git/fsck.c

#include "cache.h"
#include "object.h"
#include "blob.h"
#include "tree.h"
#include "tree-walk.h"
#include "commit.h"
#include "tag.h"
#include "fsck.h"
#include "refs.h"
#include "utf8.h"
#include "sha1-array.h"
#include "decorate.h"

#define FSCK_FATAL -1
#define FSCK_INFO -2

#define FOREACH_MSG_ID(FUNC) \
	/* fatal errors */ \
	FUNC(NUL_IN_HEADER, FATAL) \
	FUNC(UNTERMINATED_HEADER, FATAL) \
	/* errors */ \
	FUNC(BAD_DATE, ERROR) \
	FUNC(BAD_DATE_OVERFLOW, ERROR) \
	FUNC(BAD_EMAIL, ERROR) \
	FUNC(BAD_NAME, ERROR) \
	FUNC(BAD_OBJECT_SHA1, ERROR) \
	FUNC(BAD_PARENT_SHA1, ERROR) \
	FUNC(BAD_TAG_OBJECT, ERROR) \
	FUNC(BAD_TIMEZONE, ERROR) \
	FUNC(BAD_TREE, ERROR) \
	FUNC(BAD_TREE_SHA1, ERROR) \
	FUNC(BAD_TYPE, ERROR) \
	FUNC(DUPLICATE_ENTRIES, ERROR) \
	FUNC(MISSING_AUTHOR, ERROR) \
	FUNC(MISSING_COMMITTER, ERROR) \
	FUNC(MISSING_EMAIL, ERROR) \
	FUNC(MISSING_GRAFT, ERROR) \
	FUNC(MISSING_NAME_BEFORE_EMAIL, ERROR) \
	FUNC(MISSING_OBJECT, ERROR) \
	FUNC(MISSING_PARENT, ERROR) \
	FUNC(MISSING_SPACE_BEFORE_DATE, ERROR) \
	FUNC(MISSING_SPACE_BEFORE_EMAIL, ERROR) \
	FUNC(MISSING_TAG, ERROR) \
	FUNC(MISSING_TAG_ENTRY, ERROR) \
	FUNC(MISSING_TAG_OBJECT, ERROR) \
	FUNC(MISSING_TREE, ERROR) \
	FUNC(MISSING_TYPE, ERROR) \
	FUNC(MISSING_TYPE_ENTRY, ERROR) \
	FUNC(MULTIPLE_AUTHORS, ERROR) \
	FUNC(TAG_OBJECT_NOT_TAG, ERROR) \
	FUNC(TREE_NOT_SORTED, ERROR) \
	FUNC(UNKNOWN_TYPE, ERROR) \
	FUNC(ZERO_PADDED_DATE, ERROR) \
	/* warnings */ \
	FUNC(BAD_FILEMODE, WARN) \
	FUNC(EMPTY_NAME, WARN) \
	FUNC(FULL_PATHNAME, WARN) \
	FUNC(HAS_DOT, WARN) \
	FUNC(HAS_DOTDOT, WARN) \
	FUNC(HAS_DOTGIT, WARN) \
	FUNC(NULL_SHA1, WARN) \
	FUNC(ZERO_PADDED_FILEMODE, WARN) \
	FUNC(NUL_IN_COMMIT, WARN) \
	/* infos (reported as warnings, but ignored by default) */ \
	FUNC(BAD_TAG_NAME, INFO) \
	FUNC(MISSING_TAGGER_ENTRY, INFO)

#define MSG_ID(id, msg_type) FSCK_MSG_##id,
enum fsck_msg_id {
	FOREACH_MSG_ID(MSG_ID)
	FSCK_MSG_MAX
};
#undef MSG_ID

