Re: [Buildroot] [PATCH 1/1] support/testing/infra/emulator.py: prevent the commands from wrapping

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Yann,

On Tue, 5 Oct 2021 22:01:11 +0200
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> On 2021-10-05 19:17 +0200, Edgar Bonet spake thusly:
> > Traditional VT-10x terminals (and their emulators) have a "magic
> > margins" feature that enables the last character position to be updated
> > without scrolling the screen: whenever a character is printed on the
> > last column, the cursor stays over the character, instead of moving to
> > the next line.
> > 
> > The Busybox shell, ash, attempts to defeat this feature by printing
> > CF,LF right after echoing a character to the last column.[1] This
> > doesn't play well with emulator.py. The run() method of the Emulator
> > class captures the output of the emulated system and assumes the first
> > line it reads is the echo of the command, and all subsequent lines are
> > the command's output. If the line made by the command + shell prompt is
> > longer than 80 characters, then it is echoed as two or more lines, and
> > all but the first one are mistaken for the command's output.
> > 
> > We fix this by telling the emulated system that we are using an
> > ultra-wide terminal with 29999 columns. Larger values would be ignored
> > and replaced by the default, namely 80 columns.[2]
> > 
> > [1] https://git.busybox.net/busybox/tree/libbb/lineedit.c?h=1_34_0#n412
> > [2] https://git.busybox.net/busybox/tree/libbb/xfuncs.c?h=1_34_0#n258  
> 
> Woot! Very, very good commit log, thanks!

And very good investigation too!

> The thing is, as Thomas said, he had the issue with new tests he was
> adding to the infra; we currently do not have tests with commands that
> are too long to be wrapped.
> 
> Thomas?

We do:

  ./support/testing/tests/package/test_python_flask_expects_json.py

is such a test. The test is doing:

        self.assertEqual(output[-1], str(expects))

instead of:

        self.assertEqual(output[0], str(expects))

precisely to work around this issue. I.e instead of getting the first
line of the output (which would be the end of the command being
executed), I test against the last line of the output. It works in my
case because I know my "interesting" output has only a single line.

So, if that test works by using output[0] instead of output[-1], then
the fix of using stty columns 29999 would be confirmed to work!

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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