feat(router): support middleware, helper for binding middleware to handler

prometheus_express/router.py

@@ -1,19 +1,34 @@
-def response(content, status='200 OK'):
+from prometheus_express.server import http_default_status
+
+
+def response(content, status=http_default_status):
     return {
         'status': status,
         'content': content,
     }
 
 
-def errorHandler(headers, body):
+def error_handler(headers, body):
     return response('Not Found', '404 Not Found')
 
 
+def bind_middleware(handler, middleware=[]):
+    def invoke(headers, body):
+        for m in middleware:
+            r = m(headers, body)
+            if r != None:
+                return r
+
+        return handler(headers, body)
+
+    return invoke
+
+
 def validate_route(handler):
     return (len(handler) == 3 and
-        type(handler[0]) == str and
-        type(handler[1]) == str and
-        callable(handler[2]))
+            type(handler[0]) == str and
+            type(handler[1]) == str and
+            callable(handler[2]))
 
 
 class Router():
@@ -50,4 +65,4 @@ class Router():
             if r[0] == method and r[1] == path:
                 return r[2]
 
-        return errorHandler
+        return error_handler

prometheus_express/server.py

@@ -10,7 +10,8 @@ def start_http_server(port, address='0.0.0.0', depth=2, timeout=5.0):
     bind_address = (address, port)
 
     http_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-    http_socket.bind(bind_address) # lgtm [py/bind-socket-all-network-interfaces]
+    # lgtm [py/bind-socket-all-network-interfaces]
+    http_socket.bind(bind_address)
     http_socket.listen(depth)
 
     try:

tests/test_router.py

@@ -1,10 +1,11 @@
+from unittest.mock import MagicMock
 import unittest
 import prometheus_express.router as pr
 
 
 class ErrorTest(unittest.TestCase):
     def test(self):
-        r = pr.errorHandler('', '')
+        r = pr.error_handler('', '')
         self.assertEqual(r['status'], '404 Not Found')
 
 
@@ -14,7 +15,7 @@ class RouterTest(unittest.TestCase):
         r.register('GET', '/foo', lambda headers, body: pr.response(''))
 
         h = r.select('GET', '/bar')
-        self.assertEqual(h, pr.errorHandler)
+        self.assertEqual(h, pr.error_handler)
 
     def test_match(self):
         def c(headers, body): return ''
@@ -65,4 +66,22 @@ class RouterTest(unittest.TestCase):
         r = pr.Router()
 
         with self.assertRaises(ValueError):
-            r.register('GET', '/', '')
+            r.register('GET', '/', '')
+
+
+class MiddlewareTest(unittest.TestCase):
+    def test_bind(self):
+        middleware = [
+            MagicMock(return_value=None),
+            MagicMock(return_value=None),
+        ]
+        handler = MagicMock(return_value=pr.response('foo'))
+
+        bound = pr.bind_middleware(handler, middleware)
+        headers = {}
+        response = bound(headers, '')
+
+        middleware[0].assert_called_once()
+        middleware[1].assert_called_once()
+        handler.assert_called_once()
+        self.assertEqual(response['content'], 'foo')

tests/test_server.py

@@ -62,4 +62,4 @@ class ServerAcceptTest(unittest.TestCase):
     r.register('GET', '/', lambda headers, req: body)
 
     with self.assertRaises(ValueError):
-      s.accept(r)
+      s.accept(r)