#define STR(x) #x
#define MSG_ID(id, msg_type) { STR(id), NULL, FSCK_##msg_type },
static struct {
	const char *id_string;
	const char *downcased;
	int msg_type;
} msg_id_info[FSCK_MSG_MAX + 1] = {
	FOREACH_MSG_ID(MSG_ID)
	{ NULL, NULL, -1 }
};
#undef MSG_ID

static int parse_msg_id(const char *text)
{
	int i;

	if (!msg_id_info[0].downcased) {
		/* convert id_string to lower case, without underscores. */
		for (i = 0; i < FSCK_MSG_MAX; i++) {
			const char *p = msg_id_info[i].id_string;
			int len = strlen(p);
			char *q = xmalloc(len);

			msg_id_info[i].downcased = q;
			while (*p)
				if (*p == '_')
					p++;
				else
					*(q)++ = tolower(*(p)++);
			*q = '\0';
		}
	}

	for (i = 0; i < FSCK_MSG_MAX; i++)
		if (!strcmp(text, msg_id_info[i].downcased))
			return i;

	return -1;
}

static int fsck_msg_type(enum fsck_msg_id msg_id,
	struct fsck_options *options)
{
	int msg_type;

	assert(msg_id >= 0 && msg_id < FSCK_MSG_MAX);

	if (options->msg_type)
		msg_type = options->msg_type[msg_id];
	else {
		msg_type = msg_id_info[msg_id].msg_type;
		if (options->strict && msg_type == FSCK_WARN)
			msg_type = FSCK_ERROR;
	}

	return msg_type;
}

static void init_skiplist(struct fsck_options *options, const char *path)
{
	static struct oid_array skiplist = OID_ARRAY_INIT;
	int sorted, fd;
	char buffer[GIT_MAX_HEXSZ + 1];
	struct object_id oid;

	if (options->skiplist)
		sorted = options->skiplist->sorted;
	else {
		sorted = 1;
		options->skiplist = &skiplist;
	}

	fd = open(path, O_RDONLY);
	if (fd < 0)
		die("Could not open skip list: %s", path);
	for (;;) {
		const char *p;
		int result = read_in_full(fd, buffer, sizeof(buffer));
		if (result < 0)
			die_errno("Could not read '%s'", path);
		if (!result)
			break;
		if (parse_oid_hex(buffer, &oid, &p) || *p != '\n')
			die("Invalid SHA-1: %s", buffer);
		oid_array_append(&skiplist, &oid);
		if (sorted && skiplist.nr > 1 &&
				oidcmp(&skiplist.oid[skiplist.nr - 2],
				       &oid) > 0)
			sorted = 0;
	}
	close(fd);

	if (sorted)
		skiplist.sorted = 1;
}

static int parse_msg_type(const char *str)
{
	if (!strcmp(str, "error"))
		return FSCK_ERROR;
	else if (!strcmp(str, "warn"))
		return FSCK_WARN;
	else if (!strcmp(str, "ignore"))
		return FSCK_IGNORE;
	else
		die("Unknown fsck message type: '%s'", str);
}

int is_valid_msg_type(const char *msg_id, const char *msg_type)
{
	if (parse_msg_id(msg_id) < 0)
		return 0;
	parse_msg_type(msg_type);
	return 1;
}

void fsck_set_msg_type(struct fsck_options *options,
		const char *msg_id, const char *msg_type)
{
	int id = parse_msg_id(msg_id), type;

	if (id < 0)
		die("Unhandled message id: %s", msg_id);
	type = parse_msg_type(msg_type);

	if (type != FSCK_ERROR && msg_id_info[id].msg_type == FSCK_FATAL)
		die("Cannot demote %s to %s", msg_id, msg_type);

	if (!options->msg_type) {
		int i;
		int *msg_type;
		ALLOC_ARRAY(msg_type, FSCK_MSG_MAX);
		for (i = 0; i < FSCK_MSG_MAX; i++)
			msg_type[i] = fsck_msg_type(i, options);
		options->msg_type = msg_type;
	}

