为什么不能将“文件”用作http请求的“正文”？

Question

"http.Post" expects a "Reader" as the body argument. "File" implements "Reader". But if I pass file as the body argument I always receive 0 bytes at the other end. Why?

Here is the code:

package main

import (
    "fmt"
    "net/http"
    "os"
)

func main() {
    file, err := os.Open("lala.txt")
    if err != nil {
        fmt.Printf("file open errrrr %v 
", err)
    }
    defer file.Close()

    resp, err := http.Post("http://requestb.in/11fta851", "text/plain", file)
    if err != nil {
        fmt.Printf("errrrr %v 
", err)
    } else {
        fmt.Printf("resp code %d 
", resp.StatusCode)
    }
}

I know that you could do "file.ReadAll" to a buffer and use that. But it feels like double work.

Answer 1

The site requestb.in seems to ignore POST data if the header Content-Length is not specified. This code works:

package main

import (
    "fmt"
    "net/http"
    "os"
)

func main() {
    file, err := os.Open("lala.txt")
    if err != nil {
        fmt.Printf("file open errrrr %v 
", err)
    }
    defer file.Close()

    req, _ := http.NewRequest("POST", "http://requestb.in/1fry3jy1", file)
    req.ContentLength = 5
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        fmt.Printf("errrrr %v 
", err)
    } else {
        fmt.Printf("resp code %d 
", resp.StatusCode)
    }
}