pkt-line: provide a LARGE_PACKET_MAX static buffer

Most of the callers of packet_read_line just read into a
static 1000-byte buffer (callers which handle arbitrary
binary data already use LARGE_PACKET_MAX). This works fine
in practice, because:

  1. The only variable-sized data in these lines is a ref
     name, and refs tend to be a lot shorter than 1000
     characters.

  2. When sending ref lines, git-core always limits itself
     to 1000 byte packets.

However, the only limit given in the protocol specification
in Documentation/technical/protocol-common.txt is
LARGE_PACKET_MAX; the 1000 byte limit is mentioned only in
pack-protocol.txt, and then only describing what we write,
not as a specific limit for readers.

This patch lets us bump the 1000-byte limit to
LARGE_PACKET_MAX. Even though git-core will never write a
packet where this makes a difference, there are two good
reasons to do this:

  1. Other git implementations may have followed
     protocol-common.txt and used a larger maximum size. We
     don't bump into it in practice because it would involve
     very long ref names.

  2. We may want to increase the 1000-byte limit one day.
     Since packets are transferred before any capabilities,
     it's difficult to do this in a backwards-compatible
     way. But if we bump the size of buffer the readers can
     handle, eventually older versions of git will be
     obsolete enough that we can justify bumping the
     writers, as well. We don't have plans to do this
     anytime soon, but there is no reason not to start the
     clock ticking now.

Just bumping all of the reading bufs to LARGE_PACKET_MAX
would waste memory. Instead, since most readers just read
into a temporary buffer anyway, let's provide a single
static buffer that all callers can use. We can further wrap
this detail away by having the packet_read_line wrapper just
use the buffer transparently and return a pointer to the
static storage.  That covers most of the cases, and the
remaining ones already read into their own LARGE_PACKET_MAX
buffers.

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

4 files changed, 15 insertions, 20 deletions

diff --git a/builtin/archive.c b/builtin/archive.c
index d381ac4147..49178f159e 100644
--- a/builtin/archive.c
+++ b/builtin/archive.c
@@ -27,8 +27,8 @@ static int run_remote_archiver(int argc, const char **argv,
 			       const char *remote, const char *exec,
 			       const char *name_hint)
 {
-	char buf[LARGE_PACKET_MAX];
-	int fd[2], i, len, rv;
+	char *buf;
+	int fd[2], i, rv;
 	struct transport *transport;
 	struct remote *_remote;
 
@@ -53,19 +53,18 @@ static int run_remote_archiver(int argc, const char **argv,
 		packet_write(fd[1], "argument %s\n", argv[i]);
 	packet_flush(fd[1]);
 
-	len = packet_read_line(fd[0], buf, sizeof(buf));
-	if (!len)
+	buf = packet_read_line(fd[0], NULL);
+	if (!buf)
 		die(_("git archive: expected ACK/NAK, got EOF"));
 	if (strcmp(buf, "ACK")) {
-		if (len > 5 && !prefixcmp(buf, "NACK "))
+		if (!prefixcmp(buf, "NACK "))
 			die(_("git archive: NACK %s"), buf + 5);
-		if (len > 4 && !prefixcmp(buf, "ERR "))
+		if (!prefixcmp(buf, "ERR "))
 			die(_("remote error: %s"), buf + 4);
 		die(_("git archive: protocol error"));
 	}
 
-	len = packet_read_line(fd[0], buf, sizeof(buf));
-	if (len)
+	if (packet_read_line(fd[0], NULL))
 		die(_("git archive: expected a flush"));
 
 	/* Now, start reading from fd[0] and spit it out to stdout */
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index f73664f433..c21cc2c778 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -100,12 +100,11 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 			/* in stateless RPC mode we use pkt-line to read
 			 * from stdin, until we get a flush packet
 			 */
-			static char line[1000];
 			for (;;) {
-				int n = packet_read_line(0, line, sizeof(line));
-				if (!n)
+				char *line = packet_read_line(0, NULL);
+				if (!line)
 					break;
-				string_list_append(&sought, xmemdupz(line, n));
+				string_list_append(&sought, xstrdup(line));
 			}
 		}
 		else {
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 6679e636c7..ccebd74f16 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -754,14 +754,14 @@ static struct command *read_head_info(void)
 	struct command *commands = NULL;
 	struct command **p = &commands;
 	for (;;) {
-		static char line[1000];
+		char *line;
 		unsigned char old_sha1[20], new_sha1[20];
 		struct command *cmd;
 		char *refname;
 		int len, reflen;
 
-		len = packet_read_line(0, line, sizeof(line));
-		if (!len)
+		line = packet_read_line(0, &len);
+		if (!line)
 			break;
 		if (len < 83 ||
 		    line[40] != ' ' ||
diff --git a/builtin/upload-archive.c b/builtin/upload-archive.c
index d90f0aba44..af2da35e7d 100644
--- a/builtin/upload-archive.c
+++ b/builtin/upload-archive.c
@@ -21,8 +21,6 @@ int cmd_upload_archive_writer(int argc, const char **argv, const char *prefix)
 {
 	struct argv_array sent_argv = ARGV_ARRAY_INIT;
 	const char *arg_cmd = "argument ";
-	char buf[4096];
-	int len;
 
 	if (argc != 2)
 		usage(upload_archive_usage);
@@ -33,9 +31,8 @@ int cmd_upload_archive_writer(int argc, const char **argv, const char *prefix)
 	/* put received options in sent_argv[] */
 	argv_array_push(&sent_argv, "git-upload-archive");
 	for (;;) {
-		/* This will die if not enough free space in buf */
-		len = packet_read_line(0, buf, sizeof(buf));
-		if (len == 0)
+		char *buf = packet_read_line(0, NULL);
+		if (!buf)
 			break;	/* got a flush */
 		if (sent_argv.argc > MAX_ARGS)
 			die("Too many options (>%d)", MAX_ARGS - 1);