Add support for transformation/translation modules that do arbitrary request processing to generate the message

Fixes #3

config.example.toml

@@ -22,3 +22,5 @@
 		#ircchannel = '#spam'
 		# auth can be either 'user:pass' for basic authentication or false to disable auth
 		#auth = false
+		# module is the path to a Python source file that handles the message transformation. It must contain a coroutine function 'process' that takes one argument, the aiohttp.web.Request object, and returns the message string to be sent to IRC, which must not contain any linebreaks (CR or LF). It may raise an aiohttp.web.HTTPException to stop processing; any other exception will also cause the processing to be stopped and a '400 Bad Request' response to be returned to the client. The empty default value (None) causes the default processor to be used, which expects a straight message in the request body (with an optional trailing CR+LF or LF) and performs no transformations other than encoding the message as UTF-8.
+		#module =

http2irc.py

@@ -4,6 +4,8 @@ import asyncio
 import base64
 import collections
 import concurrent.futures
+import importlib.util
+import inspect
 import logging
 import os.path
 import signal
@@ -114,9 +116,11 @@ class Config(dict):
 					raise InvalidConfig(f'Invalid map key {key!r}')
 				if not isinstance(map_, collections.abc.Mapping):
 					raise InvalidConfig(f'Invalid map for {key!r}')
-				if any(x not in ('webpath', 'ircchannel', 'auth') for x in map_):
+				if any(x not in ('webpath', 'ircchannel', 'auth', 'module') for x in map_):
 					raise InvalidConfig(f'Unknown key(s) found in map {key!r}')
 				#TODO: Check values
+				if 'module' in map_ and not os.path.isfile(map_['module']):
+					raise InvalidConfig(f'Module {map_["module"]!r} in map {key!r} is not a file')
 
 		# Default values
 		finalObj = {'logging': {'level': 'INFO', 'format': '{asctime} {levelname} {message}'}, 'irc': {'host': 'irc.hackint.org', 'port': 6697, 'ssl': 'yes', 'nick': 'h2ibot', 'real': 'I am an http2irc bot.', 'certfile': None, 'certkeyfile': None}, 'web': {'host': '127.0.0.1', 'port': 8080}, 'maps': {}}
@@ -129,6 +133,33 @@ class Config(dict):
 				map_['ircchannel'] = f'#{key}'
 			if 'auth' not in map_:
 				map_['auth'] = False
+			if 'module' not in map_:
+				map_['module'] = None
+
+		# Load modules
+		modulePaths = {map_['module'] for map_ in obj['maps'].values() if 'module' in map_ and map_['module'] is not None}
+		modules = {} # path: str -> module: module
+		for i, path in enumerate(modulePaths):
+			try:
+				# Build a name that is virtually guaranteed to be unique across a process.
+				# Although importlib does not seem to perform any caching as of CPython 3.8, this is not guaranteed by spec.
+				spec = importlib.util.spec_from_file_location(f'http2irc-module-{id(self)}-{i}', path)
+				module = importlib.util.module_from_spec(spec)
+				spec.loader.exec_module(module)
+			except Exception as e: # This is ugly, but exec_module can raise virtually any exception
+				raise InvalidConfig(f'Loading module {path!r} failed: {e!s}')
+			if not hasattr(module, 'process'):
+				raise InvalidConfig(f'Module {path!r} does not have a process function')
+			if not inspect.iscoroutinefunction(module.process):
+				raise InvalidConfig(f'Module {path!r} process attribute is not a coroutine function')
+			if len(inspect.signature(module.process).parameters) != 1:
+				raise InvalidConfig(f'Module {path!r} process function does not take exactly 1 parameter')
+			modules[path] = module
+
+		# Replace module value in maps
+		for map_ in obj['maps'].values():
+			if 'module' in map_ and map_['module'] is not None:
+				map_['module'] = modules[map_['module']]
 
 		# Merge in what was read from the config file and set keys on self
 		for key in ('logging', 'irc', 'web', 'maps'):
@@ -370,7 +401,7 @@ class WebServer:
 		self.messageQueue = messageQueue
 		self.config = config
 
-		self._paths = {} # '/path' => ('#channel', auth)  where auth is either False (no authentication) or the HTTP header value for basic auth
+		self._paths = {} # '/path' => ('#channel', auth, module)  where auth is either False (no authentication) or the HTTP header value for basic auth
 
 		self._app = aiohttp.web.Application()
 		self._app.add_routes([aiohttp.web.post('/{path:.+}', self.post)])
@@ -379,7 +410,7 @@ class WebServer:
 		self._configChanged = asyncio.Event()
 
 	def update_config(self, config):
-		self._paths = {map_['webpath']: (map_['ircchannel'], f'Basic {base64.b64encode(map_["auth"].encode("utf-8")).decode("utf-8")}' if map_['auth'] else False) for map_ in config['maps'].values()}
+		self._paths = {map_['webpath']: (map_['ircchannel'], f'Basic {base64.b64encode(map_["auth"].encode("utf-8")).decode("utf-8")}' if map_['auth'] else False, map_['module']) for map_ in config['maps'].values()}
 		needRebind = self.config['web'] != config['web']
 		self.config = config
 		if needRebind:
@@ -400,7 +431,7 @@ class WebServer:
 	async def post(self, request):
 		logging.info(f'Received request for {request.path!r}')
 		try:
-			channel, auth = self._paths[request.path]
+			channel, auth, module = self._paths[request.path]
 		except KeyError:
 			logging.info(f'Bad request: no path {request.path!r}')
 			raise aiohttp.web.HTTPNotFound()
@@ -409,6 +440,24 @@ class WebServer:
 			if not authHeader or authHeader != auth:
 				logging.info(f'Bad request: authentication failed: {authHeader!r} != {auth}')
 				raise aiohttp.web.HTTPForbidden()
+		if module is not None:
+			try:
+				message = await module.process(request)
+			except aiohttp.web.HTTPException as e:
+				raise e
+			except Exception as e:
+				logging.error(f'Bad request: exception in module process function: {e!s}')
+				raise aiohttp.web.HTTPBadRequest()
+			if '\r' in message or '\n' in message:
+				logging.error(f'Bad request: module process function returned message with linebreaks: {message!r}')
+				raise aiohttp.web.HTTPBadRequest()
+		else:
+			message = await self._default_process(request)
+		logging.debug(f'Putting message {message!r} for {channel} into message queue')
+		self.messageQueue.put_nowait((channel, message))
+		raise aiohttp.web.HTTPOk()
+
+	async def _default_process(self, request):
 		try:
 			message = await request.text()
 		except Exception as e:
@@ -423,9 +472,7 @@ class WebServer:
 		if '\r' in message or '\n' in message:
 			logging.info('Bad request: linebreaks in message')
 			raise aiohttp.web.HTTPBadRequest()
-		logging.debug(f'Putting message {message!r} for {channel} into message queue')
-		self.messageQueue.put_nowait((channel, message))
-		raise aiohttp.web.HTTPOk()
+		return message
 
 
 def configure_logging(config):