Built-in git-get-tar-commit-id

By being an internal command git-get-commit-id can make use of
struct ustar_header and other stuff and stops wasting precious
disk space.

Note: I recycled one of the two "tar-tree" entries instead of
splitting that cleanup into a separate patch.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -144,7 +144,7 @@ SCRIPTS = $(patsubst %.sh,%,$(SCRIPT_SH)) \
 
 # The ones that do not have to link with lcrypto, lz nor xdiff.
 SIMPLE_PROGRAMS = \
-	git-get-tar-commit-id$X git-mailsplit$X \
+	git-mailsplit$X \
 	git-stripspace$X git-daemon$X
 
 # ... and all the rest that could be moved out of bindir to gitexecdir
@@ -169,7 +169,7 @@ BUILT_INS = git-log$X git-whatchanged$X git-show$X \
 	git-grep$X git-add$X git-rm$X git-rev-list$X \
 	git-check-ref-format$X git-rev-parse$X \
 	git-init-db$X git-tar-tree$X git-upload-tar$X git-format-patch$X \
-	git-ls-files$X git-ls-tree$X \
+	git-ls-files$X git-ls-tree$X git-get-tar-commit-id$X \
 	git-read-tree$X git-commit-tree$X \
 	git-apply$X git-show-branch$X git-diff-files$X \
 	git-diff-index$X git-diff-stages$X git-diff-tree$X git-cat-file$X

builtin-tar-tree.c

@@ -402,3 +402,28 @@ int cmd_tar_tree(int argc, const char **argv, char **envp)
 		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;
+}

builtin.h

@@ -32,6 +32,7 @@ extern int cmd_check_ref_format(int argc, const char **argv, char **envp);
 extern int cmd_init_db(int argc, const char **argv, char **envp);
 extern int cmd_tar_tree(int argc, const char **argv, char **envp);
 extern int cmd_upload_tar(int argc, const char **argv, char **envp);
+extern int cmd_get_tar_commit_id(int argc, const char **argv, char **envp);
 extern int cmd_ls_files(int argc, const char **argv, char **envp);
 extern int cmd_ls_tree(int argc, const char **argv, char **envp);
 extern int cmd_read_tree(int argc, const char **argv, char **envp);

git.c

@@ -163,7 +163,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		{ "add", cmd_add },
 		{ "rev-list", cmd_rev_list },
 		{ "init-db", cmd_init_db },
-		{ "tar-tree", cmd_tar_tree },
+		{ "get-tar-commit-id", cmd_get_tar_commit_id },
 		{ "upload-tar", cmd_upload_tar },
 		{ "check-ref-format", cmd_check_ref_format },
 		{ "ls-files", cmd_ls_files },