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Re: bash sockets: printf \x0a does TCP fragmentation

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  Re: bash sockets: printf \x0a does TCP fragmentation L A Walsh <bash@tlinx.org> - 2018-09-25 05:15 -0700

#14657 — Re: bash sockets: printf \x0a does TCP fragmentation

On 9/24/2018 6:05 AM, Greg Wooledge wrote:
> On Sat, Sep 22, 2018 at 11:50:17AM +0200, dirk+bash@testssl.sh wrote:
>   
>> On 9/22/18 7:30 AM, Bob Proulx wrote:
>>     
>>> dirk+bash@testssl.sh wrote:
>>>       
>>>> printf -- "$data" >&5 2>/dev/null
>>>>         
>>> What happens if $data contains % format strings?  What happens if the
>>> format contains a sequence such as \c?  This looks problematic.  This
>>> is not a safe programming proctice.
>>>       
>
> Looking ONLY at this one line, there is an obvious bug, which Bob has
> pointed out.  It should be
>
> printf %s "$data" >&5 2>/dev/null
>   
----
    This brings to mind a consideration:
As %s says to print a string of data (presumably not
including a NUL byte), then what happens if "$data" is
a paragraph of text with embedded newlines.  In that case,
it sounds like bash might break apart the single printf
output into smaller packets rather than transmitting the
entirety of "$data" in 1 write (presuming it is less than
the maximum data size for a network packet).

    Also, if you want to flush the data out at the end, it seems
"%s\n" would be required to force out the last line of text if
it wasn't nl terminated.

> That is utterly horrifying.
>   
---
    Hmmm....I didn't realize how sensitive some sensibilities were...
:-)

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