Implement TCP transport

src/py_dvt_ate/instruments/transport/__init__.py

@@ -8,5 +8,6 @@ Provides connection abstractions for different backends:
 
 from py_dvt_ate.instruments.transport.base import Transport
 from py_dvt_ate.instruments.transport.server import InstrumentServer, SCPIDevice
+from py_dvt_ate.instruments.transport.tcp import TCPTransport
 
-__all__ = ["Transport", "InstrumentServer", "SCPIDevice"]
+__all__ = ["Transport", "TCPTransport", "InstrumentServer", "SCPIDevice"]

src/py_dvt_ate/instruments/transport/tcp.py

@@ -0,0 +1,191 @@
+"""TCP socket transport for instrument communication."""
+
+import socket
+from typing import Any
+
+
+class TCPTransport:
+    """TCP socket transport implementation.
+
+    Implements the Transport protocol for communicating with SCPI
+    instruments over TCP/IP using newline-terminated messages.
+
+    Attributes:
+        host: Hostname or IP address of the instrument.
+        port: TCP port number.
+        timeout: Default socket timeout in seconds.
+    """
+
+    def __init__(
+        self,
+        host: str,
+        port: int,
+        timeout: float = 5.0,
+        encoding: str = "utf-8",
+    ) -> None:
+        """Initialise TCP transport.
+
+        Args:
+            host: Hostname or IP address.
+            port: TCP port number.
+            timeout: Default socket timeout in seconds.
+            encoding: Text encoding for commands and responses.
+        """
+        self._host = host
+        self._port = port
+        self._timeout = timeout
+        self._encoding = encoding
+        self._socket: socket.socket | None = None
+
+    @property
+    def host(self) -> str:
+        """Get the host address."""
+        return self._host
+
+    @property
+    def port(self) -> int:
+        """Get the port number."""
+        return self._port
+
+    @property
+    def is_connected(self) -> bool:
+        """Check if connection is active.
+
+        Returns:
+            True if connected, False otherwise.
+        """
+        return self._socket is not None
+
+    def connect(self) -> None:
+        """Establish connection to instrument.
+
+        Raises:
+            ConnectionError: If connection fails or already connected.
+        """
+        if self.is_connected:
+            raise ConnectionError("Already connected")
+
+        try:
+            self._socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            self._socket.settimeout(self._timeout)
+            self._socket.connect((self._host, self._port))
+        except (socket.error, OSError) as err:
+            self._socket = None
+            raise ConnectionError(
+                f"Failed to connect to {self._host}:{self._port}: {err}"
+            ) from err
+
+    def disconnect(self) -> None:
+        """Close connection to instrument.
+
+        Safe to call multiple times (idempotent).
+        """
+        if self._socket is not None:
+            try:
+                self._socket.close()
+            except OSError:
+                pass  # Ignore errors during close
+            finally:
+                self._socket = None
+
+    def write(self, command: str) -> None:
+        """Send command to instrument.
+
+        Commands are sent with newline terminator appended.
+
+        Args:
+            command: SCPI command string to send (without terminator).
+
+        Raises:
+            ConnectionError: If not connected.
+            IOError: If write fails.
+        """
+        if not self.is_connected or self._socket is None:
+            raise ConnectionError("Not connected")
+
+        try:
+            message = f"{command}\n".encode(self._encoding)
+            self._socket.sendall(message)
+        except (socket.error, OSError) as err:
+            raise OSError(f"Write failed: {err}") from err
+
+    def read(self, timeout: float | None = None) -> str:
+        """Read response from instrument.
+
+        Reads until newline terminator is received.
+
+        Args:
+            timeout: Read timeout in seconds. None uses default.
+
+        Returns:
+            Response string from instrument (without terminator).
+
+        Raises:
+            ConnectionError: If not connected.
+            TimeoutError: If read times out.
+            IOError: If read fails.
+        """
+        if not self.is_connected or self._socket is None:
+            raise ConnectionError("Not connected")
+
+        # Set timeout if specified
+        old_timeout = self._socket.gettimeout()
+        if timeout is not None:
+            self._socket.settimeout(timeout)
+
+        try:
+            # Read line by line (newline-terminated protocol)
+            response_bytes = b""
+            while True:
+                chunk = self._socket.recv(1)
+                if not chunk:
+                    raise ConnectionError("Connection closed by remote host")
+                response_bytes += chunk
+                if chunk == b"\n":
+                    break
+
+            # Decode and strip whitespace
+            return response_bytes.decode(self._encoding).strip()
+
+        except socket.timeout as err:
+            raise TimeoutError("Read timeout") from err
+        except (socket.error, OSError, UnicodeDecodeError) as err:
+            raise OSError(f"Read failed: {err}") from err
+        finally:
+            # Restore original timeout
+            if timeout is not None:
+                self._socket.settimeout(old_timeout)
+
+    def query(self, command: str, timeout: float | None = None) -> str:
+        """Send command and read response.
+
+        Convenience method combining write() and read().
+
+        Args:
+            command: SCPI command string to send.
+            timeout: Read timeout in seconds. None uses default.
+
+        Returns:
+            Response string from instrument.
+
+        Raises:
+            ConnectionError: If not connected.
+            TimeoutError: If read times out.
+            IOError: If communication fails.
+        """
+        self.write(command)
+        return self.read(timeout)
+
+    def __enter__(self) -> "TCPTransport":
+        """Context manager entry."""
+        self.connect()
+        return self
+
+    def __exit__(self, *args: Any) -> None:
+        """Context manager exit."""
+        self.disconnect()
+
+    def __repr__(self) -> str:
+        """String representation."""
+        status = "connected" if self.is_connected else "disconnected"
+        return f"TCPTransport({self._host}:{self._port}, {status})"