Enable WSGI for Python Function App (#45)

* Scaffolding http wsgi library

* Add converter to WSGI request

* Add wsgi handler

* Clean up syntax

* Test out basic scenario

* Added unittests

* Add exception test case

* Add middleware test case

* Fix code quality

Author: Hazhzeng

azure/functions/__init__.py

@@ -4,6 +4,7 @@
 from ._cosmosdb import Document, DocumentList  # NoQA
 from ._http import HttpRequest  # NoQA
 from ._http import HttpResponse  # NoQA
+from ._http_wsgi import WsgiMiddleware # NoQA
 from ._queue import QueueMessage  # NoQA
 from ._servicebus import ServiceBusMessage  # NoQA
 from .meta import get_binding_registry  # NoQA
@@ -34,6 +35,7 @@
     'EventHubEvent',
     'HttpRequest',
     'HttpResponse',
+    'WsgiMiddleware',
     'InputStream',
     'QueueMessage',
     'ServiceBusMessage',

azure/functions/_http_wsgi.py

@@ -0,0 +1,174 @@
+from typing import Callable, Dict, List, Optional, Any
+from io import BytesIO, StringIO
+from os import linesep
+from urllib.parse import urlparse
+from wsgiref.headers import Headers
+
+from ._abc import Context
+from ._http import HttpRequest, HttpResponse
+from ._thirdparty.werkzeug._compat import string_types, wsgi_encoding_dance
+
+
+class WsgiRequest:
+    _environ_cache: Dict[str, Any] = None
+
+    def __init__(self,
+                 func_req: HttpRequest,
+                 func_ctx: Optional[Context] = None):
+        url = urlparse(func_req.url)
+        func_req_body = func_req.get_body() or b''
+
+        # Convert function request headers to lowercase header
+        self._lowercased_headers = {
+            k.lower(): v for k, v in func_req.headers.items()
+        }
+
+        # Implement interfaces for PEP 3333 environ
+        self.request_method = getattr(func_req, 'method', None)
+        self.script_name = ''
+        self.path_info = getattr(url, 'path', None)
+        self.query_string = getattr(url, 'query', None)
+        self.content_type = self._lowercased_headers.get('content-type')
+        self.content_length = str(len(func_req_body))
+        self.server_name = getattr(url, 'hostname', None)
+        self.server_port = str(self._get_port(url, self._lowercased_headers))
+        self.server_protocol = 'HTTP/1.1'
+
+        # Propagate http request headers into HTTP_ environ
+        self._http_environ: Dict[str, str] = self._get_http_headers(
+            func_req.headers
+        )
+
+        # Wsgi environ
+        self.wsgi_version = (1, 0)
+        self.wsgi_url_scheme = url.scheme
+        self.wsgi_input = BytesIO(func_req_body)
+        self.wsgi_multithread = False
+        self.wsgi_multiprocess = False
+        self.wsgi_run_once = False
+
+        # Azure Functions context
+        self.af_function_directory = getattr(func_ctx,
+                                             'function_directory', None)
+        self.af_function_name = getattr(func_ctx, 'function_name', None)
+        self.af_invocation_id = getattr(func_ctx, 'invocation_id', None)
+
+    def to_environ(self, errors_buffer: StringIO) -> Dict[str, Any]:
+        if self._environ_cache is not None:
+            return self._environ_cache
+
+        environ = {
+            'REQUEST_METHOD': self.request_method,
+            'SCRIPT_NAME': self.script_name,
+            'PATH_INFO': self.path_info,
+            'QUERY_STRING': self.query_string,
+            'CONTENT_TYPE': self.content_type,
+            'CONTENT_LENGTH': self.content_length,
+            'SERVER_NAME': self.server_name,
+            'SERVER_PORT': self.server_port,
+            'SERVER_PROTOCOL': self.server_protocol,
+            'wsgi.version': self.wsgi_version,
+            'wsgi.url_scheme': self.wsgi_url_scheme,
+            'wsgi.input': self.wsgi_input,
