docs: prepare session file before first container start

Add touch telegram_session.session to setup instructions and clarify
that the session file must exist (even empty) before starting the container.

LICENSE

@@ -0,0 +1,201 @@
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README.md

@@ -1,7 +1,14 @@
 # Telegram Backup Downloader v5
 
+![Docker Image](https://img.shields.io/docker/v/hoelee/telegram-backup-downloader)
+![Platforms](https://img.shields.io/badge/platforms-linux%2Famd64%2C%20linux%2Farm64-blue)
+[![Docker Hub](https://img.shields.io/badge/Docker%20Hub-hoelee%2Ftelegram--backup--downloader-2496ED?logo=docker&logoColor=white)](https://hub.docker.com/r/hoelee/telegram-backup-downloader)
+[![GitHub](https://img.shields.io/badge/GitHub-hoelee%2Ftelegram--backup--downloader-181717?logo=github)](https://github.com/hoelee/telegram-backup-downloader)
+
 Downloads text, photos, videos, and documents from configured Telegram channels. Message text is stored in `messages.txt` and JSONL metadata; media is sorted into per-channel folders. SQLite tracks completed work, failed downloads, and sync progress.
 
+> **Platform support:** Docker images are built for `linux/amd64` and `linux/arm64` only. Legacy 32-bit ARM (`arm/v7`) is not supported because the `cryptg` Telethon extension has no prebuilt wheel for it. This covers servers, desktops, NAS devices, Raspberry Pi 4/5, and Apple Silicon via emulation.
+
 ## Prerequisites
 
 - Python 3.12 or Docker
@@ -18,11 +25,135 @@ Backups are written to `channels/`; logs are written to `logs/app.log`. Stop gra
 
 ## Docker
 
-1. Create and configure `config.json` from the example.
-2. Run `docker compose up -d --build`.
-3. Follow logs with `docker compose logs -f telegram-backup`.
+### Option A: Docker Compose (recommended)
 
-The compose configuration persists channels, logs, data, and the Telegram session. Set `status_port` to `8080` to use the supplied health check and publish the status API.
+The example `docker-compose.yml` uses the pre-built image from [Docker Hub](https://hub.docker.com/r/hoelee/telegram-backup-downloader) and supports `linux/amd64` and `linux/arm64`.
+
+**Before running**, create the folders and config file so the container can write to them. The compose file mounts local paths for config, session, data, channels, and logs:
+
+```bash
+mkdir -p data channels logs
+touch telegram_session.session
+cp config.example.json config.json
+# edit config.json with your Telegram values
+```
+
+> **Important:** The `telegram_session.session` file must exist (even empty) before the container starts. If the container can't find the session file, it will fail to start. Create an empty file as shown above.
+
+On Linux, if the container runs as a non-root user, make sure the current user has read+write access to these folders (the example compose runs as `root`).
+
+Then start the stack:
+
+```bash
+docker compose up -d
+docker compose logs -f telegram-backup
+```
+
+> **First-time login:** After the initial `docker compose up -d`, the container will start but won't be logged in yet. You need to authenticate interactively first:
+>
+> ```bash
+> # Stop the detached container
+> docker compose down
+>
+> # Run interactively — you'll be prompted for phone number + verification code
+> # (and password if you have 2FA enabled)
+> docker compose up
+>
+> # After successful login, press Ctrl+C to stop
+> docker compose down
+>
+> # Now start detached — session is saved
+> docker compose up -d
+> ```
+>
+> The session file is written to `./telegram_session.session` on the host, so subsequent starts won't ask for verification again (unless it expires or you delete the file).
+
+This is the `docker-compose.yml`:
+
+```yaml
+version: "3.9"
+
+services:
+  telegram-backup:
+    image: hoelee/telegram-backup-downloader:latest
+    container_name: telegram-backup
+    restart: unless-stopped
+    user: root
+    volumes:
+      - ./config.json:/app/config.json
+      - ./telegram_session.session:/app/telegram_session.session
+      - ./data:/app/data
+      - ./channels:/app/channels
+      - ./logs:/app/logs
+    ports:
+      - "8080:8080"
+    environment:
+      - TZ=Asia/Kuala_Lumpur
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8080/health', timeout=3)"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 15s
+```
+
+Set `status_port` to `8080` in `config.json` to use the health check and expose the status API.
+
+### Option B: docker run
+
+```bash
+mkdir -p data channels logs
+touch telegram_session.session
+cp config.example.json config.json
+
+docker run -d \
+  --name telegram-backup \
+  --restart unless-stopped \
+  -v $(pwd)/config.json:/app/config.json \
+  -v $(pwd)/telegram_session.session:/app/telegram_session.session \
+  -v $(pwd)/data:/app/data \
+  -v $(pwd)/channels:/app/channels \
+  -v $(pwd)/logs:/app/logs \
+  -p 8080:8080 \
+  -e TZ=Asia/Kuala_Lumpur \
+  hoelee/telegram-backup-downloader:latest
+```
+
+> **Important:** The `telegram_session.session` file must exist (even empty) before the container starts. Create an empty file as shown above.
+
+Follow logs with `docker logs -f telegram-backup`.
+
+> **First-time login:** After the initial `docker run -d`, the container will start but won't be logged in yet. You need to authenticate interactively first:
+>
+> ```bash
+> # Stop and remove the detached container
+> docker stop telegram-backup && docker rm telegram-backup
+>
+> # Run interactively — you'll be prompted for phone number + verification code
+> # (and password if you have 2FA enabled)
+> docker run -it --rm \
+>   -v $(pwd)/config.json:/app/config.json \
+>   -v $(pwd)/telegram_session.session:/app/telegram_session.session \
+>   -v $(pwd)/data:/app/data \
+>   -v $(pwd)/channels:/app/channels \
+>   -v $(pwd)/logs:/app/logs \
+>   -p 8080:8080 \
+>   -e TZ=Asia/Kuala_Lumpur \
+>   hoelee/telegram-backup-downloader:latest
+>
+> # After successful login, press Ctrl+C to exit
+> # Now run detached — session is saved to ./telegram_session.session
+> ```
+>
+> The session file is written to `./telegram_session.session` on the host, so subsequent starts won't ask for verification again (unless it expires or you delete the file).
+
+### Option C: Build from source
+
+```bash
+cp config.example.json config.json
+docker compose -f docker-compose.yml up -d --build
+docker compose logs -f telegram-backup
+```
 
