feat: add rtorrent client via PDCA

- Implement RTorrentClient extending DownloadClient abstract class
- Use xmlrpc package (v1.3.2) for XML-RPC communication
- Support HTTP Basic Auth when credentials are configured
- Map rTorrent states (d.state, d.is_active, d.is_hash_checking) to normalized statuses
- Calculate ETA from download speed and remaining bytes
- Add getRtorrentInstances() to config.js
- Register RTorrentClient in downloadClients.js registry
- Add 8 comprehensive unit tests covering all functionality
- Update .env.sample with rtorrent configuration examples
- Update ARCHITECTURE.md with rtorrent client details
- Update ADDING-A-DOWNLOAD-CLIENT.md with rtorrent-specific notes

server/clients/RTorrentClient.js

@@ -0,0 +1,185 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+const xmlrpc = require('xmlrpc');
+const DownloadClient = require('./DownloadClient');
+const { logToFile } = require('../utils/logger');
+
+/**
+ * rTorrent download client implementation.
+ * Communicates via XML-RPC over HTTP (typically ${url}/RPC2).
+ * Supports HTTP Basic Auth when username/password are configured.
+ */
+class RTorrentClient extends DownloadClient {
+  constructor(instance) {
+    super(instance);
+    this.rpcUrl = `${this.url}/RPC2`;
+    this._createClient();
+  }
+
+  _createClient() {
+    const clientOptions = { url: this.rpcUrl };
+
+    if (this.username && this.password) {
+      clientOptions.headers = {
+        Authorization: `Basic ${Buffer.from(`${this.username}:${this.password}`).toString('base64')}`
+      };
+    }
+
+    this.client = xmlrpc.createClient(clientOptions);
+  }
+
+  getClientType() {
+    return 'rtorrent';
+  }
+
+  async testConnection() {
+    try {
+      await this._methodCall('system.client_version');
+      logToFile(`[rtorrent:${this.name}] Connection test successful`);
+      return true;
+    } catch (error) {
+      logToFile(`[rtorrent:${this.name}] Connection test failed: ${error.message}`);
+      return false;
+    }
+  }
+
+  /**
+   * Wrap xmlrpc methodCall in a Promise.
+   * @param {string} method - XML-RPC method name
+   * @param {Array} params - Method parameters
+   * @returns {Promise<any>}
+   */
+  _methodCall(method, params = []) {
+    return new Promise((resolve, reject) => {
+      this.client.methodCall(method, params, (error, value) => {
+        if (error) {
+          reject(error);
+        } else {
+          resolve(value);
+        }
+      });
+    });
+  }
+
+  async getActiveDownloads() {
+    try {
+      const torrents = await this._methodCall('d.multicall2', [
+        '',
+        'd.hash=',
+        'd.name=',
+        'd.size_bytes=',
+        'd.completed_bytes=',
+        'd.down.rate=',
+        'd.up.rate=',
+        'd.state=',
+        'd.is_active=',
+        'd.is_hash_checking=',
+        'd.directory=',
+        'd.custom1='
+      ]);
+
+      logToFile(`[rtorrent:${this.name}] Retrieved ${torrents.length} torrents`);
+      return torrents.map(torrent => this.normalizeDownload(torrent));
+    } catch (error) {
+      logToFile(`[rtorrent:${this.name}] Error fetching torrents: ${error.message}`);
+      return [];
+    }
+  }
+
+  async getClientStatus() {
+    try {
+      const [downRate, upRate] = await Promise.all([
+        this._methodCall('throttle.global_down.rate'),
+        this._methodCall('throttle.global_up.rate')
+      ]);
+
+      return {
+        globalDownRate: downRate,
+        globalUpRate: upRate
+      };
+    } catch (error) {
+      logToFile(`[rtorrent:${this.name}] Error getting client status: ${error.message}`);
+      return null;
+    }
+  }
+
+  normalizeDownload(torrent) {
+    const [
+      hash,
+      name,
+      sizeBytes,
+      completedBytes,
+      downRate,
+      upRate,
+      state,
+      isActive,
+      isHashChecking,
+      directory,
+      custom1
+    ] = torrent;
+
+    const status = this._mapStatus(state, isActive, isHashChecking, completedBytes, sizeBytes);
+    const progress = sizeBytes > 0 ? Math.round((completedBytes / sizeBytes) * 100) : 0;
+
+    // Calculate ETA when actively downloading
+    let eta = null;
+    if (status === 'Downloading' && downRate > 0 && completedBytes < sizeBytes) {
+      eta = Math.round((sizeBytes - completedBytes) / downRate);
+    }
+
+    const arrInfo = this._extractArrInfo(name);
+
+    return {
+      id: hash,
+      title: name,
+      type: 'torrent',
+      client: 'rtorrent',
+      instanceId: this.id,
+      instanceName: this.name,
+      status,
+      progress,
+      size: sizeBytes,
+      downloaded: completedBytes,
+      speed: status === 'Seeding' ? upRate : downRate,
+      eta,
+      category: custom1 || undefined,
+      tags: custom1 ? [custom1] : [],
+      savePath: directory || undefined,
+      addedOn: undefined, // rtorrent does not expose added time via multicall2
+      arrQueueId: arrInfo.queueId,
+      arrType: arrInfo.type,
+      raw: torrent
+    };
+  }
+
+  _mapStatus(state, isActive, isHashChecking, completedBytes, sizeBytes) {
+    if (isHashChecking === 1) {
+      return 'Checking';
+    }
+
+    if (state === 0) {
+      return 'Stopped';
+    }
+
+    if (isActive === 1) {
+      return completedBytes >= sizeBytes && sizeBytes > 0 ? 'Seeding' : 'Downloading';
+    }
+
+    return 'Paused';
+  }
+
+  _extractArrInfo(filename) {
+    const seriesMatch = filename.match(/[-\s]S(\d{2})E(\d{2})/i);
+    if (seriesMatch) {
+      return { type: 'series' };
+    }
+
+    const movieMatch = filename.match(/\((\d{4})\)/);
+    if (movieMatch) {
+      return { type: 'movie' };
+    }
+
+    return {};
+  }
+}
+
+module.exports = RTorrentClient;