# Download Job Lifecycle When you submit a download over the REST API, the server does not block the request until it writes the file. Instead it creates a **job**, hands it back to you with an ID, and works through it in the background. Everything you do afterwards (watching progress, cancelling, retrying, reading the result) is done by referring to that job ID. This page explains the states a job moves through, how the server reports live progress, and how to cancel or retry. Clearly marked developer sections tell you how the job worker and the manager behind the queue operate the download. !!! info "Who this page is for" The first half is for anyone driving the API: the states, the fields you can read, and the calls that move a job around. The **Under the hood** sections near the end give the internal job worker and manager model, for contributors and for people who debug the server. You do not need them to use the API. For the full request and response shape of each endpoint, see [Endpoints](endpoints.md). For how the server reports errors, see [Error Responses](errors.md). ## The five states A job is always in exactly one of five states, exposed as the `status` field: | Status | Meaning | |---|---| | `queued` | Created and waiting for a free job worker. No download has started yet. | | `downloading` | A job worker has picked the job up and the download is in progress. | | `completed` | The download finished successfully; `output_files` lists the results. | | `failed` | The download stopped with an error; `error_message` and `error_code` explain why. | | `cancelled` | The job was cancelled before it could finish, from either the queued or downloading state. | The last three (`completed`, `failed`, and `cancelled`) are **terminal**: once a job reaches one of them it never changes state again. You can remove, retry, or read terminal jobs from history, but they will not resume. ## How a job moves between states ```mermaid stateDiagram-v2 [*] --> queued: POST /api/download queued --> downloading: a worker picks it up queued --> cancelled: DELETE (while queued) downloading --> completed: download succeeds downloading --> failed: download errors downloading --> cancelled: DELETE (while downloading) completed --> [*] failed --> [*] cancelled --> [*] completed --> queued: POST .../retry (as a NEW job) failed --> queued: POST .../retry (as a NEW job) cancelled --> queued: POST .../retry (as a NEW job) ``` The transitions in prose: - **`queued` → `downloading`** happens automatically. As soon as one of the server's workers is free, it takes the next job off the queue and starts it. You do not trigger this. You only observe it. - **`downloading` → `completed`** is the happy path: the download engine wrote all the requested files and reported success. - **`downloading` → `failed`** is any error during the download: a service failure, a network problem, a DRM error, and so on. The job records what went wrong. - **`queued`/`downloading` → `cancelled`** happens when you send a `DELETE` for a job that has not finished (see [Cancelling a job](#cancelling-a-job)). - **Retry** does *not* move a terminal job back to `queued`. Instead it creates a brand-new job that reuses the old job's service, title, and parameters. The original job stays in its terminal state (see [Retrying a job](#retrying-a-job)). !!! note "Priority does not change status" Moving a job to the front of the queue with the priority endpoint reorders *when* it will start, but it stays `queued` until a job worker picks it up. It is not a state change. ## Creating a job You queue a download with `POST /api/download`. The request needs at least a `service` and a `title_id`, plus any download options you want to set. On success the server replies with **`202 Accepted`** and the new job's identity: ```shell title="Queue a download" curl -X POST http://127.0.0.1:8786/api/download \ -H "X-Secret-Key: your-api-secret" \ -H "Content-Type: application/json" \ -d '{ "service": "EXAMPLE", "title_id": "81234567", "quality": ["1080"], "range": ["HDR10"] }' ``` ```json title="202 Accepted" { "job_id": "b1e6c7de-6d0a-4f2f-9d1e-3a2b4c5d6e7f", "status": "queued", "created_time": "2026-07-03T12:00:00.000000" } ``` The job starts in `queued`. The job workers auto-start on the first job you submit, so you switch nothing else on. Keep the `job_id`. Every later call uses it. !!! tip "The full parameter set" `POST /api/download` accepts the same download options as the `dl` command (quality, codecs, language selection, `wanted` episode ranges, and many more), with server-side defaults filling in anything you do not write. The [Endpoints](endpoints.md) page gives the complete list, their defaults, and the validation rules. ## Reading a job's status and progress There are two ways to look at jobs. === "One job in full" `GET /api/download/jobs/{job_id}` returns the complete detail for a