Question

I’m writing a webserver that distributes requests to out-of-process programs in Go. I’m sending the ResponseWriter and Request datatypes through Pipes using gob.

The problem is the external process is hanging when receiving the gob.

UPDATE The gob is now successfully being sent to the external process, but now the external process is blocking at fmt.Fprintf(request.Resp, "Hello") and freezes there.

dispreq.go

package dispreq

import (
    "net/http"
)

type DispReq struct {
    Resp    http.ResponseWriter
    Req *http.Request
}

dispatcher.go

package main

import (
    "encoding/gob"
    "fmt"
    "net/http"
    "os"
    "os/exec"

    "dispreq"
)

func dispatch(w http.ResponseWriter, r *http.Request) {
    process := exec.Command("./hello")
    pipe, piperr := process.StdinPipe()

    if piperr != nil {
        fmt.Fprintf(os.Stderr, piperr.Error())
        return
    }

    encoder := gob.NewEncoder(pipe)

    process.Stdout = os.Stdout

    //UPDATE: encoder.Encode(&dispreq.DispReq{w, r})
    //UPDATE: process.Start()
    process.Start()
    encoder.Encode(&dispreq.DispReq{w, r})
    pipe.Close()
    process.Wait()
}

func main() {
    http.HandleFunc("/", dispatch)
    http.ListenAndServe(":8080", nil)
}

hello.go

package main

import (
    "dispreq"
    "encoding/gob"
    "os"

    "fmt"
)

func main() {
    gobDecoder := gob.NewDecoder(os.Stdin)
    var request dispreq.DispReq
    gobDecoder.Decode(&request)
    fmt.Fprintf(request.Resp, "Hello")
}

Answer 1

You should start the process (process.Start()) before sending data to it (encoder.Encode(&dispreq.DispReq{w, r})). You might also need to flush your pipe by closing it (pipe.Close()) or sending a \n.