1 files changed, 64 insertions, 3 deletions
diff --git a/object-file.c b/object-file.c
index 54a82a5f7a..440c5c6850 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1899,11 +1899,68 @@ static void write_object_file_prepare_literally(const struct git_hash_algo *algo
 	hash_object_body(algo, &c, buf, len, oid, hdr, hdrlen);
 }
 
+static int check_collision(const char *filename_a, const char *filename_b)
+{
+	char buf_a[4096], buf_b[4096];
+	int fd_a = -1, fd_b = -1;
+	int ret = 0;
+
+	fd_a = open(filename_a, O_RDONLY);
+	if (fd_a < 0) {
+		ret = error_errno(_("unable to open %s"), filename_a);
+		goto out;
+	}
+
+	fd_b = open(filename_b, O_RDONLY);
+	if (fd_b < 0) {
+		ret = error_errno(_("unable to open %s"), filename_b);
+		goto out;
+	}
+
+	while (1) {
+		ssize_t sz_a, sz_b;
+
+		sz_a = read_in_full(fd_a, buf_a, sizeof(buf_a));
+		if (sz_a < 0) {
+			ret = error_errno(_("unable to read %s"), filename_a);
+			goto out;
+		}
+
+		sz_b = read_in_full(fd_b, buf_b, sizeof(buf_b));
+		if (sz_b < 0) {
+			ret = error_errno(_("unable to read %s"), filename_b);
+			goto out;
+		}
+
+		if (sz_a != sz_b || memcmp(buf_a, buf_b, sz_a)) {
+			ret = error(_("files '%s' and '%s' differ in contents"),
+				    filename_a, filename_b);
+			goto out;
+		}
+
+		if (sz_a < sizeof(buf_a))
+			break;
+	}
+
+out:
+	if (fd_a > -1)
+		close(fd_a);
+	if (fd_b > -1)
+		close(fd_b);
+	return ret;
+}
+
 /*
  * Move the just written object into its final resting place.
  */
 int finalize_object_file(const char *tmpfile, const char *filename)
 {
+	return finalize_object_file_flags(tmpfile, filename, 0);
+}
+
+int finalize_object_file_flags(const char *tmpfile, const char *filename,
+			       enum finalize_object_file_flags flags)
+{
 	struct stat st;
 	int ret = 0;
 
@@ -1941,7 +1998,9 @@ int finalize_object_file(const char *tmpfile, const char *filename)
 			errno = saved_errno;
 			return error_errno(_("unable to write file %s"), filename);
 		}
-		/* FIXME!!! Collision check here ? */
+		if (!(flags & FOF_SKIP_COLLISION_CHECK) &&
+		    check_collision(tmpfile, filename))
+				return -1;
 		unlink_or_warn(tmpfile);
 	}
 
@@ -2195,7 +2254,8 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 			warning_errno(_("failed utime() on %s"), tmp_file.buf);
 	}
 
-	return finalize_object_file(tmp_file.buf, filename.buf);
+	return finalize_object_file_flags(tmp_file.buf, filename.buf,
+					  FOF_SKIP_COLLISION_CHECK);
 }
 
 static int freshen_loose_object(const struct object_id *oid)
@@ -2317,7 +2377,8 @@ int stream_loose_object(struct input_stream *in_stream, size_t len,
 		strbuf_release(&dir);
 	}
 
-	err = finalize_object_file(tmp_file.buf, filename.buf);
+	err = finalize_object_file_flags(tmp_file.buf, filename.buf,
+					 FOF_SKIP_COLLISION_CHECK);
 	if (!err && compat)
 		err = repo_add_loose_object_map(the_repository, oid, &compat_oid);
 cleanup: