iptvnator/docs/architecture/download-manager.md

Download Manager Architecture

The download manager is a desktop-only feature that layers a curated queue, progress tracking, storage configuration, and playback controls on top of the existing Xtream (libs/portal/xtream) + Stalker (libs/portal/stalker) portal views. Backend work is handled in the Electron process while the Angular renderer exposes the global /workspace/downloads page, source-scoped route variants, contextual buttons, and theme-aware styling.

Backend responsibilities

• Queue control (apps/electron-backend/src/app/events/database/download-runtime.ts) DownloadTask mirrors a row of the shared downloads table (type Download in libs/shared/database/src/lib/schema.ts) plus transient cancel/pause/progress helpers (shared task types live in download-task.ts). Request validation and row creation live in download-requests.ts, while downloads.events.ts stays focused on IPC registration. enqueueDownload() pushes the task onto downloadQueue and triggers processQueue(). processQueue() keeps one active download, updates the row to downloading, and calls startDownload(). The byte transfer itself lives in download-transfer.ts, finalization and retained-partial persistence in download-finalize.ts, and the renderer update broadcast in download-broadcast.ts.
• Range-aware transfer (download-transfer.ts) The transfer streams the response through the backend's validated Axios redirect helper instead of electron-dl, and always requests Accept-Encoding: identity: Range offsets, totals, and the persisted .part must describe the same representation, and Axios's transparent gzip/brotli decoding would put decoded bytes on disk while every counter speaks encoded bytes. Headers (user agent, referer, origin) are persisted in request_headers and re-applied through the same allowlist when read back on retry/resume. Fresh Xtream movie and series-episode downloads propagate the playlist's configured headers, using its User-Agent when present and otherwise sharing the provider-compatible XTREAM_CLIENT_USER_AGENT used by Xtream API requests and stream probes. Retry, resume, and missing-file recovery resolve the owning playlist type and add that fallback to legacy Xtream rows without a stored User-Agent; known Stalker rows are left unchanged. Download rows deliberately outlive individually deleted playlists, so a headerless legacy row whose source no longer exists receives the same IPTV-player fallback because its original provider type cannot be recovered. Active pause/cancel operations abort the current request with AbortController; pause keeps the partial file and cancel removes it. Resume checks the existing .part size (rejecting anything that is not a regular file, so a symlink planted while paused is never followed). The first response's strong ETag (or Last-Modified) is persisted in resume_validator; a partial carrying that validator resumes with Range: bytes=<offset>- plus If-Range, so the server itself proves the entity is unchanged. A retained partial without a validator resumes through overlap verification instead (download-overlap.ts): the Range request rewinds by up to 256 KiB (OVERLAP_VERIFICATION_BYTES) and a transform stream compares that replayed window byte-for-byte against the partial's tail before anything is appended — a self-made validator for the many Xtream panels that send neither header. A mismatching overlap truncates the .part and restarts the transfer from byte zero (OverlapMismatchError); a partial smaller than the overlap window is verified in full from byte zero over a plain request and appended to — never rewritten in place, so a reconnect that dies early can only grow the file. Success requires the verifier to have consumed its ENTIRE window: a response that ends inside the overlap is an ordinary retained interruption when the stream died early, but a response that delivered its complete AUTHORITATIVE total inside the window — whether it then closed cleanly or reset — proves the remote entity shrank and restarts from scratch; the old suffix is never finalized as a completed file. An HTTP 416 answer to a resume request is classified by classifyRangeNotSatisfiable(): it COMPLETES only an exact-EOF request with identity proof (If-Range-backed, or the EOF probe that follows a fully verified overlap replay) whose stated bytes */N equals the partial — a bare length match on a rewound request proves nothing about whose bytes are on disk; it RESTARTS only when a STATED total proves the entity shrank — the total sits below a rewound request's first byte, or at it (the rewound range beginning exactly at the new EOF), or below the partial at an exact-EOF request; every length-less, ambiguous, or contradictory 416 RETAINS the partial, and none of these paths ever reaches generic cleanup. A validator promoted by a complete overlap match survives mid-append failures too: the promotion also runs on the error path, and retained-failure and pause persistence write resume_validator from the task, so later attempts resume via If-Range instead of replaying the window — without this, a server whose per-connection cap barely exceeds the window would stall out on sub-threshold progress. A verify-append attempt promotes the response's ETag/Last-Modified onto the row only after the complete overlap matched; until then the retained bytes are unproven and blessing them with a validator would let the next resume If-Range-append onto a foreign prefix. The response's TOTAL stays equally uncommitted (task and row) until the overlap matched — a persisted total equal to the unverified partial's size would let the completed-partial shortcut finalize unproven bytes after a pause, crash, or retained failure. Retained-interruption persistence keeps the live task in sync with the row (a stale falsified total would make the next reconnect's resume-offset guard reject the partial). Overlap replay re-counts bytes from the rewound offset, so reported progress is floored at the partial's retained size whenever the transfer appends — a response that ends inside the overlap can never move displayed progress backwards. A 206 Partial Content answer must start at the requested offset (Content-Range is verified) before bytes are appended; any other 2xx answer — the server ignoring Range, or If-Range detecting that the remote file changed — restarts the transfer from byte zero over the same .part instead of failing the download.
• Destination collision policy Existing destination files are never overwritten, inspected, or deleted. Before starting a new transfer, the backend atomically reserves a free numbered .part path while leaving the final destination path absent. The selected final filePath and fileName are persisted before transfer begins. When a retained download's recorded destination got occupied while it was paused or failed (for example by a file the user created), the retained .part is renamed aside and finalized to the next free numbered destination (Movie (1).mp4) instead of resolving the collision by size or unlink(). Completion creates the final filePath from the .part without overwriting an existing file; cancel and non-recoverable transfer failures remove the .part, while finalization failures, completed-partial failures, and allowlisted network interruptions after bytes reached disk deliberately retain it (the row keeps filePath so a later retry can finish without re-downloading); pause and restart recovery keep partials. A retry resumes through If-Range when a validator was stored and through overlap verification otherwise. Re-downloading such a failed row from a detail page (DOWNLOADS_START) deletes the retained .part before the row is reset.
• Derived file readiness and recovery DOWNLOADS_GET_LIST and DOWNLOADS_GET inspect completed destinations on every read. Only regular, non-symbolic-link files are reported as available; missing paths, directories, symlinks, and inspection errors are reported as missing without changing the persisted completed transfer status. DOWNLOADS_REDOWNLOAD_MISSING accepts only the managed row id, rechecks the file, and returns a recovered result without network access when it has reappeared. Otherwise it conditionally claims the completed row, preserves its owned destination, re-applies the stored header allowlist and URL safety policy, and enqueues a fresh transfer without overwriting an existing file.
• IPC surface
  The backend exposes DOWNLOADS_* handlers for list retrieval, start/pause/resume/cancel/retry/missing-file recovery/remove operations, folder selection/reveal, and the DOWNLOADS_UPDATE_EVENT emitter that the renderer listens to in order to refresh its signal store.