single job, including parameters (with secrets redacted), timing, output files, and error information if it failed. ```shell curl http://127.0.0.1:8786/api/download/jobs/b1e6c7de-6d0a-4f2f-9d1e-3a2b4c5d6e7f \ -H "X-Secret-Key: your-api-secret" ``` === "All jobs (summaries)" `GET /api/download/jobs` lists every job the manager currently holds. By default each entry is a **summary**. Pass `full=true` to get the same full detail as the single-job endpoint for every job. ```shell curl "http://127.0.0.1:8786/api/download/jobs?status=downloading&sort_by=progress&sort_order=desc" \ -H "X-Secret-Key: your-api-secret" ``` You can filter the list by `status` and `service`, and order it with `sort_by` (`created_time`, `started_time`, `completed_time`, `progress`, `status`, or `service`) and `sort_order` (`asc` / `desc`). See [Endpoints](endpoints.md) for the query-parameter reference. ### The progress fields While a job is `downloading`, the following fields update roughly twice a second so a client can poll and render live progress. They are present on both the summary and the full detail: | Field | Type | Meaning | |---|---|---| | `progress` | number `0` to `100` | Overall percent complete. | | `phase` | string | Human-readable phase, e.g. `downloading video 1080p HDR10, audio en 5.1`. | | `title` | string | Title being processed. | | `current_title` | string | The specific episode/movie in progress (for a batch). | | `completed_tracks` | int | Number of tracks finished so far. | | `total_tracks` | int | Total tracks selected for the download. | | `active_tracks` | list of strings | Labels of the tracks downloading right now. | | `track_progress` | list | Per-active-track `{label, progress, speed}` entries. | | `segments_done` | number | Segments downloaded for the track in progress. | | `segments_total` | number | Total segments for the track in progress. | | `speed` | string | Transfer speed of the track in progress, e.g. `4.20 MB/s`. | | `skipped_subtitles` | list | Subtitles that were skipped as non-fatal failures (when `skip_subtitle_errors` is set). | | `input_prompt` | string or `null` | The prompt the service waits on. Answer it with `POST /api/download/jobs/{job_id}/input`. | The full detail adds `started_time`, `completed_time`, `output_files`, the redacted `parameters`, and, for failed jobs, `error_message`, `error_details`, `error_code`, `error_traceback`, and `worker_stderr`. !!! example "A typical polling loop" ```shell JOB=b1e6c7de-6d0a-4f2f-9d1e-3a2b4c5d6e7f while true; do curl -s "http://127.0.0.1:8786/api/download/jobs/$JOB" \ -H "X-Secret-Key: your-api-secret" \ | python -c 'import sys,json; d=json.load(sys.stdin); print(d["status"], d["progress"], d.get("phase"))' sleep 1 done ``` !!! tip "Or subscribe instead of polling" `GET /api/download/jobs/{job_id}/events` pushes the same job object as Server-Sent Events, and closes the event stream when the job ends. See [Endpoints](endpoints.md#get-apidownloadjobsjob_idevents). !!! note "What the percentage means" `progress` climbs from `0` toward `90` while tracks download, then the final stretch to `100` covers post-download work such as decryption cleanup, repackaging, and muxing. A job that has finished downloading but is still muxing can sit near `90` for a moment before completing. On success the manager sets it to exactly `100`. !!! warning "For a batch, `progress` is per-episode, not whole-batch" A multi-episode request (a `wanted` range) is a **single job** that processes its episodes sequentially. As each new episode begins, `progress` and the track counts (`completed_tracks` / `total_tracks`) **reset to zero** and count up again for that episode alone. The top-level bar therefore tracks the *current* episode, not the batch as a whole. To derive true overall completion, compare the growing `output_files` array against `parameters.wanted` rather than trusting `progress`. ## Terminal states in detail ### Completed A `completed` job has its `output_files` populated with the paths of the muxed results, and `progress` is `100`. This is the state you want. ### Failed A `failed` job carries the error. `error_message` is the short human message, `error_code` is one of the API's structured error codes (for example `NETWORK_ERROR`, `DRM_ERROR`, `AUTH_FAILED`, or `DOWNLOAD_ERROR`), and `error_details` gives more context. When you start the server with `--debug-api`, `error_traceback` and `worker_stderr` are also filled in, to help you find the cause. !!! tip "Secrets are scrubbed from error text" A service can echo a credential or a proxy URL into its output. The server masks any known secret values out of `error_message`, `error_details`, `error_traceback`, and `worker_stderr` before returning them, so it is safe to log these fields. The error-code catalogue and how each maps to an HTTP status is on the [Error Responses](errors.md) page. ### Cancelled The server