[bug 1136840] Fix error handling for better debugging

* creates DebuggableWSGIHandler which should send more useful error
  emails so I can debug API-related problems, plus in DEBUG=True
  mode, it'll return plain formatted content rather than html formatted
  content; plain text is a lot easier to read in a terminal when
  debugging API-related problems
* created fjord/wsgi.py which gets used by "./manage.py runserver"
  and holds common WSGI setup for fjord
* adjusts wsgi/playdoh.wsgi which gets used by stage/prod environments
  to do stage/prod specific things and then use fjord/wsgi.py for
  the rest

fjord/settings/base.py

@@ -581,6 +581,7 @@ def JINJA_CONFIG():
     ]
 }
 
+WSGI_APPLICATION = 'fjord.wsgi.application'
 
 # When set to True, this will cause a message to be displayed on all
 # pages that this is not production.

fjord/wsgi.py

@@ -0,0 +1,30 @@
+# This file gets run by ./manage.py (runserver|test) and also gets
+# imported for the WSGI application building by wsgi/playdoh.wsgi
+# for stage/prod.
+#
+# It holds the setup that's common to both environments.
+
+import os
+
+import django
+from django.core.handlers.wsgi import WSGIHandler
+
+from fjord.wsgi_utils import BetterDebugMixin
+
+
+os.environ.setdefault('CELERY_LOADER', 'django')
+
+
+class DebuggableWSGIHandler(BetterDebugMixin, WSGIHandler):
+    pass
+
+
+def get_debuggable_wsgi_application():
+    # This does the same thing as
+    # django.core.wsgi.get_wsgi_application except it returns a
+    # different WSGIHandler.
+    django.setup()
+    return DebuggableWSGIHandler()
+
+
+application = get_debuggable_wsgi_application()

fjord/wsgi_utils.py

@@ -0,0 +1,87 @@
+from django.conf import settings
+
+
+class BetterDebugMixin(object):
+    """Provides better debugging data
+
+    Developing API endpoints and tired of wading through HTML for HTTP
+    500 errors?
+
+    Working on POST API debugging and not seeing the POST data show up
+    in the error logs/emails?
+
+    Then this mixin is for you!
+
+    It:
+
+    * spits out text rather than html when DEBUG = True (OMG! THANK
+      YOU!)
+    * adds a "HTTP_X_POSTBODY" META variable so you can see the raw post
+      data in error emails which is gross, but I couldn't figure out
+      a better way to do it
+
+    Usage:
+
+    Create a WSGIHandler subclass and bind that to ``application`` in
+    your wsgi file. For example::
+
+        import django
+        from django.core.handlers.wsgi import WSGIHandler
+
+        from fjord.wsgi_utils import BetterDebugMixin
+
+
+        class MyWSGIHandler(BetterDebugMixin, WSGIHandler):
+            pass
+
+
+        def get_debuggable_wsgi_application():
+            # This does the same thing as
+            # django.core.wsgi.get_wsgi_application except
+            # it returns a different WSGIHandler.
+            django.setup()
+            return MyWSGIHandler()
+
+
+        application = get_debuggable_wsgi_application()
+
+    """
+    def handle_uncaught_exception(self, request, resolver, exc_info):
+        if settings.DEBUG_PROPAGATE_EXCEPTIONS:
+            raise
+
+        # First, grab the raw POST body and put it somewhere that's
+        # guaranteed to show up in the error email.
+
+        # This should be "bytes" which is str type in Python 2.
+        #
+        # FIXME: This is probably broken with Python 3.
+        postbody = getattr(request, 'body', '')
+        try:
+            # For string-ish data, we truncate and decode/re-encode in
+            # utf-8.
+            postbody = postbody[:10000].decode('utf-8').encode('utf-8')
+        except (UnicodeDecodeError, UnicodeEncodeError):
+            # For binary, we say, 'BINARY CONTENT'
+            postbody = 'BINARY OR NON-UTF-8 CONTENT'
+
+        # The logger.error generates a record which can get handled by
+        # the AdminEmailHandler. Overriding all that machinery is
+        # daunting, so we're instead going to shove it in the META
+        # section which shows up when the machinery does a repr on
+        # WSGIRequest.
+        request.META['HTTP_X_POST_BODY'] = postbody
+
+        # Second, check the Accept header and if it's not text/html,
+        # pretend this is an AJAX request so that we get the output in
+        # text rather than html when DEBUG=True.
+        if settings.DEBUG:
+            # request.is_ajax() == True will push this into doing text
+            # instead of html which is waaaaaayyy more useful from an
+            # API perspective. So if the Accept header is anything other
+            # than html, we'll say it's an ajax request to return text.
+            if 'html' not in request.META.get('HTTP_ACCEPT', 'text/html'):
+                request.META['HTTP_X_REQUESTED_WITH'] = 'XMLHttpRequest'
+
+        return super(BetterDebugMixin, self).handle_uncaught_exception(
+            request, resolver, exc_info)

wsgi/playdoh.wsgi

@@ -1,6 +1,11 @@
+# This gets used by stage/prod to set up the WSGI application for stage/prod
+# use. We do some minor environment setup and then have `fjord/wsgi.py` do
+# the rest.
+
 import os
 import site
 
+# Set up NewRelic stuff.
 try:
     import newrelic.agent
 except ImportError:
@@ -15,7 +20,6 @@ if newrelic:
         newrelic = False
 
 
-os.environ.setdefault('CELERY_LOADER', 'django')
 # NOTE: you can also set DJANGO_SETTINGS_MODULE in your environment to override
 # the default value in manage.py
 
@@ -24,18 +28,23 @@ wsgidir = os.path.dirname(__file__)
 site.addsitedir(os.path.abspath(os.path.join(wsgidir, '../')))
 
 # Explicitly set these so that fjord.manage_utils does the right
-# thing.
+# thing in production.
 os.environ['USING_VENDOR'] = '1'
 os.environ['SKIP_CHECK'] = '1'
 
-# manage adds vendor to the Python path and otherwise sets up the
-# environment.
+# Importing manage has the side-effect of adding vendor/ stuff and
+# doing other environment setup.
 import manage
 
-from django.core.wsgi import get_wsgi_application
-application = get_wsgi_application()
+
+# This is the original Django WSGIHandler preserved here in case
+# we ever have to back out the debuggable one.
+# from django.core.wsgi import get_wsgi_application
+# application = get_wsgi_application()
+
+from fjord.wsgi import get_debuggable_wsgi_application
+application = get_debuggable_wsgi_application()
+
 
 if newrelic:
     application = newrelic.agent.wsgi_application()(application)
-
-# vim: ft=python