static void *lock_and_read_sha1_file(const unsigned char *sha1, enum object_type *type, unsigned long *size)
{
	void *data;

	if (use_threads) {
		read_sha1_lock();
		data = read_sha1_file(sha1, type, size);
		read_sha1_unlock();
	} else {
		data = read_sha1_file(sha1, type, size);
	}
	return data;
}

struct taginfo *cgit_parse_tag(struct tag *tag)
{
	void *data;
	enum object_type type;
	unsigned long size;
	const char *p;
	struct taginfo *ret = NULL;

	data = read_sha1_file(tag->object.oid.hash, &type, &size);
	if (!data || type != OBJ_TAG)
		goto cleanup;

	ret = xcalloc(1, sizeof(struct taginfo));

	for (p = data; !end_of_header(p); p = next_header_line(p)) {
		if (skip_prefix(p, "tagger ", &p)) {
			parse_user(p, &ret->tagger, &ret->tagger_email,
				&ret->tagger_date, &ret->tagger_tz);
		}
	}

	while (p && *p == '\n')
		p++;

	if (p && *p)
		ret->msg = xstrdup(p);

cleanup:
	free(data);
	return ret;
}

/* A file entry went away or appeared */
static void show_entry(struct diff_options *opt, const char *prefix,
		       struct tree_desc *desc, struct strbuf *base)
{
	unsigned mode;
	const char *path;
	const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
	int pathlen = tree_entry_len(path, sha1);
	int old_baselen = base->len;

	strbuf_add(base, path, pathlen);
	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
		enum object_type type;
		struct tree_desc inner;
		void *tree;
		unsigned long size;

		tree = read_sha1_file(sha1, &type, &size);
		if (!tree || type != OBJ_TREE)
			die("corrupt tree sha %s", sha1_to_hex(sha1));

		if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE))
			opt->add_remove(opt, *prefix, mode, sha1, base->buf, 0);

		strbuf_addch(base, '/');

		init_tree_desc(&inner, tree, size);
		show_tree(opt, prefix, &inner, base);
		free(tree);
	} else
		opt->add_remove(opt, prefix[0], mode, sha1, base->buf, 0);

	strbuf_setlen(base, old_baselen);
}

static int is_tag_in_date_range(struct object *tag, struct rev_info *revs)
{
	unsigned long size;
	enum object_type type;
	char *buf = NULL, *line, *lineend;
	unsigned long date;
	int result = 1;

	if (revs->max_age == -1 && revs->min_age == -1)
		goto out;

	buf = read_sha1_file(tag->oid.hash, &type, &size);
	if (!buf)
		goto out;
	line = memmem(buf, size, "\ntagger ", 8);
	if (!line++)
		goto out;
	lineend = memchr(line, '\n', buf + size - line);
	line = memchr(line, '>', lineend ? lineend - line : buf + size - line);
	if (!line++)
		goto out;
	date = strtoul(line, NULL, 10);
	result = (revs->max_age == -1 || revs->max_age < date) &&
		(revs->min_age == -1 || revs->min_age > date);
out:
	free(buf);
	return result;
}

static int is_tag_in_date_range(struct object *tag, struct rev_info *revs)
{
	unsigned long size;
	enum object_type type;
	char *buf, *line, *lineend;
	unsigned long date;

	if (revs->max_age == -1 && revs->min_age == -1)
		return 1;

	buf = read_sha1_file(tag->sha1, &type, &size);
	if (!buf)
		return 1;
	line = memmem(buf, size, "\ntagger ", 8);
	if (!line++)
		return 1;
	lineend = memchr(line, buf + size - line, '\n');
	line = memchr(line, lineend ? lineend - line : buf + size - line, '>');
	if (!line++)
		return 1;
	date = strtoul(line, NULL, 10);
	free(buf);
	return (revs->max_age == -1 || revs->max_age < date) &&
		(revs->min_age == -1 || revs->min_age > date);
}

static int verify_tag(const char *name, int verbose)
{
	enum object_type type;
	unsigned char sha1[20];
	char *buf;
	unsigned long size;
	int ret;

	if (get_sha1(name, sha1))
		return error("tag '%s' not found.", name);

