3 files changed, 32 insertions, 20 deletions

diff --git a/ui-refs.c b/ui-refs.c
index 5b4530e..75f2789 100644
--- a/ui-refs.c
+++ b/ui-refs.c
@@ -93,34 +93,28 @@ static void print_tag_header(void)
 static void print_tag_downloads(const struct cgit_repo *repo, const char *ref)
 {
 	const struct cgit_snapshot_format* f;
-	struct strbuf filename = STRBUF_INIT;
 	const char *basename;
-	int free_ref = 0;
+	struct strbuf filename = STRBUF_INIT;
+	size_t prefixlen;
 
 	if (!ref || strlen(ref) < 1)
 		return;
 
 	basename = cgit_repobasename(repo->url);
-	if (!starts_with(ref, basename)) {
-		if ((ref[0] == 'v' || ref[0] == 'V') && isdigit(ref[1]))
-			ref++;
-		if (isdigit(ref[0])) {
-			ref = fmtalloc("%s-%s", basename, ref);
-			free_ref = 1;
-		}
-	}
-
+	if (starts_with(ref, basename))
+		strbuf_addstr(&filename, ref);
+	else
+		cgit_compose_snapshot_prefix(&filename, basename, ref);
+	prefixlen = filename.len;
 	for (f = cgit_snapshot_formats; f->suffix; f++) {
 		if (!(repo->snapshots & f->bit))
 			continue;
-		strbuf_reset(&filename);
-		strbuf_addf(&filename, "%s%s", ref, f->suffix);
+		strbuf_setlen(&filename, prefixlen);
+		strbuf_addstr(&filename, f->suffix);
 		cgit_snapshot_link(filename.buf, NULL, NULL, NULL, NULL, filename.buf);
 		html("&nbsp;&nbsp;");
 	}
 
-	if (free_ref)
-		free((char *)ref);
 	strbuf_release(&filename);
 }
 
diff --git a/ui-shared.c b/ui-shared.c
index 562fa0e..b1a6c46 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -1069,18 +1069,34 @@ void cgit_print_filemode(unsigned short mode)
 	html_fileperm(mode);
 }
 
+void cgit_compose_snapshot_prefix(struct strbuf *filename, const char *base,
+				  const char *ref)
+{
+	unsigned char sha1[20];
+
+	/*
+	 * Prettify snapshot names by stripping leading "v" or "V" if the tag
+	 * name starts with {v,V}[0-9] and the prettify mapping is injective,
+	 * i.e. each stripped tag can be inverted without ambiguities.
+	 */
+	if (get_sha1(fmt("refs/tags/%s", ref), sha1) == 0 &&
+	    (ref[0] == 'v' || ref[0] == 'V') && isdigit(ref[1]) &&
+	    ((get_sha1(fmt("refs/tags/%s", ref + 1), sha1) == 0) +
+	     (get_sha1(fmt("refs/tags/v%s", ref + 1), sha1) == 0) +
+	     (get_sha1(fmt("refs/tags/V%s", ref + 1), sha1) == 0) == 1))
+		ref++;
+
+	strbuf_addf(filename, "%s-%s", base, ref);
+}
+
 void cgit_print_snapshot_links(const char *repo, const char *head,
 			       const char *hex, int snapshots)
 {
 	const struct cgit_snapshot_format* f;
 	struct strbuf filename = STRBUF_INIT;
 	size_t prefixlen;
-	unsigned char sha1[20];
 
-	if (get_sha1(fmt("refs/tags/%s", hex), sha1) == 0 &&
-	    (hex[0] == 'v' || hex[0] == 'V') && isdigit(hex[1]))
-		hex++;
-	strbuf_addf(&filename, "%s-%s", cgit_repobasename(repo), hex);
+	cgit_compose_snapshot_prefix(&filename, cgit_repobasename(repo), hex);
 	prefixlen = filename.len;
 	for (f = cgit_snapshot_formats; f->suffix; f++) {
 		if (!(snapshots & f->bit))
diff --git a/ui-shared.h b/ui-shared.h
index b457c97..87799f1 100644
--- a/ui-shared.h
+++ b/ui-shared.h
@@ -71,6 +71,8 @@ __attribute__((format (printf,3,4)))
 extern void cgit_print_error_page(int code, const char *msg, const char *fmt, ...);
 extern void cgit_print_pageheader(void);
 extern void cgit_print_filemode(unsigned short mode);
+extern void cgit_compose_snapshot_prefix(struct strbuf *filename,
+					 const char *base, const char *ref);
 extern void cgit_print_snapshot_links(const char *repo, const char *head,
 				      const char *hex, int snapshots);
 extern void cgit_add_hidden_formfields(int incl_head, int incl_search,