[arch-projects] [dbscripts] [PATCH 2/2] fixup: fix potential bsdtar stream close error by grep

[Eli Schwartz]

On 9/9/18 11:20 AM, Eli Schwartz wrote:
> On 9/3/18 7:50 AM, Levente Polyak via arch-projects wrote:
>> From: anthraxx <anthraxx at archlinux.org>
>>
>> bsdtar doesn't like it when the stream gets closed before it finishes
>> which may be the case when grep found its match on potentially huge
>> archives. Instead of suppressing the whole strerr , we just pipe
>> the output through cat which ensures the stream remains open for bsdtar
>> but we may still catch and see useful messages on stderr.
> 
> This is functionally 23c2b82c336bf19b7a29a90d19bca4423d8b8839 again, but
> for more locations. I'm never going to understand why some people get
> this SIGPIPE but I don't, but I guess it makes sense to do this change
> -- especially as we do the same elsewhere.
> 
> (We need to buffer it somehow with some extra command, grep doesn't have
> a way to only output the first result but still avoid propagating
> SIGPIPE. Why does bsdtar care about this anyway...)


As discussed on IRC, I can finally reproduce this, e.g.
bsdtar xOf /path/to/file | grep --binary-files=text a
(many matches for the string "a")

With grep -q or grep -m1, it errors

with cat | grep -q/-m1 it still errors due to the buffer going *into*
grep, having insufficient room :(

with grep | head -1 it only errors, if the matching buffer going *out*
of grep is too large. For our uses it should only ever match exactly
once. So this is what we should do.

(Or complain to libarchive. :p)

-- 
Eli Schwartz
Bug Wrangler and Trusted User

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