	type = sha1_object_info(sha1, NULL);
	if (type != OBJ_TAG)
		return error("%s: cannot verify a non-tag object of type %s.",
				name, typename(type));

	buf = read_sha1_file(sha1, &type, &size);
	if (!buf)
		return error("%s: unable to read file.", name);

	ret = run_gpg_verify(buf, size, verbose);

	free(buf);
	return ret;
}

int parse_commit(struct commit *item)
{
	char type[20];
	void *buffer;
	unsigned long size;
	int ret;

	if (item->object.parsed)
		return 0;
	buffer = read_sha1_file(item->object.sha1, type, &size);
	if (!buffer)
		return error("Could not read %s",
			     sha1_to_hex(item->object.sha1));
	if (strcmp(type, commit_type)) {
		free(buffer);
		return error("Object %s not a commit",
			     sha1_to_hex(item->object.sha1));
	}
	ret = parse_commit_buffer(item, buffer, size);
	if (save_commit_buffer && !ret) {
		item->buffer = buffer;
		return 0;
	}
	free(buffer);
	return ret;
}

/* A file entry went away or appeared */
static int show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
{
	unsigned mode;
	const char *path;
	const unsigned char *sha1 = extract(desc, &path, &mode);

	if (opt->recursive && S_ISDIR(mode)) {
		char type[20];
		char *newbase = malloc_base(base, path, strlen(path));
		struct tree_desc inner;
		void *tree;

		tree = read_sha1_file(sha1, type, &inner.size);
		if (!tree || strcmp(type, "tree"))
			die("corrupt tree sha %s", sha1_to_hex(sha1));

		inner.buf = tree;
		show_tree(opt, prefix, &inner, newbase);

		free(tree);
		free(newbase);
		return 0;
	}

	opt->add_remove(opt, prefix[0], mode, sha1, base, path);
	return 0;
}

/* A file entry went away or appeared */
static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
		       const char *base, int baselen)
{
	unsigned mode;
	const char *path;
	const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
	int pathlen = tree_entry_len(path, sha1);

	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
		enum object_type type;
		char *newbase = malloc_base(base, baselen, path, pathlen);
		struct tree_desc inner;
		void *tree;
		unsigned long size;

		tree = read_sha1_file(sha1, &type, &size);
		if (!tree || type != OBJ_TREE)
			die("corrupt tree sha %s", sha1_to_hex(sha1));

		init_tree_desc(&inner, tree, size);
		show_tree(opt, prefix, &inner, newbase, baselen + 1 + pathlen);

		free(tree);
		free(newbase);
	} else {
		char *fullname = malloc_fullname(base, baselen, path, pathlen);
		opt->add_remove(opt, prefix[0], mode, sha1, fullname);
		free(fullname);
	}
}

static int parse_reuse_arg(const struct option *opt, const char *arg, int unset)
{
	struct note_data *d = opt->value;
	char *buf;
	unsigned char object[20];
	enum object_type type;
	unsigned long len;

	if (d->buf.len)
		strbuf_addch(&d->buf, '\n');

	if (get_sha1(arg, object))
		die(_("Failed to resolve '%s' as a valid ref."), arg);
	if (!(buf = read_sha1_file(object, &type, &len))) {
		free(buf);
		die(_("Failed to read object '%s'."), arg);
	}
	if (type != OBJ_BLOB) {
		free(buf);
		die(_("Cannot read note data from non-blob object '%s'."), arg);
	}
	strbuf_add(&d->buf, buf, len);
	free(buf);

	d->given = 1;
	return 0;
}

/*
 * Given an origin, prepare mmfile_t structure to be used by the
 * diff machinery
 */
static void fill_origin_blob(struct diff_options *opt,
			     struct blame_origin *o, mmfile_t *file, int *num_read_blob)
{
	if (!o->file.ptr) {
		enum object_type type;
		unsigned long file_size;

