index-pack: add --max-input-size=<size> option

When receiving a pack-file, it can be useful to abort the
`git index-pack`, if the pack-file is too big.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-index-pack.txt

@@ -87,6 +87,8 @@ OPTIONS
 	Specifying 0 will cause Git to auto-detect the number of CPU's
 	and use maximum 3 threads.
 
+--max-input-size=<size>::
+	Die, if the pack is larger than <size>.
 
 Note
 ----

builtin/index-pack.c

@@ -87,6 +87,7 @@ static struct progress *progress;
 static unsigned char input_buffer[4096];
 static unsigned int input_offset, input_len;
 static off_t consumed_bytes;
+static off_t max_input_size;
 static unsigned deepest_delta;
 static git_SHA_CTX input_ctx;
 static uint32_t input_crc32;
@@ -297,6 +298,8 @@ static void use(int bytes)
 	if (signed_add_overflows(consumed_bytes, bytes))
 		die(_("pack too large for current definition of off_t"));
 	consumed_bytes += bytes;
+	if (max_input_size && consumed_bytes > max_input_size)
+		die(_("pack exceeds maximum allowed size"));
 }
 
 static const char *open_pack_file(const char *pack_name)
@@ -1714,6 +1717,8 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 					opts.off32_limit = strtoul(c+1, &c, 0);
 				if (*c || opts.off32_limit & 0x80000000)
 					die(_("bad %s"), arg);
+			} else if (skip_prefix(arg, "--max-input-size=", &arg)) {
+				max_input_size = strtoumax(arg, NULL, 10);
 			} else
 				usage(index_pack_usage);
 			continue;