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,