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package jsonrpc2
import (
// Logger allows custom log types to be used with the Client when
// Client.DebugRequest is true.
type Logger interface {
// RequestDoer is implemented by *http.Client and many other Client types are
// easily adapted to match this interface. This allows a custom HTTP Client
// type to be used with Client.
type RequestDoer interface {
Do(req *http.Request) (*http.Response, error)
// NewClient returns a newly initialized Client. If doer is nil, then
// &http.Client{} is used.
func NewClient(doer RequestDoer) *Client {
if doer == nil {
doer = &http.Client{}
return &Client{RequestDoer: doer}
// Client embeds http.Client and provides a convenient way to make JSON-RPC
// requests.
type Client struct {
DebugRequest bool
Log Logger
BasicAuth bool
User string
Password string
Header http.Header
// Request uses c to make a JSON-RPC 2.0 Request to url with the given method
// and params, and then parses the Response using the provided result for
// Response.Result. Thus, result must be a pointer in order for json.Unmarshal
// to populate it. If Request returns nil, then the request and RPC method call
// were successful and result will be populated, if applicable. If the request
// is successful but the RPC method returns an Error Response, then Request
// will return the Error, which can be checked for by attempting a type
// assertion on the returned error.
// Request uses a pseudorandom uint32 for the Request.ID.
// Requests will have the "Content-Type":"application/json" header added.
// Any populated c.Header will then be added to the http.Request, so you may
// override the "Content-Type" header with your own.
// If c.BasicAuth is true then http.Request.SetBasicAuth(c.User, c.Password)
// will be called. This will override the same header in c.Header.
// If c.DebugRequest is true then the Request and Response will be printed to
// stdout.
func (c *Client) Request(url, method string, params, result interface{}) error {
// Generate a random ID for this request.
reqID := rand.Uint32()%200 + 500
// Marshal the JSON RPC Request.
reqJrpc := NewRequest(method, reqID, params)
if c.DebugRequest {
if c.Log == nil {
c.Log = log.New(os.Stderr, "", 0)
reqBytes, err := reqJrpc.MarshalJSON()
if err != nil {
return err
// Compose the HTTP request.
req, err := http.NewRequest(http.MethodPost, url, bytes.NewBuffer(reqBytes))
if err != nil {
return err
req.Header.Add(http.CanonicalHeaderKey("Content-Type"), "application/json")
for k, v := range c.Header {
req.Header[http.CanonicalHeaderKey(k)] = v
if c.BasicAuth {
req.SetBasicAuth(c.User, c.Password)
// Make the request.
res, err := c.Do(req)
if err != nil {
return err
defer res.Body.Close()
if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusBadRequest {
return fmt.Errorf("http: %v", res.Status)
// Read the HTTP response.
resBytes, err := ioutil.ReadAll(res.Body)
if err != nil {
return fmt.Errorf("ioutil.ReadAll(http.Response.Body): %v", err)
// Unmarshal the HTTP response into a JSON RPC response.
var resID uint32
resJrpc := Response{Result: result, ID: &resID}
if err := json.Unmarshal(resBytes, &resJrpc); err != nil {
return fmt.Errorf("json.Unmarshal(%v): %v", string(resBytes), err)
if c.DebugRequest {
if resJrpc.Error != nil {
resJrpc.Result = nil
fmt.Println("<--", string(resBytes))
if resJrpc.Error != nil {
return *resJrpc.Error
if resID != reqID {
return fmt.Errorf("request/response ID mismatch")
return nil
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