		(*num_read_blob)++;
		if (DIFF_OPT_TST(opt, ALLOW_TEXTCONV) &&
		    textconv_object(o->path, o->mode, &o->blob_oid, 1, &file->ptr, &file_size))
			;
		else
			file->ptr = read_sha1_file(o->blob_oid.hash, &type,
						   &file_size);
		file->size = file_size;

		if (!file->ptr)
			die("Cannot read blob %s for path %s",
			    oid_to_hex(&o->blob_oid),
			    o->path);
		o->file = *file;
	}
	else
		*file = o->file;
}

static int show_object(const unsigned char *sha1, int show_tag_object,
	struct rev_info *rev)
{
	unsigned long size;
	enum object_type type;
	char *buf = read_sha1_file(sha1, &type, &size);
	int offset = 0;

	if (!buf)
		return error("Could not read object %s", sha1_to_hex(sha1));

	if (show_tag_object)
		while (offset < size && buf[offset] != '\n') {
			int new_offset = offset + 1;
			while (new_offset < size && buf[new_offset++] != '\n')
				; /* do nothing */
			if (!prefixcmp(buf + offset, "tagger "))
				show_tagger(buf + offset + 7,
					    new_offset - offset - 7, rev);
			offset = new_offset;
		}

	if (offset < size)
		fwrite(buf + offset, size - offset, 1, stdout);
	free(buf);
	return 0;
}

/*
 * Add the lines from the named object to list, with trailing
 * newlines removed.
 */
static int string_list_add_note_lines(struct string_list *list,
				      const unsigned char *sha1)
{
	char *data;
	unsigned long len;
	enum object_type t;

	if (is_null_sha1(sha1))
		return 0;

	/* read_sha1_file NUL-terminates */
	data = read_sha1_file(sha1, &t, &len);
	if (t != OBJ_BLOB || !data || !len) {
		free(data);
		return t != OBJ_BLOB || !data;
	}

	/*
	 * If the last line of the file is EOL-terminated, this will
	 * add an empty string to the list.  But it will be removed
	 * later, along with any empty strings that came from empty
	 * lines within the file.
	 */
	string_list_split(list, data, '\n', -1);
	free(data);
	return 0;
}

static int read_mailmap_blob(struct string_list *map,
			     const char *name,
			     char **repo_abbrev)
{
	unsigned char sha1[20];
	char *buf;
	unsigned long size;
	enum object_type type;

	if (!name)
		return 0;
	if (get_sha1(name, sha1) < 0)
		return 0;

	buf = read_sha1_file(sha1, &type, &size);
	if (!buf)
		return error("unable to read mailmap object at %s", name);
	if (type != OBJ_BLOB)
		return error("mailmap is not a blob: %s", name);

	read_mailmap_string(map, buf, repo_abbrev);

	free(buf);
	return 0;
}

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;
		}
	}

static int cat_one_file(int opt, const char *exp_type, const char *obj_name)
{
	unsigned char sha1[20];
	enum object_type type;
	void *buf;
	unsigned long size;

	if (get_sha1(obj_name, sha1))
		die("Not a valid object name %s", obj_name);

	buf = NULL;
	switch (opt) {
	case 't':
		type = sha1_object_info(sha1, NULL);
		if (type > 0) {
			printf("%s\n", typename(type));
			return 0;
		}
		break;

	case 's':
		type = sha1_object_info(sha1, &size);
		if (type > 0) {
			printf("%lu\n", size);
			return 0;
		}
		break;

	case 'e':
		return !has_sha1_file(sha1);

	case 'p':
		type = sha1_object_info(sha1, NULL);
		if (type < 0)
			die("Not a valid object name %s", obj_name);

		/* custom pretty-print here */
		if (type == OBJ_TREE) {
			const char *ls_args[3] = {"ls-tree", obj_name, NULL};
			return cmd_ls_tree(2, ls_args, NULL);
		}

		buf = read_sha1_file(sha1, &type, &size);
		if (!buf)
			die("Cannot read object %s", obj_name);
		if (type == OBJ_TAG) {
			pprint_tag(sha1, buf, size);
			return 0;
		}

