git/pkt-line.h
Jeff King 4981fe750b pkt-line: share buffer/descriptor reading implementation
The packet_read function reads from a descriptor. The
packet_get_line function is similar, but reads from an
in-memory buffer, and uses a completely separate
implementation. This patch teaches the generic packet_read
function to accept either source, and we can do away with
packet_get_line's implementation.

There are two other differences to account for between the
old and new functions. The first is that we used to read
into a strbuf, but now read into a fixed size buffer. The
only two callers are fine with that, and in fact it
simplifies their code, since they can use the same
static-buffer interface as the rest of the packet_read_line
callers (and we provide a similar convenience wrapper for
reading from a buffer rather than a descriptor).

This is technically an externally-visible behavior change in
that we used to accept arbitrary sized packets up to 65532
bytes, and now cap out at LARGE_PACKET_MAX, 65520. In
practice this doesn't matter, as we use it only for parsing
smart-http headers (of which there is exactly one defined,
and it is small and fixed-size). And any extension headers
would be breaking the protocol to go over LARGE_PACKET_MAX
anyway.

The other difference is that packet_get_line would return
on error rather than dying. However, both callers of
packet_get_line are actually improved by dying.

The first caller does its own error checking, but we can
drop that; as a result, we'll actually get more specific
reporting about protocol breakage when packet_read dies
internally. The only downside is that packet_read will not
print the smart-http URL that failed, but that's not a big
deal; anybody not debugging can already see the remote's URL
already, and anybody debugging would want to run with
GIT_CURL_VERBOSE anyway to see way more information.

The second caller, which is just trying to skip past any
extra smart-http headers (of which there are none defined,
but which we allow to keep room for future expansion), did
not error check at all. As a result, it would treat an error
just like a flush packet. The resulting mess would generally
cause an error later in get_remote_heads, but now we get
error reporting much closer to the source of the problem.

Brown-paper-bag-fixes-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-02-24 00:14:15 -08:00

82 lines
3 KiB
C

#ifndef PKTLINE_H
#define PKTLINE_H
#include "git-compat-util.h"
#include "strbuf.h"
/*
* Write a packetized stream, where each line is preceded by
* its length (including the header) as a 4-byte hex number.
* A length of 'zero' means end of stream (and a length of 1-3
* would be an error).
*
* This is all pretty stupid, but we use this packetized line
* format to make a streaming format possible without ever
* over-running the read buffers. That way we'll never read
* into what might be the pack data (which should go to another
* process entirely).
*
* The writing side could use stdio, but since the reading
* side can't, we stay with pure read/write interfaces.
*/
void packet_flush(int fd);
void packet_write(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
void packet_buf_flush(struct strbuf *buf);
void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
/*
* Read a packetized line into the buffer, which must be at least size bytes
* long. The return value specifies the number of bytes read into the buffer.
*
* If src_buffer is not NULL (and nor is *src_buffer), it should point to a
* buffer containing the packet data to parse, of at least *src_len bytes.
* After the function returns, src_buf will be incremented and src_len
* decremented by the number of bytes consumed.
*
* If src_buffer (or *src_buffer) is NULL, then data is read from the
* descriptor "fd".
*
* If options does not contain PACKET_READ_GENTLE_ON_EOF, we will die under any
* of the following conditions:
*
* 1. Read error from descriptor.
*
* 2. Protocol error from the remote (e.g., bogus length characters).
*
* 3. Receiving a packet larger than "size" bytes.
*
* 4. Truncated output from the remote (e.g., we expected a packet but got
* EOF, or we got a partial packet followed by EOF).
*
* If options does contain PACKET_READ_GENTLE_ON_EOF, we will not die on
* condition 4 (truncated input), but instead return -1. However, we will still
* die for the other 3 conditions.
*
* If options contains PACKET_READ_CHOMP_NEWLINE, a trailing newline (if
* present) is removed from the buffer before returning.
*/
#define PACKET_READ_GENTLE_ON_EOF (1u<<0)
#define PACKET_READ_CHOMP_NEWLINE (1u<<1)
int packet_read(int fd, char **src_buffer, size_t *src_len, char
*buffer, unsigned size, int options);
/*
* Convenience wrapper for packet_read that is not gentle, and sets the
* 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.
*/
char *packet_read_line(int fd, int *size);
/*
* Same as packet_read_line, but read from a buf rather than a descriptor;
* see packet_read for details on how src_* is used.
*/
char *packet_read_line_buf(char **src_buf, size_t *src_len, int *size);
#define DEFAULT_PACKET_MAX 1000
#define LARGE_PACKET_MAX 65520
extern char packet_buffer[LARGE_PACKET_MAX];
#endif