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

plugins/host-metrics/backend/managers/cron.ts

@@ -0,0 +1,127 @@
+import type { Express } from "express";
+import { execCommand } from "../../../../src/backend/hosts/metrics-shared/common-utils.js";
+import { managerHandler, ManagerInputError } from "./route-helpers.js";
+import { shellSingleQuote } from "../../../../src/backend/hosts/metrics-shared/exec-elevated.js";
+import type { ManagerRoutesDeps } from "./types.js";
+
+export interface CronEntry {
+  raw: string;
+  enabled: boolean;
+  schedule: string;
+  command: string;
+}
+
+const READ_CRONTAB_CMD = "crontab -l 2>/dev/null";
+
+/** Parse a crontab into entries (comments/blank lines are dropped except as toggles). */
+export function parseCrontab(output: string): CronEntry[] {
+  const entries: CronEntry[] = [];
+  for (const raw of output.split("\n")) {
+    const line = raw.replace(/\s+$/, "");
+    if (!line.trim()) continue;
+    // A commented-out job: "# <schedule> <command>" (our toggle convention).
+    const disabled = line.match(
+      /^#\s*((?:@\w+|\S+\s+\S+\s+\S+\s+\S+\s+\S+)\s+.+)$/,
+    );
+    if (disabled) {
+      const { schedule, command } = splitScheduleCommand(disabled[1]);
+      if (command) {
+        entries.push({ raw: line, enabled: false, schedule, command });
+        continue;
+      }
+    }
+    // Skip pure comments / env assignments.
+    if (line.trimStart().startsWith("#")) continue;
+    if (/^\s*[A-Z_]+=/.test(line)) continue;
+    const { schedule, command } = splitScheduleCommand(line.trim());
+    if (!command) continue;
+    entries.push({ raw: line, enabled: true, schedule, command });
+  }
+  return entries;
+}
+
+function splitScheduleCommand(line: string): {
+  schedule: string;
+  command: string;
+} {
+  if (line.startsWith("@")) {
+    const [sched, ...rest] = line.split(/\s+/);
+    return { schedule: sched, command: rest.join(" ") };
+  }
+  const parts = line.split(/\s+/);
+  if (parts.length < 6) return { schedule: "", command: "" };
+  return {
+    schedule: parts.slice(0, 5).join(" "),
+    command: parts.slice(5).join(" "),
+  };
+}
+
+const CRON_SCHEDULE_RE =
+  /^(@(reboot|yearly|annually|monthly|weekly|daily|midnight|hourly)|[\d*/,-]+\s+[\d*/,-]+\s+[\d*/,-]+\s+[\d*/,A-Za-z-]+\s+[\d*/,A-Za-z-]+)$/;
+
+export function isValidCronSchedule(schedule: string): boolean {
+  return CRON_SCHEDULE_RE.test(schedule.trim());
+}
+
+/** Serialize entries into a full crontab body (toggled entries are commented). */
+export function serializeCrontab(entries: CronEntry[]): string {
+  const lines = entries.map((e) => {
+    const body = `${e.schedule} ${e.command}`.trim();
+    return e.enabled ? body : `# ${body}`;
+  });
+  return lines.join("\n") + (lines.length ? "\n" : "");
+}
+
+/** Build a command that atomically replaces the user crontab from the given body. */
+export function buildApplyCrontabCommand(body: string): string {
+  // printf the exact bytes into `crontab -` (reads new crontab from stdin).
+  return `printf '%s' ${shellSingleQuote(body)} | crontab -`;
+}
+
+export function registerCronRoutes(
+  app: Express,
+  { validateHostId, runOnHost }: ManagerRoutesDeps,
+): void {
+  app.get(
+    "/host-metrics/managers/cron/:id",
+    validateHostId,
+    managerHandler(runOnHost, "connect", "cron_list", async (client) => {
+      const { stdout } = await execCommand(client, READ_CRONTAB_CMD, 15000);
+      return { entries: parseCrontab(stdout) };
+    }),
+  );
+
+  app.post(
+    "/host-metrics/managers/cron/:id",
+    validateHostId,
+    managerHandler(
+      runOnHost,
+      "connect",
+      "cron_replace",
+      async (client, _host, req) => {
+        const { entries } = req.body as { entries?: CronEntry[] };
+        if (!Array.isArray(entries)) {
+          throw new ManagerInputError("entries must be an array");
+        }
+        for (const e of entries) {
+          if (typeof e?.command !== "string" || !e.command.trim()) {
+            throw new ManagerInputError("Each entry needs a command");
+          }
+          if (e.command.includes("\n")) {
+            throw new ManagerInputError("Commands cannot contain newlines");
+          }
+          if (!isValidCronSchedule(String(e.schedule))) {
+            throw new ManagerInputError(`Invalid schedule: ${e.schedule}`);
+          }
+        }
+        const body = serializeCrontab(entries);
+        const { stdout, stderr, code } = await execCommand(
+          client,
+          buildApplyCrontabCommand(body),
+          15000,
+        );
+        return { success: code === 0, output: stdout || stderr };
+      },
+    ),
+  );
+}