Method probeConnection

src/node/runtime/sshConnectionPool.ts:458–613

* Probe connection health by running a simple command

(
    config: SSHConnectionConfig,
    timeoutMs: number,
    key: string,
    controlPath = getControlPath(config),
    abortSignal?: AbortSignal
  )

   * Probe connection health by running a simple command
   */
  private async probeConnection(
    config: SSHConnectionConfig,
    timeoutMs: number,
    key: string,
    controlPath = getControlPath(config),
    abortSignal?: AbortSignal
  ): Promise<void> {
    if (abortSignal?.aborted) {
      throw new Error(SSH_OPERATION_ABORTED_ERROR);
    }

    const promptService = sshPromptService;
    const canPromptInteractively = isInteractiveHostKeyApprovalAvailable();

    const args: string[] = ["-T"]; // No PTY needed for probe

    if (config.port) {
      args.push("-p", config.port.toString());
    }

    if (config.identityFile) {
      args.push("-i", config.identityFile);
      args.push("-o", "LogLevel=ERROR");
    }

    // Connection multiplexing
    args.push("-o", "ControlMaster=auto");
    args.push("-o", `ControlPath=${controlPath}`);
    args.push("-o", "ControlPersist=60");

    // ConnectTimeout covers the entire SSH handshake including SSH_ASKPASS waits.
    // When host-key prompts are possible, use the longer prompt timeout so SSH
    // doesn't self-terminate while the user is responding to the dialog.
    // The Node.js timer still provides fast-fail for unreachable hosts.
    const connectTimeout = canPromptInteractively
      ? Math.ceil(HOST_KEY_APPROVAL_TIMEOUT_MS / 1000)
      : Math.min(Math.ceil(timeoutMs / 1000), 15);
    args.push("-o", `ConnectTimeout=${connectTimeout}`);
    args.push("-o", "ServerAliveInterval=5");
    args.push("-o", "ServerAliveCountMax=2");

    // Scope insecure host-key fallback to explicitly headless contexts where
    // no verification service is wired (e.g. CLI/test harness without UI).
    // Responder liveness only affects askpass prompt mechanics, not trust policy.
    appendOpenSSHHostKeyPolicyArgs(args);

    args.push(config.host, "echo ok");

    log.debug(`SSH probe: ssh ${args.join(" ")}`);

    let stderr = "";
    // Wired to the probe timer inside the Promise; the askpass callback
    // calls this to transition from connection phase (10s) to interaction
    // phase (60s) when a host-key prompt is detected.
    let extendDeadline: ((ms: number) => void) | undefined;

    // Set up SSH_ASKPASS for interactive host-key verification.
    // The askpass helper exchanges prompt/response text through temp files.