Re: [PATCH] remote-curl: die on server-side errors

> On Tue, Nov 13, 2018 at 07:49:15PM -0500, Jeff King wrote:
> 
> > Yes, the packet_read_line_buf() interface will both advance the buf
> > pointer and decrement the length.  So if we want to "peek", we have to
> > do so with a copy (there's a peek function if you use the packet_reader
> > interface, but that might be overkill here).
> > 
> > You can rewrite it like this, which is a pretty faithful conversion and
> > passes the tests (but see below).
> > [...]
> 
> Here's a version which is less faithful, but I think does sensible
> things in all cases, and is much easier to follow. I get a little
> nervous just because it tightens some cases, and one never knows if
> other implementations might be relying on the looseness. E.g.:
> 
>   - in the current code we'd still drop back to dumb http if the server
>     tells us "application/x-git-upload-pack" but the initial pktline
>     doesn't start with "#" (even though if it _does_ have "#" at
>     position 5 but isn't a valid pktline, we'd complain!)
> 
>   - right now the v2 protocol does not require the server to say
>     "application/x-git-upload-pack" for the content-type
> 
> This patch tightens both of those (I also made a few stylistic tweaks,
> and added the ERR condition to show where it would go). I dunno. Part of
> me sees this as a nice cleanup, but maybe it is better to just leave it
> alone. A lot of these behaviors are just how it happens to work now, and
> not part of the spec, but we don't know what might be relying on them.

> diff --git a/remote-curl.c b/remote-curl.c
> index 762a55a75f..1adb96311b 100644
> --- a/remote-curl.c
> +++ b/remote-curl.c
> @@ -330,9 +330,61 @@ static int get_protocol_http_header(enum protocol_version version,
>  	return 0;
>  }
>  
> +static void check_smart_http(struct discovery *d, const char *service,
> +			     struct strbuf *type)
> +{
> +	char *src_buf;
> +	size_t src_len;
> +	char *line;
> +	const char *p;
> +
> +	if (!skip_prefix(type->buf, "application/x-", &p) ||
> +	    !skip_prefix(p, service, &p) ||
> +	    strcmp(p, "-advertisement"))
> +		return;
> +
> +	/*
> +	 * We speculatively try to read a packet, which means we must preserve
> +	 * the original buf/len pair in some cases.
> +	 */
> +	src_buf = d->buf;
> +	src_len = d->len;
> +	line = packet_read_line_buf(&src_buf, &src_len, NULL);
> +	if (!line)
> +		die("invalid server response; expected service, got flush packet");
> +
> +	if (skip_prefix(line, "# service=", &p) && !strcmp(p, service)) {
> +		/*
> +		 * The header can include additional metadata lines, up
> +		 * until a packet flush marker.  Ignore these now, but
> +		 * in the future we might start to scan them.
> +		 */
> +		while (packet_read_line_buf(&src_buf, &src_len, NULL))
> +			;
> +
> +		/*
> +		 * v0 smart http; callers expect us to soak up the
> +		 * service and header packets
> +		 */
> +		d->buf = src_buf;
> +		d->len = src_len;
> +		d->proto_git = 1;
> +
> +	} else if (starts_with(line, "version 2")) { /* should be strcmp()? */
> +		/*
> +		 * v2 smart http; do not consume version packet, which will
> +		 * be handled elsewhere.
> +		 */
> +		d->proto_git = 1;
> +	} else if (skip_prefix(line, "ERR ", &p)) {
> +		die(_("remote error: %s"), p);
> +	} else {
> +		die("invalid server response; got '%s'", line);
> +	}
> +}
> +
>  static struct discovery *discover_refs(const char *service, int for_push)
>  {
> -	struct strbuf exp = STRBUF_INIT;
>  	struct strbuf type = STRBUF_INIT;
>  	struct strbuf charset = STRBUF_INIT;
>  	struct strbuf buffer = STRBUF_INIT;
> @@ -405,38 +457,8 @@ static struct discovery *discover_refs(const char *service, int for_push)
>  	last->buf_alloc = strbuf_detach(&buffer, &last->len);
>  	last->buf = last->buf_alloc;
>  
> -	strbuf_addf(&exp, "application/x-%s-advertisement", service);
> -	if (maybe_smart &&
> -	    (5 <= last->len && last->buf[4] == '#') &&
> -	    !strbuf_cmp(&exp, &type)) {
> -		char *line;
> -
> -		/*
> -		 * smart HTTP response; validate that the service
> -		 * pkt-line matches our request.
> -		 */
> -		line = packet_read_line_buf(&last->buf, &last->len, NULL);
> -		if (!line)
> -			die("invalid server response; expected service, got flush packet");
> -
> -		strbuf_reset(&exp);
> -		strbuf_addf(&exp, "# service=%s", service);
> -		if (strcmp(line, exp.buf))
> -			die("invalid server response; got '%s'", line);
> -		strbuf_release(&exp);
> -
> -		/* The header can include additional metadata lines, up
> -		 * until a packet flush marker.  Ignore these now, but
> -		 * in the future we might start to scan them.
> -		 */
> -		while (packet_read_line_buf(&last->buf, &last->len, NULL))
> -			;
> -
> -		last->proto_git = 1;
> -	} else if (maybe_smart &&
> -		   last->len > 5 && starts_with(last->buf + 4, "version 2")) {
> -		last->proto_git = 1;
> -	}
> +	if (maybe_smart)
> +		check_smart_http(last, service, &type);
>  
>  	if (last->proto_git)
>  		last->refs = parse_git_refs(last, for_push);
> @@ -444,7 +466,6 @@ static struct discovery *discover_refs(const char *service, int for_push)
>  		last->refs = parse_info_refs(last);
>  
>  	strbuf_release(&refs_url);
> -	strbuf_release(&exp);
>  	strbuf_release(&type);
>  	strbuf_release(&charset);
>  	strbuf_release(&effective_url);