 ## Configuration
 
@@ -45,10 +176,28 @@ The compose configuration persists channels, logs, data, and the Telegram sessio
 | `resync_interval_minutes` | No | `60` | Periodic backfill interval; `0` disables it. |
 | `status_port` | No | `0` | HTTP port; `0` disables the server. |
 | `db_path` | No | `telegram_state.db` | SQLite state database path. |
-| `channel_overrides` | No | `{}` | Per-channel `turnon` controls, for example `{"-1001":{"turnon":false}}`. |
-| `manual_downloads` | No | `{}` | Message IDs to prioritize, keyed by channel ID. |
+| `channel_overrides` | No | `{}` | Per-channel controls. Only `turnon` is supported. Use `turnon: false` to skip a channel without removing it from `channels`. Example: `{"-100321012345":{"turnon":false}}`. Change is detected by config watcher — no restart needed. |
+| `channel_last_message_id_overrides` | No | `{}` | One-time per-channel sync cursor overrides. With `updateonce: true`, sets the channel's SQLite `last_message_id` to the specified value, then automatically changes `updateonce` to `false` in `config.json`. Use numeric Telegram peer IDs that are included in `channels`. |
+| `manual_downloads` | No | `{}` | Message IDs to prioritize, keyed by channel ID. Useful to force-retry specific messages. Example: `{"-1001":[42,43,44]}`. Change is detected by config watcher — no restart needed. |
 
-`config.json` is watched every 10 seconds. Changes to channels, overrides, and manual downloads are applied without restarting. Do not set `status_port`, `db_path`, worker count, or API credentials expecting a live process to rebind/recreate those resources; restart after changing them.
+`config.json` must be mounted read-write. The program writes back to it directly — for example, when `channel_last_message_id_overrides` runs with `updateonce: true`, the downloader updates the database and then flips `updateonce` to `false` in the same file. A read-only mount (`:ro`) would break this and any other live config update.
+
+`config.json` is watched every 10 seconds. Changes to channels, overrides, cursor overrides, and manual downloads are applied without restarting. Do not set `status_port`, `db_path`, worker count, or API credentials expecting a live process to rebind/recreate those resources; restart after changing them.
+
+### One-Time Sync Cursor Override
+
+Use `channel_last_message_id_overrides` to resume a channel from a known message ID or re-download messages after a cursor correction. The channel must be present in `channels`. When the running downloader detects `updateonce: true`, it updates the database cursor and writes `updateonce: false` only after the database change succeeds.
+
+```json
+"channel_last_message_id_overrides": {
+  "-1004295572354": {
+    "updateonce": true,
+    "last_message_id": 21321
+  }
+}
+```
+
+The next sync starts from a small overlap before that cursor, so existing message and media records prevent duplicate output.
 
