How Can I Access a Go HTTP Server Using JSON-RPC with the Standard Library?

JSON RPC Access to HTTP Server using Standard Library

JSON RPC is an RPC protocol that uses JSON as its data format. It allows clients to communicate with servers over HTTP using POST requests. The standard library in Go provides packages for implementing RPC servers, but there is currently no direct support for JSON RPC.

Problem:

The provided server setup uses the standard library's net/rpc package, which expects clients to establish a CONNECT connection and send JSON RPC requests over the stream. This is not a common or compatible approach for web-facing applications.

Solution:

The solution to this problem is to create a custom HTTP handler that adapts the HTTP request/response to a ServerCodec. This allows the server to handle JSON RPC requests over POST requests:

import (
    "bytes"
    "io"
    "net/http"
    "net/rpc"
    "net/rpc/jsonrpc"
)

type HttpConn struct {
    in  io.Reader
    out io.Writer
}

func (c *HttpConn) Read(p []byte) (n int, err error)  { return c.in.Read(p) }
func (c *HttpConn) Write(d []byte) (n int, err error) { return c.out.Write(d) }
func (c *HttpConn) Close() error                      { return nil }

http.HandleFunc("/rpc", func(w http.ResponseWriter, r *http.Request) {
    serverCodec := jsonrpc.NewServerCodec(&HttpConn{in: r.Body, out: w})
    w.Header().Set("Content-type", "application/json")
    w.WriteHeader(200)
    server.ServeRequest(serverCodec)
})

Implementation:

In the example code snippet, a CakeBaker service is registered with the server. The HTTP handler is added to the HTTP server, and the server listens on port 4321. A client can now send a POST request to "http://localhost:4321/rpc" with a JSON RPC request payload. The server will parse the request, execute the corresponding method, and return the result in the response.

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