	options->msg_type[id] = type;
}

void fsck_set_msg_types(struct fsck_options *options, const char *values)
{
	char *buf = xstrdup(values), *to_free = buf;
	int done = 0;

	while (!done) {
		int len = strcspn(buf, " ,|"), equal;

		done = !buf[len];
		if (!len) {
			buf++;
			continue;
		}
		buf[len] = '\0';

		for (equal = 0;
		     equal < len && buf[equal] != '=' && buf[equal] != ':';
		     equal++)
			buf[equal] = tolower(buf[equal]);
		buf[equal] = '\0';

		if (!strcmp(buf, "skiplist")) {
			if (equal == len)
				die("skiplist requires a path");
			init_skiplist(options, buf + equal + 1);
			buf += len + 1;
			continue;
		}

		if (equal == len)
			die("Missing '=': '%s'", buf);

		fsck_set_msg_type(options, buf, buf + equal + 1);
		buf += len + 1;
	}
	free(to_free);
}

static void append_msg_id(struct strbuf *sb, const char *msg_id)
{
	for (;;) {
		char c = *(msg_id)++;

		if (!c)
			break;
		if (c != '_')
			strbuf_addch(sb, tolower(c));
		else {
			assert(*msg_id);
			strbuf_addch(sb, *(msg_id)++);
		}
	}

	strbuf_addstr(sb, ": ");
}

__attribute__((format (printf, 4, 5)))
static int report(struct fsck_options *options, struct object *object,
	enum fsck_msg_id id, const char *fmt, ...)
{
	va_list ap;
	struct strbuf sb = STRBUF_INIT;
	int msg_type = fsck_msg_type(id, options), result;

	if (msg_type == FSCK_IGNORE)
		return 0;

	if (options->skiplist && object &&
			oid_array_lookup(options->skiplist, &object->oid) >= 0)
		return 0;

	if (msg_type == FSCK_FATAL)
		msg_type = FSCK_ERROR;
	else if (msg_type == FSCK_INFO)
		msg_type = FSCK_WARN;

	append_msg_id(&sb, msg_id_info[id].id_string);

	va_start(ap, fmt);
	strbuf_vaddf(&sb, fmt, ap);
	result = options->error_func(options, object, msg_type, sb.buf);
	strbuf_release(&sb);
	va_end(ap);

	return result;
}

static char *get_object_name(struct fsck_options *options, struct object *obj)
{
	if (!options->object_names)
		return NULL;
	return lookup_decoration(options->object_names, obj);
}

static void put_object_name(struct fsck_options *options, struct object *obj,
	const char *fmt, ...)
{
	va_list ap;
	struct strbuf buf = STRBUF_INIT;
	char *existing;

	if (!options->object_names)
		return;
	existing = lookup_decoration(options->object_names, obj);
	if (existing)
		return;
	va_start(ap, fmt);
	strbuf_vaddf(&buf, fmt, ap);
	add_decoration(options->object_names, obj, strbuf_detach(&buf, NULL));
	va_end(ap);
}

static const char *describe_object(struct fsck_options *o, struct object *obj)
{
	static struct strbuf buf = STRBUF_INIT;
	char *name;

	strbuf_reset(&buf);
	strbuf_addstr(&buf, oid_to_hex(&obj->oid));
	if (o->object_names && (name = lookup_decoration(o->object_names, obj)))
		strbuf_addf(&buf, " (%s)", name);

	return buf.buf;
}

static int fsck_walk_tree(struct tree *tree, void *data, struct fsck_options *options)
{
	struct tree_desc desc;
	struct name_entry entry;
	int res = 0;
	const char *name;

	if (parse_tree(tree))
		return -1;

	name = get_object_name(options, &tree->object);
	if (init_tree_desc_gently(&desc, tree->buffer, tree->size))
		return -1;
	while (tree_entry_gently(&desc, &entry)) {
		struct object *obj;
		int result;

		if (S_ISGITLINK(entry.mode))
			continue;