Renderer architecture

• Downloads service (libs/services/src/lib/downloads.service.ts) DownloadsService.downloads is the renderer's authoritative global list. loadDownloads() therefore always invokes the Electron list IPC without its legacy optional playlist scope. Route scope, category, and search must never replace or narrow that signal. Loads are serialized: at most one list IPC is active, and callers arriving during it coalesce behind one trailing refresh. Each response therefore commits in request order. A caller assigned to the trailing refresh resolves after that refresh settles even when later broadcasts queue the following refresh, preventing both stale continuation and starvation during frequent progress updates. hasLoadedDownloads records that the latest attempt completed, including an error, while hasAuthoritativeDownloadList becomes true after a successful request, remains true while a later refresh is in flight, and clears only if the latest request fails. Series download actions require both loaded and authoritative state so a failed refresh cannot restart rows missing from a stale or empty renderer snapshot. Before each fresh download or resume the service asks the main process for an authorized folder and calls the corresponding IPC command. The onDownloadsUpdate broadcast triggers a new global load.
• Series season queueing SeasonDownloadCoordinator owns synchronous, per-identity pending reservations and submits an individual episode or selected-season snapshot through DownloadsService.startDownload(). Season batches are sequential and best-effort: one candidate failing does not stop later candidates. After added or stable duplicate submissions, one authoritative list refresh closes the pending-to-queued/downloaded handoff, and the coordinator returns added, skipped, and failed counts. Xtream and Stalker adapters own provider URL, request header, and metadata preparation; the coordinator owns only provider-neutral orchestration. When a reserved candidate matches a completed-missing row, the coordinator performs one authoritative preflight refresh before any provider preparation. If another list request is active, the preflight joins the single trailing refresh; later download-update broadcasts cannot delay that assigned refresh. Restored files therefore become stable skips without requiring a Stalker URL/network request. Both providers use normalized episode.id as the canonical episode xtreamId; Stalker originalCmd and originalId participate only in URL resolution. Provider adapters preserve numeric season zero, including a fallback season key of "0", so Specials keep distinct S00 coordinates. The exact (playlistId, contentType, xtreamId) identity is authoritative. Complete (playlistId, seriesXtreamId, seasonNumber, episodeNumber) coordinates are a legacy episode-compatibility fallback. Stalker also stores an episode_identity_scope for regular /series, embedded VOD series[], and lazy Ministra VOD is_series origins. A known different scope is a different episode owner; an older coordinate row without a provable scope fails closed instead of being migrated across modes. Exact canonical legacy rows remain authoritative. Other ambiguous or conflicting matches resolve to the same explicit renderer conflict state rather than masquerading as a missing row, so both the episode action and season count fail closed. SQLite null and optional undefined coordinates both mean that a canonical legacy row is incomplete, matching the backend resolver. Renderer-pending, queued, downloading, and paused episodes are skipped, as are completed rows whose file is available or whose availability is still unknown. Failed, canceled, completed-missing, and unambiguous row-less episodes are eligible; a completed-missing row is restarted as a fresh download. Before resetting such a completed row, DOWNLOADS_START asynchronously rechecks its retained path in the main process. A restored file returns stable reason: 'already-downloaded' without mutation; active matches return reason: 'already-in-progress'. The recheck has a one-second caller deadline that starts before shared-slot acquisition; timeout or probe failure leaves the row untouched and returns a failed submission, allowing the sequential season loop to continue. Completed-file list callers have the same deadline and report a timeout as missing for that snapshot. The underlying filesystem operation remains coalesced and charged against the four-probe cap until it actually settles, so later callers get independent bounded waits without duplicating stalled native work. Only ENOENT and ENOTDIR are authoritative absence; permission, I/O, and other probe errors remain unknown, so DOWNLOADS_START leaves the completed row and file path