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>

1 files changed, 7 insertions, 2 deletions

diff --git a/pkt-line.h b/pkt-line.h
index 6927ea521b..fa93e32071 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -54,12 +54,17 @@ int packet_read(int fd, char *buffer, unsigned size, int options);
 
 /*
  * Convenience wrapper for packet_read that is not gentle, and sets the
- * CHOMP_NEWLINE option.
+ * CHOMP_NEWLINE option. The return value is NULL for a flush packet,
+ * and otherwise points to a static buffer (that may be overwritten by
+ * subsequent calls). If the size parameter is not NULL, the length of the
+ * packet is written to it.
  */
-int packet_read_line(int fd, char *buffer, unsigned size);
+char *packet_read_line(int fd, int *size);
+
 
 #define DEFAULT_PACKET_MAX 1000
 #define LARGE_PACKET_MAX 65520
+extern char packet_buffer[LARGE_PACKET_MAX];
 
 int packet_get_line(struct strbuf *out, char **src_buf, size_t *src_len);