Subject: Re: [PATCH v4 5/8] test-http-server: add HTTP request parsing

From: Victoria Dye <[email-masked]>
Date: Wed, 14 Dec 2022 15:18:08 -0800

Matthew John Cheetham via GitGitGadget wrote:
> +/*
> + * Read the HTTP request up to the start of the optional message-body.
> + * We do this byte-by-byte because we have keep-alive turned on and
> + * cannot rely on an EOF.
> + *
> + * https://tools.ietf.org/html/rfc7230
> + *
> + * We cannot call die() here because our caller needs to properly
> + * respond to the client and/or close the socket before this
> + * child exits so that the client doesn't get a connection reset
> + * by peer error.
> + */
> +static enum worker_result req__read(struct req *req, int fd)
> +{
> +	struct strbuf h = STRBUF_INIT;
> +	struct string_list start_line_fields = STRING_LIST_INIT_DUP;
> +	int nr_start_line_fields;
> +	const char *uri_target;
> +	const char *query;
> +	char *hp;
> +	const char *hv;
> +
> +	enum worker_result result = WR_OK;
> +
> +	/*
> +	 * Read line 0 of the request and split it into component parts:
> +	 *
> +	 *    <method> SP <uri-target> SP <HTTP-version> CRLF
> +	 *
> +	 */
> +	if (strbuf_getwholeline_fd(&req->start_line, fd, '\n') == EOF) {
> +		result = WR_OK | WR_HANGUP;
> +		goto done;
> +	}
> +
> +	strbuf_trim_trailing_newline(&req->start_line);
> +
> +	nr_start_line_fields = string_list_split(&start_line_fields,
> +						 req->start_line.buf,
> +						 ' ', -1);
> +	if (nr_start_line_fields != 3) {
> +		logerror("could not parse request start-line '%s'",
> +			 req->start_line.buf);
> +		result = WR_IO_ERROR;
> +		goto done;
> +	}
> +
> +	req->method = xstrdup(start_line_fields.items[0].string);
> +	req->http_version = xstrdup(start_line_fields.items[2].string);
> +
> +	uri_target = start_line_fields.items[1].string;
> +
> +	if (strcmp(req->http_version, "HTTP/1.1")) {
> +		logerror("unsupported version '%s' (expecting HTTP/1.1)",
> +			 req->http_version);
> +		result = WR_IO_ERROR;
> +		goto done;
> +	}
> +
> +	query = strchr(uri_target, '?');
> +
> +	if (query) {
> +		strbuf_add(&req->uri_path, uri_target, (query - uri_target));
> +		strbuf_trim_trailing_dir_sep(&req->uri_path);
> +		strbuf_addstr(&req->query_args, query + 1);
> +	} else {
> +		strbuf_addstr(&req->uri_path, uri_target);
> +		strbuf_trim_trailing_dir_sep(&req->uri_path);
> +	}

This "line 0" parsing looks good, and aligns with the RFC you linked
(specifically section 3.1.1 [1]).

[1] https://www.rfc-editor.org/rfc/rfc7230#section-3.1.1

> +
> +	/*
> +	 * Read the set of HTTP headers into a string-list.
> +	 */
> +	while (1) {
> +		if (strbuf_getwholeline_fd(&h, fd, '\n') == EOF)
> +			goto done;
> +		strbuf_trim_trailing_newline(&h);
> +
> +		if (!h.len)
> +			goto done; /* a blank line ends the header */
> +
> +		hp = strbuf_detach(&h, NULL);
> +		string_list_append(&req->header_list, hp);
> +
> +		/* store common request headers separately */
> +		if (skip_prefix(hp, "Content-Type: ", &hv)) {
> +			req->content_type = hv;
> +		} else if (skip_prefix(hp, "Content-Length: ", &hv)) {
> +			req->content_length = strtol(hv, &hp, 10);
> +		}

The "separately" is somewhat confusing - you unconditionally add 'hp' to
'req->header_list', so the "Content-Type" and "Content-Length" headers are
included there as well. If that's the desired behavior, a comment like "Also
store common headers as 'req' fields" might be clearer.

> +	}
> +
> +	/*
> +	 * We do not attempt to read the <message-body>, if it exists.
> +	 * We let our caller read/chunk it in as appropriate.
> +	 */
> +
> +done:
> +	string_list_clear(&start_line_fields, 0);
> +
> +	/*
> +	 * This is useful for debugging the request, but very noisy.
> +	 */
> +	if (trace2_is_enabled()) {

'trace2_printf()' is gated internally by 'trace2_enabled' anyway, so I don't
think this 'if()' is necessary. You could add a 'DEBUG_HTTP_SERVER'
preprocessor directive (like 'DEBUG_CACHE_TREE' in 'cache-tree.c') if you
wanted to prevent these printouts unless a developer sets it to '1'.

> +		struct string_list_item *item;
> +		trace2_printf("%s: %s", TR2_CAT, req->start_line.buf);
> +		trace2_printf("%s: hver: %s", TR2_CAT, req->http_version);
> +		trace2_printf("%s: hmth: %s", TR2_CAT, req->method);
> +		trace2_printf("%s: path: %s", TR2_CAT, req->uri_path.buf);
> +		trace2_printf("%s: qury: %s", TR2_CAT, req->query_args.buf);
> +		if (req->content_length >= 0)
> +			trace2_printf("%s: clen: %d", TR2_CAT, req->content_length);
> +		if (req->content_type)
> +			trace2_printf("%s: ctyp: %s", TR2_CAT, req->content_type);
> +		for_each_string_list_item(item, &req->header_list)
> +			trace2_printf("%s: hdrs: %s", TR2_CAT, item->string);
> +	}
> +
> +	return result;
> +}
> +
> +static enum worker_result dispatch(struct req *req)
> +{
> +	return send_http_error(1, 501, "Not Implemented", -1, NULL,
> +			       WR_OK | WR_HANGUP);

Although the request is now being read & parsed, the response creation code
is still a hardcoded "Not Implemented". This means that the now-parsed 'req'
is be temporarily unused, but I think that's reasonable (since it allows for
breaking up the implementation of 'test-http-server' into multiple, less
overwhelming patches).

> +}
> +
>  static enum worker_result worker(void)
>  {
> +	struct req req = REQ__INIT;
>  	char *client_addr = getenv("REMOTE_ADDR");
>  	char *client_port = getenv("REMOTE_PORT");
>  	enum worker_result wr = WR_OK;
> @@ -160,8 +324,16 @@ static enum worker_result worker(void)
>  	set_keep_alive(0);
>  
>  	while (1) {
> -		wr = send_http_error(1, 501, "Not Implemented", -1, NULL,
> -			WR_OK | WR_HANGUP);
> +		req__release(&req);
> +
> +		alarm(init_timeout ? init_timeout : timeout);
> +		wr = req__read(&req, 0);
> +		alarm(0);

I know 'init_timeout' and 'timeout' were pulled from 'daemon.c', but what's
the difference between them/why do they both exist? It looks like
'init_timeout' just acts as a permanent override to the value of 'timeout'.

> +
> +		if (wr & WR_STOP_THE_MUSIC)
> +			break;
> +
> +		wr = dispatch(&req);
>  		if (wr & WR_STOP_THE_MUSIC)
>  			break;
>  	}