Re: [PATCH 5/5] diff: handle NULs in get_string_hash()

From: Stefan Beller <sbeller@google.com>
Date: Oct 19, 2017, 21:50 UTC
Message-ID: <CAGZ79kahvE=S_SwZqzC_VrAPURVCkqjaa9sVN-bCecYLoA4yRw@mail.gmail.com>
In-Reply-To: <20171019213958.d6rp2upiga5tsvys@sigill.intra.peff.net>

On Thu, Oct 19, 2017 at 2:39 PM, Jeff King <peff@peff.net> wrote:

Show 33 quoted lines

> On Thu, Oct 19, 2017 at 02:31:20PM -0700, Stefan Beller wrote:
>
>> > This is unlikely to ever come up in practice since our line
>> > boundaries generally come from calling strlen() in the first
>> > place.
>>
>> get_string_hash is called from
>>  prepare_entry, which in turn is called from
>>   add_lines_to_move_detection or mark_color_as_moved
>>    diff_flush_patch_all_file_pairs
>>
>> that constructs the arguments in
>> diff_flush_patch
>>  run_diff
>>   run_diff_cmd
>>    builtin_diff (part "/* Crazy xdl interfaces.. */")
>>     xdi_diff_outf( fn_out_consume as arg!)
>>      xdi_diff
>>       xdl_diff
>>        xdl_call_hunk_func
>>         -> fn_out_consume(cb, line, len)
>>
>> xdl_call_hunk_func however uses pointer arithmetic instead
>> of strlen. So I think this sentence is not a good idea to put in
>> the commit message.
>>
>> It may not occur in practice, due to binary files detection using
>> NUL as a signal, but conceptually our move-colored(!) diffs
>> should be compatible with NULs with this patch now.
>
> Good catch. I just skimmed over all the diff_emit_* functions, which use
> strlen(). But at the bottom is emit_add_line(), which has a real length
> marker from xdiff.

Doh! There is diff_emit_submodule_* but I presume you meant emit_diff_* actually as there the strlen is legit, as we generate known non-NUL data to print.

The submodule output may get mangled in diff_emit_submodule_{add,del} as the input is coming from user data.

> I agree we wouldn't see NULs in general, but this is maybe fixing "diff
> --color-moved -a". I dunno. It's probably not worth digging too much,
> since it seems like the right thing to do regardless.

I agree, that this digging seems not worth it; I was just agitated at the seemingly incorrect commit message.

Thanks, Stefan

>
> -Peff