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

[Eli Schwartz]

On 9/9/18 12:20 PM, Eli Schwartz wrote:
> 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)

As discussed on IRC, applying modified version of the patch (with
amended commit message) which uses tail (since that should never close
early at all). Thanks.

-- 
Eli Schwartz
Bug Wrangler and Trusted User

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