feat: ship host metrics as a first-party in-process plugin

plugins/host-metrics/backend/helpers.ts

@@ -0,0 +1,62 @@
+import type { Client } from "ssh2";
+import { usesIssuedCertificate } from "../../../src/backend/hosts/issued-certificate-auth.js";
+
+export type StatsCapableHost = {
+  connectionType?: string;
+  authType?: string;
+};
+
+export type TcpPingStatsConfig = {
+  statusCheckEnabled: boolean;
+  disableTcpPing?: boolean;
+};
+
+export function supportsMetrics(host: StatsCapableHost): boolean {
+  const connectionType = host.connectionType || "ssh";
+  if (connectionType !== "ssh") return false;
+  if (host.authType === "none" || usesIssuedCertificate(host.authType))
+    return false;
+  return true;
+}
+
+export function isTcpPingEnabled(statsConfig: TcpPingStatsConfig): boolean {
+  return statsConfig.statusCheckEnabled && !statsConfig.disableTcpPing;
+}
+
+export function parseStatusHostIds(value: unknown): Set<number> | null {
+  if (value === undefined) return null;
+  if (typeof value !== "string") return new Set();
+
+  return new Set(
+    value
+      .split(",")
+      .map(Number)
+      .filter((id) => Number.isSafeInteger(id) && id > 0),
+  );
+}
+
+export function tcpPingThroughJumpHost(
+  jumpClient: Pick<Client, "forwardOut" | "end">,
+  host: string,
+  port: number,
+  timeoutMs = 5000,
+): Promise<boolean> {
+  return new Promise((resolve) => {
+    let settled = false;
+
+    const finish = (result: boolean) => {
+      if (settled) return;
+      settled = true;
+      clearTimeout(timeout);
+      jumpClient.end();
+      resolve(result);
+    };
+
+    const timeout = setTimeout(() => finish(false), timeoutMs);
+
+    jumpClient.forwardOut("127.0.0.1", 0, host, port, (error, stream) => {
+      stream?.destroy();
+      finish(!error && !!stream);
+    });
+  });
+}