+struct packed_ref_entry {
+ const char *start;
+ size_t len;
+};
+
+static int cmp_packed_ref_entries(const void *v1, const void *v2)
+{
+ const struct packed_ref_entry *e1 = v1, *e2 = v2;
+ const char *r1 = e1->start + GIT_SHA1_HEXSZ + 1;
+ const char *r2 = e2->start + GIT_SHA1_HEXSZ + 1;
+
+ while (1) {
+ if (*r1 == '\n')
+ return *r2 == '\n' ? 0 : -1;
+ if (*r1 != *r2) {
+ if (*r2 == '\n')
+ return 1;
+ else
+ return (unsigned char)*r1 < (unsigned char)*r2 ? -1 : +1;
+ }
+ r1++;
+ r2++;
+ }
+}
+
+/*
+ * `packed_refs->buf` is not known to be sorted. Check whether it is,
+ * and if not, sort it into new memory and munmap/free the old
+ * storage.
+ */
+static void sort_packed_refs(struct packed_ref_cache *packed_refs)
+{
+ struct packed_ref_entry *entries = NULL;
+ size_t alloc = 0, nr = 0;
+ int sorted = 1;
+ const char *pos, *eof, *eol;
+ size_t len, i;
+ char *new_buffer, *dst;
+
+ pos = packed_refs->buf + packed_refs->header_len;
+ eof = packed_refs->eof;
+ len = eof - pos;
+
+ if (!len)
+ return;
+
+ /*
+ * Initialize entries based on a crude estimate of the number
+ * of references in the file (we'll grow it below if needed):
+ */
+ ALLOC_GROW(entries, len / 80 + 20, alloc);
+
+ while (pos < eof) {
+ eol = memchr(pos, '\n', eof - pos);
+ if (!eol)
+ /* The safety check should prevent this. */
+ BUG("unterminated line found in packed-refs");
+ if (eol - pos < GIT_SHA1_HEXSZ + 2)
+ die_invalid_line(packed_refs->refs->path,
+ pos, eof - pos);
+ eol++;
+ if (eol < eof && *eol == '^') {
+ /*
+ * Keep any peeled line together with its
+ * reference:
+ */
+ const char *peeled_start = eol;
+
+ eol = memchr(peeled_start, '\n', eof - peeled_start);
+ if (!eol)
+ /* The safety check should prevent this. */
+ BUG("unterminated peeled line found in packed-refs");
+ eol++;
+ }
+
+ ALLOC_GROW(entries, nr + 1, alloc);
+ entries[nr].start = pos;
+ entries[nr].len = eol - pos;
+ nr++;
+
+ if (sorted &&
+ nr > 1 &&
+ cmp_packed_ref_entries(&entries[nr - 2],
+ &entries[nr - 1]) >= 0)
+ sorted = 0;
+
+ pos = eol;
+ }
+
+ if (sorted)
+ goto cleanup;
+
+ /* We need to sort the memory. First we sort the entries array: */
+ QSORT(entries, nr, cmp_packed_ref_entries);
+
+ /*
+ * Allocate a new chunk of memory, and copy the old memory to
+ * the new in the order indicated by `entries` (not bothering
+ * with the header line):
+ */
+ new_buffer = xmalloc(len);
+ for (dst = new_buffer, i = 0; i < nr; i++) {
+ memcpy(dst, entries[i].start, entries[i].len);
+ dst += entries[i].len;
+ }
+
+ /*
+ * Now munmap the old buffer and use the sorted buffer in its
+ * place:
+ */
+ release_packed_ref_buffer(packed_refs);
+ packed_refs->buf = new_buffer;
+ packed_refs->eof = new_buffer + len;
+ packed_refs->header_len = 0;
+
+cleanup:
+ free(entries);
+}
+
+/*
+ * Return a pointer to the start of the record that contains the
+ * character `*p` (which must be within the buffer). If no other
+ * record start is found, return `buf`.
+ */
+static const char *find_start_of_record(const char *buf, const char *p)
+{
+ while (p > buf && (p[-1] != '\n' || p[0] == '^'))
+ p--;
+ return p;
+}
+
+/*
+ * We want to be able to compare mmapped reference records quickly,
+ * without totally parsing them. We can do so because the records are
+ * LF-terminated, and the refname should start exactly (GIT_SHA1_HEXSZ
+ * + 1) bytes past the beginning of the record.
+ *
+ * But what if the `packed-refs` file contains garbage? We're willing
+ * to tolerate not detecting the problem, as long as we don't produce
+ * totally garbled output (we can't afford to check the integrity of
+ * the whole file during every Git invocation). But we do want to be
+ * sure that we never read past the end of the buffer in memory and
+ * perform an illegal memory access.
+ *
+ * Guarantee that minimum level of safety by verifying that the last
+ * record in the file is LF-terminated, and that it has at least
+ * (GIT_SHA1_HEXSZ + 1) characters before the LF. Die if either of
+ * these checks fails.
+ */
+static void verify_buffer_safe(struct packed_ref_cache *packed_refs)
+{
+ const char *buf = packed_refs->buf + packed_refs->header_len;
+ const char *eof = packed_refs->eof;
+ const char *last_line;
+
+ if (buf == eof)
+ return;
+
+ last_line = find_start_of_record(buf, eof - 1);
+ if (*(eof - 1) != '\n' || eof - last_line < GIT_SHA1_HEXSZ + 2)
+ die_invalid_line(packed_refs->refs->path,
+ last_line, eof - last_line);
+}
+