 ## HTTP API
 

config.example.json

@@ -4,7 +4,7 @@
   "api_hash": "your_api_hash_here",
   "phone_number": "+1234567890",
   "session_name": "telegram_session",
-  "channels": ["@channel_username", "-1001234567890"],
+  "channels": ["@channel_username", "-1001231231231", "-1003213213213"],
   "parallel_downloads": 3,
   "download_timeout_seconds": 600,
   "download_retry_count": 3,
@@ -16,7 +16,20 @@
   "retry_drop_log": true,
   "resync_interval_minutes": 60,
   "status_port": 8080,
-  "db_path": "telegram_state.db",
-  "channel_overrides": {},
+  "db_path": "/app/data/telegram_state.db",
+  "channel_overrides": {
+    "-1001231231231":{"turnon":false},
+    "-1003213213213":{"turnon":false}
+  },
+  "channel_last_message_id_overrides": {
+    "-1001231231231": {
+      "updateonce": false,
+      "last_message_id": 123123
+    },
+    "-1003213213213": {
+      "updateonce": false,
+      "last_message_id": 321321
+    }
+  },
   "manual_downloads": {}
-}
+}

docker-compose.yml

@@ -1,13 +1,15 @@
 version: "3.9"
+
 services:
   telegram-backup:
-    build: .
+    image: hoelee/telegram-backup-downloader:latest
     container_name: telegram-backup
     restart: unless-stopped
+    user: root
     volumes:
-      - ./config.json:/app/config.json:ro
+      # config.json must be read-write — the program writes back to it (e.g. flips updateonce to false)
+      - ./config.json:/app/config.json
       - ./telegram_session.session:/app/telegram_session.session
-      - ./data:/app/data
       - ./channels:/app/channels
       - ./logs:/app/logs
     ports:
@@ -19,4 +21,4 @@ services:
       interval: 30s
       timeout: 5s
       retries: 3
-      start_period: 15s
+      start_period: 15s

downloadv5.py

@@ -125,6 +125,17 @@ def validate_config(cfg):
         raise ValueError("Config key 'api_id' must be a positive integer")
     if not all(isinstance(channel, (str, int)) for channel in cfg["channels"]):
         raise ValueError("Config key 'channels' must contain strings or integers")
+    overrides = cfg.get("channel_last_message_id_overrides", {})
+    if not isinstance(overrides, dict):
+        raise ValueError("Config key 'channel_last_message_id_overrides' must be an object")
+    for channel_id, override in overrides.items():
+        if not isinstance(channel_id, str) or not isinstance(override, dict):
+            raise ValueError("Each channel_last_message_id_overrides entry must have a string channel ID and object value")
+        if not isinstance(override.get("updateonce"), bool):
+            raise ValueError(f"Override for channel '{channel_id}' must include boolean 'updateonce'")
+        message_id = override.get("last_message_id")
+        if not isinstance(message_id, int) or isinstance(message_id, bool) or message_id < 0:
+            raise ValueError(f"Override for channel '{channel_id}' must include a non-negative integer 'last_message_id'")
 
 
 def sanitize_filename(name):
@@ -192,6 +203,27 @@ async def update_last_message_id(channel_id, message_id):
     await db.commit()
 
 
+async def apply_last_message_id_overrides():
+    overrides = CONFIG.get("channel_last_message_id_overrides", {})
+    changed = False
+    for channel_id, override in overrides.items():
+        if not override["updateonce"]:
+            continue
+        if channel_id not in MONITORED_CHANNEL_IDS:
+            logger.warning("[CURSOR OVERRIDE] Channel %s is not resolved; will retry", channel_id)
+            continue
+        message_id = override["last_message_id"]
+        await db.execute("""INSERT INTO channel_state(channel_id,last_message_id) VALUES (?,?)
+            ON CONFLICT(channel_id) DO UPDATE SET last_message_id=excluded.last_message_id""",
+                         (channel_id, message_id))
+        await db.commit()
+        override["updateonce"] = False
+        changed = True
+        logger.info("[CURSOR OVERRIDE] Set channel %s last_message_id to %d", channel_id, message_id)
+    if changed:
+        await save_config()
+
+
 async def media_exists(channel_id, message_id):
     async with db.execute("SELECT 1 FROM downloaded_media WHERE channel_id=? AND message_id=?", (channel_id, message_id)) as cur:
         return await cur.fetchone() is not None
@@ -319,6 +351,7 @@ async def reload_config():
         RETRY_DROP_LOG = CONFIG.get("retry_drop_log", True)
         apply_channel_overrides()
         await resolve_channels()
+        await apply_last_message_id_overrides()
         if manual_changed:
             await process_manual_downloads()
         logger.info("[CONFIG] Reloaded")
@@ -339,6 +372,8 @@ async def config_watcher():
             if mtime != last_mtime:
                 last_mtime = mtime
                 await reload_config()
+            else:
+                await apply_last_message_id_overrides()
         except asyncio.CancelledError:
             break
         except Exception as error:
@@ -627,6 +662,7 @@ async def connection_supervisor():
         try:
             await client.connect()
             await resolve_channels()
+            await apply_last_message_id_overrides()
             if sync_task and not sync_task.done():
                 sync_task.cancel()
                 await asyncio.gather(sync_task, return_exceptions=True)
@@ -751,6 +787,7 @@ async def main():
     me = await client.get_me()
     logger.info("[CONNECTED] Logged in as %s", me.first_name)
     await resolve_channels()
+    await apply_last_message_id_overrides()
     await process_manual_downloads()
     for index in range(PARALLEL_DOWNLOADS):
         worker_tasks.append(asyncio.create_task(worker(index + 1)))