untouched. Before a completed-missing, failed, or canceled row clears its path, the same start IPC asynchronously removes any retained .part. Cleanup coalesces same-path work and allows at most four underlying unlinks. A one-second admission deadline rejects queued work before it can mutate the filesystem; once an unlink starts, the request awaits its authoritative result so no late side effect can race a retry. Permission and I/O failures keep the row's ownership intact, while ENOENT and ENOTDIR safely proceed. The coordinator counts both stable duplicate reasons as skipped. There is no batch IPC, parallel transfer, or queue reordering: destination authorization, persisted header handling, and the backend's one-active-transfer FIFO semantics remain unchanged.
• Pure manager model (download-manager.viewmodel.ts and download-library.viewmodel.ts) derives the current route scope, search/category filtering, queue partitions, stable ordering, counts, and tracked byte total without mutating service state. queued, downloading, and paused rows form the active surface; failed and canceled rows form the attention surface. A completed row whose derived file availability is missing also enters attention with a dedicated recovery reason; only available completed rows enter the offline library. Completed episodes with a valid seriesXtreamId are grouped by (playlistId, seriesXtreamId), ordered by season and episode, and represented by one poster card. Episodes without a usable series id remain standalone cards so they never disappear.
• Downloads workspace (libs/portal/downloads/feature) keeps orchestration in DownloadsComponent, async mutations in the component-scoped DownloadManagerActionsService, source-route resolution in DownloadLibraryNavigationService, and rendering in the presentational DownloadQueueComponent, DownloadLibraryComponent, and DownloadedSeriesDialogComponent. Presentational children emit typed DownloadItemAction values and do not inject the download service, router, dialogs, or snackbars. The fixed header and filter row sit above one vertical scroll owner. The queue and library sections share one heading treatment (the dashboard-rail title style with an .app-count-badge item count) so same-level sections read alike; the queue's bordered panel wraps only the row list. Queue rows expose exactly one visible primary action — pause, resume, or retry — while cancel, copy-URL, and remove live in the row's overflow menu, so two adjacent destructive icons never compete. Completed movies and grouped series reuse the portal's canonical content grid as compact poster cards borrowed from the dashboard-rail card language: a type badge and an always-visible ⋮ trigger sit on the artwork, the title and series facts sit below it, and Play / Show in folder / Copy URL / Remove live in that overflow menu. File size is not repeated on the card; it belongs to the focused offline detail. Both completed cards and their loading skeleton consume the global --cover-grid-min-width / --cover-gap tokens, so the Small, Medium, and Large cover preference behaves like it does elsewhere in the app. All surfaces use the existing --app-* and Material system tokens. Ready cards do not repeat an Offline badge; source provenance is available at the top of their overflow menus. The global workspace download shortcut displays the service's active count, while the page badge and filter counts reflect the current route scope.
• Honest interactions Every asynchronous item command owns a pending id until the IPC result settles, preventing duplicate dispatch without optimistically changing a status. Service failures surface through the established snackbar path. Removing a completed entry explicitly says the finalized media file remains on disk. Removing a paused, failed, or canceled entry says retained partial data is deleted. “Clear finished” communicates both outcomes and preserves playlist scope when the page is opened under a source route. VOD and episode detail views continue to render a paused download as an active Resume button (DownloadsService.isPaused() / resumeDownloadByContent()). Artwork and titles on every completed card — movie, grouped series, and standalone episode alike — open the focused offline detail for that download; the explicit Play command in the poster's overflow menu still starts the local file directly. A legacy standalone episode without a usable series id resolves to a single-episode offline detail built from its own row. Missing completed rows show File missing under Needs attention with Download again; Play and Show in folder are withheld. A file-action race that returns File not found refreshes the authoritative list and returns the user from focused details to the manager.

