golang中net.http请求时header中的Content-Length无效坑

在一次和国内某云厂商对接对象存储时，因为他们对象存储服务，是直接使用的是第三方开源服务，开源服务默认并不支持chunked编码（而国内其它大厂一般都是支持chunked编码）。导致上传文件一直报HTTP/1.1 411 Length Required错误，出现问题的原因是说，我没有传Content-Length。

而明明我在header里设置了Content-Length，但是抓包发现，实际却变成了chunked

经过反复的测试情况都依旧，直到在github上找到了这个https://github.com/golang/go/issues/16264

然后查看了golang源码

func NewRequest(method, url string, body io.Reader) (*Request, error) {
    if method == "" {
        // We document that "" means "GET" for Request.Method, and people have
        // relied on that from NewRequest, so keep that working.
        // We still enforce validMethod for non-empty methods.
        method = "GET"
    }
    if !validMethod(method) {
        return nil, fmt.Errorf("net/http: invalid method %q", method)
    }
    u, err := parseURL(url) // Just url.Parse (url is shadowed for godoc).
    if err != nil {
        return nil, err
    }
    rc, ok := body.(io.ReadCloser)
    if !ok && body != nil {
        rc = ioutil.NopCloser(body)
    }
    // The host's colon:port should be normalized. See Issue 14836.
    u.Host = removeEmptyPort(u.Host)
    req := &Request{
        Method:     method,
        URL:        u,
        Proto:      "HTTP/1.1",
        ProtoMajor: 1,
        ProtoMinor: 1,
        Header:     make(Header),
        Body:       rc,
        Host:       u.Host,
    }
    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 }
        }
    }

    return req, nil
}

可以看到，这里面居然有个switch，当你使用bytes.Buffer,bytes.Reader或者strings.Reader作为Body的时候，它会自动给你设置req.ContentLength…

所以，问题不是当你Post一个ReadCloser的时候，就会变成chunked，而是你Post非这三种类型的body进来的时候都没有Content-Length，需要自己显式设置。代码如下：

req, _ := http.NewRequest(method, url, bodyReader)
req.ContentLength = req.Header.Get("Content-Length")

设置了req.ContentLength之后，抓包如下确实不再是chunked编码了，抓包如下

至此问题解决。