builtin-tar-tree.c - jrn/git - Git at Google

 /*
  * Copyright (c) 2005, 2006 Rene Scharfe
  */
 #include <time.h>
 #include "cache.h"
 #include "tree-walk.h"
 #include "commit.h"
 #include "strbuf.h"
 #include "tar.h"
 #include "builtin.h"
 #include "pkt-line.h"

 #define RECORDSIZE	(512)
 #define BLOCKSIZE	(RECORDSIZE * 20)

 static const char tar_tree_usage[] =
 "git-tar-tree [--remote=<repo>] <ent> [basedir]";

 static char block[BLOCKSIZE];
 static unsigned long offset;

 static time_t archive_time;

 /* tries hard to write, either succeeds or dies in the attempt */
 static void reliable_write(const void *data, unsigned long size)
 {
 	const char *buf = data;

 	while (size > 0) {
 		long ret = xwrite(1, buf, size);
 		if (ret < 0) {
 			if (errno == EPIPE)
 				exit(0);
 			die("git-tar-tree: %s", strerror(errno));
 		} else if (!ret) {
 			die("git-tar-tree: disk full?");
 		}
 		size -= ret;
 		buf += ret;
 	}
 }

 /* writes out the whole block, but only if it is full */
 static void write_if_needed(void)
 {
 	if (offset == BLOCKSIZE) {
 		reliable_write(block, BLOCKSIZE);
 		offset = 0;
 	}
 }

 /*
  * queues up writes, so that all our write(2) calls write exactly one
  * full block; pads writes to RECORDSIZE
  */
 static void write_blocked(const void *data, unsigned long size)
 {
 	const char *buf = data;
 	unsigned long tail;

 	if (offset) {
 		unsigned long chunk = BLOCKSIZE - offset;
 		if (size < chunk)
 			chunk = size;
 		memcpy(block + offset, buf, chunk);
 		size -= chunk;
 		offset += chunk;
 		buf += chunk;
 		write_if_needed();
 	}
 	while (size >= BLOCKSIZE) {
 		reliable_write(buf, BLOCKSIZE);
 		size -= BLOCKSIZE;
 		buf += BLOCKSIZE;
 	}
 	if (size) {
 		memcpy(block + offset, buf, size);
 		offset += size;
 	}
 	tail = offset % RECORDSIZE;
 	if (tail)  {
 		memset(block + offset, 0, RECORDSIZE - tail);
 		offset += RECORDSIZE - tail;
 	}
 	write_if_needed();
 }

 /*
  * The end of tar archives is marked by 2*512 nul bytes and after that
  * follows the rest of the block (if any).
  */
 static void write_trailer(void)
 {
 	int tail = BLOCKSIZE - offset;
 	memset(block + offset, 0, tail);
 	reliable_write(block, BLOCKSIZE);
 	if (tail < 2 * RECORDSIZE) {
 		memset(block, 0, offset);
 		reliable_write(block, BLOCKSIZE);
 	}
 }

 static void strbuf_append_string(struct strbuf *sb, const char *s)
 {
 	int slen = strlen(s);
 	int total = sb->len + slen;
 	if (total > sb->alloc) {
 		sb->buf = xrealloc(sb->buf, total);
 		sb->alloc = total;
 	}
 	memcpy(sb->buf + sb->len, s, slen);
 	sb->len = total;
 }

 /*
  * pax extended header records have the format "%u %s=%s\n".  %u contains
  * the size of the whole string (including the %u), the first %s is the
  * keyword, the second one is the value.  This function constructs such a
  * string and appends it to a struct strbuf.
  */
 static void strbuf_append_ext_header(struct strbuf *sb, const char *keyword,
                                      const char *value, unsigned int valuelen)
 {
 	char *p;
 	int len, total, tmp;