+            'wsgi.errors': errors_buffer,
+            'wsgi.multithread': self.wsgi_multithread,
+            'wsgi.multiprocess': self.wsgi_multiprocess,
+            'wsgi.run_once': self.wsgi_run_once,
+            'azure_functions.function_directory': self.af_function_directory,
+            'azure_functions.function_name': self.af_function_name,
+            'azure_functions.invocation_id': self.af_invocation_id
+        }
+        environ.update(self._http_environ)
+
+        # Ensure WSGI string fits in IOS-8859-1 code points
+        for k, v in environ.items():
+            if isinstance(v, string_types):
+                environ[k] = wsgi_encoding_dance(v)
+
+        # Remove None values
+        self._environ_cache = {
+            k: v for k, v in environ.items() if v is not None
+        }
+        return self._environ_cache
+
+    def _get_port(self, parsed_url, lowercased_headers: Dict[str, str]) -> int:
+        port: int = 80
+        if lowercased_headers.get('x-forwarded-port'):
+            return int(lowercased_headers['x-forwarded-port'])
+        elif getattr(parsed_url, 'port', None):
+            return parsed_url.port
+        elif parsed_url.scheme == 'https':
+            return 443
+        return port
+
+    def _get_http_headers(self,
+                          func_headers: Dict[str, str]) -> Dict[str, str]:
+        # Content-Type -> HTTP_CONTENT_TYPE
+        return {f'HTTP_{k.upper().replace("-", "_")}': v for k, v in
+                func_headers.items()}
+
+
+class WsgiResponse:
+    def __init__(self):
+        self._status = ''
+        self._status_code = 0
+        self._headers = {}
+        self._buffer: List[bytes] = []
+
+    @classmethod
+    def from_app(cls, app, environ) -> 'WsgiResponse':
+        res = cls()
+        res._buffer = [x or b'' for x in app(environ, res._start_response)]
+        return res
+
+    def to_func_response(self) -> HttpResponse:
+        lowercased_headers = {k.lower(): v for k, v in self._headers.items()}
+        return HttpResponse(
+            body=b''.join(self._buffer),
+            status_code=self._status_code,
+            headers=self._headers,
+            mimetype=lowercased_headers.get('content-type'),
+            charset=lowercased_headers.get('content-encoding')
+        )
+
+    # PEP 3333 start response implementation
+    def _start_response(self, status: str, response_headers: List[Any]):
+        self._status = status
+        self._headers = Headers(response_headers)
+        self._status_code = int(self._status.split(' ')[0])  # 200 OK
+
+
+class WsgiMiddleware:
+    def __init__(self, app):
+        self._app = app
+        self._wsgi_error_buffer = StringIO()
+
+    # Usage
+    # main = func.WsgiMiddleware(app).main
+    @property
+    def main(self) -> Callable[[HttpRequest, Optional[Context]], HttpResponse]:
+        return self._handle
+
+    # Usage
+    # return func.WsgiMiddlewawre(app).handle(req, context)
+    def handle(self,
+               req: HttpRequest,
+               context: Optional[Context] = None) -> HttpResponse:
+        return self._handle(req, context)
+
+    def _handle(self,
+                req: HttpRequest,
+                context: Context) -> HttpResponse:
+        wsgi_request = WsgiRequest(req, context)
+        environ = wsgi_request.to_environ(self._wsgi_error_buffer)
+        wsgi_response = WsgiResponse.from_app(self._app, environ)
+        self._handle_errors()
+        return wsgi_response.to_func_response()
+
+    def _handle_errors(self):
+        if self._wsgi_error_buffer.tell() > 0:
+            self._wsgi_error_buffer.seek(0)
+            error_message = linesep.join(
+                self._wsgi_error_buffer.readline()
+            )
+            raise Exception(error_message)