HTTP服务器在单独的goroutine中显示进度

Question

Let's say I have a long-running programme in Go that is being ran on a server and, from time to time, the user needs to view its results (stats). We of course can create a screen session and make him login by SSH, reattach to the session etc, but it doesn't seem practical. As a better option, I want to launch some sort of embedded HTTP server which shall listen on some port like 8081 and, whenever requested, return the info in form of text (or JSON or XML or whatever). Basically it should just compose a string and return it through HTTP/1.1. It obviously should run in its own goroutin (in background). It is guarantied that the server receives low volume of traffic (e.g. no simultaneous requests) So probably there's something ready-to-use?

Answer 1

This will require some cooperative programming with your long-running program to listen for requests. It's also the perfect use case for a chan chan

// inside your main package

// MakeResponse listens for a request for information and serves it back on
// request's channel.
func MakeResponse(request chan chan interface{}) {
    // I'm not sure what kind of raw data you're trying to throw back, but
    // you probably don't want to do your encoding to json here. Do that in
    // your webserver instead.

    for resp := range request {
        resp <- getInternalStateInformation()
    }
}

// inside your listener package

var requests chan chan interface{}

func init() {
    requests = make(chan chan interface{}, 10)
}

func RequestInfo(w http.ResponseWriter, r *http.Request) {
    response := make(chan interface{})
    requests<-response
    data := <-response
    outData, err := json.Marshal(data)
    if err != nil {
        log.Printf("Couldn't marshal data %v
", data)
    }
    fmt.Fprint(w, outData) // or more likely execute a template with this
                           // context
}

func main() {
    defer close(requests)
    go longrunningprog.MakeResponse(requests)
    http.HandleFunc("/", RequestInfo)
    http.ListenAndServe(":8081", nil)
}