		if (S_ISDIR(entry.mode)) {
			obj = &lookup_tree(entry.oid->hash)->object;
			if (name)
				put_object_name(options, obj, "%s%s/", name,
					entry.path);
			result = options->walk(obj, OBJ_TREE, data, options);
		}
		else if (S_ISREG(entry.mode) || S_ISLNK(entry.mode)) {
			obj = &lookup_blob(entry.oid->hash)->object;
			if (name)
				put_object_name(options, obj, "%s%s", name,
					entry.path);
			result = options->walk(obj, OBJ_BLOB, data, options);
		}
		else {
			result = error("in tree %s: entry %s has bad mode %.6o",
					describe_object(options, &tree->object), entry.path, entry.mode);
		}
		if (result < 0)
			return result;
		if (!res)
			res = result;
	}
	return res;
}

static int fsck_walk_commit(struct commit *commit, void *data, struct fsck_options *options)
{
	int counter = 0, generation = 0, name_prefix_len = 0;
	struct commit_list *parents;
	int res;
	int result;
	const char *name;

	if (parse_commit(commit))
		return -1;

	name = get_object_name(options, &commit->object);
	if (name)
		put_object_name(options, &commit->tree->object, "%s:", name);

	result = options->walk((struct object *)commit->tree, OBJ_TREE, data, options);
	if (result < 0)
		return result;
	res = result;

	parents = commit->parents;
	if (name && parents) {
		int len = strlen(name), power;

		if (len && name[len - 1] == '^') {
			generation = 1;
			name_prefix_len = len - 1;
		}
		else { /* parse ~<generation> suffix */
			for (generation = 0, power = 1;
			     len && isdigit(name[len - 1]);
			     power *= 10)
				generation += power * (name[--len] - '0');
			if (power > 1 && len && name[len - 1] == '~')
				name_prefix_len = len - 1;
		}
	}

	while (parents) {
		if (name) {
			struct object *obj = &parents->item->object;

			if (++counter > 1)
				put_object_name(options, obj, "%s^%d",
					name, counter);
			else if (generation > 0)
				put_object_name(options, obj, "%.*s~%d",
					name_prefix_len, name, generation + 1);
			else
				put_object_name(options, obj, "%s^", name);
		}
		result = options->walk((struct object *)parents->item, OBJ_COMMIT, data, options);
		if (result < 0)
			return result;
		if (!res)
			res = result;
		parents = parents->next;
	}
	return res;
}

static int fsck_walk_tag(struct tag *tag, void *data, struct fsck_options *options)
{
	char *name = get_object_name(options, &tag->object);

	if (parse_tag(tag))
		return -1;
	if (name)
		put_object_name(options, tag->tagged, "%s", name);
	return options->walk(tag->tagged, OBJ_ANY, data, options);
}

int fsck_walk(struct object *obj, void *data, struct fsck_options *options)
{
	if (!obj)
		return -1;

	if (obj->type == OBJ_NONE)
		parse_object(obj->oid.hash);

	switch (obj->type) {
	case OBJ_BLOB:
		return 0;
	case OBJ_TREE:
		return fsck_walk_tree((struct tree *)obj, data, options);
	case OBJ_COMMIT:
		return fsck_walk_commit((struct commit *)obj, data, options);
	case OBJ_TAG:
		return fsck_walk_tag((struct tag *)obj, data, options);
	default:
		error("Unknown object type for %s", describe_object(options, obj));
		return -1;
	}
}

/*
 * The entries in a tree are ordered in the _path_ order,
 * which means that a directory entry is ordered by adding
 * a slash to the end of it.
 *
 * So a directory called "a" is ordered _after_ a file
 * called "a.c", because "a/" sorts after "a.c".
 */
#define TREE_UNORDERED (-1)
#define TREE_HAS_DUPS  (-2)

static int verify_ordered(unsigned mode1, const char *name1, unsigned mode2, const char *name2)
{
	int len1 = strlen(name1);
	int len2 = strlen(name2);
	int len = len1 < len2 ? len1 : len2;
	unsigned char c1, c2;
	int cmp;

	cmp = memcmp(name1, name2, len);
	if (cmp < 0)
		return 0;
	if (cmp > 0)
		return TREE_UNORDERED;