Focused offline details

• Ready movies and grouped series open a local-focused detail view rather than a provider catalog page. A movie exposes local Play and Show in folder. A series projects only completed episode rows whose finalized files are still available, grouped into seasons; every episode Play and Show in folder action targets that row's local file. The provider's other seasons and episodes are deliberately absent from this view.
• View in portal resolves an exact category/item route for Xtream. For Stalker it accepts a matching recently-viewed snapshot only when its raw movie/regular-series/VOD-series markers agree with the download type, so overlapping movie and series ids cannot select the wrong item. An exact numeric category stored in the download snapshot wins over the recent collection's virtual vod/series category. Without a matching recent shape, only a movie with that exact numeric category can form a metadata-only target; episodes and legacy movies without one leave the handoff unavailable. The normal provider detail opens in one-shot provider-only presentation: provider content and playback remain available when that host resolves them, while local, Offline, and download actions are hidden.
• A completed row that is no longer locally available is never rendered as a ready offline detail. Direct or stale detail URLs return to the manager; if navigation fails, the detail shell shows the missing-file error with Back and Retry. Invalid or removed download ids render a focused not-found state.
• Movie and episode downloads capture a versioned, display-only metadata snapshot at start time from the already-rendered Xtream or Stalker detail, including any TMDB fields already present. The snapshot keeps provider identity/category separately from presentation metadata and lets the offline view render even when the source portal is unavailable.
• A grouped series selects its newest valid parent snapshot, then fills only missing parent metadata from older valid member snapshots. Newer values, per-episode metadata, language, and freshness identity remain authoritative. Each episode row still uses its own stored episode metadata.
• Legacy rows and sparse, stale, or wrong-language snapshots are backfilled when focused details open: row metadata supplies a safe local fallback, provider data is merged when it can be resolved, and opt-in TMDB enrichment uses the same app language and merge rules as provider details. Successful refreshes persist to the representative row; transient failures keep safe improvements without falsely marking the snapshot fresh, and concurrent refreshes are request-ordered so only the latest generation may write.
• Snapshot artwork accepts only safe HTTP(S) image URLs. Renderer normalization and main-process persistence independently reject credential-shaped path and query keys, including username, so provider credentials cannot be cached in offline metadata.

Global API surface

• Preload + types
  apps/electron-backend/src/app/api/main.preload.ts wires every download IPC command plus the onDownloadsUpdate listener to window.electron. The shared ElectronBridgeApi contract in libs/shared/interfaces/src/lib/electron-api.interface.ts owns the download and playback-position method types; global.d.ts and apps/web/src/typings.d.ts reference that contract instead of redeclaring the bridge.

