Allow proxying websockets over simple stream connections

This incorporates the functionality of websockify.  In doing so, it
eliminates an extra proxy layer and process, improving performance with
a fairly small amount of code.  Fixes #75.

This also generalizes and combines the _make_namedproxy_handler and
_make_supervisedproxy_handler functions into a single case to allow more
flexibility.

docs/source/server-process.md

@@ -153,6 +153,18 @@ One of:
 
 (server-process:callable-arguments)=
 
+### `websockify`
+
+_True_ to proxy only websocket connections into raw stream connections.
+_False_ (default) if the proxied server speaks full HTTP.
+
+If _True_, the proxied server is treated a raw TCP (or unix socket) server that
+does not use HTTP.
+In this mode, only websockets are handled, and messages are sent to the backend
+server as stream data. This is equivalent to running a
+[websockify](https://github.com/novnc/websockify) wrapper.
+All other HTTP requests return 405.
+
 #### Callable arguments
 
 Any time you specify a callable in the config, it can ask for any arguments it needs

jupyter_server_proxy/config.py

@@ -15,6 +15,7 @@
 from traitlets.config import Configurable
 
 from .handlers import AddSlashHandler, NamedLocalProxyHandler, SuperviseAndProxyHandler
+from .websockify import WebsockifyHandler, SuperviseAndWebsockifyHandler
 
 try:
     # Traitlets >= 4.3.3
@@ -41,52 +42,55 @@
         "new_browser_tab",
         "request_headers_override",
         "rewrite_response",
+        "websockify",
     ],
 )
 
 
-def _make_namedproxy_handler(sp: ServerProcess):
-    class _Proxy(NamedLocalProxyHandler):
-        def __init__(self, *args, **kwargs):
-            super().__init__(*args, **kwargs)
-            self.name = sp.name
-            self.proxy_base = sp.name
-            self.absolute_url = sp.absolute_url
-            self.port = sp.port
-            self.unix_socket = sp.unix_socket
-            self.mappath = sp.mappath
-            self.rewrite_response = sp.rewrite_response
-
-        def get_request_headers_override(self):
-            return self._realize_rendered_template(sp.request_headers_override)
-
-    return _Proxy
-
-
-def _make_supervisedproxy_handler(sp: ServerProcess):
+def _make_proxy_handler(sp: ServerProcess):
     """
-    Create a SuperviseAndProxyHandler subclass with given parameters
+    Create an appropriate handler with given parameters
     """
+    if sp.command:
+        cls = SuperviseAndWebsockifyHandler if sp.websockify else SuperviseAndProxyHandler
+        args = dict(state={})
+    elif not (sp.port or isinstance(sp.unix_socket, str)):
+        warn(
+            f"Server proxy {sp.name} does not have a command, port "
+            f"number or unix_socket path. At least one of these is "
+            f"required."
+        )
+        return
+    else:
+        cls = WebsockifyHandler if sp.websockify else NamedLocalProxyHandler
+        args = {}
 
     # FIXME: Set 'name' properly
-    class _Proxy(SuperviseAndProxyHandler):
+    class _Proxy(cls):
+        kwargs = args
+
         def __init__(self, *args, **kwargs):
             super().__init__(*args, **kwargs)
             self.name = sp.name
             self.command = sp.command
             self.proxy_base = sp.name
             self.absolute_url = sp.absolute_url
-            self.requested_port = sp.port
-            self.requested_unix_socket = sp.unix_socket
+            if sp.command:
+                self.requested_port = sp.port
+                self.requested_unix_socket = sp.unix_socket
+            else:
+                self.port = sp.port
+                self.unix_socket = sp.unix_socket
             self.mappath = sp.mappath
             self.rewrite_response = sp.rewrite_response
 
-        def get_env(self):
-            return self._realize_rendered_template(sp.environment)
-
         def get_request_headers_override(self):
             return self._realize_rendered_template(sp.request_headers_override)
 
+        # these two methods are only used in supervise classes, but do no harm otherwise
+        def get_env(self):
+            return self._realize_rendered_template(sp.environment)
+
         def get_timeout(self):
             return sp.timeout
 
