10. 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)