codec suports RPC notifications
	OptionSubscriptions = 1 << iota // support pub sub
)

type Conn added in v1.9.0 

type Conn interface {
	io.ReadWriteCloser
	SetWriteDeadline(time.Time) error
}

Conn is a subset of the methods of net.Conn which are sufficient for ServerCodec.

type ConnRemoteAddr added in v1.9.0 

type ConnRemoteAddr interface {
	RemoteAddr() string
}

ConnRemoteAddr wraps the RemoteAddr operation, which returns a description of the peer address of a connection. If a Conn also implements ConnRemoteAddr, this description is used in log messages.

type Error added in v1.5.0 

type Error interface {
	Error() string  // returns the message
	ErrorCode() int // returns the code
}

Error wraps RPC errors, which contain an error code in addition to the message.

type HTTPTimeouts added in v1.8.13 

type HTTPTimeouts struct {
	// ReadTimeout is the maximum duration for reading the entire
	// request, including the body.
	//
	// Because ReadTimeout does not let Handlers make per-request
	// decisions on each request body's acceptable deadline or
	// upload rate, most users will prefer to use
	// ReadHeaderTimeout. It is valid to use them both.
	ReadTimeout time.Duration

	// WriteTimeout is the maximum duration before timing out
	// writes of the response. It is reset whenever a new
	// request's header is read. Like ReadTimeout, it does not
	// let Handlers make decisions on a per-request basis.
	WriteTimeout time.Duration

	// IdleTimeout is the maximum amount of time to wait for the
	// next request when keep-alives are enabled. If IdleTimeout
	// is zero, the value of ReadTimeout is used. If both are
	// zero, ReadHeaderTimeout is used.
	IdleTimeout time.Duration
}

HTTPTimeouts represents the configuration params for the HTTP RPC server.

type ID added in v1.5.0 

type ID string

ID defines a pseudo random number that is used to identify RPC subscriptions.

func NewID added in v1.5.0 

func NewID() ID

NewID returns a new, random ID.

type Notifier added in v1.4.0 

type Notifier struct {
	// contains filtered or unexported fields
}

Notifier is tied to a RPC connection that supports subscriptions. Server callbacks use the notifier to send notifications.

func NotifierFromContext added in v1.4.0 

func NotifierFromContext(ctx context.Context) (*Notifier, bool)

NotifierFromContext returns the Notifier value stored in ctx, if any.

func (*Notifier) Closed added in v1.5.0 

func (n *Notifier) Closed() <-chan interface{}

Closed returns a channel that is closed when the RPC connection is closed. Deprecated: use subscription error channel

func (*Notifier) CreateSubscription added in v1.5.0 

func (n *Notifier) CreateSubscription() *Subscription

CreateSubscription returns a new subscription that is coupled to the RPC connection. By default subscriptions are inactive and notifications are dropped until the subscription is marked as active. This is done by the RPC server after the subscription ID is send to the client.

func (*Notifier) Notify added in v1.5.0 

func (n *Notifier) Notify(id ID, data interface{}) error

Notify sends a notification to the client with the given data as payload. If an error occurs the RPC connection is closed and the error is returned.

type RPCService added in v1.4.0 

type RPCService struct {
	// contains filtered or unexported fields
}

RPCService gives meta information about the server. e.g. gives information about the loaded modules.

func (*RPCService) Modules added in v1.4.0 

func (s *RPCService) Modules() map[string]string

Modules returns the list of RPC services with their version number

type Server added in v1.4.0 

type Server struct {
	// contains filtered or unexported fields
}

Server is an RPC server.

func NewServer added in v1.4.0 

func NewServer() *Server

NewServer creates a new server instance with no registered handlers.

func StartHTTPEndpoint added in v1.8.4 

func StartHTTPEndpoint(endpoint string, apis []API, modules []string, cors []string, vhosts []string, timeouts HTTPTimeouts) (net.Listener, *Server, error)

StartHTTPEndpoint starts the HTTP RPC endpoint, configured with cors/vhosts/modules

func StartIPCEndpoint added in v1.8.4 

func StartIPCEndpoint(ipcEndpoint string, apis []API) (net.Listener, *Server, error)

StartIPCEndpoint starts an IPC endpoint.

func StartWSEndpoint added in v1.8.4 

func StartWSEndpoint(endpoint string, apis []API, modules []string, wsOrigins []string, exposeAll bool) (net.Listener, *Server, error)

StartWSEndpoint starts a websocket endpoint

func (*Server) RegisterName added in v1.4.0 

func (s *Server) RegisterName(name string, receiver interface{}) error

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 server provides to clients.

func (*Server) ServeCodec added in v1.4.0 

func (s *Server) ServeCodec(codec ServerCodec, options CodecOption)

ServeCodec reads incoming requests from codec, calls the appropriate callback and writes the response back using the given codec. It will block until the codec is closed or the server is stopped. In either case the codec is closed.

Note that codec options are no longer supported.

func (*Server) ServeHTTP added in v1.5.0 

func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request)

ServeHTTP serves JSON-RPC requests over HTTP.

func (*Server) ServeListener added in v1.5.0 

func (s *Server) ServeListener(l net.Listener) error

ServeListener accepts connections on l, serving JSON-RPC on them.

func (*Server) Stop added in v1.4.0 

func (s *Server) Stop()

Stop stops reading new requests, waits for stopPendingRequestTimeout to allow pending requests to finish, then closes all codecs which will cancel pending requests and subscriptions.

func (*Server) WebsocketHandler added in v1.5.0 

func (s *Server) WebsocketHandler(allowedOrigins []string) http.Handler

WebsocketHandler returns a handler that serves JSON-RPC to WebSocket connections.

allowedOrigins should be a comma-separated list of allowed origin URLs. To allow connections with any origin, pass "*".

type ServerCodec added in v1.4.0 

type ServerCodec interface {
	Read() (msgs []*jsonrpcMessage, isBatch bool, err error)
	Close()
	// contains filtered or unexported methods
}

ServerCodec implements reading, parsing and writing RPC messages for the server side of a RPC session. Implementations must be go-routine safe since the codec can be called in multiple go-routines concurrently.

func NewJSONCodec added in v1.4.0 

func NewJSONCodec(conn Conn) ServerCodec

NewJSONCodec creates a codec that reads from the given connection. If conn implements ConnRemoteAddr, log messages will use it to include the remote address of the connection.

type Subscription added in v1.4.0 

type Subscription struct {
	ID ID
	// contains filtered or unexported fields
}

A Subscription is created by a notifier and tight to that notifier. The client can use this subscription to wait for an unsubscribe request for the client, see Err().

func (*Subscription) Err added in v1.5.0 

func (s *Subscription) Err() <-chan error

Err returns a channel that is closed when the client send an unsubscribe request.

func (*Subscription) MarshalJSON added in v1.9.0 

func (s *Subscription) MarshalJSON() ([]byte, error)

MarshalJSON marshals a subscription as its ID.

Source Files

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