Re: [PATCH v2] urlmatch.c: recompute ptr after append_normalized_escapes

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On Sep 12, 2013, at 11:30, Junio C Hamano wrote:

+		/* append_normalized_escapes can cause norm.buf to change */
+		seg_start = norm.buf + seg_start_off;

The change looks good, but I find that this comment is not placed in
the right place.  It is good if the reader knows about an old bug to
put it here, but if the first thing a reader reads is this updated
version, the comment is better placed close to the place where the
start_ofs variable captures the original value (i.e. "because the
next call may relocate the buffer, we cannot grab seg_start upfront;
instead we need to record the start_ofs here, and that is what this
variable is about").

It is too minor a point for a reroll, so I'll try to tweak it
locally.  Something like this (but now I think about it, the comment
may not even be necessary).

The longer comment looks good to me. If you think the code will be safe from simplification patches without a comment, that works for me too. I've just seen so many "simplification" patches go by on the list I'm concerned it will be a
target otherwise leading to re-introduction of the problem.

diff --git a/urlmatch.c b/urlmatch.c
index 01c6746..d1600e2 100644
--- a/urlmatch.c
+++ b/urlmatch.c
@@ -282,9 +282,17 @@ char *url_normalize(const char *url, struct url_info *out_info)
	}
	for (;;) {
		const char *seg_start;
-		size_t seg_start_off = norm.len;
+		size_t seg_start_off;
		const char *next_slash = url + strcspn(url, "/?#");
		int skip_add_slash = 0;
+
+		/*
+		 * record the starting offset; appending escapes may
+		 * relocate the buffer, so we cannot capture seg_start
+		 * upfront and use it later.
+		 */
+		seg_start_off = norm.len;
+
		/*
		 * RFC 3689 indicates that any . or .. segments should be
		 * unescaped before being checked for.
@@ -298,7 +306,7 @@ char *url_normalize(const char *url, struct url_info *out_info)
			strbuf_release(&norm);
			return NULL;
		}
-		/* append_normalized_escapes can cause norm.buf to change */
+
		seg_start = norm.buf + seg_start_off;
		if (!strcmp(seg_start, ".")) {
			/* ignore a . segment; be careful not to remove initial '/' */

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