Sympathy-MCP

Instructions

Args:
    vm: Name of the host (as configured in hosts.toml).
    path: Absolute path to the file on the remote host.

Returns:
    File contents as a string, or an error message.

Implementation Reference

• src/sympathy_mcp/server.py:129-144 (handler)

  MCP tool handler registration and execution logic for vm_file_read. Decorated with @mcp.tool() and calls the transport implementation (_vm_file_read) with error handling.

  @mcp.tool()
  async def vm_file_read(vm: str, path: str) -> str:
      """Read a file from a remote host via SSH.
  
      Args:
          vm: Name of the host (as configured in hosts.toml).
          path: Absolute path to the file on the remote host.
  
      Returns:
          File contents as a string, or an error message.
      """
      try:
          content = await _vm_file_read(vm, path)
          return content
      except (ValueError, KeyError, RuntimeError, OSError) as e:
          return f"ERROR: {e}"

• src/sympathy_mcp/transport.py:239-262 (handler)

  Core implementation of vm_file_read that reads a file from remote host via SSH using 'cat' command. Validates inputs, resolves host config, executes SSH command, and returns file contents or raises RuntimeError on failure.

  async def vm_file_read(vm: str, path: str) -> str:
      """Read a file from a remote host via SSH.
  
      Uses `ssh user@host cat <path>`.
  
      Args:
          vm: Name of the host (as configured in hosts.toml).
          path: Absolute path to the file on the remote host.
  
      Returns:
          File contents as a string.
  
      Raises:
          RuntimeError: If the file cannot be read.
      """
      host = _resolve_host(vm)
      _validate_path(path)
  
      result = await _run_ssh(host, ["cat", path])
      if result.exit_code != 0:
          raise RuntimeError(
              f"Failed to read {path} from {vm}: {result.stderr.strip()}"
          )
      return result.stdout

• src/sympathy_mcp/transport.py:77-124 (helper)

  Low-level SSH transport function (_run_ssh) used by vm_file_read to execute remote commands. Handles subprocess creation, timeout management, and returns ExecResult with stdout, stderr, and exit code.

  async def _run_ssh(
      host_config: HostConfig,
      remote_command: list[str],
      timeout: int = 120,
      stdin_data: bytes | None = None,
  ) -> ExecResult:
      """Run a command on a remote host via SSH.
  
      Args:
          host_config: SSH connection details for the target host.
          remote_command: Command and arguments to run remotely.
          timeout: Maximum seconds to wait.
          stdin_data: Optional bytes to pipe to stdin.
  
      Returns:
          ExecResult with stdout, stderr, and exit code.
  
      Raises:
          TimeoutError: If the command exceeds the timeout.
          OSError: If the ssh binary is not found.
      """
      ssh_args = host_config.ssh_args()
      full_cmd = ["ssh"] + ssh_args + remote_command
  
      proc = await asyncio.create_subprocess_exec(
          *full_cmd,
          stdout=asyncio.subprocess.PIPE,
          stderr=asyncio.subprocess.PIPE,
          stdin=asyncio.subprocess.PIPE if stdin_data else asyncio.subprocess.DEVNULL,
      )
  
      try:
          stdout_bytes, stderr_bytes = await asyncio.wait_for(
              proc.communicate(input=stdin_data),
              timeout=timeout,
          )
      except asyncio.TimeoutError:
          proc.kill()
          await proc.wait()
          raise TimeoutError(
              f"SSH command timed out after {timeout}s on {host_config.name}"
          )
  
      return ExecResult(
          stdout=stdout_bytes.decode("utf-8", errors="replace"),
          stderr=stderr_bytes.decode("utf-8", errors="replace"),
          exit_code=proc.returncode or 0,
      )

• src/sympathy_mcp/transport.py:55-62 (schema)

  Path validation helper (_validate_path) used by vm_file_read to ensure paths are absolute, non-empty, and don't contain null bytes for security.

  def _validate_path(path: str) -> None:
      """Validate a file path on the remote host (basic safety checks)."""
      if not path or not path.strip():
          raise ValueError("Path cannot be empty")
      if "\x00" in path:
          raise ValueError("Path cannot contain null bytes")
      if not path.startswith("/"):
          raise ValueError(f"Path must be absolute (start with /): '{path}'")

• src/sympathy_mcp/transport.py:193-197 (helper)

  Host resolution function (_resolve_host) that validates VM name and looks up HostConfig from the loaded configuration, used by vm_file_read to get SSH connection details.

  def _resolve_host(vm: str) -> HostConfig:
      """Resolve a VM/host name to its SSH config."""
      _validate_host_name(vm)
      config = _get_config()
      return config.get_host(vm)