@@ -108,24 +112,14 @@ def make_handlers(base_url, server_processes):
     """
     handlers = []
     for sp in server_processes:
-        if sp.command:
-            handler = _make_supervisedproxy_handler(sp)
-            kwargs = dict(state={})
-        else:
-            if not (sp.port or isinstance(sp.unix_socket, str)):
-                warn(
-                    f"Server proxy {sp.name} does not have a command, port "
-                    f"number or unix_socket path. At least one of these is "
-                    f"required."
-                )
-                continue
-            handler = _make_namedproxy_handler(sp)
-            kwargs = {}
+        handler = _make_proxy_handler(sp)
+        if not handler:
+            continue
         handlers.append(
             (
                 ujoin(base_url, sp.name, r"(.*)"),
                 handler,
-                kwargs,
+                handler.kwargs
             )
         )
         handlers.append((ujoin(base_url, sp.name), AddSlashHandler))
@@ -157,6 +151,7 @@ def make_server_process(name, server_process_config, serverproxy_config):
             "rewrite_response",
             tuple(),
         ),
+        websockify=server_process_config.get("websockify", False),
     )
 
 
@@ -273,6 +268,12 @@ def cats_only(response, path):
             instead of "dogs not allowed".
 
             Defaults to the empty tuple ``tuple()``.
+
+          websockify
+            Proxy websocket requests as a TCP (or unix socket) stream.
+            In this mode, only websockets are handled, and messages are sent to the backend,
+            equivalent to running a websockify layer (https://github.com/novnc/websockify).
+            All other HTTP requests return 405.
         """,
         config=True,
     )

jupyter_server_proxy/websockify.py

@@ -0,0 +1,88 @@
+"""
+A simple translation layer between tornado websockets and asyncio stream
+connections.
+
+This subsumes the functionality of websockify
+(https://github.com/novnc/websockify) without needing an extra proxy hop
+or process through with all messages pass for translation.
+"""
+
+import asyncio
+
+from .handlers import NamedLocalProxyHandler, SuperviseAndProxyHandler
+
+class WebsockifyProtocol(asyncio.Protocol):
+    """
+    A protocol handler for the proxied stream connection.
+    Sends any received blocks directly as websocket messages.
+    """
+    def __init__(self, handler):
+        self.handler = handler
+
+    def data_received(self, data):
+        "Send the buffer as a websocket message."
+        self.handler._record_activity()
+        self.handler.write_message(data, binary=True) # async, no wait
+
+    def connection_lost(self, exc):
+        "Close the websocket connection."
+        self.handler.log.info(f"Websockify {self.handler.name} connection lost: {exc}")
+        self.handler.close()
+
+class WebsockifyHandler(NamedLocalProxyHandler):
+    """
+    HTTP handler that proxies websocket connections into a backend stream.
+    All other HTTP requests return 405.
+    """
+    def _create_ws_connection(self, proto: asyncio.BaseProtocol):
+        "Create the appropriate backend asyncio connection"
+        loop = asyncio.get_running_loop()
+        if self.unix_socket is not None:
+            self.log.info(f"Websockify {self.name} connecting to {self.unix_socket}")
+            return loop.create_unix_connection(proto, self.unix_socket)
+        else:
+            self.log.info(f"Websockify {self.name} connecting to port {self.port}")
+            return loop.create_connection(proto, 'localhost', self.port)
+
+    async def proxy(self, port, path):
+        raise web.HTTPError(405, "websockets only")
+
+    async def proxy_open(self, host, port, proxied_path=""):
+        """
+        Open the backend connection. host and port are ignored (as they are in
+        the parent for unix sockets) since they are always passed known values.
+        """
+        transp, proto = await self._create_ws_connection(lambda: WebsockifyProtocol(self))
+        self.ws_transp = transp
+        self.ws_proto = proto
+        self._record_activity()
+        self.log.info(f"Websockify {self.name} connected")
+
+    def on_message(self, message):
+        "Send websocket messages as stream writes, encoding if necessary."
+        self._record_activity()
+        if hasattr(self, "ws_transp"):
+            if isinstance(message, str):
+                message = message.encode('utf-8')
+            self.ws_transp.write(message) # buffered non-blocking. should block?
+
+    def on_ping(self, message):
+        "No-op"
+        self._record_activity()
+
+    def on_close(self):
+        "Close the backend connection."
+        self.log.info(f"Websockify {self.name} connection closed")
+        if hasattr(self, "ws_transp"):
+            self.ws_transp.close()
+
+class SuperviseAndWebsockifyHandler(SuperviseAndProxyHandler, WebsockifyHandler):
+    async def _http_ready_func(self, p):
+        # not really HTTP here, just try an empty connection
+        try:
+            transp, _ = await self._create_ws_connection(asyncio.Protocol)
+        except OSError as exc:
+            self.log.debug(f"Websockify {self.name} connection check failed: {exc}")
+            return False
+        transp.close()
+        return True