testing: Add a simple grpc-web proxy

This proxy is used in the local testing environment to provide
node-access to browser based clients. It strips the transport
authentication, and replaces it with the payload authentication
already used for the signer context.

libs/gl-testing/gltesting/grpcweb.py

@@ -0,0 +1,108 @@
+# A simple grpc-web proxy enabling web-clients to talk to
+# Greenlight. Unlike the direct grpc interface exposed by the node and
+# the node domain proxy, the grpc-web proxy does not require a client
+# certificate from the client, making it possible for browsers to talk
+# to it. The client authentication via client certificates is no
+# longer present, but the payloads are still signed by the authorized
+# client, assuring authentication of the client.
+
+from gltesting.scheduler import Scheduler
+from ephemeral_port_reserve import reserve
+from threading import Thread, Event
+from http.server import ThreadingHTTPServer, BaseHTTPRequestHandler
+import logging
+import struct
+
+
+class GrpcWebProxy(object):
+    def __init__(self, scheduler: Scheduler, grpc_port: int):
+        self.logger = logging.getLogger("gltesting.grpcweb.GrpcWebProxy")
+        self.scheduler = scheduler
+        self.web_port = reserve()
+        self._thread: None | Thread = None
+        self.running = False
+        self.grpc_port = grpc_port
+        self.httpd: None | ThreadingHTTPServer = None
+        self.logger.info(
+            f"GrpcWebProxy configured to forward requests from web_port={self.web_port} to grpc_port={self.grpc_port}"
+        )
+
+    def start(self):
+        self._thread = Thread(target=self.run, daemon=True)
+        self.logger.info(f"Starting grpc-web-proxy on port {self.web_port}")
+        self.running = True
+        server_address = ("127.0.0.1", self.web_port)
+
+        self.httpd = ThreadingHTTPServer(server_address, Handler)
+        self.httpd.grpc_port = self.grpc_port
+        self.logger.debug(f"Server startup complete")
+        self._thread.start()
+
+    def run(self):
+        self.httpd.serve_forever()
+
+    def stop(self):
+        self.logger.info(f"Stopping grpc-web-proxy running on port {self.web_port}")
+        self.httpd.shutdown()
+        self._thread.join()
+
+
+class Handler(BaseHTTPRequestHandler):
+    def __init__(self, *args, **kwargs):
+        self.logger = logging.getLogger("gltesting.grpcweb.Handler")
+        BaseHTTPRequestHandler.__init__(self, *args, **kwargs)
+
+    def do_POST(self):
+        # We don't actually touch the payload, so we do not really
+        # care about the flags ourselves. The upstream sysmte will
+        # though.
+        flags = self.rfile.read(1)
+
+        # We have the length from above already, but that includes the
+        # header. Ensure that the two values match up.
+        strlen = self.rfile.read(4)
+        (length,) = struct.unpack_from("!I", strlen)
+        l = int(self.headers.get("Content-Length"))
+        assert l == length + 5
+
+        # Now we can finally read the body, It is kept as is, so no
+        # need to decode it, and we can treat it as opaque blob.
+        body = self.rfile.read(length)
+
+        # TODO extract the `glauthpubkey` and the `glauthsig`, then
+        # verify them. Fail the call if the verification fails,
+        # forward otherwise.
+        # This is just a test server, and we don't make use of the
+        # multiplexing support in `h2`, which simplifies this proxy
+        # quite a bit. The production server maintains a cache of
+        # connections and multiplexes correctly.
+
+        import httpx
+
+        url = f"http://localhost:{self.server.grpc_port}{self.path}"
+        self.logger.debug(f"Forwarding request to '{url}'")
+        headers = {
+            "te": "trailers",
+            "Content-Type": "application/grpc",
+            "grpc-accept-encoding": "idenity",
+            "user-agent": "My bloody hacked up script",
+        }
+        content = struct.pack("!cI", flags, length) + body
+        req = httpx.Request(
+            "POST",
+            url,
+            headers=headers,
+            content=content,
+        )
+        client = httpx.Client(http1=False, http2=True)
+
+        res = client.send(req)
+        res = client.send(req)
+
+        canned = b"\n\rheklllo world"
+        l = struct.pack("!I", len(canned))
+        self.wfile.write(b"HTTP/1.0 200 OK\n\n")
+        self.wfile.write(b"\x00")
+        self.wfile.write(l)
+        self.wfile.write(canned)
+        self.wfile.flush()