Re: [PATCH v5 04/15] pkt-line: add packet_write_gently()

From: Jeff King <peff@peff.net>
Date: Aug 10, 2016, 13:28 UTC
Message-ID: <20160810132814.gqnipsdwyzjmuqjy@sigill.intra.peff.net>
In-Reply-To: <20160810130411.12419-5-larsxschneider@gmail.com>

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

Show 9 quoted lines

> 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()?

Show 9 quoted lines

> 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).

Show 6 quoted lines

> +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