go - 来自 golang : upload fails without properly setting ContentLength 文件的 HTTP PUT 请求正文

Question

我正在尝试发布一个简单的 PUT请求上传文件。 http.NewRequest接受 body (作为 io.Reader )。但是通过 os.File如body不起作用，而首先将其读入缓冲区可以解决问题:

file, _ := os.Open(filePath)

// request, _ := http.NewRequest("PUT", myURL, file)
// ^^^ why does this not work???

var buf bytes.Buffer
tee := io.TeeReader(file, &buf)
ioutil.ReadAll(tee)                                 
request, _ := http.NewRequest("PUT", myURL, &buf)   // this works fine

request.Header.Set("Content-Type", "application/octet-stream")
http.DefaultClient.Do(request)

编辑:问题不是设置 ContentLength header (即它被设置为默认值 0)；这导致服务器不处理上传。使用缓冲区时，golang 确实将 header 设置为缓冲区长度，从而导致不同的行为。
是 ContentLength header 语义服务器依赖？？浏览所以我的印象是标题是可选的，这显然不是这里的情况。

Answer 1

此源代码可能会有所帮助。

    // /usr/lib/go/src/net/http/request.go:872
    if body != nil {
        switch v := body.(type) {
        case *bytes.Buffer:
            req.ContentLength = int64(v.Len())
            buf := v.Bytes()
            req.GetBody = func() (io.ReadCloser, error) {
                r := bytes.NewReader(buf)
                return ioutil.NopCloser(r), nil
            }
        case *bytes.Reader:
            req.ContentLength = int64(v.Len())
            snapshot := *v
            req.GetBody = func() (io.ReadCloser, error) {
                r := snapshot
                return ioutil.NopCloser(&r), nil
            }
        case *strings.Reader:
            req.ContentLength = int64(v.Len())
            snapshot := *v
            req.GetBody = func() (io.ReadCloser, error) {
                r := snapshot
                return ioutil.NopCloser(&r), nil
            }
        default:
            // This is where we'd set it to -1 (at least
            // if body != NoBody) to mean unknown, but
            // that broke people during the Go 1.8 testing
            // period. People depend on it being 0 I
            // guess. Maybe retry later. See Issue 18117.
        }
        // For client requests, Request.ContentLength of 0
        // means either actually 0, or unknown. The only way
        // to explicitly say that the ContentLength is zero is
        // to set the Body to nil. But turns out too much code
        // depends on NewRequest returning a non-nil Body,
        // so we use a well-known ReadCloser variable instead
        // and have the http package also treat that sentinel
        // variable to mean explicitly zero.
        if req.GetBody != nil && req.ContentLength == 0 {
            req.Body = NoBody
            req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
        }
    }