无法在golang网络应用中重定向。 坚持一页

Question

This is code snippet from a file called upload.go. I tried a lot of ways to redirect to another pages. I want to redirect to another page when the statements in POST are completed running.

package main

import (
    "fmt"
    "io"
    "net/http"
    "os"
    "text/template"
)

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

    if r.Method == "GET" {
        // GET
        t, _ := template.ParseFiles("upload.gtpl")

        t.Execute(w, nil)

    } else if r.Method == "POST" {
        // Post
        file, handler, err := r.FormFile("uploadfile")
        if err != nil {
            fmt.Println(err)
            return
        }
        defer file.Close()

        fmt.Fprintf(w, "%v", handler.Header)
        f, err := os.OpenFile("./test/"+handler.Filename, os.O_WRONLY|os.O_CREATE, 0666)
        if err != nil {
            fmt.Println(err)
            return
        }
        defer f.Close()

        io.Copy(f, file)

        img, err := imgio.Open("./test/" + handler.Filename)
        if err != nil {
            panic(err)
        }

        inverted := effect.Invert(img)
        if err := imgio.Save("filename.png", inverted, imgio.PNGEncoder()); err != nil {
            panic(err)
        }

        fmt.Fprintf(w, "%v", handler.Header)
        http.Redirect(w, r, "www.google.com", http.StatusMovedPermanently)

    } else {
        fmt.Println("Unknown HTTP " + r.Method + "  Method")
    }
}

func main() {
    http.HandleFunc("/upload", upload)
    http.HandleFunc("/hi", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Hi")
        http.Redirect(w, r, "www.google.com", http.StatusMovedPermanently)
    })

    http.ListenAndServe(":9090", nil) // setting listening port
}

It stays on the upload page what ever I do. Can anyone help me debug this?

Answer 1

Your code is writing to the ResponseWriter before trying to send a redirect.

Upon the first write to the ResponseWriter, the status code (200 OK) and headers are sent, if they haven't already been sent, and then the data you passed to the writer.

If you intend to send an HTTP redirect, you can't write any response body to the ResponseWriter. From reading your code, it doesn't make much sense why you are writing to it in the first place. They look like debugging print statements, which you probably ought to send to os.Stderr or a logger instead of the web page response body.