 	/* "%u %s=%s\n" */
 	len = 1 + 1 + strlen(keyword) + 1 + valuelen + 1;
 	for (tmp = len; tmp > 9; tmp /= 10)
 		len++;

 	total = sb->len + len;
 	if (total > sb->alloc) {
 		sb->buf = xrealloc(sb->buf, total);
 		sb->alloc = total;
 	}

 	p = sb->buf;
 	p += sprintf(p, "%u %s=", len, keyword);
 	memcpy(p, value, valuelen);
 	p += valuelen;
 	*p = '\n';
 	sb->len = total;
 }

 static unsigned int ustar_header_chksum(const struct ustar_header *header)
 {
 	char *p = (char *)header;
 	unsigned int chksum = 0;
 	while (p < header->chksum)
 		chksum += *p++;
 	chksum += sizeof(header->chksum) * ' ';
 	p += sizeof(header->chksum);
 	while (p < (char *)header + sizeof(struct ustar_header))
 		chksum += *p++;
 	return chksum;
 }

 static int get_path_prefix(const struct strbuf *path, int maxlen)
 {
 	int i = path->len;
 	if (i > maxlen)
 		i = maxlen;
 	do {
 		i--;
 	} while (i > 0 && path->buf[i] != '/');
 	return i;
 }

 static void write_entry(const unsigned char *sha1, struct strbuf *path,
                         unsigned int mode, void *buffer, unsigned long size)
 {
 	struct ustar_header header;
 	struct strbuf ext_header;

 	memset(&header, 0, sizeof(header));
 	ext_header.buf = NULL;
 	ext_header.len = ext_header.alloc = 0;

 	if (!sha1) {
 		*header.typeflag = TYPEFLAG_GLOBAL_HEADER;
 		mode = 0100666;
 		strcpy(header.name, "pax_global_header");
 	} else if (!path) {
 		*header.typeflag = TYPEFLAG_EXT_HEADER;
 		mode = 0100666;
 		sprintf(header.name, "%s.paxheader", sha1_to_hex(sha1));
 	} else {
 		if (S_ISDIR(mode)) {
 			*header.typeflag = TYPEFLAG_DIR;
 			mode |= 0777;
 		} else if (S_ISLNK(mode)) {
 			*header.typeflag = TYPEFLAG_LNK;
 			mode |= 0777;
 		} else if (S_ISREG(mode)) {
 			*header.typeflag = TYPEFLAG_REG;
 			mode |= (mode & 0100) ? 0777 : 0666;
 		} else {
 			error("unsupported file mode: 0%o (SHA1: %s)",
 			      mode, sha1_to_hex(sha1));
 			return;
 		}
 		if (path->len > sizeof(header.name)) {
 			int plen = get_path_prefix(path, sizeof(header.prefix));
 			int rest = path->len - plen - 1;
 			if (plen > 0 && rest <= sizeof(header.name)) {
 				memcpy(header.prefix, path->buf, plen);
 				memcpy(header.name, path->buf + plen + 1, rest);
 			} else {
 				sprintf(header.name, "%s.data",
 				        sha1_to_hex(sha1));
 				strbuf_append_ext_header(&ext_header, "path",
 				                         path->buf, path->len);
 			}
 		} else
 			memcpy(header.name, path->buf, path->len);
 	}

 	if (S_ISLNK(mode) && buffer) {
 		if (size > sizeof(header.linkname)) {
 			sprintf(header.linkname, "see %s.paxheader",
 			        sha1_to_hex(sha1));
 			strbuf_append_ext_header(&ext_header, "linkpath",
 			                         buffer, size);
 		} else
 			memcpy(header.linkname, buffer, size);
 	}

 	sprintf(header.mode, "%07o", mode & 07777);
 	sprintf(header.size, "%011lo", S_ISREG(mode) ? size : 0);
 	sprintf(header.mtime, "%011lo", archive_time);

