terminating docker attach container prints context canceled error

[thaJeztah]

Description

I noticed this while updating the docs in #5289. Terminating an attach (CTRL-c, killing the container) prints a context canceled error.

Based on the example I was updating (assuming the example was correct!), older versions did not print these errors, and as they don't provide much value to the user, we should probably not print them 🤔

docker run -d --name topdemo alpine /usr/bin/top -b

docker attach topdemo
Mem: 1397860K used, 6629032K free, 928K shrd, 168848K buff, 329628K cached
CPU:   0% usr   0% sys   0% nic  97% idle   1% io   0% irq   0% sirq
Load average: 0.25 0.16 0.08 1/342 6
  PID  PPID USER     STAT   VSZ %VSZ CPU %CPU COMMAND
    1     0 root     R     1712   0%   4   0% /usr/bin/top -b
^Ccontext canceled

I reproduced this with v27.0.3 and v27.1.1 (but haven't checked older versions)

[thaJeztah]

cc @Benehiko @laurazard

[laurazard]

Bisect says it was introduced in 3f0d90a (cc @Benehiko)

[laurazard]

I can take a quick look, and add a test.

[Benehiko]

This should've been fixed in #5247

[thaJeztah]

This should've been fixed in #5247

Oh! Hm.. need to double check now if I checked with 27.0 or 27.1 (or if there's still an issue at hand)

[laurazard]

I don't think it is,attach uses different code paths from run. I've got a commit with some tests and a fix on the way :)

[Benehiko]

I don't think it is,attach uses different code paths from run. I've got a commit with some tests and a fix on the way :)

oh you're right! I didn't look too closely at the issue my mind just went to the code that was problematic at the "attach" section in the run command 😅