golang http+jsonrpc access from web page - json

Question

I've used Go's net/rpc and net/rpc/jsonrpc packages a bit to perform connections between Go processes, however I'm wondering if there is a way to connect to an HTTP JSONRPC server using only the server tooling from the standard library (not that I have a problem writing my own, just don't want to do it if I don't have to).
This is the basic server setup I have:
arith := new(server.Arith)
server := rpc.NewServer()
server.Register(arith)
server.HandleHTTP(rpc.DefaultRPCPath, rpc.DefaultDebugPath)
listener, e := net.Listen("tcp", ":4321")
if e != nil {
log.Fatal("listen error:", e)
}
defer listener.Close()
http.Serve(listener, http.DefaultServeMux)
And I'd like to be able to be hitting this from a web page or a simple command line CURL call - just a regular POST.
However, this line: http://golang.org/src/net/rpc/server.go?s=20445:20475#L670 appears to indicate that it expects an HTTP client to issue a CONNECT and then directly write the JSON RPC request to the stream and receive the reply back the same way. I don't know if this is even possible from a browser, but it certainly is not as common or compatible as a simple POST.
Is there a way to start a JSON RPC server that I can just POST to using good ol' XMLHttpRequest ?
EDIT: Crap - the above is not even using the jsonrpc stuff - this is probably trying to use Gob, but whatever - the problem is the same - the code in src/net/rpc/server.go is not going to handle POSTs, so this route overall isn't going to work regardless of server codec.

Answer 1

FWIW, I got this working by making a simple HTTP handler that adapts the HTTP request/response to a ServerCodec. Seems to work like a charm.
Here's the working code as a test:
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"net/http"
"net/rpc"
"net/rpc/jsonrpc"
"testing"
)
// adapt HTTP connection to ReadWriteCloser
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 }
// our service
type CakeBaker struct{}
func (cb *CakeBaker) BakeIt(n int, msg *string) error {
*msg = fmt.Sprintf("your cake has been bacon (%d)", n)
return nil
}
func TestHTTPServer(t *testing.T) {
fmt.Printf("TestHTTPServer\n")
cb := &CakeBaker{}
server := rpc.NewServer()
server.Register(cb)
listener, e := net.Listen("tcp", ":4321")
if e != nil {
log.Fatal("listen error:", e)
}
defer listener.Close()
go http.Serve(listener, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == "/bake-me-a-cake" {
serverCodec := jsonrpc.NewServerCodec(&HttpConn{in: r.Body, out: w})
w.Header().Set("Content-type", "application/json")
w.WriteHeader(200)
err := server.ServeRequest(serverCodec)
if err != nil {
log.Printf("Error while serving JSON request: %v", err)
http.Error(w, "Error while serving JSON request, details have been logged.", 500)
return
}
}
}))
resp, err := http.Post("http://localhost:4321/bake-me-a-cake", "application/json", bytes.NewBufferString(
`{"jsonrpc":"2.0","id":1,"method":"CakeBaker.BakeIt","params":[10]}`,
))
if err != nil {
panic(err)
}
defer resp.Body.Close()
b, err := ioutil.ReadAll(resp.Body)
if err != nil {
panic(err)
}
fmt.Printf("returned JSON: %s\n", string(b))
}

Answer 2

a RPC framework shoud have language supports list, I not used json-rpc, but it should support javascript language by this link. you need add one of the javascript client sdk listed there.