Re: bash sockets: printf \x0a does TCP fragmentation

[L A Walsh]

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...
:-)