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Published: Sep 18, 2021 License: MIT Imports: 12 Imported by: 46



JSON RPC is "A light weight remote procedure call protocol". It allows for the creation of simple RPC-style APIs with human-readable messages that are front-end friendly.

Using JSON RPC with Go-Kit

Using JSON RPC and go-kit together is quite simple.

A JSON RPC server acts as an HTTP Handler, receiving all requests to the JSON RPC's URL. The server looks at the method property of the Request Object, and routes it to the corresponding code.

Each JSON RPC method is implemented as an EndpointCodec, a go-kit Endpoint, sandwiched between a decoder and encoder. The decoder picks apart the JSON RPC request params, which can be passed to your endpoint. The encoder receives the output from the endpoint and encodes a JSON-RPC result.

Example — Add Service

Let's say we want a service that adds two ints together. We'll serve this at http://localhost/rpc. So a request to our sum method will be a POST to http://localhost/rpc with a request body of:

    "id": 123,
    "jsonrpc": "2.0",
    "method": "sum",
    "params": {
    	"A": 2,
    	"B": 2

The routing table for incoming JSON RPC requests is the EndpointCodecMap. The key of the map is the JSON RPC method name. Here, we're routing the sum method to an EndpointCodec wrapped around sumEndpoint.

	"sum": jsonrpc.EndpointCodec{
		Endpoint: sumEndpoint,
		Decode:   decodeSumRequest,
		Encode:   encodeSumResponse,
type DecodeRequestFunc func(context.Context, json.RawMessage) (request interface{}, err error)

A DecodeRequestFunc is given the raw JSON from the params property of the Request object, not the whole request object. It returns an object that will be the input to the Endpoint. For our purposes, the output should be a SumRequest, like this:

type SumRequest struct {
	A, B int

So here's our decoder:

func decodeSumRequest(ctx context.Context, msg json.RawMessage) (interface{}, error) {
	var req SumRequest
	err := json.Unmarshal(msg, &req)
	if err != nil {
		return nil, err
	return req, nil

So our SumRequest will now be passed to the endpoint. Once the endpoint has done its work, we hand over to the…


The encoder takes the output of the endpoint, and builds the raw JSON message that will form the result field of a Response Object. Our result is going to be a plain int. Here's our encoder:

func encodeSumResponse(ctx context.Context, result interface{}) (json.RawMessage, error) {
	sum, ok := result.(int)
	if !ok {
		return nil, errors.New("result is not an int")
	b, err := json.Marshal(sum)
	if err != nil {
		return nil, err
	return b, nil

Now that we have an EndpointCodec with decoder, endpoint, and encoder, we can wire up the server:

handler := jsonrpc.NewServer(jsonrpc.EndpointCodecMap{
	"sum": jsonrpc.EndpointCodec{
		Endpoint: sumEndpoint,
		Decode:   decodeSumRequest,
		Encode:   encodeSumResponse,
http.Handle("/rpc", handler)
http.ListenAndServe(":80", nil)

With all of this done, our example request above should result in a response like this:

    "jsonrpc": "2.0",
    "result": 4



Package jsonrpc provides a JSON RPC (v2.0) binding for endpoints. See http://www.jsonrpc.org/specification



View Source
const (
	// ParseError defines invalid JSON was received by the server.
	// An error occurred on the server while parsing the JSON text.
	ParseError int = -32700

	// InvalidRequestError defines the JSON sent is not a valid Request object.
	InvalidRequestError int = -32600

	// MethodNotFoundError defines the method does not exist / is not available.
	MethodNotFoundError int = -32601

	// InvalidParamsError defines invalid method parameter(s).
	InvalidParamsError int = -32602

	// InternalError defines a server error
	InternalError int = -32603
View Source
const (
	// Version defines the version of the JSON RPC implementation
	Version string = "2.0"

	// ContentType defines the content type to be served.
	ContentType string = "application/json; charset=utf-8"
View Source
const (
	ContextKeyRequestMethod contextKey = iota


This section is empty.


func DefaultErrorEncoder

func DefaultErrorEncoder(ctx context.Context, err error, w http.ResponseWriter)

DefaultErrorEncoder writes the error to the ResponseWriter, as a json-rpc error response, with an InternalError status code. The Error() string of the error will be used as the response error message. If the error implements ErrorCoder, the provided code will be set on the response error. If the error implements Headerer, the given headers will be set.

func DefaultRequestEncoder

func DefaultRequestEncoder(_ context.Context, req interface{}) (json.RawMessage, error)

DefaultRequestEncoder marshals the given request to JSON.

func DefaultResponseDecoder

func DefaultResponseDecoder(_ context.Context, res Response) (interface{}, error)

