Create pack-write.c for common pack writing code

Include a generalized fixup_pack_header_footer() in this new file.
Needed by git-repack --max-pack-size feature in a later patchset.

[sp: Moved close(pack_fd) to callers, to support index-pack, and
     changed name to better indicate it is for packfiles.]

Signed-off-by: Dana L. How <danahow@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/pack-write.c b/pack-write.c
new file mode 100644
index 0000000000..de72f44dc8
--- /dev/null
+++ b/pack-write.c
@@ -0,0 +1,39 @@
+#include "cache.h"
+#include "pack.h"
+
+void fixup_pack_header_footer(int pack_fd,
+			 unsigned char *pack_file_sha1,
+			 const char *pack_name,
+			 uint32_t object_count)
+{
+	static const int buf_sz = 128 * 1024;
+	SHA_CTX c;
+	struct pack_header hdr;
+	char *buf;
+
+	if (lseek(pack_fd, 0, SEEK_SET) != 0)
+		die("Failed seeking to start: %s", strerror(errno));
+	if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
+		die("Unable to reread header of %s: %s", pack_name, strerror(errno));
+	if (lseek(pack_fd, 0, SEEK_SET) != 0)
+		die("Failed seeking to start: %s", strerror(errno));
+	hdr.hdr_entries = htonl(object_count);
+	write_or_die(pack_fd, &hdr, sizeof(hdr));
+
+	SHA1_Init(&c);
+	SHA1_Update(&c, &hdr, sizeof(hdr));
+
+	buf = xmalloc(buf_sz);
+	for (;;) {
+		size_t n = xread(pack_fd, buf, buf_sz);
+		if (!n)
+			break;
+		if (n < 0)
+			die("Failed to checksum %s: %s", pack_name, strerror(errno));
+		SHA1_Update(&c, buf, n);
+	}
+	free(buf);
+
+	SHA1_Final(pack_file_sha1, &c);
+	write_or_die(pack_fd, pack_file_sha1, 20);
+}