1 files changed, 62 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/Async.swift b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/Async.swift
new file mode 100644
index 0000000000..695208861d
--- /dev/null
+++ b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/Async.swift
@@ -0,0 +1,62 @@
+private let UNIFFI_RUST_FUTURE_POLL_READY: Int8 = 0
+private let UNIFFI_RUST_FUTURE_POLL_MAYBE_READY: Int8 = 1
+
+fileprivate func uniffiRustCallAsync<F, T>(
+    rustFutureFunc: () -> UnsafeMutableRawPointer,
+    pollFunc: (UnsafeMutableRawPointer, UnsafeMutableRawPointer) -> (),
+    completeFunc: (UnsafeMutableRawPointer, UnsafeMutablePointer<RustCallStatus>) -> F,
+    freeFunc: (UnsafeMutableRawPointer) -> (),
+    liftFunc: (F) throws -> T,
+    errorHandler: ((RustBuffer) throws -> Error)?
+) async throws -> T {
+    // Make sure to call uniffiEnsureInitialized() since future creation doesn't have a
+    // RustCallStatus param, so doesn't use makeRustCall()
+    uniffiEnsureInitialized()
+    let rustFuture = rustFutureFunc()
+    defer {
+        freeFunc(rustFuture)
+    }
+    var pollResult: Int8;
+    repeat {
+        pollResult = await withUnsafeContinuation {
+            pollFunc(rustFuture, ContinuationHolder($0).toOpaque())
+        }
+    } while pollResult != UNIFFI_RUST_FUTURE_POLL_READY
+
+    return try liftFunc(makeRustCall(
+        { completeFunc(rustFuture, $0) },
+        errorHandler: errorHandler
+    ))
+}
+
+// Callback handlers for an async calls.  These are invoked by Rust when the future is ready.  They
+// lift the return value or error and resume the suspended function.
+fileprivate func uniffiFutureContinuationCallback(ptr: UnsafeMutableRawPointer, pollResult: Int8) {
+    ContinuationHolder.fromOpaque(ptr).resume(pollResult)
+}
+
+// Wraps UnsafeContinuation in a class so that we can use reference counting when passing it across
+// the FFI
+fileprivate class ContinuationHolder {
+    let continuation: UnsafeContinuation<Int8, Never>
+
+    init(_ continuation: UnsafeContinuation<Int8, Never>) {
+        self.continuation = continuation
+    }
+
+    func resume(_ pollResult: Int8) {
+        self.continuation.resume(returning: pollResult)
+    }
+
+    func toOpaque() -> UnsafeMutableRawPointer {
+        return Unmanaged<ContinuationHolder>.passRetained(self).toOpaque()
+    }
+
+    static func fromOpaque(_ ptr: UnsafeRawPointer) -> ContinuationHolder {
+        return Unmanaged<ContinuationHolder>.fromOpaque(ptr).takeRetainedValue()
+    }
+}
+
+fileprivate func uniffiInitContinuationCallback() {
+    {{ ci.ffi_rust_future_continuation_callback_set().name() }}(uniffiFutureContinuationCallback)
+}