	/*
	 * Ok, the first <len> characters are the same.
	 * Now we need to order the next one, but turn
	 * a '\0' into a '/' for a directory entry.
	 */
	c1 = name1[len];
	c2 = name2[len];
	if (!c1 && !c2)
		/*
		 * git-write-tree used to write out a nonsense tree that has
		 * entries with the same name, one blob and one tree.  Make
		 * sure we do not have duplicate entries.
		 */
		return TREE_HAS_DUPS;
	if (!c1 && S_ISDIR(mode1))
		c1 = '/';
	if (!c2 && S_ISDIR(mode2))
		c2 = '/';
	return c1 < c2 ? 0 : TREE_UNORDERED;
}

static int fsck_tree(struct tree *item, struct fsck_options *options)
{
	int retval = 0;
	int has_null_sha1 = 0;
	int has_full_path = 0;
	int has_empty_name = 0;
	int has_dot = 0;
	int has_dotdot = 0;
	int has_dotgit = 0;
	int has_zero_pad = 0;
	int has_bad_modes = 0;
	int has_dup_entries = 0;
	int not_properly_sorted = 0;
	struct tree_desc desc;
	unsigned o_mode;
	const char *o_name;

	if (init_tree_desc_gently(&desc, item->buffer, item->size)) {
		retval += report(options, &item->object, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
		return retval;
	}

	o_mode = 0;
	o_name = NULL;

	while (desc.size) {
		unsigned mode;
		const char *name;
		const struct object_id *oid;

		oid = tree_entry_extract(&desc, &name, &mode);

		has_null_sha1 |= is_null_oid(oid);
		has_full_path |= !!strchr(name, '/');
		has_empty_name |= !*name;
		has_dot |= !strcmp(name, ".");
		has_dotdot |= !strcmp(name, "..");
		has_dotgit |= (!strcmp(name, ".git") ||
			       is_hfs_dotgit(name) ||
			       is_ntfs_dotgit(name));
		has_zero_pad |= *(char *)desc.buffer == '0';
		if (update_tree_entry_gently(&desc)) {
			retval += report(options, &item->object, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
			break;
		}

		switch (mode) {
		/*
		 * Standard modes..
		 */
		case S_IFREG | 0755:
		case S_IFREG | 0644:
		case S_IFLNK:
		case S_IFDIR:
		case S_IFGITLINK:
			break;
		/*
		 * This is nonstandard, but we had a few of these
		 * early on when we honored the full set of mode
		 * bits..
		 */
		case S_IFREG | 0664:
			if (!options->strict)
				break;
		default:
			has_bad_modes = 1;
		}

		if (o_name) {
			switch (verify_ordered(o_mode, o_name, mode, name)) {
			case TREE_UNORDERED:
				not_properly_sorted = 1;
				break;
			case TREE_HAS_DUPS:
				has_dup_entries = 1;
				break;
			default:
				break;
			}
		}