 	/* XXX: should we provide more meaningful info here? */
 	sprintf(header.uid, "%07o", 0);
 	sprintf(header.gid, "%07o", 0);
 	safe_strncpy(header.uname, "git", sizeof(header.uname));
 	safe_strncpy(header.gname, "git", sizeof(header.gname));
 	sprintf(header.devmajor, "%07o", 0);
 	sprintf(header.devminor, "%07o", 0);

 	memcpy(header.magic, "ustar", 6);
 	memcpy(header.version, "00", 2);

 	sprintf(header.chksum, "%07o", ustar_header_chksum(&header));

 	if (ext_header.len > 0) {
 		write_entry(sha1, NULL, 0, ext_header.buf, ext_header.len);
 		free(ext_header.buf);
 	}
 	write_blocked(&header, sizeof(header));
 	if (S_ISREG(mode) && buffer && size > 0)
 		write_blocked(buffer, size);
 }

 static void write_global_extended_header(const unsigned char *sha1)
 {
 	struct strbuf ext_header;
 	ext_header.buf = NULL;
 	ext_header.len = ext_header.alloc = 0;
 	strbuf_append_ext_header(&ext_header, "comment", sha1_to_hex(sha1), 40);
 	write_entry(NULL, NULL, 0, ext_header.buf, ext_header.len);
 	free(ext_header.buf);
 }

 static void traverse_tree(struct tree_desc *tree, struct strbuf *path)
 {
 	int pathlen = path->len;
 	struct name_entry entry;

 	while (tree_entry(tree, &entry)) {
 		void *eltbuf;
 		char elttype[20];
 		unsigned long eltsize;

 		eltbuf = read_sha1_file(entry.sha1, elttype, &eltsize);
 		if (!eltbuf)
 			die("cannot read %s", sha1_to_hex(entry.sha1));

 		path->len = pathlen;
 		strbuf_append_string(path, entry.path);
 		if (S_ISDIR(entry.mode))
 			strbuf_append_string(path, "/");

 		write_entry(entry.sha1, path, entry.mode, eltbuf, eltsize);

 		if (S_ISDIR(entry.mode)) {
 			struct tree_desc subtree;
 			subtree.buf = eltbuf;
 			subtree.size = eltsize;
 			traverse_tree(&subtree, path);
 		}
 		free(eltbuf);
 	}
 }

 static int generate_tar(int argc, const char **argv, char** envp)
 {
 	unsigned char sha1[20], tree_sha1[20];
 	struct commit *commit;
 	struct tree_desc tree;
 	struct strbuf current_path;

 	current_path.buf = xmalloc(PATH_MAX);
 	current_path.alloc = PATH_MAX;
 	current_path.len = current_path.eof = 0;

 	setup_git_directory();
 	git_config(git_default_config);

 	switch (argc) {
 	case 3:
 		strbuf_append_string(&current_path, argv[2]);
 		strbuf_append_string(&current_path, "/");
 		/* FALLTHROUGH */
 	case 2:
 		if (get_sha1(argv[1], sha1))
 			die("Not a valid object name %s", argv[1]);
 		break;
 	default:
 		usage(tar_tree_usage);
 	}

 	commit = lookup_commit_reference_gently(sha1, 1);
 	if (commit) {
 		write_global_extended_header(commit->object.sha1);
 		archive_time = commit->date;
 	} else
 		archive_time = time(NULL);

 	tree.buf = read_object_with_reference(sha1, tree_type, &tree.size,
 	                                      tree_sha1);
 	if (!tree.buf)
 		die("not a reference to a tag, commit or tree object: %s",
 		    sha1_to_hex(sha1));

 	if (current_path.len > 0)
 		write_entry(tree_sha1, &current_path, 040777, NULL, 0);
 	traverse_tree(&tree, &current_path);
 	write_trailer();
 	free(current_path.buf);
 	return 0;
 }

 static const char *exec = "git-upload-tar";

 static int remote_tar(int argc, const char **argv)
 {
 	int fd[2], ret, len;
 	pid_t pid;
 	char buf[1024];
 	char *url;

 	if (argc < 3 || 4 < argc)
 		usage(tar_tree_usage);