Routing and navigation

• The global workspace is /workspace/downloads. Source-scoped variants are available under both portal flavors: /workspace/xtreams/:id/downloads and /workspace/stalker/:id/downloads. All three routes render the same global store; the :id routes derive a view-only playlist scope.
• Each scope exposes the same focused child route: /workspace/downloads/:downloadId, /workspace/xtreams/:id/downloads/:downloadId, and /workspace/stalker/:id/downloads/:downloadId. The workspace shell treats all three as focused content: route search is disabled and the context panel is none, so provider categories are not shown beside a local-only item.
• The manager persists its selected All/Movies/Series/In progress filter in the current route query with replaceUrl. Opening a focused item then keeps that exact scoped URL as its validated return target, so Back restores the manager's scope, search query, filter, and browser-history position.
• Downloads navigation is data-driven: libs/portal/shared/util/src/lib/navigation/portal-rail-links.ts emits a downloads section link (path: [...root, 'downloads']) for both portals, so they reuse the same download page.

Queuing, persistence, and UX notes

• Every download row writes to the shared downloads table with statuses (queued, downloading, paused, completed, failed, canceled) plus metadata such as bytesDownloaded, totalBytes, errorMessage, requestHeaders, resumeValidator, the offline-detail metadata snapshot, and Xtream identifiers. Downloads are locally owned records rather than playlist children: deleting a source retains its rows and local files, keeps them visible in the global library, and disables provider handoff until that source exists again. Startup rebuilds older tables that still carry the playlist foreign key, while additive columns use the idempotent column migrations.
• Download-list and focused-detail reads verify completed files with asynchronous lstat probes in the main process. One shared probe queue permits at most four filesystem calls at once and coalesces only in-flight checks for the same path; it does not cache completed results, so external file deletion is visible on the next refresh without letting frequent progress broadcasts block Electron's main thread.
• On startup, download-recovery.ts converts stale downloading rows with a non-empty .part file to paused, converts stale queued rows to paused while keeping any retained .part (a resumed download waiting behind an active one persists as queued with its partial), and marks stale downloading rows without recoverable partial bytes as failed.
• Queue cancellation removes a queued task or records an active cancellation request and aborts the request when available. Pausing follows the same abort path but persists paused and keeps the .part. Retries reuse the same database entry: a failed row with a retained filePath resumes its .part through HTTP Range, otherwise the retry starts from zero. Resume appends to the existing .part through HTTP Range with If-Range validation when a validator is stored, and through 256 KiB overlap verification when none is.
• A .part that cannot be deleted (locked, permission denied) never loses its database path: cancel persists canceled while retaining filePath for later cleanup, and DOWNLOADS_REMOVE keeps the row and answers success: false (surfaced as a snackbar) so retrying the remove re-attempts the deletion once the lock is released.
• Resume claims the row atomically (paused → queued as a conditional update) and the runtime queue rejects duplicate ids, so two rapid Resume clicks racing the status refresh can never produce two transfers for the same download.
• A response that ends cleanly before the advertised representation size (for example a proxy that caps each response) is never committed as completed: the transfer fails with Transfer ended before the advertised size while retaining the .part and filePath, so a retry continues via Range from where it stopped.
• An allowlisted network failure retains ANY nonempty .part: since overlap verification owns resume correctness, the next attempt can safely prove, resume, or restart over whatever was retained — deleting bytes is the only unrecoverable outcome, so retention needs no total, validator, or range evidence. A total the bytes on disk have falsified is persisted as unknown, never as the falsified value. The failed row exposes a stable DOWNLOAD_NETWORK_INTERRUPTED (<code>) message without a URL; Retry continues through the same resume validation. Only non-network errors, empty fresh failures, and a partial that shrank mid-attempt keep the generic failure path.
