从网页访问golang http + jsonrpc

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
")

    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
", string(b))

}