Re: [PATCH v4] Refactor recv_sideband()

[Nicolas Pitre <nico@fluxnic.net>]

On Tue, 28 Jun 2016, Junio C Hamano wrote:

> Junio C Hamano <gitster@pobox.com> writes:
> 
> > It's just that if you take the latter, then the conditional after
> > the loop exits (i.e. the last transmission was an incomplete line)
> > cannot be "is outbuf empty?", as your base state is "has PREFIX and
> > can never be empty".  I was working back from that if statement.
> 
> Let's try this again.  How does this look?

Still broken.

> In this version:
> 
>  - "outbuf" is where we keep the (possibly partial) data collected
>    to be eventually shown;
> 
>  - output of pending (possibly partial) data is handled by a helper
>    function drain().  It is responsible for prepending of the
>    PREFIX, which is treated purely as a cosmetic thing.  It also is
>    responsible for completing an incomplete line at the end of the
>    transmission (e.g. flushing of the buffered input upon reception of
>    the emergency exit packet).

It uses strbuf_complete_line() which destroys the intended result for 
lines that end with '\r'.

>  - locally generated errors go directly to fprintf(stderr),
>    bypassing outbuf (hence drain()).
> 
>  sideband.c | 43 +++++++++++++++++++++++++------------------
>  1 file changed, 25 insertions(+), 18 deletions(-)
> 
> diff --git a/sideband.c b/sideband.c
> index 226a8c2..6873137 100644
> --- a/sideband.c
> +++ b/sideband.c
> @@ -18,6 +18,16 @@
>  #define ANSI_SUFFIX "\033[K"
>  #define DUMB_SUFFIX "        "
>  
> +static void drain(struct strbuf *outbuf)
> +{
> +	if (!outbuf->len)
> +		return;
> +	strbuf_splice(outbuf, 0, 0, PREFIX, strlen(PREFIX));
> +	strbuf_complete_line(outbuf);
> +	fwrite(outbuf->buf, 1, outbuf->len, stderr);
> +	strbuf_reset(outbuf);
> +}
> +
>  int recv_sideband(const char *me, int in_stream, int out)
>  {
>  	const char *term, *suffix;
> @@ -26,20 +36,21 @@ int recv_sideband(const char *me, int in_stream, int out)
>  	const char *b, *brk;
>  	int retval = 0;
>  
> -	strbuf_addf(&outbuf, "%s", PREFIX);
>  	term = getenv("TERM");
>  	if (isatty(2) && term && strcmp(term, "dumb"))
>  		suffix = ANSI_SUFFIX;
>  	else
>  		suffix = DUMB_SUFFIX;
>  
> -	while (retval == 0) {
> +	while (!retval) {
>  		int band, len;
>  		len = packet_read(in_stream, NULL, NULL, buf, LARGE_PACKET_MAX, 0);
>  		if (len == 0)
>  			break;
>  		if (len < 1) {
> -			fprintf(stderr, "%s: protocol error: no band designator\n", me);
> +			drain(&outbuf);
> +			fprintf(stderr, "%s: protocol error: no band designator\n",
> +				me);
>  			retval = SIDEBAND_PROTOCOL_ERROR;
>  			break;
>  		}
> @@ -48,7 +59,8 @@ int recv_sideband(const char *me, int in_stream, int out)
>  		len--;
>  		switch (band) {
>  		case 3:
> -			fprintf(stderr, "%s%s\n", PREFIX, buf + 1);
> +			drain(&outbuf);
> +			strbuf_addf(&outbuf, "%s\n", buf + 1);
>  			retval = SIDEBAND_REMOTE_ERROR;
>  			break;
>  		case 2:
> @@ -58,13 +70,12 @@ int recv_sideband(const char *me, int in_stream, int out)
>  			 * Append a suffix to each nonempty line to clear the
>  			 * end of the screen line.
>  			 *
> -			 * The output is accumulated in a buffer and each line
> -			 * is printed to stderr using fprintf() with a single
> -			 * conversion specifier. This is a "best effort"
> -			 * approach to supporting both inter-process atomicity
> -			 * (single conversion specifiers are likely to end up
> -			 * in single atomic write() system calls) and the ANSI
> -			 * control code emulation under Windows.
> +			 * The output is accumulated in a buffer and
> +			 * each line is printed to stderr using
> +			 * fwrite(3).  This is a "best effort"
> +			 * approach to support inter-process atomicity
> +			 * (single fwrite(3) call is likely to end up
> +			 * in single atomic write() system calls).
>  			 */
>  			while ((brk = strpbrk(b, "\n\r"))) {
>  				int linelen = brk - b;
> @@ -75,11 +86,7 @@ int recv_sideband(const char *me, int in_stream, int out)
>  				} else {
>  					strbuf_addf(&outbuf, "%c", *brk);
>  				}
> -				fprintf(stderr, "%.*s", (int)outbuf.len,
> -					outbuf.buf);
> -				strbuf_reset(&outbuf);
> -				strbuf_addf(&outbuf, "%s", PREFIX);
> -
> +				drain(&outbuf);
>  				b = brk + 1;
>  			}
>  
> @@ -90,6 +97,7 @@ int recv_sideband(const char *me, int in_stream, int out)
>  			write_or_die(out, buf + 1, len);
>  			break;
>  		default:
> +			drain(&outbuf);
>  			fprintf(stderr, "%s: protocol error: bad band #%d\n",
>  				me, band);
>  			retval = SIDEBAND_PROTOCOL_ERROR;
> @@ -97,8 +105,7 @@ int recv_sideband(const char *me, int in_stream, int out)
>  		}
>  	}
>  
> -	if (outbuf.len > 0)
> -		fprintf(stderr, "%.*s", (int)outbuf.len, outbuf.buf);
> +	drain(&outbuf);
>  	strbuf_release(&outbuf);
>  	return retval;
>  }
> --
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