+ const char *name = patch->old_name ? patch->old_name : patch->new_name;
+
+ if (patch->is_binary) {
+ unsigned char sha1[20];
+
+ if (!allow_binary_replacement)
+ return error("cannot apply binary patch to '%s' "
+ "without --allow-binary-replacement",
+ name);
+
+ /* For safety, we require patch index line to contain
+ * full 40-byte textual SHA1 for old and new, at least for now.
+ */
+ if (strlen(patch->old_sha1_prefix) != 40 ||
+ strlen(patch->new_sha1_prefix) != 40 ||
+ get_sha1_hex(patch->old_sha1_prefix, sha1) ||
+ get_sha1_hex(patch->new_sha1_prefix, sha1))
+ return error("cannot apply binary patch to '%s' "
+ "without full index line", name);
+
+ if (patch->old_name) {
+ unsigned char hdr[50];
+ int hdrlen;
+
+ /* See if the old one matches what the patch
+ * applies to.
+ */
+ write_sha1_file_prepare(desc->buffer, desc->size,
+ "blob", sha1, hdr, &hdrlen);
+ if (strcmp(sha1_to_hex(sha1), patch->old_sha1_prefix))
+ return error("the patch applies to '%s' (%s), "
+ "which does not match the "
+ "current contents.",
+ name, sha1_to_hex(sha1));
+ }
+ else {
+ /* Otherwise, the old one must be empty. */
+ if (desc->size)
+ return error("the patch applies to an empty "
+ "'%s' but it is not empty", name);
+ }
+
+ /* For now, we do not record post-image data in the patch,
+ * and require the object already present in the recipient's
+ * object database.
+ */
+ if (desc->buffer) {
+ free(desc->buffer);
+ desc->alloc = desc->size = 0;
+ }
+ get_sha1_hex(patch->new_sha1_prefix, sha1);
+
+ if (memcmp(sha1, null_sha1, 20)) {
+ char type[10];
+ unsigned long size;
+
+ desc->buffer = read_sha1_file(sha1, type, &size);
+ if (!desc->buffer)
+ return error("the necessary postimage %s for "
+ "'%s' does not exist",
+ patch->new_sha1_prefix, name);
+ desc->alloc = desc->size = size;
+ }
+
+ return 0;
+ }