Add PYINSTRUMENT_PROFILE_DIR option to Django middleware

This option allows users to profile every request, and save the HTML
output to a folder for later examination. This is especially good for
profiling API calls.

pyinstrument/middleware.py

@@ -2,6 +2,8 @@
 from django.conf import settings
 from pyinstrument import Profiler
 from pyinstrument.profiler import NotMainThreadError
+import time
+import os
 
 not_main_thread_message = (
     'pyinstrument can only be used on the main thread in signal mode. Run your server process in '
@@ -15,9 +17,10 @@
 
 class ProfilerMiddleware(object):
     def process_request(self, request):
+        profile_dir = getattr(settings, 'PYINSTRUMENT_PROFILE_DIR', None)
         use_signal = getattr(settings, 'PYINSTRUMENT_USE_SIGNAL', True)
 
-        if getattr(settings, 'PYINSTRUMENT_URL_ARGUMENT', 'profile') in request.GET:
+        if getattr(settings, 'PYINSTRUMENT_URL_ARGUMENT', 'profile') in request.GET or profile_dir:
             profiler = Profiler(use_signal=use_signal)
             try:
                 profiler.start()
@@ -31,7 +34,29 @@ def process_response(self, request, response):
             try:
                 request.profiler.stop()
 
-                return HttpResponse(request.profiler.output_html())
+                output_html = request.profiler.output_html()
+
+                profile_dir = getattr(settings, 'PYINSTRUMENT_PROFILE_DIR', None)
+
+                if profile_dir:
+                    filename = '{total_time:.3f}s {path} {timestamp:.0f}.html'.format(
+                        total_time=request.profiler.root_frame().time(),
+                        path=request.get_full_path().replace('/', '_'),
+                        timestamp=time.time()
+                    )
+
+                    file_path = os.path.join(profile_dir, filename)
+
+                    if not os.path.exists(profile_dir):
+                        os.mkdir(profile_dir)
+
+                    with open(file_path, 'w') as f:
+                        f.write(output_html)
+
+                if getattr(settings, 'PYINSTRUMENT_URL_ARGUMENT', 'profile') in request.GET:
+                    return HttpResponse(output_html)
+                else:
+                    return response
             except NotMainThreadError:
                 raise NotMainThreadError(not_main_thread_message)
         else: