Function extractHeaderOrderFromReader

decoder/stream/http/http_reader.go:530–602

extractHeaderOrderFromReader extracts HTTP header order from a bufio.Reader by peeking at the raw bytes before http.ReadRequest consumes them. This is needed for JA4H fingerprinting which requires header order preservation.

(b *bufio.Reader)

// by peeking at the raw bytes before http.ReadRequest consumes them.
// This is needed for JA4H fingerprinting which requires header order preservation.
func extractHeaderOrderFromReader(b *bufio.Reader) (headerOrder []string, cookieFields []string, acceptLang string) {
	// Try to peek enough bytes to see the headers
	// HTTP headers typically end with \r\n\r\n
	// We'll peek progressively larger amounts until we find the header end

	peekSizes := []int{1024, 4096, 8192, 16384, 32768}
	var peeked []byte

	for _, size := range peekSizes {
		data, err := b.Peek(size)
		if err != nil && len(data) == 0 {
			// Can't peek, return empty
			return nil, nil, ""
		}
		peeked = data

		// Check if we have the complete headers (ends with \r\n\r\n or \n\n)
		if bytes.Contains(peeked, []byte("\r\n\r\n")) || bytes.Contains(peeked, []byte("\n\n")) {
			break
		}

		// If we got less than requested, we've read all available data
		if len(data) < size {
			break
		}
	}

	if len(peeked) == 0 {
		return nil, nil, ""
	}

	// Find the end of headers
	headerEnd := bytes.Index(peeked, []byte("\r\n\r\n"))
	if headerEnd == -1 {
		headerEnd = bytes.Index(peeked, []byte("\n\n"))
		if headerEnd == -1 {
			headerEnd = len(peeked)
		}
	}

	headerBytes := peeked[:headerEnd]
	lines := bytes.Split(headerBytes, []byte("\n"))

	// Skip the request line (first line)
	for i := 1; i < len(lines); i++ {
		line := bytes.TrimRight(lines[i], "\r")
		if len(line) == 0 {
			continue
		}

		colonIdx := bytes.Index(line, []byte(":"))
		if colonIdx <= 0 {
			continue
		}

		headerName := string(bytes.TrimSpace(line[:colonIdx]))
		headerValue := string(bytes.TrimSpace(line[colonIdx+1:]))