		o_mode = mode;
		o_name = name;
	}

	if (has_null_sha1)
		retval += report(options, &item->object, FSCK_MSG_NULL_SHA1, "contains entries pointing to null sha1");
	if (has_full_path)
		retval += report(options, &item->object, FSCK_MSG_FULL_PATHNAME, "contains full pathnames");
	if (has_empty_name)
		retval += report(options, &item->object, FSCK_MSG_EMPTY_NAME, "contains empty pathname");
	if (has_dot)
		retval += report(options, &item->object, FSCK_MSG_HAS_DOT, "contains '.'");
	if (has_dotdot)
		retval += report(options, &item->object, FSCK_MSG_HAS_DOTDOT, "contains '..'");
	if (has_dotgit)
		retval += report(options, &item->object, FSCK_MSG_HAS_DOTGIT, "contains '.git'");
	if (has_zero_pad)
		retval += report(options, &item->object, FSCK_MSG_ZERO_PADDED_FILEMODE, "contains zero-padded file modes");
	if (has_bad_modes)
		retval += report(options, &item->object, FSCK_MSG_BAD_FILEMODE, "contains bad file modes");
	if (has_dup_entries)
		retval += report(options, &item->object, FSCK_MSG_DUPLICATE_ENTRIES, "contains duplicate file entries");
	if (not_properly_sorted)
		retval += report(options, &item->object, FSCK_MSG_TREE_NOT_SORTED, "not properly sorted");
	return retval;
}

static int verify_headers(const void *data, unsigned long size,
			  struct object *obj, struct fsck_options *options)
{
	const char *buffer = (const char *)data;
	unsigned long i;

	for (i = 0; i < size; i++) {
		switch (buffer[i]) {
		case '\0':
			return report(options, obj,
				FSCK_MSG_NUL_IN_HEADER,
				"unterminated header: NUL at offset %ld", i);
		case '\n':
			if (i + 1 < size && buffer[i + 1] == '\n')
				return 0;
		}
	}

	/*
	 * We did not find double-LF that separates the header
	 * and the body.  Not having a body is not a crime but
	 * we do want to see the terminating LF for the last header
	 * line.
	 */
	if (size && buffer[size - 1] == '\n')
		return 0;

	return report(options, obj,
		FSCK_MSG_UNTERMINATED_HEADER, "unterminated header");
}

static int fsck_ident(const char **ident, struct object *obj, struct fsck_options *options)
{
	const char *p = *ident;
	char *end;

	*ident = strchrnul(*ident, '\n');
	if (**ident == '\n')
		(*ident)++;

	if (*p == '<')
		return report(options, obj, FSCK_MSG_MISSING_NAME_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
	p += strcspn(p, "<>\n");
	if (*p == '>')
		return report(options, obj, FSCK_MSG_BAD_NAME, "invalid author/committer line - bad name");
	if (*p != '<')
		return report(options, obj, FSCK_MSG_MISSING_EMAIL, "invalid author/committer line - missing email");
	if (p[-1] != ' ')
		return report(options, obj, FSCK_MSG_MISSING_SPACE_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
	p++;
	p += strcspn(p, "<>\n");
	if (*p != '>')
		return report(options, obj, FSCK_MSG_BAD_EMAIL, "invalid author/committer line - bad email");
	p++;
	if (*p != ' ')
		return report(options, obj, FSCK_MSG_MISSING_SPACE_BEFORE_DATE, "invalid author/committer line - missing space before date");
	p++;
	if (*p == '0' && p[1] != ' ')
		return report(options, obj, FSCK_MSG_ZERO_PADDED_DATE, "invalid author/committer line - zero-padded date");
	if (date_overflows(parse_timestamp(p, &end, 10)))
		return report(options, obj, FSCK_MSG_BAD_DATE_OVERFLOW, "invalid author/committer line - date causes integer overflow");
	if ((end == p || *end != ' '))
		return report(options, obj, FSCK_MSG_BAD_DATE, "invalid author/committer line - bad date");
	p = end + 1;
	if ((*p != '+' && *p != '-') ||
	    !isdigit(p[1]) ||
	    !isdigit(p[2]) ||
	    !isdigit(p[3]) ||
	    !isdigit(p[4]) ||
	    (p[5] != '\n'))
		return report(options, obj, FSCK_MSG_BAD_TIMEZONE, "invalid author/committer line - bad time zone");
	p += 6;
	return 0;
}

static int fsck_commit_buffer(struct commit *commit, const char *buffer,
	unsigned long size, struct fsck_options *options)
{
	unsigned char tree_sha1[20], sha1[20];
	struct commit_graft *graft;
	unsigned parent_count, parent_line_count = 0, author_count;
	int err;
	const char *buffer_begin = buffer;

