Merge ~kissiel/checkbox-support:add-interactive-cmd into checkbox-support:master

[Maciej Kisielewski]

I would like to start proposing changes to providers that use this module.
Instead of vendorizing the module in each provider, I think it's better to land it here.

[Maciej Kisielewski (kissiel)]

Here are tests / examples how to use it.

https://github.com/kissiel/gallows/blob/master/test_functional.py

[Jonathan Cave (jocave)]

Comment below.

Otherwise looks good.

review: Needs Information

[Maciej Kisielewski (kissiel)]

Old cruft it is.
Fixing...

review: Needs Fixing

[Maciej Kisielewski (kissiel)]

Removed cruft, and also changed mode to -x.

review: Needs Resubmitting

[Maciej Kisielewski (kissiel)]

Let's land it, so I can base some other work on it

diff --git a/checkbox_support/interactive_cmd.py b/checkbox_support/interactive_cmd.py
new file mode 100644
index 0000000..981a21b
--- /dev/null
+++ b/checkbox_support/interactive_cmd.py
@@ -0,0 +1,112 @@
+# Copyright 2017 Canonical Ltd.
+# All rights reserved.
+#
+# Written by:
+#    Authors: Maciej Kisielewski <[e-mail]>
+# This is a copy of the original module located here:
+# https://github.com/kissiel/gallows
+import re
+import select
+import subprocess
+import sys
+import time
+
+
+class InteractiveCommand:
+    def __init__(self, args):
+        self._args = args
+        self._is_running = False
+        self._pending = 0
+
+    def __enter__(self):
+        self.start()
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.kill()
+
+    def start(self):
+        self._proc = subprocess.Popen(
+            self._args, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT)
+        self._is_running = True
+        self._poller = select.poll()
+        self._poller.register(self._proc.stdout, select.POLLIN)
+
+    def kill(self):
+        if self._is_running:
+            # explicitly closing files to make test not complain about leaking
+            # them (GC race condition?)
+            self._close_fds([self._proc.stdin, self._proc.stdout])
+            self._proc.terminate()
+            self._is_running = False
+            self._proc.wait()
+
+    def writeline(self, line, sleep=0.1):
+        if not self._is_running:
+            raise Exception('Process is not running')
+        try:
+            self._proc.stdin.write((line + '\n').encode(sys.stdin.encoding))
+            self._proc.stdin.flush()
+        except BrokenPipeError:
+            self._close_fds([self._proc.stdin])
+            raise
+        time.sleep(sleep)
+
+    def wait_for_output(self, timeout=5):
+        events = self._poller.poll(timeout * 1000)
+        if not events:
+            self._pending = 0
+            return None
+        else:
+            self._pending = len(self._proc.stdout.peek())
+            return self._pending
+
+    def wait_until_matched(self, pattern, timeout):
+        assert timeout >= 0, "cannot wait until past times"
+        deadline = time.time() + timeout
+        output = ''
+        while timeout > 0:
+            self.wait_for_output(timeout)
+            output += self.read_all()
+            re_match = re.search(pattern, output)
+            if re_match:
+                return re_match
+            timeout = deadline - time.time()
+        return None
+
+    def read_all(self):
+        if not self._pending:
+            return ''
+        else:
+            raw = self._proc.stdout.read(self._pending)
+            self._pending = 0
+            return raw.decode(sys.stdout.encoding)
+
+    def write_repeated(self, command, pattern, attempts, timeout):
+        """
+        Write `command`, try matching `pattern` in the response and repeat
+        for `attempts` times if pattern not matched.
+
+        return True if it matched at any point. Or
+        return False if attempts were depleted and pattern hasn't been matched
+        """
+        matched = None
+        while not matched and attempts > 0:
+            self.writeline(command)
+            matched = self.wait_until_matched(pattern, timeout)
+            if matched:
+                break
+            attempts -= 1
+        return matched
+
+    @property
+    def is_running(self):
+        return self._is_running
+
+    def _close_fds(self, fds):
+        for pipe in fds:
+            try:
+                pipe.close()
+            except BrokenPipeError:
+                pass