stopped a `cancelled` job on request, before it finished. It may have partial output, but it is not considered complete. See below. ## Cancelling a job Send `DELETE /api/download/jobs/{job_id}`. The behaviour depends on the job's current state, and this is important because the response differs: | Job state when you DELETE | What happens | Response | |---|---|---| | `queued` or `downloading` | The job is cancelled. A running download's worker process is terminated. | `200` with `{"status": "success", "message": "Job cancelled"}` | | `completed`, `failed`, or `cancelled` (terminal) | The job is **removed** from the manager entirely. | `204 No Content`, empty body | | Not found | - | `404` with error code `JOB_NOT_FOUND` | In other words, `DELETE` on a live job *cancels* it, while `DELETE` on an already finished job *deletes it from the list*. This dual meaning is deliberate: one verb both stops in-flight work and tidies up afterwards. !!! warning "Do not parse the body of a 204" Removing a terminal job returns `204 No Content` with an empty body. A client must not try to decode JSON from it. Examine the status code first. ```shell title="Cancel a running job" curl -X DELETE http://127.0.0.1:8786/api/download/jobs/b1e6c7de-6d0a-4f2f-9d1e-3a2b4c5d6e7f \ -H "X-Secret-Key: your-api-secret" ``` To remove *all* terminal jobs at once, use `POST /api/download/jobs/clear-finished`, which returns `{"removed": }`. ## Retrying a job `POST /api/download/jobs/{job_id}/retry` re-runs a finished job by creating a **new** job with the same service, title, and parameters. The retry does not change the original job. It stays in its terminal state, and the response gives you the new job's ID with `202`. - You can retry only terminal jobs. A retry of a `queued` or `downloading` job returns `409` with error code `CONFLICT`. - A missing job returns `404` (`JOB_NOT_FOUND`). - The server examines the service allowlist and any download gates again for the new job, exactly as for the original submission. Thus the server can reject a retry with `INVALID_SERVICE` or `FORBIDDEN` if permissions changed. ```json title="202 Accepted, a fresh job" { "job_id": "c2f7d8ef-7e1b-5a3a-ae2f-4b3c5d6e7f80", "status": "queued", "created_time": "2026-07-03T12:30:00.000000" } ``` ## Prioritising a job `POST /api/download/jobs/{job_id}/priority` moves a **queued** job to the front of the line, so it will be the next one a free job worker picks up. - The job must be `queued`. Prioritising a job in any other state returns `409` (`CONFLICT`). A missing job returns `404`. - On success the response is `{"job_id": "", "position": "front"}`. This only reorders the queue. The job's status stays `queued` until a job worker starts it. ## History and retention The server also writes every job that reaches a terminal state once to a persistent history log. The job survives there even after the server removes it from the live list. - Read it with `GET /api/history` (newest first, with `limit` and `service` filters). - Delete a single entry with `DELETE /api/history/{job_id}` (returns `204`). The live in-memory jobs are separate from this on-disk history. A background cleanup task periodically drops old terminal jobs from the live list based on a retention period. The history file keeps them for later reference. See [Endpoints](endpoints.md) for the history response shape. !!! note "Why the history file lives under the cache directory" unshackle puts `api_history.jsonl` under the cache directory on purpose, so it stays out of the config/data tree. It is disposable runtime state, not user configuration or curated data, which is exactly why clearing the cache is a safe operation against it. --- ## Under the hood: the job worker and manager model !!! info "Developer section" Everything below describes server internals. It is useful for contributors and for anyone debugging the server, but it is not needed to *use* the API. ### The manager and its queue A single process-wide **download queue manager** owns all jobs. It holds them in memory keyed by ID, backs the wait list with a FIFO queue, and keeps a separate priority deque for the jobs it bumped to the front. On the first job, it starts a fixed pool of job worker tasks plus one cleanup task. The start is idempotent, so later jobs reuse the same pool. - **Concurrency**: `max_concurrent_downloads` (default **2**) caps it. That many jobs can be in `downloading` at once. The rest wait in `queued`. - **Retention**: `job_retention_hours` (default **24**) controls it. An hourly cleanup task removes terminal jobs whose completion time (or, if never started, creation time) is older than the retention window. !!! note "Two concurrency knobs that are easy to conflate" `max_concurrent_downloads` caps how many separate download **jobs** operate at once. The separate `serve.downloads` setting controls how many **tracks** download in