 	/* --remote=<repo> */
 	url = strdup(argv[1]+9);
 	pid = git_connect(fd, url, exec);
 	if (pid < 0)
 		return 1;

 	packet_write(fd[1], "want %s\n", argv[2]);
 	if (argv[3])
 		packet_write(fd[1], "base %s\n", argv[3]);
 	packet_flush(fd[1]);

 	len = packet_read_line(fd[0], buf, sizeof(buf));
 	if (!len)
 		die("git-tar-tree: expected ACK/NAK, got EOF");
 	if (buf[len-1] == '\n')
 		buf[--len] = 0;
 	if (strcmp(buf, "ACK")) {
 		if (5 < len && !strncmp(buf, "NACK ", 5))
 			die("git-tar-tree: NACK %s", buf + 5);
 		die("git-tar-tree: protocol error");
 	}
 	/* expect a flush */
 	len = packet_read_line(fd[0], buf, sizeof(buf));
 	if (len)
 		die("git-tar-tree: expected a flush");

 	/* Now, start reading from fd[0] and spit it out to stdout */
 	ret = copy_fd(fd[0], 1);
 	close(fd[0]);

 	ret |= finish_connect(pid);
 	return !!ret;
 }

 int cmd_tar_tree(int argc, const char **argv, char **envp)
 {
 	if (argc < 2)
 		usage(tar_tree_usage);
 	if (!strncmp("--remote=", argv[1], 9))
 		return remote_tar(argc, argv);
 	return generate_tar(argc, argv, envp);
 }

 /* ustar header + extended global header content */
 #define HEADERSIZE (2 * RECORDSIZE)

 int cmd_get_tar_commit_id(int argc, const char **argv, char **envp)
 {
 	char buffer[HEADERSIZE];
 	struct ustar_header *header = (struct ustar_header *)buffer;
 	char *content = buffer + RECORDSIZE;
 	ssize_t n;

 	n = xread(0, buffer, HEADERSIZE);
 	if (n < HEADERSIZE)
 		die("git-get-tar-commit-id: read error");
 	if (header->typeflag[0] != 'g')
 		return 1;
 	if (memcmp(content, "52 comment=", 11))
 		return 1;

 	n = xwrite(1, content + 11, 41);
 	if (n < 41)
 		die("git-get-tar-commit-id: write error");

 	return 0;
 }
	/*
	* Copyright (c) 2005, 2006 Rene Scharfe
	*/
	#include <time.h>
	#include "cache.h"
	#include "tree-walk.h"
	#include "commit.h"
	#include "strbuf.h"
	#include "tar.h"
	#include "builtin.h"
	#include "pkt-line.h"

	#define RECORDSIZE (512)
	#define BLOCKSIZE (RECORDSIZE * 20)

	static const char tar_tree_usage[] =
	"git-tar-tree [--remote=<repo>] <ent> [basedir]";

	static char block[BLOCKSIZE];
	static unsigned long offset;

	static time_t archive_time;

	/* tries hard to write, either succeeds or dies in the attempt */
	static void reliable_write(const void *data, unsigned long size)
	{
	const char *buf = data;

	while (size > 0) {
	long ret = xwrite(1, buf, size);
	if (ret < 0) {
	if (errno == EPIPE)
	exit(0);
	die("git-tar-tree: %s", strerror(errno));
	} else if (!ret) {
	die("git-tar-tree: disk full?");
	}
	size -= ret;
	buf += ret;
	}
	}

	/* writes out the whole block, but only if it is full */
	static void write_if_needed(void)
	{
	if (offset == BLOCKSIZE) {
	reliable_write(block, BLOCKSIZE);
	offset = 0;
	}
	}

