Function fixLength

transfer.go:596–678

Determine the expected body length, using RFC 7230 Section 3.3. This function is not a method, because ultimately it should be shared by ReadResponse and ReadRequest.

(isResponse bool, status int, requestMethod string, header http.Header, chunked bool)

// function is not a method, because ultimately it should be shared by
// ReadResponse and ReadRequest.
func fixLength(isResponse bool, status int, requestMethod string, header http.Header, chunked bool) (n int64, err error) {
	isRequest := !isResponse
	contentLens := header["Content-Length"]

	// Hardening against HTTP request smuggling
	if len(contentLens) > 1 {
		// Per RFC 7230 Section 3.3.2, prevent multiple
		// Content-Length headers if they differ in value.
		// If there are dups of the value, remove the dups.
		// See Issue 16490.
		first := textproto.TrimString(contentLens[0])
		for _, ct := range contentLens[1:] {
			if first != textproto.TrimString(ct) {
				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
			}
		}

		// deduplicate Content-Length
		header.Del("Content-Length")
		header.Add("Content-Length", first)

		contentLens = header["Content-Length"]
	}

	// Reject requests with invalid Content-Length headers.
	if len(contentLens) > 0 {
		n, err = parseContentLength(contentLens)
		if err != nil {
			return -1, err
		}
	}

	// Logic based on response type or status
	if isResponse && noResponseBodyExpected(requestMethod) {
		return 0, nil
	}
	if status/100 == 1 {
		return 0, nil
	}
	switch status {
	case 204, 304:
		return 0, nil
	}

	// According to RFC 9112, "If a message is received with both a
	// Transfer-Encoding and a Content-Length header field, the Transfer-Encoding
	// overrides the Content-Length. Such a message might indicate an attempt to
	// perform request smuggling (Section 11.2) or response splitting (Section 11.1)
	// and ought to be handled as an error. An intermediary that chooses to forward
	// the message MUST first remove the received Content-Length field and process
	// the Transfer-Encoding (as described below) prior to forwarding the message downstream."
	//
	// Chunked-encoding requests with either valid Content-Length
	// headers or no Content-Length headers are accepted after removing
	// the Content-Length field from header.
	//
	// Logic based on Transfer-Encoding
	if chunked {