Added HTTP override middleware to docs. This fixes #582

docs/patterns/index.rst

@@ -37,3 +37,4 @@ Snippet Archives <http://flask.pocoo.org/snippets/>`_.
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    deferredcallbacks
+   methodoverrides

docs/patterns/methodoverrides.rst

@@ -0,0 +1,43 @@
+Adding HTTP Method Overrides
+============================
+
+Some HTTP proxies do not support arbitrary HTTP methods or newer HTTP
+methods (such as PATCH).  In that case it's possible to “proxy” HTTP
+methods through another HTTP method in total violation of the protocol.
+
+The way this works is by letting the client do an HTTP POST request and
+set the ``X-HTTP-Method-Override`` header and set the value to the
+intended HTTP method (such as ``PATCH``).
+
+This can easily be accomplished with an HTTP middleware::
+
+    class HTTPMethodOverrideMiddleware(object):
+        allowed_methods = frozenset([
+            'GET',
+            'HEAD',
+            'POST',
+            'DELETE',
+            'PUT',
+            'PATCH',
+            'OPTIONS'
+        ])
+        bodyless_methods = frozenset(['GET', 'HEAD', 'OPTIONS', 'DELETE'])
+
+        def __init__(self, app):
+            self.app = app
+
+        def __call__(self, environ, start_response):
+            method = environ.get('HTTP_X_HTTP_METHOD_OVERRIDE', '').upper()
+            if method in self.allowed_methods:
+                method = method.encode('ascii', 'replace')
+                environ['REQUEST_METHOD'] = method
+            if method in self.bodyless_methods:
+                environ['CONTENT_LENGTH'] = '0'
+            return self.app(environ, start_response)
+
+To use this with Flask this is all that is necessary::
+
+    from flask import Flask
+
+    app = Flask(__name__)
+    app.wsgi_app = HTTPMethodOverrideMiddleware(app.wsgi_app)