I believe that `(lookahead-char port)` really blocks when the client has
finished sending the request and there is no more data from `port` to consume.
If I understand it correctly, then per HTTP/1.1 [1] the request ends with CRLF at the last line, and then comes the message. So I we have read an
empty string, then we shouldn't proceed with further lookaheads.
Specifically, the following code works out for me:
(define (read-header-line port)
"Read an HTTP header line, including any continuation lines, and
return the combined string without its final CRLF or LF. Raise a
'bad-header' exception if the line does not end in CRLF or LF, or if EOF
is reached."
(format #t "Reading header line now: ")
(match (%read-line port)
(((? string? line) . #\newline)
;; '%read-line' does not consider #\return a delimiter; so if it's
;; there, remove it. We are more tolerant than the RFC in that we
;; tolerate LF-only endings.
(let ((line (if (string-suffix? "\r" line)
(string-drop-right line 1)
line)))
;; If the next character is a space or tab, then there's at least
;; one continuation line. Read the continuation lines by calling
;; 'read-header-line' recursively, and append them to this header
;; line, folding the leading spaces and tabs to a single space.
(if (and (not (string-null? line))
(space-or-tab? (lookahead-char port)))
(string-append line " " (string-trim (read-header-line port)
spaces-and-tabs))
line)))
((line . _) ;EOF or missing delimiter
(bad-header 'read-header-line line))))
Moreover, the continuation lines in general have been deprecated: [2].
I have to say I would be in favor of removing support for continuation lines in
general.
Best regards,
-Dan
[1]: https://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html
[2]: https://tools.ietf.org/html/rfc7230#section-3.2.4