	/*
	* queues up writes, so that all our write(2) calls write exactly one
	* full block; pads writes to RECORDSIZE
	*/
	static void write_blocked(const void *data, unsigned long size)
	{
	const char *buf = data;
	unsigned long tail;

	if (offset) {
	unsigned long chunk = BLOCKSIZE - offset;
	if (size < chunk)
	chunk = size;
	memcpy(block + offset, buf, chunk);
	size -= chunk;
	offset += chunk;
	buf += chunk;
	write_if_needed();
	}
	while (size >= BLOCKSIZE) {
	reliable_write(buf, BLOCKSIZE);
	size -= BLOCKSIZE;
	buf += BLOCKSIZE;
	}
	if (size) {
	memcpy(block + offset, buf, size);
	offset += size;
	}
	tail = offset % RECORDSIZE;
	if (tail) {
	memset(block + offset, 0, RECORDSIZE - tail);
	offset += RECORDSIZE - tail;
	}
	write_if_needed();
	}

	/*
	* The end of tar archives is marked by 2*512 nul bytes and after that
	* follows the rest of the block (if any).
	*/
	static void write_trailer(void)
	{
	int tail = BLOCKSIZE - offset;
	memset(block + offset, 0, tail);
	reliable_write(block, BLOCKSIZE);
	if (tail < 2 * RECORDSIZE) {
	memset(block, 0, offset);
	reliable_write(block, BLOCKSIZE);
	}
	}

	static void strbuf_append_string(struct strbuf sb, const char s)
	{
	int slen = strlen(s);
	int total = sb->len + slen;
	if (total > sb->alloc) {
	sb->buf = xrealloc(sb->buf, total);
	sb->alloc = total;
	}
	memcpy(sb->buf + sb->len, s, slen);
	sb->len = total;
	}

	/*
	* pax extended header records have the format "%u %s=%s\n". %u contains
	* the size of the whole string (including the %u), the first %s is the
	* keyword, the second one is the value. This function constructs such a
	* string and appends it to a struct strbuf.
	*/
	static void strbuf_append_ext_header(struct strbuf sb, const char keyword,
	const char *value, unsigned int valuelen)
	{
	char *p;
	int len, total, tmp;

	/* "%u %s=%s\n" */
	len = 1 + 1 + strlen(keyword) + 1 + valuelen + 1;
	for (tmp = len; tmp > 9; tmp /= 10)
	len++;

	total = sb->len + len;
	if (total > sb->alloc) {
	sb->buf = xrealloc(sb->buf, total);
	sb->alloc = total;
	}

	p = sb->buf;
	p += sprintf(p, "%u %s=", len, keyword);
	memcpy(p, value, valuelen);
	p += valuelen;
	*p = '\n';
	sb->len = total;
	}

	static unsigned int ustar_header_chksum(const struct ustar_header *header)
	{
	char p = (char )header;
	unsigned int chksum = 0;
	while (p < header->chksum)
	chksum += *p++;
	chksum += sizeof(header->chksum) * ' ';
	p += sizeof(header->chksum);
	while (p < (char *)header + sizeof(struct ustar_header))
	chksum += *p++;
	return chksum;
	}

	static int get_path_prefix(const struct strbuf *path, int maxlen)
	{
	int i = path->len;
	if (i > maxlen)
	i = maxlen;
	do {
	i--;
	} while (i > 0 && path->buf[i] != '/');
	return i;
	}

	static void write_entry(const unsigned char sha1, struct strbuf path,
	unsigned int mode, void *buffer, unsigned long size)
	{
	struct ustar_header header;
	struct strbuf ext_header;

	memset(&header, 0, sizeof(header));
	ext_header.buf = NULL;
	ext_header.len = ext_header.alloc = 0;

