WIP: initial step towards websocket-based remote card [reader] access

Change-Id: I588bf4b3d9891766dd688a6818057ca20fb26e3f

pySim/wsrc/client_blocking.py

@@ -0,0 +1,68 @@
+"""Connect smartcard to a remote server, so the remote server can take control and
+perform commands on it."""
+
+import abc
+import json
+import logging
+from typing import Optional
+from websockets.sync.client import connect
+from osmocom.utils import b2h
+
+logger = logging.getLogger(__name__)
+
+class WsClientBlocking(abc.ABC):
+    """Generalized synchronous/blocking client for the WSRC (Web Socket Remote Card) protocol"""
+
+    def __init__(self, cltype: str, ws_uri: str):
+        self.client_type = cltype
+        self.ws_uri = ws_uri
+        self.ws = None
+
+    def connect(self):
+        self.ws = connect(uri=self.ws_uri)
+        self.perform_outbound_hello()
+
+    def tx_json(self, msg_type: str, d: dict = {}):
+        """JSON-Encode and transmit a message to the given websocket."""
+        d['msg_type'] = msg_type
+        d_js = json.dumps(d)
+        logger.debug("Tx: %s", d_js)
+        self.ws.send(d_js)
+
+    def tx_error(self, message: str):
+        event = {
+            'message': message,
+        }
+        self.tx_json('error', event)
+
+    def rx_json(self):
+        """Receive a single message from the given websocket and JSON-decode it."""
+        rx = self.ws.recv()
+        rx_js = json.loads(rx)
+        logger.debug("Rx: %s", rx_js)
+        assert 'msg_type' in rx
+        return rx_js
+
+    def transceive_json(self, tx_msg_type: str, tx_d: Optional[dict], rx_msg_type: str) -> dict:
+        self.tx_json(tx_msg_type, tx_d)
+        rx = self.rx_json()
+        assert rx['msg_type'] == rx_msg_type
+        return rx
+
+    def perform_outbound_hello(self, tx: dict = {}):
+        if not 'client_type' in tx:
+            tx['client_type'] = self.client_type
+        self.tx_json('hello', tx)
+        rx = self.rx_json()
+        assert rx['msg_type'] == 'hello_ack'
+        return rx
+
+    def rx_and_execute_cmd(self):
+        """Receve and dispatch/execute a single command from the server."""
+        rx = self.rx_json()
+        handler = getattr(self, 'handle_rx_%s' % rx['msg_type'], None)
+        if handler:
+            handler(rx)
+        else:
+            logger.error('Received unknown/unsupported msg_type %s' % rx['msg_type'])
+            self.tx_error('Message type "%s" is not supported' % rx['msg_type'])