parallel *within* a single job. They are independent, and raising one does not affect the other. !!! note "Concurrency and retention config keys" The manager reads these as top-level config attributes (`config.max_concurrent_downloads` and `config.download_job_retention_hours`). Those keys are not part of the standard config schema, so in practice the built-in defaults of **2** and **24** apply. [`GET /api/config`](endpoints.md) gives the live values. The related `serve.history_limit` (default **100**) instead controls how many entries the on-disk history file keeps. Each job worker loop drains the priority deque first, then the FIFO queue. The loop skips the stale FIFO copy of a promoted job, so it does not do the job twice. When a job worker takes a job it flips it to `downloading`, stamps `started_time`, does the download, and on finish stamps `completed_time` and records history. ### Each job runs in its own subprocess The manager does **not** operate the download in the server's event loop or even in the server process. For each job it spawns a separate Python subprocess: ```text python -m unshackle.core.api.download_worker ``` Three temporary files bridge the parent and the job worker: - **`payload.json`**: the manager writes it before launch. It contains the job ID, service, title ID, and merged parameters. - **`progress.json`**: the job worker writes it continuously as the download proceeds. - **`result.json`**: the job worker writes it at the end. The job worker has no terminal. When a service asks the user for input, the job worker writes the prompt to `progress.json` as `input_prompt` and waits. The answer from `POST /api/download/jobs/{job_id}/input` goes to the job worker on its stdin. Running each download out-of-process isolates the server from crashes, memory growth, and blocking work inside the download engine, and makes hard cancellation (killing the process) reliable. The job worker's exit codes are `0` for success, `1` for a download error, and `2` for bad arguments. Its `result.json` is either `{"status": "success", "output_files": [...]}` or `{"status": "error", "message", "error_details", "error_code", "traceback"}`. If the process exits non-zero, or the result is missing or not a success, the parent marks the job `failed` and adopts the job worker's `error_code` (or derives one by categorising the exception). ### How progress reaches the API While the job worker operates, the manager polls `progress.json` every **0.5 s** and copies the fields it finds onto the live `DownloadJob`. That is what the `GET` endpoints return. The job worker aggregates progress across all selected tracks. It weights each track's completion fraction by its bitrate, so video and audio dominate the bar and subtitles barely move it (subtitles get a small fixed weight). Track fractions are kept **monotonic**: the percentage only ever climbs. The job worker scales the download portion to fill `0` to `90`. The download engine drives the remaining `90` to `100` as it repackages and muxes. A track counts as done when it reaches a terminal state such as `Downloaded`, `Decrypted`, or a skipped subtitle. ### How cancellation works Each job carries a cancellation event. When you `DELETE` a live job: - If it is **`queued`**, it flips straight to `cancelled`, the manager records its history immediately (it never reaches a job worker), and the job worker loop skips it if it later pops it off the queue. - If it is **`downloading`**, the manager sets the cancellation event and flips the job to `cancelled`. The polling loop notices the event, `terminate()`s the job worker subprocess (escalating to `kill()` if it does not exit within 5 seconds), and raises a cancellation so the task unwinds. The subprocess model is what makes this a clean, immediate stop rather than a cooperative one. ### Secret handling in serialized jobs Job parameters may carry secrets: a raw `user:pass` credential, or a proxy URL with embedded userinfo. Whenever the manager serializes a job (for an API response or the history file), it masks the sensitive keys (`credential`, `credentials`, `password`, `token`, `api_key`) and strips userinfo from proxy URLs. The manager also scrubs free-text fields that a service might have leaked a secret into (`error_message`, `error_details`, `error_traceback`, `worker_stderr`, and job worker stdout/stderr in the logs). It removes the job's known secret values, longest-match first, before it returns or logs them. ## See also - [Endpoints](endpoints.md): the full request/response reference for every job endpoint. - [Error Responses](errors.md): the error envelope, codes, and HTTP statuses a failed job reports. - [Authentication](authentication.md): the `X-Secret-Key` header and per-key service allowlists that gate job creation and retry. - [Downloading](../../guide/downloading.md): the equivalent options on the `dl` command line.