Improve handling of ImportErrors to notify users that they need to install new dependencies (#389)

* Improve handling of ImportErrors to notify users that they need to install new dependencies

Also added missing dependency to requirements.txt

* Mention installing dependencies in virtualenv if used

* Move requirements used only by output modules to a separate file

* Using a virtualenv is now the only officially supported method

* Handle ImportErrors when loading output plugins so different install instructions can be given

* Cleanup requirements-output.txt

twisted/plugins/cowrie_plugin.py

@@ -32,7 +32,7 @@ FIXME: This module contains ...
 
 from __future__ import print_function
 
-from zope.interface import implementer
+from zope.interface import implementer, provider
 
 import os
 import sys
@@ -42,6 +42,7 @@ from twisted.plugin import IPlugin
 from twisted.application.service import IServiceMaker
 from twisted.application import internet, service
 from twisted.cred import portal
+from twisted.logger import ILogObserver, globalLogPublisher
 
 from cowrie.core.config import readConfigFile
 from cowrie import core
@@ -61,6 +62,16 @@ class Options(usage.Options):
         ]
 
 
+@provider(ILogObserver)
+def importFailureObserver(event):
+    if 'failure' in event and event['failure'].type is ImportError:
+        log.err("ERROR: %s. Please run `pip install -U -r requirements.txt` "
+                "from Cowrie's install directory and virtualenv to install "
+                "the new dependency" % event['failure'].value.message)
+
+
+globalLogPublisher.addObserver(importFailureObserver)
+
 
 @implementer(IServiceMaker, IPlugin)
 class CowrieServiceMaker(object):
@@ -132,7 +143,10 @@ class CowrieServiceMaker(object):
                 log.addObserver(output.emit)
                 self.output_plugins.append(output)
                 log.msg("Loaded output engine: {}".format(engine))
-            except:
+            except ImportError as e:
+                log.err("Failed to load output engine: {} due to ImportError: {}".format(engine, e))
+                log.msg("Please install the dependencies for {} listed in requirements-output.txt".format(engine))
+            except Exception:
                 log.err()
                 log.msg("Failed to load output engine: {}".format(engine))