Initial Commit

vm/vmd/client.py

@@ -0,0 +1,81 @@
+"""Client for vmd's unix socket.
+
+Newline-delimited JSON, one request per line, one reply per line. There
+is no framing beyond that and no session state in the protocol - vmd
+holds the session, because there is only ever one.
+
+Used by two callers: `vmctl` on the host, for driving a session by hand
+with no model in the loop, and the agent container, where each verb
+becomes a tool the sub-agent can call. Keeping them on the same client is
+deliberate: whatever the agent can do, a person can do by hand in the
+same order, which is what makes a misbehaving session reproducible.
+"""
+
+from __future__ import annotations
+
+import json
+import socket
+from typing import Any
+
+SOCKET_PATH = "/run/owuivm/agent/agent.sock"
+
+
+class VmdError(RuntimeError):
+    """vmd refused a verb. The message is written for a model to read."""
+
+
+class VmdUnavailable(RuntimeError):
+    """vmd is not running, or the socket is not reachable from here."""
+
+
+class Vmd:
+    def __init__(self, path: str = SOCKET_PATH, timeout: float = 1800.0) -> None:
+        self.path = path
+        self.timeout = timeout
+        self._sock: socket.socket | None = None
+        self._buf = b""
+
+    def __enter__(self) -> "Vmd":
+        self.connect()
+        return self
+
+    def __exit__(self, *_exc: object) -> None:
+        self.close()
+
+    def connect(self) -> None:
+        try:
+            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+            sock.settimeout(self.timeout)
+            sock.connect(self.path)
+        except OSError as exc:
+            raise VmdUnavailable(
+                f"cannot reach the VM daemon at {self.path}: {exc}. "
+                "It is not running, or this process is not in the group that "
+                "may talk to it."
+            ) from exc
+        self._sock = sock
+
+    def close(self) -> None:
+        if self._sock is not None:
+            try:
+                self._sock.close()
+            finally:
+                self._sock = None
+
+    def call(self, verb: str, **args: Any) -> dict[str, Any]:
+        if self._sock is None:
+            self.connect()
+        assert self._sock is not None
+        self._sock.sendall(json.dumps({"verb": verb, "args": args}).encode() + b"\n")
+        while True:
+            line, sep, rest = self._buf.partition(b"\n")
+            if sep:
+                self._buf = rest
+                reply = json.loads(line)
+                if not reply.get("ok"):
+                    raise VmdError(reply.get("error", "the VM daemon refused, with no reason given"))
+                return reply.get("result") or {}
+            chunk = self._sock.recv(1 << 20)
+            if not chunk:
+                raise VmdUnavailable("the VM daemon closed the connection")
+            self._buf += chunk