Go net/rpc over ssh+netcat and unix domain sockets It would be nice if ssh.Session implemented io.ReaderWriter

.gitignore

local_client
server
client
ext

client.go

package main

import (
	"code.google.com/p/go.crypto/ssh"
	"fmt"
	"io"
	"log"
	"net"
	"net/rpc"
	"os"
	"strings"
)

// RPC response container
type Response struct {
	Greeting string
}

// RPC request container
type Request struct {
	Name string
}

// It would be nice if ssh.Session was an io.ReaderWriter
// proposal submitted :-)
type NetCatSession struct {
	*ssh.Session // define Close()
	writer       io.Writer
	reader       io.Reader
}

// io.Reader
func (s NetCatSession) Read(p []byte) (n int, err error) {
	return s.reader.Read(p)
}

// io.Writer
func (s NetCatSession) Write(p []byte) (n int, err error) {
	return s.writer.Write(p)
}

// given the established ssh connection, start a session against netcat and
// return a io.ReaderWriterCloser appropriate for rpc.NewClient(...)
func StartNetCat(client *ssh.ClientConn, path string) (rwc *NetCatSession, err error) {
	session, err := client.NewSession()
	if err != nil {
		return
	}

	cmd := fmt.Sprintf("/usr/bin/nc -U %s", path)
	in, err := session.StdinPipe()
	if err != nil {
		return nil, fmt.Errorf("unable to get stdin: %s", err)
	}

	out, err := session.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("unable to get stdout: %s", err)
	}

	err = session.Start(cmd)
	if err != nil {
		return nil, fmt.Errorf("unable to start '%s': %s", cmd, err)
	}

	return &NetCatSession{session, in, out}, nil
}

// ./client localhost:/tmp/foo Brian
func main() {
	parts := strings.Split(os.Args[1], ":")
	host := parts[0]
	path := parts[1]
	name := os.Args[2]

	// SSH setup, we assume current username and use the ssh agent
	// for auth
	agent_sock, err := net.Dial("unix", os.Getenv("SSH_AUTH_SOCK"))
	if err != nil {
		log.Fatalf("sorry, this example requires the ssh agent: %s", err)
	}
	defer agent_sock.Close()

	config := &ssh.ClientConfig{
		User: os.Getenv("USER"),
		Auth: []ssh.ClientAuth{
			ssh.ClientAuthAgent(ssh.NewAgentClient(agent_sock)),
		},
	}
	ssh_client, err := ssh.Dial("tcp", fmt.Sprintf("%s:22", host), config)
	if err != nil {
		panic("Failed to dial: " + err.Error())
	}
	defer ssh_client.Close()

	// Establish sesstion to netcat talking to the domain socket
	s, err := StartNetCat(ssh_client, path)
	if err != nil {
		log.Fatalf("unable to start netcat session: %s", err)
	}

	// now comes the RPC!
	client := rpc.NewClient(s)
	defer client.Close()

	req := &Request{name}
	var res Response

	err = client.Call("Greeter.Greet", req, &res)
	if err != nil {
		log.Fatalf("error in rpc: %s", err)
	}
	fmt.Println(res.Greeting)
}

local_client.go

package main

import (
	"fmt"
	"log"
	"net/rpc"
	"os"
)

type Response struct {
	Greeting string
}

type Request struct {
	Name string
}

// ./local_client /tmp/foo Brian
func main() {
	client, err := rpc.Dial("unix", os.Args[1])
	if err != nil {
		log.Fatalf("failed: %s", err)
	}

	req := &Request{os.Args[2]}
	var res Response

	err = client.Call("Greeter.Greet", req, &res)
	if err != nil {
		log.Fatalf("error in rpc: %s", err)
	}

	fmt.Println(res.Greeting)
}

Makefile

build: setup
	GOPATH=$(PWD):$(PWD)/ext go build server.go
	GOPATH=$(PWD):$(PWD)/ext go build client.go
	GOPATH=$(PWD):$(PWD)/ext go build local_client.go

fmt:
	GOPATH=$(PWD) go fmt *.go

clean:
	rm -rf server client local_client ext/pkg

setup:
	GOPATH=$(PWD)/ext go get code.google.com/p/go.crypto/ssh

godoc:
	GOPATH=$(PWD):$(PWD)/ext godoc -http=:6060

server.go

package main

import (
	"fmt"
	"log"
	"net"
	"net/rpc"
	"os"
	"os/signal"
	"syscall"
)

// rpc response
type Response struct {
	Greeting string
}

// rpc request
type Request struct {
	Name string
}

// rpc host struct thing
type Greeter struct{}

// our remotely invocable function
func (g *Greeter) Greet(req Request, res *Response) (err error) {
	res.Greeting = fmt.Sprintf("Hello %s", req.Name)
	return
}

// start up rpc listener at path
func ServeAt(path string) (err error) {
	rpc.Register(&Greeter{})

	listener, err := net.Listen("unix", path)
	if err != nil {
		return fmt.Errorf("unable to listen at %s: %s", path, err)
	}

	go rpc.Accept(listener)
	return
}

// ./server /tmp/foo
func main() {
	path := os.Args[1]

	err := ServeAt(path)
	if err != nil {
		log.Fatalf("failed: %s", err)
	}
	defer os.Remove(path)

	// block until we are signalled to quit
	wait()
}

func wait() {
	signals := make(chan os.Signal)
	signal.Notify(signals, syscall.SIGINT, syscall.SIGKILL, syscall.SIGHUP)
	<-signals
}