Iron Curtain — Design Documentation

Replay Sharing via P2P

Parent: D049 — Workshop Asset Formats & Distribution

This page documents how .icrep replay files are distributed via P2P, complementing the replay UX design in player-flow/replays.md and the binary format spec in formats/save-replay-formats.md.

Two Distribution Paths

Match ID Sharing — Detailed Flow

1. Match completes. The relay stores the .icrep file (all participating clients contributed their order streams during the match). The relay assigns a Match ID — a short alphanumeric hash (e.g., IC-7K3M9X).

2. Sharer copies Match ID. Available in:

   • Post-game summary screen: [Copy Match ID] button
   • Replay browser detail panel
   • Player profile → match history

3. Recipient enters Match ID. In the replay browser: [Enter Match ID…] → text field → the client queries the relay (or any relay that hosted the match) for the replay metadata.

4. Download. The relay seeds the .icrep file. For popular replays (tournament finals, viral moments), p2p-distribute forms a swarm — the relay is the initial seed, and subsequent downloaders become peers. Download priority: user-requested.

5. Verify & add to library. Client verifies the .icrep integrity (header checksum, order stream hash). The replay appears in the local replay browser.

URL scheme: ic://replay/IC-7K3M9X — registered as an OS URL handler. Clicking this link in a browser or chat client opens IC directly to the replay. If IC is not running, it launches and navigates to the replay viewer.

Workshop Replay Collections

Community curators can publish replay packs as Workshop resources:

# manifest.yaml for a replay collection
name: "season-3-finals"
publisher: "cral-casters"
version: "1.0.0"
license: "CC-BY-4.0"
description: "All grand final matches from CRAL Season 3"
tags: [replays, competitive, season-3, tournament]
game_modules: [ra]

contents:
  - replays/gf-match1.icrep
  - replays/gf-match2.icrep
  - replays/gf-match3.icrep
  - metadata/commentary-notes.yaml

Standard Workshop discovery, dependency resolution, and P2P distribution apply. Replay packs can depend on the mods/maps used in the replays — the Workshop resolves these dependencies so the viewer has the correct content loaded.

.icrep and P2P Piece Alignment

The .icrep binary format (see formats/save-replay-formats.md) uses per-256-tick LZ4-compressed order chunks. P2P piece boundaries should align with these chunk boundaries where practical, enabling:

• Streaming playback: A recipient can begin watching a replay before the full file has downloaded, as completed pieces correspond to playable tick ranges
• Partial sharing: A player who watched only the first 10 minutes of a replay can seed those pieces to others, even without the complete file

Piece length for replay files follows the standard D049 size-based table: most replays are <5 MB (HTTP-only tier), so P2P applies primarily to large replay collections published as Workshop packages.

Privacy Considerations

• Voice audio: .icrep files can include voice recordings (D059) as an opt-in separate stream. The sharer’s voice consent flag is recorded at match time. Replays shared via Match ID inherit the original consent settings — voice audio is only included if all speakers opted in to voice-in-replay.
• Replay anonymization (D056): The replay browser offers an anonymization mode that strips player names/identities before sharing. This produces a derivative .icrep with anonymized metadata.
• Ranked vs. private: Ranked match IDs are public by default (discoverable via match history). Custom/private match IDs are generated only if the host enables sharing in the room settings.

Relay Retention & Lifecycle

• Default retention: 90 days from match end (server-operator configurable via D072)
• After expiry: Only locally-saved copies remain. Players who downloaded the replay via Match ID retain their local copy indefinitely
• Seed promotion: If a replay is downloaded frequently (configurable threshold), the relay can promote it to the Workshop seed infrastructure for longer-term availability
• Storage budget: Relay operators configure maximum replay storage via server_config.toml § [storage.replays]. LRU eviction applies when the budget is exceeded, with pinned replays (operator-marked) exempt

Phase

• Phase 2 (M4): .icrep format and local replay browser. No P2P sharing yet — replay files are manual file transfers only.
• Phase 5 (M8): Match ID system via relay. P2P swarm formation for popular replays. URL scheme handler (ic://replay/).
• Phase 6a (M9): Workshop replay collections. Replay packs with dependency resolution.

Cross-References