mosquitto: run mosquitto_ctrl inside the broker's container

The module's code moved out of its container and took mosquitto_ctrl from a host package. A
machine whose package index is stale cannot install it (hq issue 205), so the tools failed. The
broker's own image carries the tool at the broker's version: the tools exec into the running
broker, and the bootstrap seeds from a throwaway container of the same image.

modules/mosquitto/client.ts

@@ -18,6 +18,7 @@ import { randomBytes } from "node:crypto";
 import { connect as tcpConnect } from "node:net";
 import { readFileSync } from "node:fs";
 import { execFile } from "node:child_process";
+import { basename, dirname } from "node:path";
 import { promisify } from "node:util";
 
 import { missingAcls, parseRoleAcls, staleAcls, wantedAcls } from "./topics.js";
@@ -30,6 +31,14 @@ export interface MqttConn {
   /** The Dynamic Security admin client the runtime authenticates as. */
   readonly adminUser: string;
   readonly adminPassword: string;
+  /**
+   * The broker's own container, when `mosquitto_ctrl` is run inside it rather than from this
+   * machine's packages. The broker's image carries the tool at the broker's version, and inside it
+   * the broker listens on 127.0.0.1:1883 whatever port the machine publishes.
+   */
+  readonly container?: string;
+  /** The broker's image, to seed the security file before the broker has ever started. */
+  readonly image?: string;
 }
 
 export class MosquittoClient {
@@ -53,7 +62,11 @@ export class MosquittoClient {
         "mosquitto host or admin password is not set — mosquitto's own code cannot reach the broker",
       );
     }
-    return new MosquittoClient({ host, port, adminUser, adminPassword: adminPassword ?? "" });
+    return new MosquittoClient({
+      host, port, adminUser, adminPassword: adminPassword ?? "",
+      container: env.MESH_MQTT_CTRL_CONTAINER || undefined,
+      image: env.MESH_MQTT_CTRL_IMAGE || undefined,
+    });
   }
 
   get host(): string {
@@ -84,16 +97,18 @@ export class MosquittoClient {
    * to this single-purpose runtime container; see the module README.
    */
   async ctl(...args: string[]): Promise<string> {
+    const inside = this.conn.container !== undefined;
     const base = [
-      "-h", this.conn.host,
-      "-p", String(this.conn.port),
+      "-h", inside ? "127.0.0.1" : this.conn.host,
+      "-p", inside ? "1883" : String(this.conn.port),
       "-u", this.conn.adminUser,
       "-P", this.conn.adminPassword,
     ];
     let stdout: string;
     let stderr: string;
     try {
-      ({ stdout, stderr } = await run("mosquitto_ctrl", [...base, "dynsec", ...args], {
+      const [command, argv] = this.ctrl([...base, "dynsec", ...args]);
+      ({ stdout, stderr } = await run(command, argv, {
         maxBuffer: 16 << 20,
         timeout: 30_000,
       }));
@@ -240,10 +255,27 @@ export class MosquittoClient {
   async initBootstrapFile(configFile: string): Promise<void> {
     // `dynsec init <file> <admin-username> [admin-password]` is an offline file operation — it does
     // not connect to the broker. The password is a positional argument (omitting it prompts).
+    if (this.conn.image) {
+      // Before the broker has ever started there is no container to enter: a throwaway one from the
+      // broker's own image writes the file into the directory the broker will mount.
+      await run("docker", [
+        "run", "--rm", "--entrypoint", "mosquitto_ctrl",
+        "-v", `${dirname(configFile)}:/mosquitto/data`,
+        this.conn.image,
+        "dynsec", "init", `/mosquitto/data/${basename(configFile)}`, this.conn.adminUser, this.conn.adminPassword,
+      ], { maxBuffer: 16 << 20 });
+      return;
+    }
     await run("mosquitto_ctrl", ["dynsec", "init", configFile, this.conn.adminUser, this.conn.adminPassword], {
       maxBuffer: 16 << 20,
     });
   }
+
+  /** How `mosquitto_ctrl` is run here: inside the broker's container when one is named. */
+  ctrl(argv: string[]): [string, string[]] {
+    if (this.conn.container) return ["docker", ["exec", this.conn.container, "mosquitto_ctrl", ...argv]];
+    return ["mosquitto_ctrl", argv];
+  }
 }
 
 /** Generate a URL-safe password with no argv- or MQTT-hostile characters. */