Zip can't be opened with Go because of incorrect mime from server

Question

I have an application that sends a zip file to a server. The zip is then manipulated and a new zip is send back in the response.

The problem is that the response sent back has a mime of application/octet-stream instead of application/zip message.

I think this is the reason why the resulting zip can't be opened by archive/zip and I get a zip: not a valid zip file.

Is there any way for me to change the mime when retrieving the zip file?

My code for getting the zip:

func GetZipFromServer(zipname string) {

    ////////////////////////////////////////////////////
    // Open local zip file

    file, err := os.Open(zipname + ".zip")
    log1.Check(err, "File open failed")
    defer file.Close()

    stat, err := file.Stat()
    log1.Check(err, "Stat failed")

    fmt.Println(stat.Size())

    ////////////////////////////////////////////////////
    // Get new zip from server

    url := "http://some_server123.com/rest/"
    res, err := http.Post(url, "application/zip", file)
    log1.Check(err, "Response failed")

    ////////////////////////////////////////////////////
    // Save new zip from server as file

    f, err := os.Create(zipname + ".html.zip")
    log1.Check(err, "Cannot create file")

    err = res.Write(f)
    log1.Check(err, "Cannot write file")

    err = f.Close()
    log1.Check(err, "Cannot close file")
}

Answer 1

The Response.Write method writes the response in server response format to the argument. That's not what you want.

Use io.Copy to copy the response body to the file:

func GetZipFromServer(zipname string) {
    file, err := os.Open(zipname + ".zip")
    log1.Check(err, "File open failed")
    defer file.Close()

    stat, err := file.Stat()
    log1.Check(err, "Stat failed")

    fmt.Println(stat.Size())

    url := "http://some_server123.com/rest/"
    res, err := http.Post(url, "application/zip", file)
    log1.Check(err, "Response failed")

    defer resp.Body.Close()

    f, err := os.Create(zipname + ".html.zip")
    log1.Check(err, "Cannot create file")

    _, err := io.Copy(f, resp.Body)
    log1.Check(err, "Cannot write file")

    err = f.Close()
    log1.Check(err, "Cannot close file")
}

Also, close the response body.