1 files changed, 52 insertions, 0 deletions
diff --git a/builtin/get-tar-commit-id.c b/builtin/get-tar-commit-id.c
new file mode 100644
index 000000000000..491af9202dc9
--- /dev/null
+++ b/builtin/get-tar-commit-id.c
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2005, 2006 Rene Scharfe
+ */
+#include "cache.h"
+#include "commit.h"
+#include "tar.h"
+#include "builtin.h"
+#include "quote.h"
+
+static const char builtin_get_tar_commit_id_usage[] =
+"git get-tar-commit-id";
+
+/* ustar header + extended global header content */
+#define RECORDSIZE	(512)
+#define HEADERSIZE (2 * RECORDSIZE)
+
+int cmd_get_tar_commit_id(int argc, const char **argv, const char *prefix)
+{
+	char buffer[HEADERSIZE];
+	struct ustar_header *header = (struct ustar_header *)buffer;
+	char *content = buffer + RECORDSIZE;
+	const char *comment;
+	ssize_t n;
+	long len;
+	char *end;
+
+	if (argc != 1)
+		usage(builtin_get_tar_commit_id_usage);
+
+	n = read_in_full(0, buffer, HEADERSIZE);
+	if (n < 0)
+		die_errno("git get-tar-commit-id: read error");
+	if (n != HEADERSIZE)
+		die_errno("git get-tar-commit-id: EOF before reading tar header");
+	if (header->typeflag[0] != 'g')
+		return 1;
+
+	len = strtol(content, &end, 10);
+	if (errno == ERANGE || end == content || len < 0)
+		return 1;
+	if (!skip_prefix(end, " comment=", &comment))
+		return 1;
+	len -= comment - content;
+	if (len < 1 || !(len % 2) ||
+	    hash_algo_by_length((len - 1) / 2) == GIT_HASH_UNKNOWN)
+		return 1;
+
+	if (write_in_full(1, comment, len) < 0)
+		die_errno("git get-tar-commit-id: write error");
+
+	return 0;
+}