Add JSON-RPC echo server for validation suite

Replaces the external jrpces binary dependency with a self-contained
Python script. The server supports TCP (newline-delimited JSON, port 4321)
and UDP (port 4323), handles JSON-RPC 1.0 and 2.0, and implements:
  - echo(*args) -> [args, {}]
  - unknown methods -> error {code: -32000, message: "function not found"}

test.tum is updated to launch jrpc_echo_server.py via python3 and wait
for the "ready" readiness message before running tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/validation/items/jsonrpc/jrpc_echo_server.py

@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+"""JSON-RPC echo server for the testium validation suite.
+
+Listens on TCP (newline-delimited JSON) and UDP.
+Supports JSON-RPC 1.0 and 2.0.
+
+Handlers:
+  echo(*args)  -> [args, {}]
+  <unknown>    -> error {code: -32000, message: "function not found"}
+
+Usage:
+  python3 jrpc_echo_server.py -c jrpces.ini
+"""
+import argparse
+import configparser
+import json
+import socket
+import sys
+import threading
+
+
+def _dispatch(method, params):
+    if method == "echo":
+        if not isinstance(params, list):
+            params = [params]
+        return True, [params, {}]
+    return False, {"code": -32000, "message": "function not found"}
+
+
+def _build_response(req, success, data):
+    req_id = req.get("id", None)
+    if req.get("jsonrpc") == "2.0":
+        if success:
+            return {"jsonrpc": "2.0", "result": data, "id": req_id}
+        else:
+            return {"jsonrpc": "2.0", "error": data, "id": req_id}
+    else:
+        if success:
+            return {"result": data, "error": None, "id": req_id}
+        else:
+            return {"result": None, "error": data, "id": req_id}
+
+
+def handle(raw: str) -> str:
+    try:
+        req = json.loads(raw)
+        method = req.get("method", "")
+        params = req.get("params", [])
+        success, data = _dispatch(method, params)
+        return json.dumps(_build_response(req, success, data))
+    except Exception as exc:
+        return json.dumps({"result": None, "error": {"code": -32700, "message": str(exc)}, "id": None})
+
+
+# ── TCP ──────────────────────────────────────────────────────────────────────
+
+def _handle_tcp_client(conn):
+    buf = b""
+    with conn:
+        conn.settimeout(5.0)
+        while True:
+            try:
+                chunk = conn.recv(4096)
+            except (socket.timeout, ConnectionResetError, OSError):
+                break
+            if not chunk:
+                break
+            buf += chunk
+            while b"\n" in buf:
+                line, buf = buf.split(b"\n", 1)
+                line = line.strip()
+                if line:
+                    resp = handle(line.decode())
+                    conn.sendall((resp + "\n").encode())
+
+
+def _tcp_server(host, port):
+    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    srv.bind((host, port))
+    srv.listen(5)
+    srv.settimeout(1.0)
+    print(f"TCP listening on {host}:{port}", flush=True)
+    while True:
+        try:
+            conn, _ = srv.accept()
+        except socket.timeout:
+            continue
+        threading.Thread(target=_handle_tcp_client, args=(conn,), daemon=True).start()
+
+
+# ── UDP ──────────────────────────────────────────────────────────────────────
+
+def _udp_server(host, port):
+    srv = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    srv.bind((host, port))
+    print(f"UDP listening on {host}:{port}", flush=True)
+    while True:
+        data, addr = srv.recvfrom(65535)
+        resp = handle(data.decode())
+        srv.sendto(resp.encode(), addr)
+
+
+# ── Main ─────────────────────────────────────────────────────────────────────
+
+def main():
+    parser = argparse.ArgumentParser(description="JSON-RPC echo server")
+    parser.add_argument("-c", "--config", required=True, help="Path to .ini config file")
+    args = parser.parse_args()
+
+    cfg = configparser.ConfigParser()
+    cfg.read(args.config)
+
+    tcp_host = cfg.get("jsonrpc_tcp", "host", fallback="0.0.0.0")
+    tcp_port = cfg.getint("jsonrpc_tcp", "port", fallback=4321)
+    udp_host = cfg.get("jsonrpc_udp", "host", fallback="0.0.0.0")
+    udp_port = cfg.getint("jsonrpc_udp", "port", fallback=4323)
+
+    tcp_thread = threading.Thread(target=_tcp_server, args=(tcp_host, tcp_port), daemon=True)
+    udp_thread = threading.Thread(target=_udp_server, args=(udp_host, udp_port), daemon=True)
+    tcp_thread.start()
+    udp_thread.start()
+
+    print("JSON-RPC echo server ready", flush=True)
+
+    try:
+        tcp_thread.join()
+    except KeyboardInterrupt:
+        sys.exit(0)
+
+
+if __name__ == "__main__":
+    main()

test/validation/items/jsonrpc/test.tum

@@ -1,27 +1,27 @@
 
 - console:
     name: json rpc echo server
-    doc: check if the jsonrpc echo server is installed
+    doc: check if jrpc_echo_server.py is available
     console_name: jrpces
     key: $(test)_PASS
     steps:
         - open:
             protocol: terminal
         - read_until: {expected: $(terminal_prompt), timeout: 1, no_fail: True}
-        - writeln: which jrpces
+        - writeln: test -f {{include_directory}}/jrpc_echo_server.py && echo JRPC_OK
-        - read_until: {expected: jrpces, timeout: 2}
+        - read_until: {expected: JRPC_OK, timeout: 2, no_fail: True}
 
 - group:
     name: jsonrpc tests
-    condition: <| '/jrpces' in r'''$(cn_json rpc echo server)''' |>
+    condition: <| 'JRPC_OK' in r'''$(cn_json rpc echo server)''' |>
     steps:
         - console:
             name: Start the json rpc echo server
             console_name: jrpces
             key: $(test)_PASS
             steps:
-                - writeln: jrpces -c {{include_directory}}/jrpces.ini
+                - writeln: python3 {{include_directory}}/jrpc_echo_server.py -c {{include_directory}}/jrpces.ini
-                - read_until: {expected: $(terminal_prompt), timeout: 1, no_fail: True}
+                - read_until: {expected: ready, timeout: 5}
 
         - console:
             name: Open the raw tcp Console