Never lose an HTTP request because the network dropped — offline-first HTTP request replay for Kotlin Multiplatform.
Every pending request costs exactly one Long (8 bytes) in memory, with O(1) lookup no matter how deep the backlog gets — real numbers in the benchmarks.
retry-journal is a lightweight, durable HTTP Request Replay Queue for Android, iOS, and JVM. It intercepts outgoing Ktor requests on network failures, saves them to disk, and replays them exactly as sent when connectivity returns.
Note
This is a dedicated HTTP outbox queue, not a general-purpose database synchronizer (like Room/SQLDelight state sync). It focuses purely on guaranteeing HTTP delivery.
| Without retry-journal | With retry-journal |
|---|---|
| User offline → request fails, data lost | Request queued on disk, clear "saved for later" UX |
| App killed mid-request → maybe nothing persisted | Crash-safe append-only file + CRC recovery |
| Background worker + UI both sync → duplicate POSTs | Cross-process locks + replay claims |
| Server returns 400 → infinite retry loop | Dead letter queue — inspect, retry, or discard |
// libs.versions.toml
retry-journal = { module = "com.ghostserializer:retry-journal", version = "1.1.0" }// build.gradle.kts
dependencies {
implementation(libs.retry.journal)
}Targets: android, iosArm64, iosSimulatorArm64, jvm. Details: docs/installation.md.
val retryJournal = RetryJournal.create(engineFactory = CIO, queuePath = dataDir.resolve("queue.bin"))
try {
retryJournal.client.post("https://api.example.com/orders") { setBody(order) }
} catch (_: OfflineQueuedException) {
showMessage("Saved — will sync when you're back online.")
}
// later, when you decide there's connectivity:
val result = retryJournal.flush()Full walkthrough: docs/quick-start.md.
| Topic | What's in it |
|---|---|
| Installation | Adding the dependency |
| Quick start | Create the queue, send requests, flush |
| Architecture & Reliability | Append-only logs, memory index, locking, claims |
Scheduling flush() |
DIY patterns, or the out-of-the-box worker |
Background worker (:retry-worker) |
WorkManager / BGTaskScheduler, zero glue code |
| RetryJournalRuntime | Serialize flush() across multiple callers |
| File & image uploads | Multipart uploads captured and replayed offline |
| Dead letters | What happens when the server says no |
| Guarantees & honest limits | What's strong, what to watch out for |
| Build, test & publish | Contributing to retry-journal itself |
Full index: docs/README.md.
See it in action: sample app — a working Compose Multiplatform demo (desktop/Android/iOS).
Apache 2.0 — see LICENSE.