shepherd-api

Protocol types for Shepherd IPC communication.

Overview

This crate defines the stable API between the Shepherd service (shepherdd) and its clients (launcher UI, HUD overlay, admin tools). It contains:

Commands - Requests from clients to the service
Responses - Service replies to commands
Events - Asynchronous notifications from service to clients
Shared types - Entry views, session info, reason codes, etc.

Purpose

shepherd-api establishes the contract between components, ensuring:

Stability - Versioned protocol with backward compatibility
Type safety - Strongly typed messages prevent protocol errors
Decoupling - Clients and service can evolve independently

API Version

use shepherd_api::API_VERSION;

// Current API version
assert_eq!(API_VERSION, 1);

Key Types

Commands

Commands are requests sent by clients to the service:

use shepherd_api::Command;

// Request available entries
let cmd = Command::ListEntries;

// Request to launch an entry
let cmd = Command::Launch { 
    entry_id: "minecraft".into() 
};

// Request to stop current session
let cmd = Command::StopCurrent { 
    mode: StopMode::Graceful 
};

// Subscribe to real-time events
let cmd = Command::SubscribeEvents;

Available commands:

GetState - Get full service state snapshot
ListEntries - List all entries with availability
Launch { entry_id } - Launch an entry
StopCurrent { mode } - Stop the current session
ReloadConfig - Reload configuration (admin only)
SubscribeEvents - Subscribe to event stream
GetHealth - Get service health status
SetVolume { level } - Set system volume
GetVolume - Get current volume

Events

Events are pushed from the service to subscribed clients:

use shepherd_api::{Event, EventPayload};

// Events received by clients
match event.payload {
    EventPayload::StateChanged(snapshot) => { /* Update UI */ }
    EventPayload::SessionStarted(info) => { /* Show HUD */ }
    EventPayload::WarningIssued { threshold, remaining, severity, message } => { /* Alert user */ }
    EventPayload::SessionExpired { session_id } => { /* Time's up */ }
    EventPayload::SessionEnded { session_id, reason } => { /* Return to launcher */ }
    EventPayload::PolicyReloaded { entry_count } => { /* Refresh entry list */ }
    EventPayload::VolumeChanged(info) => { /* Update volume display */ }
}

Entry Views

Entries as presented to UIs:

use shepherd_api::EntryView;

let view: EntryView = /* from service */;

if view.enabled {
    // Entry can be launched
    println!("Max run time: {:?}", view.max_run_if_started_now);
} else {
    // Entry unavailable, show reasons
    for reason in &view.reasons {
        match reason {
            ReasonCode::OutsideTimeWindow { next_window_start } => { /* ... */ }
            ReasonCode::QuotaExhausted { used, quota } => { /* ... */ }
            ReasonCode::CooldownActive { available_at } => { /* ... */ }
            ReasonCode::SessionActive { entry_id, remaining } => { /* ... */ }
            ReasonCode::InternetUnavailable { check } => { /* ... */ }
            // ...
        }
    }
}

Session Info

Information about active sessions:

use shepherd_api::{SessionInfo, SessionState};

let session: SessionInfo = /* from snapshot */;

match session.state {
    SessionState::Launching => { /* Show spinner */ }
    SessionState::Running => { /* Show countdown */ }
    SessionState::Warned => { /* Highlight urgency */ }
    SessionState::Expiring => { /* Terminating... */ }
    SessionState::Ended => { /* Session over */ }
}

Reason Codes

Structured explanations for unavailability:

OutsideTimeWindow - Not within allowed time window
QuotaExhausted - Daily time limit reached
CooldownActive - Must wait after previous session
SessionActive - Another session is running
UnsupportedKind - Host doesn't support this entry type
Disabled - Entry explicitly disabled in config

Design Philosophy

Service is authoritative - Clients display state, service enforces policy
Structured reasons - UIs can explain "why is this unavailable?"
Event-driven - Clients subscribe and react to changes
Serializable - All types derive Serialize/Deserialize for JSON transport

Dependencies

serde - Serialization/deserialization
chrono - Timestamp types
shepherd-util - ID types

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