Re: [PATCH v2 3/4] sideband: append suffix for message whose CR in next pktline

[Jiang Xin <worldhello.net@gmail.com>]

Junio C Hamano <gitster@pobox.com> 于2021年6月14日周一 上午11:50写道：
>
> Jiang Xin <worldhello.net@gmail.com> writes:
>
> > From: Jiang Xin <zhiyou.jx@alibaba-inc.com>
> >
> > When calling "demultiplex_sideband" on a sideband-2 message, will try to
> > split the message by line breaks, and append a suffix to each nonempty
> > line to clear the end of the screen line.
>
> Subject of "will try" and "append" is missing.  Do you mean that
> the helper function in question does these two things?  I.e.
>
>         demultiplex_sideband() used on a sideband #2 will try
>         to... and appends ...
>
> > But in the following example,
> > there will be no suffix (8 spaces) for "<message-3>":
> >
> >     PKT-LINE(\2 <message-1> CR <message-2> CR <message-3>)
> >     PKT-LINE(\2 CR <message-4> CR <message-5> CR)
>
> That description may mechanically correct, but
>
>    after <message-3>, we fail to clear to the end of line
>
> may make it easier to understand what the problem we are trying to
> solve for those who do not remember what these suffix games are
> about.
>
> > This is because the line break of "<message-3>" is placed in the next
> > pktline message.
> >
> > Without this fix, t5411 must remove trailing spaces of the actual output
> > of "git-push" command before comparing.
> >
> > Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
> > ---
> >  sideband.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/sideband.c b/sideband.c
> > index 6f9e026732..abf2be98e1 100644
> > --- a/sideband.c
> > +++ b/sideband.c
> > @@ -185,6 +185,10 @@ int demultiplex_sideband(const char *me, int status,
> >
> >                       if (!scratch->len)
> >                               strbuf_addstr(scratch, DISPLAY_PREFIX);
> > +                     else if (!linelen)
> > +                             /* buf has a leading CR which ends the remaining
> > +                              * scratch of last round of "demultiplex_sideband" */
> > +                             strbuf_addstr(scratch, suffix);
>
> The style of multi-line comment needs fixing, but the contents of
> the comment is a bit hard to grok.
>
> >                       if (linelen > 0) {
> >                               maybe_colorize_sideband(scratch, b, linelen);
> >                               strbuf_addstr(scratch, suffix);
>
> I wonder if the following is simpler to read, though.
>
> -- >8 --
> Subject: [PATCH] sideband: don't lose clear-to-eol at packet boundary
>
> When demultiplex_sideband() sees a CR or LF on the sideband #2, it
> adds "suffix" string to clear to the end of the current line, which
> helps when relaying a progress display whose records are terminated
> with CRs.
>
> The code however forgot that depending on the length of the payload
> line, such a CR may fall exactly at the packet boundary and the
> number of bytes before the CR from the beginning of the packet could
> be zero.  In such a case, the message that was terminated by the CR
> were leftover in the "scratch" buffer in the previous call to the
> function and we still need to clear to the end of the current line.
>
> Just remove the unnecessary check on linelen; maybe_colorize_sideband()
> on 0-byte payload turns into a no-op, and we should be adding clear-to-eol
> for each and every CR/LF anyway.
>
>  sideband.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git c/sideband.c w/sideband.c
> index 6f9e026732..1575bf16dd 100644
> --- c/sideband.c
> +++ w/sideband.c
> @@ -185,10 +185,9 @@ int demultiplex_sideband(const char *me, int status,
>
>                         if (!scratch->len)
>                                 strbuf_addstr(scratch, DISPLAY_PREFIX);
> -                       if (linelen > 0) {
> -                               maybe_colorize_sideband(scratch, b, linelen);
> -                               strbuf_addstr(scratch, suffix);
> -                       }
> +
> +                       maybe_colorize_sideband(scratch, b, linelen);
> +                       strbuf_addstr(scratch, suffix);
>
>                         strbuf_addch(scratch, *brk);
>                         xwrite(2, scratch->buf, scratch->len);

The above changes will add suffix to the end of each line, and even an
empty lines.  However, according to the comment in commit ebe8fa738d
(fix display overlap between remote and local progress, 2007-11-04)
which introduced the suffix implementation for the first time, no
suffix should be appended for empty lines.

    /*
     * Let's insert a suffix to clear the end
     * of the screen line, but only if current
     * line data actually contains something.
     */

So my implementation is to try not to break the original
implementation, and keep the linelen unchanged.

The strbuf "scratch" will be reset at line 18th in the while block, so
the nonempty scratch at line 7 indicates the parameter scratch of
demultiplex_sideband() is not empty. With the following patch,
additional suffix is only added before a leading CR in a packet which
is seperated with its message by packet boundary.

```
01    while ((brk = strpbrk(b, "\n\r"))) {
02            int linelen = brk - b;
03
04 +         /* Has no empty scratch from last call of "demultiplex_sideband"
05 +          * and has a leading CR in buf.
06 +          */
07 +         if (scratch->len && !linelen)
08 +                   strbuf_addstr(scratch, suffix);
09            if (!scratch->len)
10                    strbuf_addstr(scratch, DISPLAY_PREFIX);
11            if (linelen > 0) {
12                    maybe_colorize_sideband(scratch, b, linelen);
13                    strbuf_addstr(scratch, suffix);
14            }
15
16            strbuf_addch(scratch, *brk);
17            xwrite(2, scratch->buf, scratch->len);
18            strbuf_reset(scratch);
19
20            b = brk + 1;
21    }
```