Write pipe reading into http response in golang

Question

Here is the schema :

Client sends a POST request to server A

server A process this and sends a GET to server B

server B sends a response through A to the client

I though the best idea was to make a pipe which would read the response of the GET, and write into the response of the POST, but I got many types problems.

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/test/{hash}", testHandler)

    log.Fatal(http.ListenAndServe(":9095", r))
}

func handleErr(err error) {
    if err != nil {
        log.Fatalf("%s\n", err)
    }
}


func testHandler(w http.ResponseWriter, r *http.Request){

    fmt.Println("FIRST REQUEST RECEIVED")
    vars := mux.Vars(r)
    hash := vars["hash"]
    read, write := io.Pipe()

    // writing without a reader will deadlock so write in a goroutine
    go func() {
        write, _ = http.Get("http://localhost:9090/test/" + hash)
        defer write.Close()
    }()

    w.Write(read)
}

When I run this I get the following error:

./ReverseProxy.go:61: cannot use read (type *io.PipeReader) as type []byte in argument to w.Write

Is there a way, to properly insert a io.PipeReader format into an http response? Or am I doing this in a totally wrong way?

I think you're misunderstanding the purpose of an io.Pipe. Why not just copy the data from the response.Body to the ReponseWriter? (also, an http.Response doesn't have a Close method, you're shadowing the PipeWriter with the http.Response, and you need to check the error first) — Mr_Pink
– Mr_Pink, Commented Nov 22, 2016 at 16:50

OneOfOne · Accepted Answer · 2016-11-22 16:53:47Z

9

You are not actually writing to it, you're replacing the pipe's write.

Something along the lines of:

func testHandler(w http.ResponseWriter, r *http.Request) {

    fmt.Println("FIRST REQUEST RECEIVED")

    vars := mux.Vars(r)
    hash := vars["hash"]

    read, write := io.Pipe()

    // writing without a reader will deadlock so write in a goroutine
    go func() {
        defer write.Close()
        resp, err := http.Get("http://localhost:9090/test/" + hash)
        if err != nil {
            return
        }
        defer resp.Body.Close()
        io.Copy(write, resp.Body)

    }()

    io.Copy(w, read)

}

Although, I agree with @JimB, for this instance, the pipe isn't even needed, something like this should be more efficient:

func testHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    hash := vars["hash"]

    resp, err := http.Get("http://localhost:9090/test/" + hash)
    if err != nil {
        // handle error
        return
    }
    defer resp.Body.Close()

    io.Copy(w, resp.Body)
}

edited Nov 22, 2016 at 16:53

answered Nov 22, 2016 at 16:51

OneOfOne

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2 Comments

Mr_Pink Over a year ago

though there's no point in this io.Pipe fiasco, this is just an io.Copy with more copies.

OneOfOne Over a year ago

@JimB I agree but I figured he might be trying to learn how to use it, I'll add another snip without it.

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