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From: Jeff King <peff@peff.net>
To: larsxschneider@gmail.com
Cc: git@vger.kernel.org, gitster@pobox.com, jnareb@gmail.com,
	mlbright@gmail.com, e@80x24.org, Johannes.Schindelin@gmx.de,
	ben@wijen.net
Subject: Re: [PATCH v5 04/15] pkt-line: add packet_write_gently()
Date: Wed, 10 Aug 2016 09:28:15 -0400	[thread overview]
Message-ID: <20160810132814.gqnipsdwyzjmuqjy@sigill.intra.peff.net> (raw)
In-Reply-To: <20160810130411.12419-5-larsxschneider@gmail.com>

On Wed, Aug 10, 2016 at 03:04:00PM +0200, larsxschneider@gmail.com wrote:

> From: Lars Schneider <larsxschneider@gmail.com>
> 
> packet_write() has two shortcomings. First, it uses format_packet() which
> lets the caller only send string data via "%s". That means it cannot be
> used for arbitrary data that may contain NULs. Second, it will always
> die on error.
> 
> Add packet_write_gently() which writes arbitrary data and returns `0` for
> success and `-1` for an error.

So now we have packet_write() and packet_write_gently(), but they differ
in more than just whether they are gentle. That seems like a weird
interface.

Should we either be picking a new name (e.g., packet_write_mem() or
something), or migrating packet_write() to packet_write_fmt()?

> diff --git a/pkt-line.c b/pkt-line.c
> index e6b8410..4f25748 100644
> --- a/pkt-line.c
> +++ b/pkt-line.c
> @@ -3,6 +3,7 @@
>  #include "run-command.h"
>  
>  char packet_buffer[LARGE_PACKET_MAX];
> +char packet_write_buffer[LARGE_PACKET_MAX];

Should this be static? I.e., are random other bits of the code allowed
to write into it (I guess not because it's not declared in pkt-line.h).

> +int packet_write_gently(const int fd_out, const char *buf, size_t size)
> +{
> +	if (size > PKTLINE_DATA_MAXLEN)
> +		return -1;
> +	packet_trace(buf, size, 1);
> +	memmove(packet_write_buffer + 4, buf, size);

It looks like this iteration drops the idea of callers using a
LARGE_PACKET_MAX buffer and only filling it at "buf+4" with
PKTLINE_DATA_MAXLEN bytes (which is fine).

I wonder if we still need PKTLINE_DATA_MAXLEN, or of it is just
obscuring things. The magic number "4" still appears separately here,
and it actually makes it harder to see that things are correct.  I.e.,
doing:

  if (size > sizeof(packet_write_buffer) - 4)
	return -1;
  memmove(packet_write_buffer + 4, buf, size);

is more obviously correct, because you do not have to wonder about the
relationship between the size of your buffer and the macro.

It might still be worth having PKTLINE_DATA_MAXLEN public, though, if
callers use it to size their input to packet_write_gently().

-Peff

  reply	other threads:[~2016-08-10 19:33 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20160803164225.46355-1-larsxschneider@gmail.com/>
2016-08-10 13:03 ` [PATCH v5 00/15] Git filter protocol larsxschneider
2016-08-10 13:03   ` [PATCH v5 01/15] pkt-line: extract set_packet_header() larsxschneider
2016-08-10 13:03   ` [PATCH v5 02/15] pkt-line: call packet_trace() only if a packet is actually send larsxschneider
2016-08-10 13:13     ` Jeff King
2016-08-10 13:24       ` Lars Schneider
2016-08-10 13:30         ` Jeff King
2016-08-10 13:51           ` Lars Schneider
2016-08-10 14:33             ` Jeff King
2016-08-10 13:03   ` [PATCH v5 03/15] pkt-line: add `gentle` parameter to format_packet() larsxschneider
2016-08-10 13:15     ` Jeff King
2016-08-10 13:29       ` Lars Schneider
2016-08-10 13:37         ` Jeff King
2016-08-10 13:59           ` Lars Schneider
2016-08-10 14:34             ` Jeff King
2016-08-10 13:04   ` [PATCH v5 04/15] pkt-line: add packet_write_gently() larsxschneider
2016-08-10 13:28     ` Jeff King [this message]
2016-08-10 13:36       ` Lars Schneider
2016-08-10 13:40         ` Jeff King
2016-08-10 17:17           ` Junio C Hamano
2016-08-10 17:49             ` Lars Schneider
2016-08-10 18:21               ` Junio C Hamano
2016-08-10 19:15                 ` Lars Schneider
2016-08-10 13:04   ` [PATCH v5 05/15] pkt-line: add packet_write_gently_fmt() larsxschneider
2016-08-10 13:43     ` Jeff King
2016-08-10 14:10       ` Lars Schneider
2016-08-10 15:01         ` Jeff King
2016-08-10 17:18       ` Junio C Hamano
2016-08-10 17:53         ` Lars Schneider
2016-08-10 18:42           ` Junio C Hamano
2016-08-10 13:04   ` [PATCH v5 06/15] pkt-line: add packet_flush_gently() larsxschneider
2016-08-10 13:04   ` [PATCH v5 07/15] pkt-line: add functions to read/write flush terminated packet streams larsxschneider
2016-08-10 13:04   ` [PATCH v5 08/15] pkt-line: rename packet_write() to packet_write_fmt() larsxschneider
2016-08-10 13:04   ` [PATCH v5 09/15] pack-protocol: fix maximum pkt-line size larsxschneider
2016-08-10 13:04   ` [PATCH v5 10/15] convert: quote filter names in error messages larsxschneider
2016-08-10 13:04   ` [PATCH v5 11/15] convert: modernize tests larsxschneider
2016-08-10 13:04   ` [PATCH v5 12/15] convert: generate large test files only once larsxschneider
2016-08-10 13:04   ` [PATCH v5 13/15] convert: make apply_filter() adhere to standard Git error handling larsxschneider
2016-08-10 13:04   ` [PATCH v5 14/15] convert: add filter.<driver>.process option larsxschneider
2016-08-12 16:33     ` Stefan Beller
2016-08-12 16:38       ` Jeff King
2016-08-12 16:48         ` Stefan Beller
2016-08-12 17:08           ` Lars Schneider
2016-08-12 17:13             ` Junio C Hamano
2016-08-12 17:21               ` Lars Schneider
2016-08-12 18:03                 ` Junio C Hamano
2016-08-12 16:59       ` Lars Schneider
2016-08-12 17:07         ` Stefan Beller
2016-08-12 17:14           ` Lars Schneider
2016-08-10 13:04   ` [PATCH v5 15/15] read-cache: make sure file handles are not inherited by child processes larsxschneider
2016-08-18 14:23     ` Johannes Schindelin

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