Compose Multiplatform chat UI and client for chatbase — streaming replies, model picker, voice input, image attachments, image generation, web search and local history.

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The server half is chatbase, an npm library that runs inside your own Cloudflare Worker. This library is the whole client side: the screen, the SSE engine, the Room-backed history and the wire protocol. Your app provides sign-in, the Pro decision and a few preferences through one interface; the SDK never sees a user or a subscription.

• A full chat screen in one call. ChatScreen(onBack = ...) renders threads, the input bar, the model picker, Markdown with code highlighting, images and the quota / Pro gates. The host only paints the shell around it.
• The protocol stays in the SDK. Chat, transcribe, models and quota are all spoken here against the /api/chat/* endpoints that chatbase serves. The host never builds a request.
• Local history that survives updates. Threads and messages live in a Room database (chat.db) with versioned schema and migration tests.
• Identity and billing stay yours. ChatHost asks the app whether the user is signed in and whether they are Pro, and asks it to open the sign-in and paywall screens. The SDK does not store tokens or know about products.
• Analytics as events, not as a dependency. Requests, completions and voice input are reported as ChatAiEvent; the host maps them into its own vocabulary.

1. Add the dependency. The SDK brings its own Ktor engine per platform.

dependencies {
    implementation("wang.harlon:chatbase-kmp:<version>")
}

2. Implement ChatHost and install it before any chat UI is reached, in Application.onCreate on Android and in the MainViewController factory on iOS.

object MyChatHost : ChatHost {
    override val apiBaseUrl = "https://api.example.com/api"

    override val canSignIn = true
    override fun isLoggedInNow() = auth.state.value is LoggedIn
    override val isLoggedIn = auth.state.map { it is LoggedIn }
    override fun signIn(source: String) = auth.signIn(source)
    override fun openPaywall(source: String) = Paywall.open(source)
    override fun reportGeneratedImage(imageUrl: String) = Feedback.open(imageUrl)

    override fun currentIsPro() = settings.isPro
    override val isPro = settings.isProFlow

    override val chatModelChoice = settings.chatModelFlow
    override fun currentChatModelChoice() = settings.chatModel
    override fun pinChatModel(id: String) = settings.setChatModel(id)
    override fun followServerDefault() = settings.setChatModel(FOLLOW_SERVER_DEFAULT)

    override fun imagesMaxCount() = 9
    override fun imagesPerImageJpegKb() = 300
    override fun installId() = settings.installId
    override suspend fun requestLang() = if (settings.language == "zh") "zh" else "en"

    override fun configureHttpAuth(config: HttpClientConfig<*>) = config.installAuth(auth)
    override fun onAiEvent(event: ChatAiEvent) = analytics.track(event)
    override val proBadge: (@Composable () -> Unit)? = { ProBadge() }
}

fun installChatHost() { chatHost = MyChatHost }

3. Warm the model catalog at startup and show the screen.

ChatModelsProvider.warmUp(appScope)

ChatScreen(
    onBack = { navController.popBackStack() },
    suggestions = listOf(ChatSuggestion(label = "What can you do?", prompt = "What can you do?")),
)

A minimal host that runs without any backend is in sample/.

Documented with the server: chatbase docs/chat-protocol.md. Endpoints are relative to ChatHost.apiBaseUrl.

• Android: ./gradlew :library:testAndroidHostTest runs the common and Android tests under Robolectric.
• iOS: Markdown parsing binds cmark-gfm. library/native/build-cmark.sh builds the static libraries with CMake on first use; they are packed into the klib, so consumers need nothing extra.
• Consuming the local source tree from an app: add chatbase-kmp.dir=<path> to the app's local.properties if the app supports composite builds through gradle/composite-substitutions.

MIT. cmark-gfm is bundled under its own license, see library/native/cmark-gfm-COPYING.