• The runtime reconnects interrupted transfers on its own (download-reconnect.ts, wrapping the transfer in startDownload): a recoverable interruption or clean short response triggers an automatic reconnect after a 1 s delay, because servers that cap each connection at N bytes or seconds — common Xtream anti-download throttling — would otherwise demand a manual Retry click per ~130 MB slice. The loop is structurally bounded: an attempt must end at least 64 KiB past the previous attempt to reset the stall budget, and three consecutive attempts without that progress surface the last interruption as the ordinary retained failure. Restarts are an EXPLICIT signal, never byte inference: the transfer layer increments task.transferRestarts whenever it rewrites the .part from byte zero (overlap mismatch, shrunk entity, HTTP 416, or a server that ignored Range), and the loop opens a fresh progress epoch on that signal — clean stall budget, no baseline — because a rebuilt file that happens to land near the previous attempt's byte count is indistinguishable from a stall by byte comparison alone. Only two restarts are tolerated per transfer, or an always-restarting server would reset the budget forever; an unsignalled byte regression is an ordinary stall. Cancel and pause are re-checked around every reconnect. A reconnect attempt that fails before any response (for example ECONNREFUSED against a rebooting panel) is converted into the same retained interruption instead of falling into the generic partial-deleting failure path, so an automatic reconnect can never destroy a multi-gigabyte partial the user did not touch. Total handling separates authority from information: the response's own total is the ONLY thing that authorizes completion. An indeterminate range's advertised end (bytes X-Y/* → Y+1) flags short delivery, and an indeterminate range that ends cleanly at Y stays incomplete too — reaching Y proves only that the selected range was delivered, so the transfer reconnects from the new offset instead of finalizing; only a response with no range and no total keeps the clean-EOF completion contract of unknown-length HTTP. A reset after the final byte of an AUTHORITATIVE total (overlap proven, totals in agreement) completes the transfer instead of resuming at EOF into a 416-truncate loop; a total carried forward from an earlier response is informational only — it can flag a short transfer, is dropped once the bytes on disk falsify it OR once an indeterminate range can even REACH it (strictly-below guard — settled to unknown on every exit path, clean deliveries and mid-stream pauses included, keeping row and live task consistent), and never authorizes finalization. A verified replay of an indeterminate range that appends nothing arms a one-shot EOF probe: the next attempt requests the byte after the partial outright, so a compliant 416 with bytes */N can confirm completion — the ordinary rewound request can never observe it; a probe answered with more data is retired unappended (no overlap proof at that offset) and ordinary rewound verification resumes; a 416 WITHOUT a confirming length answered to ANY request starting at the partial's exact end — the EOF probe and every validator-backed resume alike — is inconclusive, since a request at the entity's true end always collects one and the length is optional: the partial is retained rather than restarted, and only a stated total BELOW the partial proves the entity shrank. Only a fresh or restarted transfer drops the carried total entirely, since it described a discarded file. When no total was ever known, a retained failure persists totalBytes as null rather than fabricating one from the byte count — a fabricated total equal to the partial's size would let Retry's completed-partial shortcut finalize an unverified partial without a request; only a finalization failure after a COMPLETE transfer records its byte count as the total, which is what lets its Retry finalize the proven partial directly.
• Retained filePaths recorded in the database stay usable after the user switches download folders — resume/retry of a retained row does not re-require the folder to be the current selection. Fresh downloads still authorize against the currently selected folder.
• Startup recovery recognizes a finalization that crashed between creating the final file and committing the row (downloading row, no partial, final file present with the recorded size) and marks it completed instead of failing it and orphaning the file.
• Pause/resume is covered end to end by apps/electron-backend-e2e/src/downloads.e2e.ts: a throttled Range-capable mock server verifies the paused .part on disk, the Range/If-Range resume request, and byte-exact assembly of the final file. Automatic reconnects are covered by apps/electron-backend-e2e/src/download-reliability.e2e.ts: a validator-carrying interrupting server must complete without a manual Retry via Range/If-Range, and a validator-less interrupting server must complete through the rewound overlap-verification Range request.
• The OS downloads path is always authorized. A custom folder becomes authorized only after native folder selection, and the main process persists that selection under Electron userData. Renderer settings may display the path, but they are not trusted as authorization.
• The manager's search and All/Movies/Series/In progress filters affect visible queue and library entities only. The tracked-byte summary deliberately ignores search/category filtering while honoring route scope, so hiding a card never makes its disk footprint appear to vanish.

Keeping the backend queue, IPC handlers, shared schema, and renderer signals synchronized minimizes drift between platform rules and the UI. Future work might cover recordings, queue reordering, bulk pause/cancel actions, disk-free space telemetry, or playback analytics.