	if (verify_headers(buffer, size, &commit->object, options))
		return -1;

	if (!skip_prefix(buffer, "tree ", &buffer))
		return report(options, &commit->object, FSCK_MSG_MISSING_TREE, "invalid format - expected 'tree' line");
	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n') {
		err = report(options, &commit->object, FSCK_MSG_BAD_TREE_SHA1, "invalid 'tree' line format - bad sha1");
		if (err)
			return err;
	}
	buffer += 41;
	while (skip_prefix(buffer, "parent ", &buffer)) {
		if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n') {
			err = report(options, &commit->object, FSCK_MSG_BAD_PARENT_SHA1, "invalid 'parent' line format - bad sha1");
			if (err)
				return err;
		}
		buffer += 41;
		parent_line_count++;
	}
	graft = lookup_commit_graft(commit->object.oid.hash);
	parent_count = commit_list_count(commit->parents);
	if (graft) {
		if (graft->nr_parent == -1 && !parent_count)
			; /* shallow commit */
		else if (graft->nr_parent != parent_count) {
			err = report(options, &commit->object, FSCK_MSG_MISSING_GRAFT, "graft objects missing");
			if (err)
				return err;
		}
	} else {
		if (parent_count != parent_line_count) {
			err = report(options, &commit->object, FSCK_MSG_MISSING_PARENT, "parent objects missing");
			if (err)
				return err;
		}
	}
	author_count = 0;
	while (skip_prefix(buffer, "author ", &buffer)) {
		author_count++;
		err = fsck_ident(&buffer, &commit->object, options);
		if (err)
			return err;
	}
	if (author_count < 1)
		err = report(options, &commit->object, FSCK_MSG_MISSING_AUTHOR, "invalid format - expected 'author' line");
	else if (author_count > 1)
		err = report(options, &commit->object, FSCK_MSG_MULTIPLE_AUTHORS, "invalid format - multiple 'author' lines");
	if (err)
		return err;
	if (!skip_prefix(buffer, "committer ", &buffer))
		return report(options, &commit->object, FSCK_MSG_MISSING_COMMITTER, "invalid format - expected 'committer' line");
	err = fsck_ident(&buffer, &commit->object, options);
	if (err)
		return err;
	if (!commit->tree) {
		err = report(options, &commit->object, FSCK_MSG_BAD_TREE, "could not load commit's tree %s", sha1_to_hex(tree_sha1));
		if (err)
			return err;
	}
	if (memchr(buffer_begin, '\0', size)) {
		err = report(options, &commit->object, FSCK_MSG_NUL_IN_COMMIT,
			     "NUL byte in the commit object body");
		if (err)
			return err;
	}
	return 0;
}

static int fsck_commit(struct commit *commit, const char *data,
	unsigned long size, struct fsck_options *options)
{
	const char *buffer = data ?  data : get_commit_buffer(commit, &size);
	int ret = fsck_commit_buffer(commit, buffer, size, options);
	if (!data)
		unuse_commit_buffer(commit, buffer);
	return ret;
}

static int fsck_tag_buffer(struct tag *tag, const char *data,
	unsigned long size, struct fsck_options *options)
{
	unsigned char sha1[20];
	int ret = 0;
	const char *buffer;
	char *to_free = NULL, *eol;
	struct strbuf sb = STRBUF_INIT;

	if (data)
		buffer = data;
	else {
		enum object_type type;

		buffer = to_free =
			read_sha1_file(tag->object.oid.hash, &type, &size);
		if (!buffer)
			return report(options, &tag->object,
				FSCK_MSG_MISSING_TAG_OBJECT,
				"cannot read tag object");

		if (type != OBJ_TAG) {
			ret = report(options, &tag->object,
				FSCK_MSG_TAG_OBJECT_NOT_TAG,
				"expected tag got %s",
			    typename(type));
			goto done;
		}
	}