	if (!sha1) {
	*header.typeflag = TYPEFLAG_GLOBAL_HEADER;
	mode = 0100666;
	strcpy(header.name, "pax_global_header");
	} else if (!path) {
	*header.typeflag = TYPEFLAG_EXT_HEADER;
	mode = 0100666;
	sprintf(header.name, "%s.paxheader", sha1_to_hex(sha1));
	} else {
	if (S_ISDIR(mode)) {
	*header.typeflag = TYPEFLAG_DIR;
	mode \|= 0777;
	} else if (S_ISLNK(mode)) {
	*header.typeflag = TYPEFLAG_LNK;
	mode \|= 0777;
	} else if (S_ISREG(mode)) {
	*header.typeflag = TYPEFLAG_REG;
	mode \|= (mode & 0100) ? 0777 : 0666;
	} else {
	error("unsupported file mode: 0%o (SHA1: %s)",
	mode, sha1_to_hex(sha1));
	return;
	}
	if (path->len > sizeof(header.name)) {
	int plen = get_path_prefix(path, sizeof(header.prefix));
	int rest = path->len - plen - 1;
	if (plen > 0 && rest <= sizeof(header.name)) {
	memcpy(header.prefix, path->buf, plen);
	memcpy(header.name, path->buf + plen + 1, rest);
	} else {
	sprintf(header.name, "%s.data",
	sha1_to_hex(sha1));
	strbuf_append_ext_header(&ext_header, "path",
	path->buf, path->len);
	}
	} else
	memcpy(header.name, path->buf, path->len);
	}

	if (S_ISLNK(mode) && buffer) {
	if (size > sizeof(header.linkname)) {
	sprintf(header.linkname, "see %s.paxheader",
	sha1_to_hex(sha1));
	strbuf_append_ext_header(&ext_header, "linkpath",
	buffer, size);
	} else
	memcpy(header.linkname, buffer, size);
	}

	sprintf(header.mode, "%07o", mode & 07777);
	sprintf(header.size, "%011lo", S_ISREG(mode) ? size : 0);
	sprintf(header.mtime, "%011lo", archive_time);

	/* XXX: should we provide more meaningful info here? */
	sprintf(header.uid, "%07o", 0);
	sprintf(header.gid, "%07o", 0);
	safe_strncpy(header.uname, "git", sizeof(header.uname));
	safe_strncpy(header.gname, "git", sizeof(header.gname));
	sprintf(header.devmajor, "%07o", 0);
	sprintf(header.devminor, "%07o", 0);

	memcpy(header.magic, "ustar", 6);
	memcpy(header.version, "00", 2);

	sprintf(header.chksum, "%07o", ustar_header_chksum(&header));

	if (ext_header.len > 0) {
	write_entry(sha1, NULL, 0, ext_header.buf, ext_header.len);
	free(ext_header.buf);
	}
	write_blocked(&header, sizeof(header));
	if (S_ISREG(mode) && buffer && size > 0)
	write_blocked(buffer, size);
	}

	static void write_global_extended_header(const unsigned char *sha1)
	{
	struct strbuf ext_header;
	ext_header.buf = NULL;
	ext_header.len = ext_header.alloc = 0;
	strbuf_append_ext_header(&ext_header, "comment", sha1_to_hex(sha1), 40);
	write_entry(NULL, NULL, 0, ext_header.buf, ext_header.len);
	free(ext_header.buf);
	}

	static void traverse_tree(struct tree_desc tree, struct strbuf path)
	{
	int pathlen = path->len;
	struct name_entry entry;

	while (tree_entry(tree, &entry)) {
	void *eltbuf;
	char elttype[20];
	unsigned long eltsize;

	eltbuf = read_sha1_file(entry.sha1, elttype, &eltsize);
	if (!eltbuf)
	die("cannot read %s", sha1_to_hex(entry.sha1));

	path->len = pathlen;
	strbuf_append_string(path, entry.path);
	if (S_ISDIR(entry.mode))
	strbuf_append_string(path, "/");

	write_entry(entry.sha1, path, entry.mode, eltbuf, eltsize);

	if (S_ISDIR(entry.mode)) {
	struct tree_desc subtree;
	subtree.buf = eltbuf;
	subtree.size = eltsize;
	traverse_tree(&subtree, path);
	}
	free(eltbuf);
	}
	}

