Hoppie ACARS Android App

A native Android application for Hoppie's ACARS network built with Kotlin + Jetpack Compose.

Features

Feature	Details
Live Message Feed	Poll inbox with auto-scroll, filter by message type
Compose Messages	Telex, CPDLC, and custom message types
Weather & ATIS	METAR, TAF, VATSIM/IVAO/PilotEdge ATIS via inforeq
PDC Templates	Pre-Departure Clearance quick-fill form
CPDLC Templates	WILCO, UNABLE, ROGER, FL request shortcuts
Auto-Polling	Randomized 45–75s interval (per Hoppie spec)
Background Worker	WorkManager polling when app is backgrounded
Persistent Settings	Logon code + callsign saved to DataStore
Dark Cockpit Theme	Aviation-inspired color palette

Architecture

app/
└── java/com/hoppieacars/
    ├── HoppieApp.kt                     @HiltAndroidApp
    ├── MainActivity.kt                  NavHost + BottomNav
    ├── data/
    │   ├── api/
    │   │   ├── HoppieApiService.kt      Retrofit interface
    │   │   ├── HoppieResponseParser.kt  Plain-text response parser
    │   │   └── ScalarConverterFactory   String body converter
    │   ├── model/
    │   │   └── Models.kt               AcarsMessage, MessageType, etc.
    │   └── repository/
    │       ├── AcarsRepository.kt       Business logic, message store
    │       └── SettingsRepository.kt    DataStore persistence
    ├── di/
    │   └── NetworkModule.kt             Hilt → OkHttp/Retrofit
    ├── ui/
    │   ├── AcarsViewModel.kt            StateFlow ViewModel
    │   ├── Navigation.kt                Screen routes
    │   ├── screens/
    │   │   ├── MessagesScreen.kt        Live feed + filter chips
    │   │   ├── ComposeScreen.kt         Telex / CPDLC / custom
    │   │   ├── WeatherScreen.kt         METAR / TAF / ATIS
    │   │   └── SettingsScreen.kt        Logon + callsign config
    │   ├── components/
    │   │   └── SharedComponents.kt      MessageCard, StatusDot, etc.
    │   └── theme/
    │       └── Theme.kt                 Dark aviation palette
    └── util/
        └── AcarsPollWorker.kt           Background WorkManager worker

Getting Started

Prerequisites

• Android Studio Hedgehog (2023.1.1) or newer
• Android SDK 26+ (Android 8.0)
• A free Hoppie logon code: https://www.hoppie.nl/acars/system/register.html

Build

1. Clone / unzip this project
2. Open in Android Studio
3. Let Gradle sync
4. Run on device or emulator (API 26+)

First-Time Setup

1. Open Settings tab
2. Enter your Hoppie Logon Code
3. Enter your Station Callsign (e.g. BAW123 for aircraft, EGLL_GND for ATC)
4. Tap Save Settings
5. Go to Messages tab and tap START

Hoppie API Reference

Base URL: https://www.hoppie.nl/acars/system/connect.html

Request Parameters

Param	Description
logon	Secret logon code (≥24 chars)
from	Your callsign
to	Recipient callsign or SERVER
type	poll, telex, cpdlc, ping, inforeq, posreq, position, progress
packet	Message payload (empty for poll/ping)

Poll Response Format

ok                                          ← no messages
ok {CALLSIGN type {payload}} {…} {…}       ← one or more messages
error {reason}                             ← error

Polling Rules (important!)

• Poll once per 45–75 seconds (randomized to spread server load)
• After sending a message, may poll once after 20 seconds
• Don't poll until your station has sent its first message
• Use ping (not poll) to test connectivity — ping doesn't register you as online

Message Types

Type	Direction	Description
telex	Both	General text messages
cpdlc	Both	Controller-Pilot Data Link Communications
progress	Aircraft → Dispatch	OUT/OFF/ON/IN times
position	Aircraft → Ground	Position reports
posreq	Either	Request a position report
ping	→ Server	Link test (doesn't register online)
inforeq	→ Server	Weather/ATIS requests

InfoReq Packet Format

metar KLAX
taf EGLL
shorttaf KJFK
vatatis EDDM
ivaoatis LFPG-GND
peatis KSAN

Dependencies

Library	Version	Purpose
Jetpack Compose BOM	2024.08.00	UI framework
Hilt	2.51.1	Dependency injection
Retrofit	2.11.0	HTTP client
OkHttp	4.12.0	Network layer
DataStore	1.1.1	Settings persistence
WorkManager	2.9.1	Background polling
Navigation Compose	2.7.7	Screen navigation

Notes

• The app uses cleartext HTTP (android:usesCleartextTraffic="true") since the Hoppie server is HTTP only
• Logon codes expire after 3 months of inactivity — any login renews them
• The in-memory message log holds up to 500 messages and resets on process death
• CPDLC packet format follows ICAO FANS-1/A specification — see Hoppie CPDLC docs

License

MIT — free to use, modify, and redistribute.