Nit: https://chromium.googlesource.com/infra/luci/luci-py/+/master/appengine/isolate/doc/client/Design.md claims that read_only defaults to 1?

Forked off  issue 841878 .

The default is true on python code base, but not the Go one. That's why it silently regressed. We cannot easily just turn it on and hope for it work, it doesn't. Even the python code had regression creep in, e.g. the internal failure in https://chromium-swarm.appspot.com/task?id=3d78d4a3d9d2f210 is due to a mishandling of symlink that happens only if read_only:1 is set.

Here's two examples of a regression of a task that writes to input files:
https://chromium-swarm.appspot.com/task?id=3d78d4aa5abe6210
https://chromium-swarm.appspot.com/task?id=3d78d50f380f5710

Oh, I see. I thought are we talking about the code on the client (i.e., archive/exparchive) or code on the bot? I thought the bot was still python?

run_isolated.py defaults to read_only:0 sadly if read_only is not specified. And yes it should default to 1 but that cannot be switched wholesale now.

got it.

Issue 813413 becomes kinda important. :/

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/luci/luci-py.git/+/a2c9980f9c3ae27a7b44fd5e1b04ac469e70636f

commit a2c9980f9c3ae27a7b44fd5e1b04ac469e70636f
Author: Marc-Antoine Ruel <maruel@chromium.org>
Date: Mon May 14 20:25:16 2018

[client] fix isolateserver client file mode handling with tarred filed

It was a bit too relax. Tighten it down a lot. Update test to confirm that
tarred files are correctly written as read-only.

Bug: 842802
Change-Id: I95c9c9ace7aa0a7f6c69ce8edb3ae400a9e5ffe8
Reviewed-on: https://chromium-review.googlesource.com/1057878
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>

[modify] https://crrev.com/a2c9980f9c3ae27a7b44fd5e1b04ac469e70636f/client/isolateserver.py
[modify] https://crrev.com/a2c9980f9c3ae27a7b44fd5e1b04ac469e70636f/client/tests/isolateserver_test.py

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/luci/luci-py.git/+/7e767c526988faa3d684ec74f47b49c3b022a948

commit 7e767c526988faa3d684ec74f47b49c3b022a948
Author: Marc-Antoine Ruel <maruel@chromium.org>
Date: Tue May 15 01:42:07 2018

[client] stop mocking the file system in some unit test

Test only change.

I wanted to confirm a suspicion with file mode bug with links, so removed the
mock of file I/O and look at file system. Sadly I didn't reproduce the bug but
this makes the test more useful.

Bug: 842802
Change-Id: I5a389af9a0b1fc2fae3b6a876f6762c9067362fa
Reviewed-on: https://chromium-review.googlesource.com/1058467
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>

[modify] https://crrev.com/7e767c526988faa3d684ec74f47b49c3b022a948/client/tests/isolateserver_test.py

FYI, tests I'm currently adding to the chromeos-amd64-generic-rel trybot rely heavily on being able to modify parts of their input isolate. It's partly a consequence of a funky toolchain cache the tests use, which isn't entirely under our control (mainly owned by cros folks). Depending on how we do it, breaking that dependency would be non-trivial. As it stands, adding more tests to that bot probably takes a higher priority than fixing the cache-modifications... Sorry :(

But once the bot's in a good place, I can try to work on making those tests less broken.

(discovered this issues btw 'cause I'm continuously on the watch for failures on that bot)

FWIW, I think I've resolved the chromeos issue I mentioned in #10. So those tests should be compatible w/ a read-only isolate cache now... (I think).