	static int generate_tar(int argc, const char argv, char envp)
	{
	unsigned char sha1[20], tree_sha1[20];
	struct commit *commit;
	struct tree_desc tree;
	struct strbuf current_path;

	current_path.buf = xmalloc(PATH_MAX);
	current_path.alloc = PATH_MAX;
	current_path.len = current_path.eof = 0;

	setup_git_directory();
	git_config(git_default_config);

	switch (argc) {
	case 3:
	strbuf_append_string(&current_path, argv[2]);
	strbuf_append_string(&current_path, "/");
	/* FALLTHROUGH */
	case 2:
	if (get_sha1(argv[1], sha1))
	die("Not a valid object name %s", argv[1]);
	break;
	default:
	usage(tar_tree_usage);
	}

	commit = lookup_commit_reference_gently(sha1, 1);
	if (commit) {
	write_global_extended_header(commit->object.sha1);
	archive_time = commit->date;
	} else
	archive_time = time(NULL);

	tree.buf = read_object_with_reference(sha1, tree_type, &tree.size,
	tree_sha1);
	if (!tree.buf)
	die("not a reference to a tag, commit or tree object: %s",
	sha1_to_hex(sha1));

	if (current_path.len > 0)
	write_entry(tree_sha1, &current_path, 040777, NULL, 0);
	traverse_tree(&tree, &current_path);
	write_trailer();
	free(current_path.buf);
	return 0;
	}

	static const char *exec = "git-upload-tar";

	static int remote_tar(int argc, const char **argv)
	{
	int fd[2], ret, len;
	pid_t pid;
	char buf[1024];
	char *url;

	if (argc < 3 \|\| 4 < argc)
	usage(tar_tree_usage);

	/* --remote=<repo> */
	url = strdup(argv[1]+9);
	pid = git_connect(fd, url, exec);
	if (pid < 0)
	return 1;

	packet_write(fd[1], "want %s\n", argv[2]);
	if (argv[3])
	packet_write(fd[1], "base %s\n", argv[3]);
	packet_flush(fd[1]);

	len = packet_read_line(fd[0], buf, sizeof(buf));
	if (!len)
	die("git-tar-tree: expected ACK/NAK, got EOF");
	if (buf[len-1] == '\n')
	buf[--len] = 0;
	if (strcmp(buf, "ACK")) {
	if (5 < len && !strncmp(buf, "NACK ", 5))
	die("git-tar-tree: NACK %s", buf + 5);
	die("git-tar-tree: protocol error");
	}
	/* expect a flush */
	len = packet_read_line(fd[0], buf, sizeof(buf));
	if (len)
	die("git-tar-tree: expected a flush");

	/* Now, start reading from fd[0] and spit it out to stdout */
	ret = copy_fd(fd[0], 1);
	close(fd[0]);

	ret \|= finish_connect(pid);
	return !!ret;
	}

	int cmd_tar_tree(int argc, const char argv, char envp)
	{
	if (argc < 2)
	usage(tar_tree_usage);
	if (!strncmp("--remote=", argv[1], 9))
	return remote_tar(argc, argv);
	return generate_tar(argc, argv, envp);
	}

	/* ustar header + extended global header content */
	#define HEADERSIZE (2 * RECORDSIZE)

	int cmd_get_tar_commit_id(int argc, const char argv, char envp)
	{
	char buffer[HEADERSIZE];
	struct ustar_header header = (struct ustar_header )buffer;
	char *content = buffer + RECORDSIZE;
	ssize_t n;

	n = xread(0, buffer, HEADERSIZE);
	if (n < HEADERSIZE)
	die("git-get-tar-commit-id: read error");
	if (header->typeflag[0] != 'g')
	return 1;
	if (memcmp(content, "52 comment=", 11))
	return 1;

	n = xwrite(1, content + 11, 41);
	if (n < 41)
	die("git-get-tar-commit-id: write error");

	return 0;
	}