DefaultResponseDecoder unmarshals the result to interface{}, or returns an error, if found.

func ErrorMessage

func ErrorMessage(code int) string

ErrorMessage returns a message for the JSON RPC error code. It returns the empty string if the code is unknown.


type Client

type Client struct {
	// contains filtered or unexported fields

Client wraps a JSON RPC method and provides a method that implements endpoint.Endpoint.

func NewClient

func NewClient(
	tgt *url.URL,
	method string,
	options ...ClientOption,
) *Client

NewClient constructs a usable Client for a single remote method.

func (Client) Endpoint

func (c Client) Endpoint() endpoint.Endpoint

Endpoint returns a usable endpoint that invokes the remote endpoint.

type ClientFinalizerFunc

type ClientFinalizerFunc func(ctx context.Context, err error)

ClientFinalizerFunc can be used to perform work at the end of a client HTTP request, after the response is returned. The principal intended use is for error logging. Additional response parameters are provided in the context under keys with the ContextKeyResponse prefix. Note: err may be nil. There maybe also no additional response parameters depending on when an error occurs.

type ClientOption

type ClientOption func(*Client)

ClientOption sets an optional parameter for clients.

func BufferedStream

func BufferedStream(buffered bool) ClientOption

BufferedStream sets whether the Response.Body is left open, allowing it to be read from later. Useful for transporting a file as a buffered stream.

func ClientAfter

func ClientAfter(after ...httptransport.ClientResponseFunc) ClientOption

ClientAfter sets the ClientResponseFuncs applied to the server's HTTP response prior to it being decoded. This is useful for obtaining anything from the response and adding onto the context prior to decoding.

func ClientBefore

func ClientBefore(before ...httptransport.RequestFunc) ClientOption

ClientBefore sets the RequestFuncs that are applied to the outgoing HTTP request before it's invoked.

func ClientFinalizer

ClientFinalizer is executed at the end of every HTTP request. By default, no finalizer is registered.

func ClientRequestEncoder

func ClientRequestEncoder(enc EncodeRequestFunc) ClientOption

ClientRequestEncoder sets the func used to encode the request params to JSON. If not set, DefaultRequestEncoder is used.

func ClientRequestIDGenerator

func ClientRequestIDGenerator(g RequestIDGenerator) ClientOption

ClientRequestIDGenerator is executed before each request to generate an ID for the request. By default, AutoIncrementRequestID is used.

func ClientResponseDecoder

func ClientResponseDecoder(dec DecodeResponseFunc) ClientOption

ClientResponseDecoder sets the func used to decode the response params from JSON. If not set, DefaultResponseDecoder is used.

func SetClient

func SetClient(client httptransport.HTTPClient) ClientOption

SetClient sets the underlying HTTP client used for requests. By default, http.DefaultClient is used.

type DecodeRequestFunc

type DecodeRequestFunc func(context.Context, json.RawMessage) (request interface{}, err error)

DecodeRequestFunc extracts a user-domain request object from raw JSON It's designed to be used in JSON RPC servers, for server-side endpoints. One straightforward DecodeRequestFunc could be something that unmarshals JSON from the request body to the concrete request type.

type DecodeResponseFunc

type DecodeResponseFunc func(context.Context, Response) (response interface{}, err error)

DecodeResponseFunc extracts a user-domain response object from an JSON RPC response object. It's designed to be used in JSON RPC clients, for client-side endpoints. It is the responsibility of this function to decide whether any error present in the JSON RPC response should be surfaced to the client endpoint.

type EncodeRequestFunc

type EncodeRequestFunc func(context.Context, interface{}) (request json.RawMessage, err error)

EncodeRequestFunc encodes the given request object to raw JSON. It's designed to be used in JSON RPC clients, for client-side endpoints. One straightforward EncodeResponseFunc could be something that JSON encodes the object directly.

type EncodeResponseFunc

type EncodeResponseFunc func(context.Context, interface{}) (response json.RawMessage, err error)

EncodeResponseFunc encodes the passed response object to a JSON RPC result. It's designed to be used in HTTP servers, for server-side endpoints. One straightforward EncodeResponseFunc could be something that JSON encodes the object directly.

type EndpointCodec

type EndpointCodec struct {
	Endpoint endpoint.Endpoint
	Decode   DecodeRequestFunc
	Encode   EncodeResponseFunc

EndpointCodec defines a server Endpoint and its associated codecs

type EndpointCodecMap

type EndpointCodecMap map[string]EndpointCodec

EndpointCodecMap maps the Request.Method to the proper EndpointCodec

type Error

type Error struct {
	Code    int         `json:"code"`
	Message string      `json:"message"`
	Data    interface{} `json:"data,omitempty"`

Error defines a JSON RPC error that can be returned in a Response from the spec http://www.jsonrpc.org/specification#error_object

func (Error) Error

func (e Error) Error() string

Error implements error.

func (Error) ErrorCode

func (e Error) ErrorCode() int

ErrorCode returns the JSON RPC error code associated with the error.

type ErrorCoder

type ErrorCoder interface {
	ErrorCode() int

ErrorCoder is checked by DefaultErrorEncoder. If an error value implements ErrorCoder, the integer result of ErrorCode() will be used as the JSONRPC error code when encoding the error.