		/* otherwise just spit out the data */
		break;
	case 0:
		buf = read_object_with_reference(sha1, exp_type, &size, NULL);
		break;

	default:
		die("git cat-file: unknown option: %s", exp_type);
	}

/*
 * A tree "hash1" has a subdirectory at "prefix".  Come up with a
 * tree object by replacing it with another tree "hash2".
 */
static int splice_tree(const unsigned char *hash1,
		       const char *prefix,
		       const unsigned char *hash2,
		       unsigned char *result)
{
	char *subpath;
	int toplen;
	char *buf;
	unsigned long sz;
	struct tree_desc desc;
	unsigned char *rewrite_here;
	const unsigned char *rewrite_with;
	unsigned char subtree[20];
	enum object_type type;
	int status;

	subpath = strchrnul(prefix, '/');
	toplen = subpath - prefix;
	if (*subpath)
		subpath++;

	buf = read_sha1_file(hash1, &type, &sz);
	if (!buf)
		die("cannot read tree %s", sha1_to_hex(hash1));
	init_tree_desc(&desc, buf, sz);

	rewrite_here = NULL;
	while (desc.size) {
		const char *name;
		unsigned mode;
		const unsigned char *sha1;

		sha1 = tree_entry_extract(&desc, &name, &mode);
		if (strlen(name) == toplen &&
		    !memcmp(name, prefix, toplen)) {
			if (!S_ISDIR(mode))
				die("entry %s in tree %s is not a tree",
				    name, sha1_to_hex(hash1));
			rewrite_here = (unsigned char *) sha1;
			break;
		}
		update_tree_entry(&desc);
	}
	if (!rewrite_here)
		die("entry %.*s not found in tree %s",
		    toplen, prefix, sha1_to_hex(hash1));
	if (*subpath) {
		status = splice_tree(rewrite_here, subpath, hash2, subtree);
		if (status)
			return status;
		rewrite_with = subtree;
	}
	else
		rewrite_with = hash2;
	hashcpy(rewrite_here, rewrite_with);
	status = write_sha1_file(buf, sz, tree_type, result);
	free(buf);
	return status;
}

static int handle_cache(const char *path, unsigned char *sha1, const char *output)
{
	mmfile_t mmfile[3];
	mmbuffer_t result = {NULL, 0};
	struct cache_entry *ce;
	int pos, len, i, hunk_no;
	struct rerere_io_mem io;
	int marker_size = ll_merge_marker_size(path);

	/*
	 * Reproduce the conflicted merge in-core
	 */
	len = strlen(path);
	pos = cache_name_pos(path, len);
	if (0 <= pos)
		return -1;
	pos = -pos - 1;

	for (i = 0; i < 3; i++) {
		enum object_type type;
		unsigned long size;

		mmfile[i].size = 0;
		mmfile[i].ptr = NULL;
		if (active_nr <= pos)
			break;
		ce = active_cache[pos++];
		if (ce_namelen(ce) != len || memcmp(ce->name, path, len)
		    || ce_stage(ce) != i + 1)
			break;
		mmfile[i].ptr = read_sha1_file(ce->sha1, &type, &size);
		mmfile[i].size = size;
	}
	for (i = 0; i < 3; i++) {
		if (!mmfile[i].ptr && !mmfile[i].size)
			mmfile[i].ptr = xstrdup("");
	}
	ll_merge(&result, path, &mmfile[0],
		 &mmfile[1], "ours",
		 &mmfile[2], "theirs", 0);
	for (i = 0; i < 3; i++)
		free(mmfile[i].ptr);

	memset(&io, 0, sizeof(io));
	io.io.getline = rerere_mem_getline;
	if (output)
		io.io.output = fopen(output, "w");
	else
		io.io.output = NULL;
	strbuf_init(&io.input, 0);
	strbuf_attach(&io.input, result.ptr, result.size, result.size);

	hunk_no = handle_path(sha1, (struct rerere_io *)&io, marker_size);
	strbuf_release(&io.input);
	if (io.io.output)
		fclose(io.io.output);
	return hunk_no;
}

static void *lock_and_read_sha1_file(const unsigned char *sha1, enum object_type *type, unsigned long *size)
{
	void *data;

	grep_read_lock();
	data = read_sha1_file(sha1, type, size);
	grep_read_unlock();
	return data;
}

static void *lock_and_read_oid_file(const struct object_id *oid, enum object_type *type, unsigned long *size)
{
	void *data;

	grep_read_lock();
	data = read_sha1_file(oid->hash, type, size);
	grep_read_unlock();
	return data;
}