host-extensions

Extension framework for host-sdk. Extensions add new capabilities to a Polkadot host application without touching core — each extension is an independent JS/native bridge registered under window.host.ext.<namespace>.

Purpose

The core window.host bridge (host-api) handles signing, storage, navigation, and chain interaction. Extensions cover everything else: structured data, media, notifications, payments, identity, etc.

Extensions are experimental by design. A new API lives under window.host.ext.* while it is being qualified. Once an API is stable and widely adopted it graduates to core (window.host.*) with a compatibility shim keeping the old path alive.

Extension lifecycle

experimental              qualified              core
window.host.ext.data  →  (shim period)  →  window.host.data

For the full guide — including how to implement an extension, the JS contract, the manifest format, and the graduation path — see docs/extensions.md.

Quick start

use host_extensions::{HostExtension, ExtensionRegistry};

struct MyExtension;

impl HostExtension for MyExtension {
    fn namespace(&self) -> &str { "my" }
    fn channel(&self) -> &str { "hostMyBridge" }
    fn inject_script(&self) -> &str { include_str!("my_inject.js") }
    fn handle_message(&self, method: &str, params: &str) -> Option<String> {
        match method {
            "ping" => Some(r#"{"pong":true}"#.into()),
            _ => None,
        }
    }
}

let mut registry = ExtensionRegistry::new();
registry.register(Box::new(MyExtension));

// Inject into WebView after HOST_API_BRIDGE_SCRIPT
let script = registry.combined_inject_script();

// Register WKScriptMessageHandler for each channel
for channel in registry.channels() {
    webview.add_message_handler(channel);
}

// Dispatch incoming messages
let result = registry.dispatch("hostMyBridge", "ping", "{}");