	ret = verify_headers(buffer, size, &tag->object, options);
	if (ret)
		goto done;

	if (!skip_prefix(buffer, "object ", &buffer)) {
		ret = report(options, &tag->object, FSCK_MSG_MISSING_OBJECT, "invalid format - expected 'object' line");
		goto done;
	}
	if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n') {
		ret = report(options, &tag->object, FSCK_MSG_BAD_OBJECT_SHA1, "invalid 'object' line format - bad sha1");
		if (ret)
			goto done;
	}
	buffer += 41;

	if (!skip_prefix(buffer, "type ", &buffer)) {
		ret = report(options, &tag->object, FSCK_MSG_MISSING_TYPE_ENTRY, "invalid format - expected 'type' line");
		goto done;
	}
	eol = strchr(buffer, '\n');
	if (!eol) {
		ret = report(options, &tag->object, FSCK_MSG_MISSING_TYPE, "invalid format - unexpected end after 'type' line");
		goto done;
	}
	if (type_from_string_gently(buffer, eol - buffer, 1) < 0)
		ret = report(options, &tag->object, FSCK_MSG_BAD_TYPE, "invalid 'type' value");
	if (ret)
		goto done;
	buffer = eol + 1;

	if (!skip_prefix(buffer, "tag ", &buffer)) {
		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAG_ENTRY, "invalid format - expected 'tag' line");
		goto done;
	}
	eol = strchr(buffer, '\n');
	if (!eol) {
		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAG, "invalid format - unexpected end after 'type' line");
		goto done;
	}
	strbuf_addf(&sb, "refs/tags/%.*s", (int)(eol - buffer), buffer);
	if (check_refname_format(sb.buf, 0)) {
		ret = report(options, &tag->object, FSCK_MSG_BAD_TAG_NAME,
			   "invalid 'tag' name: %.*s",
			   (int)(eol - buffer), buffer);
		if (ret)
			goto done;
	}
	buffer = eol + 1;

	if (!skip_prefix(buffer, "tagger ", &buffer)) {
		/* early tags do not contain 'tagger' lines; warn only */
		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAGGER_ENTRY, "invalid format - expected 'tagger' line");
		if (ret)
			goto done;
	}
	else
		ret = fsck_ident(&buffer, &tag->object, options);

done:
	strbuf_release(&sb);
	free(to_free);
	return ret;
}

static int fsck_tag(struct tag *tag, const char *data,
	unsigned long size, struct fsck_options *options)
{
	struct object *tagged = tag->tagged;

	if (!tagged)
		return report(options, &tag->object, FSCK_MSG_BAD_TAG_OBJECT, "could not load tagged object");

	return fsck_tag_buffer(tag, data, size, options);
}

int fsck_object(struct object *obj, void *data, unsigned long size,
	struct fsck_options *options)
{
	if (!obj)
		return report(options, obj, FSCK_MSG_BAD_OBJECT_SHA1, "no valid object to fsck");

	if (obj->type == OBJ_BLOB)
		return 0;
	if (obj->type == OBJ_TREE)
		return fsck_tree((struct tree *) obj, options);
	if (obj->type == OBJ_COMMIT)
		return fsck_commit((struct commit *) obj, (const char *) data,
			size, options);
	if (obj->type == OBJ_TAG)
		return fsck_tag((struct tag *) obj, (const char *) data,
			size, options);

	return report(options, obj, FSCK_MSG_UNKNOWN_TYPE, "unknown type '%d' (internal fsck error)",
			  obj->type);
}

int fsck_error_function(struct fsck_options *o,
	struct object *obj, int msg_type, const char *message)
{
	if (msg_type == FSCK_WARN) {
		warning("object %s: %s", describe_object(o, obj), message);
		return 0;
	}
	error("object %s: %s", describe_object(o, obj), message);
	return 1;
}