move config to toml and add optional debug logging

.gitignore

@@ -1 +1,3 @@
 __pycache__/
+*.toml
+!*.example.toml

app.py

@@ -4,61 +4,55 @@
 import io
 import os
 import sys
+import random
 import asyncio
 import aiohttp
 import contextlib
 import contextvars
 from yarl import URL
 from aiohttp import web
+import pytomlpp as toml
+from utils import build_dprint, ContextVar
 
-class ContextVar:
-	"""
-	contextvars.ContextVar, but you can call the var to get its value, rather than calling var.get()
-	"""
-	__slots__ = frozenset({'_var'})
-	def __init__(self, *a, **kw): self._var = contextvars.ContextVar(*a, **kw)
-	def __call__(self, *args): return self._var.get(*args)  # convenience
-	def get(self, *args): return self._var.get(*args)
-	def set(self, *args): return self._var.set(*args)
-	def reset(self, *args): return self._var.reset(*args)
+with open(sys.argv[1] if len(sys.argv) > 1 else 'config.toml') as f:
+	config = toml.load(f)
 
-pattern = os.environ['PATTERN'].encode()
-repl = os.environ['REPL'].encode()
-# TODO support upstream unix sockets
-upstream = os.environ['UPSTREAM']
-bind = sys.argv[1]
-socket_mod = int(os.environ.get('SOCKET_MODE', '775'), 8)
-replace_for = os.environ.get('REPLACE_FOR_HOST')
-try:
-	port = int(sys.argv[2])
-except IndexError:
-	port = 8080
+for host in config['hosts'].values():
+	if not host.get('replace', True): continue
+	host['pattern_decoded'] = host['pattern']
+	host['pattern'] = host['pattern'].encode()
+	host['repl_decoded'] = host['repl']
+	host['repl'] = host['repl'].encode()
+
+dprint = build_dprint(config.get('debug'))
 http = ContextVar('http')
 
 async def handler(request):
-	async with http().request(
+	hconfig = config['hosts'][request.host]
+	async with dprint() as print, http().request(
 		request.method,
-		URL(upstream).with_path(request.path),
+		# TODO support upstream unix sockets
+		URL(hconfig['upstream']).with_path(request.path),
 		headers=request.headers.copy(),
 		params=request.query.copy(),
 		data=await request.read() if request.can_read_body else None,
 		# proxy redirects as-is
 		allow_redirects=False,
 	) as upstream_resp:
+		print('proceeding for', request.host, request.path, '→', hconfig['upstream'])
 		headers = upstream_resp.headers.copy()
 		# we're not using gzip here so don't confuse our client
 		with contextlib.suppress(KeyError): del headers['Content-Encoding']
 		resp = web.StreamResponse(status=upstream_resp.status, headers=headers)
 		await resp.prepare(request)
 
-		if (
-			upstream_resp.content_type == 'text/html'
-			and (replace_for is None or request.host == replace_for)
-		):
+		if upstream_resp.content_type == 'text/html' and hconfig.get('replace', True):
 			# iter_lines when
+			print('replacing', repr(hconfig['pattern_decoded']), 'with', repr(hconfig['repl_decoded']))
 			while (line := await upstream_resp.content.readline()):
-				await resp.write(line.replace(pattern, repl))
+				await resp.write(line.replace(hconfig['pattern'], hconfig['repl']))
 		else:
+			print('not replacing')
 			async for chunk in upstream_resp.content.iter_chunked(io.DEFAULT_BUFFER_SIZE):
 				await resp.write(chunk)
 
@@ -69,16 +63,18 @@ async def amain():
 	srv = web.Server(handler)
 	runner = web.ServerRunner(srv)
 	await runner.setup()
-	if '/' in bind:
+	bind = os.path.expandvars(config['bind'])
+	if (unix := '/' in bind):
 		site = web.UnixSite(runner, bind)
 	else:
-		site = web.TCPSite(runner, host=bind, port=port)
+		site = web.TCPSite(runner, host=bind, port=(port := config.get('port', 8080)))
 	async with aiohttp.ClientSession() as http_:
 		http.set(http_)
 		await site.start()
+		print('Listening on', bind if unix else f'{bind}:{port}', end='...\n')
 		if '/' in bind:
 			with contextlib.suppress(KeyError):
-				os.chmod(bind, socket_mod)
+				os.chmod(bind, config.get('socket_mod', 0o775))
 		await asyncio.sleep(float('inf'))
 
 def main():

config.example.toml

@@ -0,0 +1,19 @@
+bind = '127.0.0.1'
+# you can also bind to a unix socket, and environment vars are supported:
+# bind = '$RUNTIME_DIRECTORY/replacer.sock'
+port = '8000'
+# if using a unix socket, you can specify the file access mode here. it defaults to 0o775.
+socket_mod = 0o777
+# whether to enable request logging. disabled by default
+debug = True
+
+# replace foo with bar for site1.example
+[hosts."site1.example"]
+upstream = 'http://localhost:3001'
+pattern = 'foo'
+repl = 'bar'
+
+# just pass through site2.example unmodified
+[hosts."site2.example"]
+upstream = 'http://localhost:3001'
+replace = false

utils.py

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+
+import random
+import contextlib
+import contextvars
+
+class ContextVar:
+	"""
+	contextvars.ContextVar, but you can call the var to get its value, rather than calling var.get()
+	"""
+	__slots__ = frozenset({'_var'})
+	def __init__(self, *a, **kw): self._var = contextvars.ContextVar(*a, **kw)
+	def __call__(self, *args): return self._var.get(*args)  # convenience
+	def get(self, *args): return self._var.get(*args)
+	def set(self, *args): return self._var.set(*args)
+	def reset(self, *args): return self._var.reset(*args)
+
+class asyncnullcontext(contextlib.AbstractAsyncContextManager):
+	async def __aenter__(self): return None
+	async def __aexit__(self, *excinfo): return None
+
+def build_dprint(debug: bool):
+	if debug:
+		class dprint(asyncnullcontext):
+			# 8 byte pseudo-random request tag
+			def __init__(self): self.req_id = ''.join(random.choices('0123456789abcdef', k=8 * 2))
+			def print(self, *args, **kwargs): print(f'[{self.req_id}]', *args, **kwargs)
+			async def __aenter__(self): return self.print
+	else:
+		class dprint(asyncnullcontext):
+			async def __aenter__(self):
+				return lambda *args, **kwargs: None
+
+	return dprint