deprecate the new loose object header format

Now that we encourage and actively preserve objects in a packed form
more agressively than we did at the time the new loose object format and
core.legacyheaders were introduced, that extra loose object format
doesn't appear to be worth it anymore.

Because the packing of loose objects has to go through the delta match
loop anyway, and since most of them should end up being deltified in
most cases, there is really little advantage to have this parallel loose
object format as the CPU savings it might provide is rather lost in the
noise in the end.

This patch gets rid of core.legacyheaders, preserve the legacy format as
the only writable loose object format and deprecate the other one to
keep things simpler.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/config.txt

@@ -209,19 +209,6 @@ core.compression::
 	compression, and 1..9 are various speed/size tradeoffs, 9 being
 	slowest.
 
-core.legacyheaders::
-	A boolean which
-	changes the format of loose objects so that they are more
-	efficient to pack and to send out of the repository over git
-	native protocol, since v1.4.2.  However, loose objects
-	written in the new format cannot be read by git older than
-	that version; people fetching from your repository using
-	older versions of git over dumb transports (e.g. http)
-	will also be affected.
-+
-To let git use the new loose object format, you have to
-set core.legacyheaders to false.
-
 core.packedGitWindowSize::
 	Number of bytes of a pack file to map into memory in a
 	single mapping operation.  Larger window sizes may allow

builtin-pack-objects.c

@@ -346,56 +346,6 @@ static void copy_pack_data(struct sha1file *f,
 	}
 }
 
-static int check_loose_inflate(unsigned char *data, unsigned long len, unsigned long expect)
-{
-	z_stream stream;
-	unsigned char fakebuf[4096];
-	int st;
-
-	memset(&stream, 0, sizeof(stream));
-	stream.next_in = data;
-	stream.avail_in = len;
-	stream.next_out = fakebuf;
-	stream.avail_out = sizeof(fakebuf);
-	inflateInit(&stream);
-
-	while (1) {
-		st = inflate(&stream, Z_FINISH);
-		if (st == Z_STREAM_END || st == Z_OK) {
-			st = (stream.total_out == expect &&
-			      stream.total_in == len) ? 0 : -1;
-			break;
-		}
-		if (st != Z_BUF_ERROR) {
-			st = -1;
-			break;
-		}
-		stream.next_out = fakebuf;
-		stream.avail_out = sizeof(fakebuf);
-	}
-	inflateEnd(&stream);
-	return st;
-}
-
-static int revalidate_loose_object(struct object_entry *entry,
-				   unsigned char *map,
-				   unsigned long mapsize)
-{
-	/* we already know this is a loose object with new type header. */
-	enum object_type type;
-	unsigned long size, used;
-
-	if (pack_to_stdout)
-		return 0;
-
-	used = unpack_object_header_gently(map, mapsize, &type, &size);
-	if (!used)
-		return -1;
-	map += used;
-	mapsize -= used;
-	return check_loose_inflate(map, mapsize, size);
-}
-
 static unsigned long write_object(struct sha1file *f,
 				  struct object_entry *entry)
 {
@@ -427,25 +377,6 @@ static unsigned long write_object(struct sha1file *f,
 				 * and we do not need to deltify it.
 				 */
 
-	if (!no_reuse_object && !entry->in_pack && !entry->delta) {
-		unsigned char *map;
-		unsigned long mapsize;
-		map = map_sha1_file(entry->sha1, &mapsize);
-		if (map && !legacy_loose_object(map)) {
-			/* We can copy straight into the pack file */
-			if (revalidate_loose_object(entry, map, mapsize))
-				die("corrupt loose object %s",
-				    sha1_to_hex(entry->sha1));
-			sha1write(f, map, mapsize);
-			munmap(map, mapsize);
-			written++;
-			reused++;
-			return mapsize;
-		}
-		if (map)
-			munmap(map, mapsize);
-	}
-
 	if (!to_reuse) {
 		buf = read_sha1_file(entry->sha1, &type, &size);
 		if (!buf)

cache.h

@@ -273,7 +273,6 @@ extern void rollback_lock_file(struct lock_file *);
 extern int delete_ref(const char *, const unsigned char *sha1);
 