By default, InternalError (-32603) is used.

type Request

type Request struct {
	JSONRPC string          `json:"jsonrpc"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params"`
	ID      *RequestID      `json:"id"`

Request defines a JSON RPC request from the spec http://www.jsonrpc.org/specification#request_object

type RequestFunc added in v0.11.0

type RequestFunc func(context.Context, *http.Request, Request) context.Context

RequestFunc may take information from decoded json body and place in request context. In Servers, RequestFuncs are executed after json is parsed but prior to invoking the codec

type RequestID

type RequestID struct {
	// contains filtered or unexported fields

RequestID defines a request ID that can be string, number, or null. An identifier established by the Client that MUST contain a String, Number, or NULL value if included. If it is not included it is assumed to be a notification. The value SHOULD normally not be Null and Numbers SHOULD NOT contain fractional parts.

func (*RequestID) Float32

func (id *RequestID) Float32() (float32, error)

Float32 returns the ID as a float value. An error is returned if the ID can't be treated as an float.

func (*RequestID) Int

func (id *RequestID) Int() (int, error)

Int returns the ID as an integer value. An error is returned if the ID can't be treated as an int.

func (*RequestID) MarshalJSON added in v0.8.0

func (id *RequestID) MarshalJSON() ([]byte, error)

func (*RequestID) String

func (id *RequestID) String() (string, error)

String returns the ID as a string value. An error is returned if the ID can't be treated as an string.

func (*RequestID) UnmarshalJSON

func (id *RequestID) UnmarshalJSON(b []byte) error

UnmarshalJSON satisfies json.Unmarshaler

type RequestIDGenerator

type RequestIDGenerator interface {
	Generate() interface{}

RequestIDGenerator returns an ID for the request.

func NewAutoIncrementID

func NewAutoIncrementID(init uint64) RequestIDGenerator

NewAutoIncrementID returns an auto-incrementing request ID generator, initialised with the given value.

type Response

type Response struct {
	JSONRPC string          `json:"jsonrpc"`
	Result  json.RawMessage `json:"result,omitempty"`
	Error   *Error          `json:"error,omitempty"`
	ID      *RequestID      `json:"id"`

Response defines a JSON RPC response from the spec http://www.jsonrpc.org/specification#response_object

type Server

type Server struct {
	// contains filtered or unexported fields

Server wraps an endpoint and implements http.Handler.

func NewServer

func NewServer(
	ecm EndpointCodecMap,
	options ...ServerOption,
) *Server

NewServer constructs a new server, which implements http.Server.

func (Server) ServeHTTP

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

ServeHTTP implements http.Handler.

type ServerOption

type ServerOption func(*Server)

ServerOption sets an optional parameter for servers.

func ServerAfter

func ServerAfter(after ...httptransport.ServerResponseFunc) ServerOption

ServerAfter functions are executed on the HTTP response writer after the endpoint is invoked, but before anything is written to the client.

func ServerBefore

func ServerBefore(before ...httptransport.RequestFunc) ServerOption

ServerBefore functions are executed on the HTTP request object before the request is decoded.

func ServerBeforeCodec added in v0.11.0

func ServerBeforeCodec(beforeCodec ...RequestFunc) ServerOption

ServerBeforeCodec functions are executed after the JSON request body has been decoded, but before the method's decoder is called. This provides an opportunity for middleware to inspect the contents of the rpc request before being passed to the codec.

func ServerErrorEncoder

func ServerErrorEncoder(ee httptransport.ErrorEncoder) ServerOption

ServerErrorEncoder is used to encode errors to the http.ResponseWriter whenever they're encountered in the processing of a request. Clients can use this to provide custom error formatting and response codes. By default, errors will be written with the DefaultErrorEncoder.

func ServerErrorLogger

func ServerErrorLogger(logger log.Logger) ServerOption

ServerErrorLogger is used to log non-terminal errors. By default, no errors are logged. This is intended as a diagnostic measure. Finer-grained control of error handling, including logging in more detail, should be performed in a custom ServerErrorEncoder or ServerFinalizer, both of which have access to the context.

func ServerFinalizer

ServerFinalizer is executed at the end of every HTTP request. By default, no finalizer is registered.

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