show-branch: use strbuf instead of static buffer

When we generate relative names (e.g., "master~20^2"), we
format the name into a static buffer, then xstrdup the
result to attach it to the commit. Since the first thing we
add into the static buffer is the already-computed name of
the child commit, the names may get longer and longer as
the traversal gets deeper, and we may eventually overflow
the fixed-size buffer.

Fix this by converting the fixed-size buffer into a dynamic
strbuf.  The performance implications should be minimal, as
we end up allocating a heap copy of the name anyway (and now
we can just detach the heap copy from the strbuf).

Reported-by: Eric Roman <eroman@chromium.org>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index d208fd6c6821c729a713edb485a20bbe8d5e2692..90fc6b1b9d2a397ae43dfc4c0aba6bc192c9823c 100644 (file)
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -162,29 +162,28 @@ static void name_commits(struct commit_list *list,
                        nth = 0;
                        while (parents) {
                                struct commit *p = parents->item;
-                               char newname[1000], *en;
+                               struct strbuf newname = STRBUF_INIT;
                                parents = parents->next;
                                nth++;
                                if (p->util)
                                        continue;
-                               en = newname;
                                switch (n->generation) {
                                case 0:
-                                       en += sprintf(en, "%s", n->head_name);
+                                       strbuf_addstr(&newname, n->head_name);
                                        break;
                                case 1:
-                                       en += sprintf(en, "%s^", n->head_name);
+                                       strbuf_addf(&newname, "%s^", n->head_name);
                                        break;
                                default:
-                                       en += sprintf(en, "%s~%d",
-                                               n->head_name, n->generation);
+                                       strbuf_addf(&newname, "%s~%d",
+                                                   n->head_name, n->generation);
                                        break;
                                }
                                if (nth == 1)
-                                       en += sprintf(en, "^");
+                                       strbuf_addch(&newname, '^');
                                else
-                                       en += sprintf(en, "^%d", nth);
-                               name_commit(p, xstrdup(newname), 0);
+                                       strbuf_addf(&newname, "^%d", nth);
+                               name_commit(p, strbuf_detach(&newname, NULL), 0);
                                i++;
                                name_first_parent_chain(p);
                        }