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GIGABAIT93andClaude Opus 5.5
267e7063d5
- `--name` leaves OPTIONS: the game still takes it, but the contract doesn't promise offline play. The guide's first step is now the owner rule, and a session the game can't read is stated as a fact, not an option. - A bad value names its option (`Horizon: --width: invalid digit ...`), since a launcher shows that line to the player. - Session errors say "the session", true for --session-stdin too. - --quickPlaySingleplayer takes one folder name of saves/, as vanilla's level id; a path is refused. --world still takes a path for harnesses. Co-Authored-By: Claude Opus 5.5 <[email protected]>
78 lines
3.5 KiB
Markdown
78 lines
3.5 KiB
Markdown
# Launch API
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What another launcher (Prism Launcher, MultiMC, ATLauncher, Modrinth App, HMCL or your own) needs to start Horizon:
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the options `horizon-client` takes, how it hands over an account, and how it ends. `horizon-launcher` is the
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reference implementation. Proposed in horizon-rust/horizon#3545.
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## Overview
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| --- | --- |
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| Version | 0.1.0, printed by `horizon-client --launch-api` |
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| Level | experimental ([stability.md](stability.md)): preview once preparing and the guide are covered too |
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| Covers | starting `horizon-client`: its options, the session JSON, the exit codes, the crash report's path |
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| Not yet | finding a build, preparing it with `horizon-prepare` (see Not there yet) |
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## Guide
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1. Start Horizon only for a player signed in with a Microsoft account that owns Minecraft: Java Edition, and
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hand over that account's session (`--session-stdin`, or `--session-file`), never on the command line. This
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is the same owner gate `horizon-launcher` applies before every start. Horizon never downloads Mojang's
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files; a launcher that does downloads them only for that owner.
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2. Ask the build what it takes: `horizon-client --launch-api` prints JSON with `launch_api` (the version) and
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`options`. Pass only options it lists: any other is refused with exit code 2.
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3. Start it with a folder per instance:
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```sh
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horizon-client --resources PREPARED --game-dir INSTANCE --home INSTANCE --width 1280 --height 720 --session-stdin
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```
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4. Watch the exit code. On 2, stderr names the refused option (`Horizon: --width: …`). On 1 or 101, the last
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line on stderr names the crash report.
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## Reference
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[launch-reference.md](launch-reference.md), generated from `crates/horizon-client/src/game/launch_api.rs`: every
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option, the `--launch-api` reply and the exit codes.
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### The session JSON
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The account the game joins online-mode servers with ([microsoft-account.md](../microsoft-account.md)):
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```json
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{"name": "Alex", "uuid": "069a79f444e94726a5befca90e38aaf5", "access_token": "…", "user_type": "msa", "xuid": "…"}
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```
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- `name`, `uuid` (with or without dashes) and `access_token` are required; `user_type`, when present, is `msa`;
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`xuid` is optional.
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- `--session-stdin`: write the JSON to the game's standard input and close it.
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- `--session-file PATH`: a file the game reads once and deletes at once. On Unix its mode must be 0600; a file
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older than two minutes is refused (and deleted).
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- A session the game can't read is reported on stderr (`Horizon: not signed in: …`), and online-mode servers
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will refuse the player.
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## Examples
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```sh
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horizon-client --launch-api
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printf '%s' "$SESSION_JSON" | horizon-client --resources ~/horizon/prepared --game-dir ~/instances/a --session-stdin --fullscreen
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```
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## Stability
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Experimental: the options in the reference, the session JSON, the exit codes and the crash report line may still
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change before preview. From preview on, they change only as [stability.md](stability.md) says, and the reference's
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test keeps the contract and the code together.
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## Not there yet
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- **Preparing:** `horizon-prepare` with `--output`, explicit inputs (`--version-json`, `--client-jar`,
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`--libraries-dir`, `--assets-dir`), one complete preparation, `--progress json` and `--check`.
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- **Finding a build:** a signed release index and builds kept longer than seven days.
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- **A guide**, "Running Horizon from another launcher", from picking a build to playing.
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## Changelog
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- 0.1.0: `--game-dir`, `--home`, `--fullscreen`, `--session-stdin`, `--launch-api`, exit code 2 for a refused
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command line.
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