cat-file: teach --batch to stream blob objects

The regular "git cat-file -p" and "git cat-file blob" code
paths already learned to stream large blobs. Let's do the
same here.

Note that this means we look up the type and size before
making a decision of whether to load the object into memory
or stream (just like the "-p" code path does). That can lead
to extra work, but it should be dwarfed by the cost of
actually accessing the object itself. In my measurements,
there was a 1-2% slowdown when using "--batch" on a large
number of objects.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/cat-file.c

@@ -117,12 +117,36 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name)
 	return 0;
 }
 
+static void print_object_or_die(int fd, const unsigned char *sha1,
+				enum object_type type, unsigned long size)
+{
+	if (type == OBJ_BLOB) {
+		if (stream_blob_to_fd(fd, sha1, NULL, 0) < 0)
+			die("unable to stream %s to stdout", sha1_to_hex(sha1));
+	}
+	else {
+		enum object_type rtype;
+		unsigned long rsize;
+		void *contents;
+
+		contents = read_sha1_file(sha1, &rtype, &rsize);
+		if (!contents)
+			die("object %s disappeared", sha1_to_hex(sha1));
+		if (rtype != type)
+			die("object %s changed type!?", sha1_to_hex(sha1));
+		if (rsize != size)
+			die("object %s change size!?", sha1_to_hex(sha1));
+
+		write_or_die(fd, contents, size);
+		free(contents);
+	}
+}
+
 static int batch_one_object(const char *obj_name, int print_contents)
 {
 	unsigned char sha1[20];
 	enum object_type type = 0;
 	unsigned long size;
-	void *contents = NULL;
 
 	if (!obj_name)
 	   return 1;
@@ -133,16 +157,10 @@ static int batch_one_object(const char *obj_name, int print_contents)
 		return 0;
 	}
 
-	if (print_contents == BATCH)
-		contents = read_sha1_file(sha1, &type, &size);
-	else
-		type = sha1_object_info(sha1, &size);
-
+	type = sha1_object_info(sha1, &size);
 	if (type <= 0) {
 		printf("%s missing\n", obj_name);
 		fflush(stdout);
-		if (print_contents == BATCH)
-			free(contents);
 		return 0;
 	}
 
@@ -150,12 +168,9 @@ static int batch_one_object(const char *obj_name, int print_contents)
 	fflush(stdout);
 
 	if (print_contents == BATCH) {
-		write_or_die(1, contents, size);
-		printf("\n");
-		fflush(stdout);
-		free(contents);
+		print_object_or_die(1, sha1, type, size);
+		write_or_die(1, "\n", 1);
 	}
-
 	return 0;
 }