deploy: Allow extensions to write to Morph log file

This is achieved by passing it the write end of a pipe, so that the
extension has somewhere to write debug messages without clobbering either
stdout or stderr.

Previously deployment extensions could only display status messages on
stdout, which is good for telling the user what is happening but is not
useful when trying to do post-mortem debugging, when more information is
usually required.

This uses the asyncore asynchronous event framework, which is rather
specific to sockets, but can be made to work with file descriptors, and
has the advantage that it's part of the python standard library.

It relies on polling file descriptors, but there's a trick with pipes to
use them as a notification that a process has exited:

1.  Ensure the write-end of the pipe is only open in the process you
    want to know when it exits
2.  Make sure the pipe's FDs are set in non-blocking read/write mode
3.  Call select or poll on the read-end of the file descriptor
4.  If select/poll says you can read from that FD, but you get an EOF,
    then the process has closed it, and if you know it doesn't do that
    in normal operation, then the process has terminated.

It took a few weird hacks to get the async_chat module to unregister
its event handlers on EOF, but the result is an event loop that is
asleep until the kernel tells it that it has to do something.

1 files changed, 30 insertions, 23 deletions

diff --git a/morphlib/plugins/deploy_plugin.py b/morphlib/plugins/deploy_plugin.py
index f3e43fa8..a80079fa 100644
--- a/morphlib/plugins/deploy_plugin.py
+++ b/morphlib/plugins/deploy_plugin.py
@@ -14,18 +14,19 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
 
-import cliapp
-import contextlib
 import json
+import logging
 import os
 import shutil
-import stat
+import sys
 import tarfile
 import tempfile
 import uuid
 
+import cliapp
 import morphlib
 
+
 class DeployPlugin(cliapp.Plugin):
 
     def enable(self):
@@ -540,33 +541,39 @@ class DeployPlugin(cliapp.Plugin):
             self.app.status(msg='Cleaning up')
             shutil.rmtree(deploy_private_tempdir)
 
+    def _report_extension_stdout(self, line):
+        self.app.status(msg=line.replace('%s', '%%'))
+    def _report_extension_stderr(self, error_list):
+        def cb(line):
+            error_list.append(line)
+            sys.stderr.write('%s\n' % line)
+        return cb
+    def _report_extension_logger(self, name, kind):
+        return lambda line: logging.debug('%s%s: %s', name, kind, line)
     def _run_extension(self, gd, name, kind, args, env):
         '''Run an extension.
-        
+
         The ``kind`` should be either ``.configure`` or ``.write``,
         depending on the kind of extension that is sought.
-        
+
         The extension is found either in the git repository of the
         system morphology (repo, ref), or with the Morph code.
-        
+
         '''
-        with morphlib.extensions.get_extension_filename(
-                name, kind) as ext_filename:
-            self.app.status(msg='Running extension %(name)s%(kind)s',
-                            name=name, kind=kind)
-            self.app.runcmd(
-                [ext_filename] + args,
-                ['sh',
-                 '-c',
-                 'while read l; do echo `date "+%F %T"` "$1$l"; done',
-                 '-',
-                 '%s[%s]' % (self.app.status_prefix, name + kind)],
-                cwd=gd.dirname, env=env, stdout=None, stderr=None)
-
-    def _is_executable(self, filename):
-        st = os.stat(filename)
-        mask = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
-        return (stat.S_IMODE(st.st_mode) & mask) != 0
+        error_list = []
+        with morphlib.extensions.get_extension_filename(name, kind) as fn:
+            ext = morphlib.extensions.ExtensionSubprocess(
+                report_stdout=self._report_extension_stdout,
+                report_stderr=self._report_extension_stderr(error_list),
+                report_logger=self._report_extension_logger(name, kind),
+            )
+            returncode = ext.run(fn, args, env=env, cwd=gd.dirname)
+        if returncode == 0:
+            logging.info('%s%s succeeded', name, kind)
+        else:
+            message = '%s%s failed with code %s: %s' % (
+                name, kind, returncode, '\n'.join(error_list))
+            raise cliapp.AppException(message)
 
     def create_metadata(self, system_artifact, root_repo_dir, deployment_type,
                         location, env):