builtin/cat-file.c: support NUL-delimited input with `-z`
When callers are using `cat-file` via one of the stdin-driven `--batch`
modes, all input is newline-delimited. This presents a problem when
callers wish to ask about, e.g. tree-entries that have a newline
character present in their filename.
To support this niche scenario, introduce a new `-z` mode to the
`--batch`, `--batch-check`, and `--batch-command` suite of options that
instructs `cat-file` to treat its input as NUL-delimited, allowing the
individual commands themselves to have newlines present.
The refactoring here is slightly unfortunate, since we turn loops like:
while (strbuf_getline(&buf, stdin) != EOF)
into:
while (1) {
int ret;
if (opt->nul_terminated)
ret = strbuf_getline_nul(&input, stdin);
else
ret = strbuf_getline(&input, stdin);
if (ret == EOF)
break;
}
It's tempting to think that we could use `strbuf_getwholeline()` and
specify either `\n` or `\0` as the terminating character. But for input
on platforms that include a CR character preceeding the LF, this
wouldn't quite be the same, since `strbuf_getline(...)` will trim any
trailing CR, while `strbuf_getwholeline(&buf, stdin, '\n')` will not.
In the future, we could clean this up further by introducing a variant
of `strbuf_getwholeline()` that addresses the aforementioned gap, but
that approach felt too heavy-handed for this pair of uses.
Some tests are added in t1006 to ensure that `cat-file` produces the
same output in `--batch`, `--batch-check`, and `--batch-command` modes
with and without the new `-z` option.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>