 /* Environment bits from configuration mechanism */
-extern int use_legacy_headers;
 extern int trust_executable_bit;
 extern int has_symlinks;
 extern int assume_unchanged;
@@ -354,7 +353,6 @@ extern int move_temp_to_file(const char *tmpfile, const char *filename);
 extern int has_sha1_pack(const unsigned char *sha1, const char **ignore);
 extern int has_sha1_file(const unsigned char *sha1);
 extern void *map_sha1_file(const unsigned char *sha1, unsigned long *);
-extern int legacy_loose_object(unsigned char *);
 
 extern int has_pack_file(const unsigned char *sha1);
 extern int has_pack_index(const unsigned char *sha1);

config.c

@@ -299,11 +299,6 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
-	if (!strcmp(var, "core.legacyheaders")) {
-		use_legacy_headers = git_config_bool(var, value);
-		return 0;
-	}
-
 	if (!strcmp(var, "core.compression")) {
 		int level = git_config_int(var, value);
 		if (level == -1)

environment.c

@@ -11,7 +11,6 @@
 
 char git_default_email[MAX_GITNAME];
 char git_default_name[MAX_GITNAME];
-int use_legacy_headers = 1;
 int trust_executable_bit = 1;
 int has_symlinks = 1;
 int assume_unchanged;

sha1_file.c

@@ -972,7 +972,7 @@ void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 	return map;
 }
 
-int legacy_loose_object(unsigned char *map)
+static int legacy_loose_object(unsigned char *map)
 {
 	unsigned int word;
 
@@ -1034,6 +1034,14 @@ static int unpack_sha1_header(z_stream *stream, unsigned char *map, unsigned lon
 		return inflate(stream, 0);
 	}
 
+
+	/*
+	 * There used to be a second loose object header format which
+	 * was meant to mimic the in-pack format, allowing for direct
+	 * copy of the object data.  This format turned up not to be
+	 * really worth it and we don't write it any longer.  But we
+	 * can still read it.
+	 */
 	used = unpack_object_header_gently(map, mapsize, &type, &size);
 	if (!used || !valid_loose_object_type[type])
 		return -1;
@@ -1962,40 +1970,6 @@ static int write_buffer(int fd, const void *buf, size_t len)
 	return 0;
 }
 
-static int write_binary_header(unsigned char *hdr, enum object_type type, unsigned long len)
-{
-	int hdr_len;
-	unsigned char c;
-
-	c = (type << 4) | (len & 15);
-	len >>= 4;
-	hdr_len = 1;
-	while (len) {
-		*hdr++ = c | 0x80;
-		hdr_len++;
-		c = (len & 0x7f);
-		len >>= 7;
-	}
-	*hdr = c;
-	return hdr_len;
-}
-
-static void setup_object_header(z_stream *stream, const char *type, unsigned long len)
-{
-	int obj_type, hdrlen;
-
-	if (use_legacy_headers) {
-		while (deflate(stream, 0) == Z_OK)
-			/* nothing */;
-		return;
-	}
-	obj_type = type_from_string(type);
-	hdrlen = write_binary_header(stream->next_out, obj_type, len);
-	stream->total_out = hdrlen;
-	stream->next_out += hdrlen;
-	stream->avail_out -= hdrlen;
-}
-
 int hash_sha1_file(const void *buf, unsigned long len, const char *type,
                    unsigned char *sha1)
 {
@@ -2062,7 +2036,8 @@ int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned cha
 	/* First header.. */
 	stream.next_in = (unsigned char *)hdr;
 	stream.avail_in = hdrlen;
-	setup_object_header(&stream, type, len);
+	while (deflate(&stream, 0) == Z_OK)
+		/* nothing */;
 
 	/* Then the data itself.. */
 	stream.next_in = buf;