[DRAFT] Rx Observable as Flow

reactive/kotlinx-coroutines-rx2/README.md

@@ -14,10 +14,11 @@ Coroutine builders:
 
 Integration with [Flow]:
 
-| **Name**             | **Result**      | **Description**
-| ---------------      | --------------  | ---------------
-| [Flow.asFlowable]    | `Flowable`      | Converts the given flow to a cold Flowable.
-| [Flow.asObservable]  | `Observable`    | Converts the given flow to a cold Observable.
+| **Name**                   | **Result**      | **Description**
+| ---------------            | --------------  | ---------------
+| [Flow.asFlowable]          | `Flowable`      | Converts the given flow to a cold Flowable.
+| [Flow.asObservable]        | `Observable`    | Converts the given flow to a cold Observable.
+| [ObservableSource.asFlow]  | `Flow`          | Converts the given cold ObservableSource to flow
 
 Suspending extension functions and suspending iteration:
 
@@ -65,6 +66,7 @@ Conversion functions:
 [rxFlowable]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/rx-flowable.html
 [Flow.asFlowable]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/kotlinx.coroutines.flow.-flow/as-flowable.html
 [Flow.asObservable]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/kotlinx.coroutines.flow.-flow/as-observable.html
+[ObservableSource.asFlow]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-observable-source/as-flow.html
 [io.reactivex.CompletableSource.await]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-completable-source/await.html
 [io.reactivex.MaybeSource.await]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-maybe-source/await.html
 [io.reactivex.MaybeSource.awaitOrDefault]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-maybe-source/await-or-default.html

reactive/kotlinx-coroutines-rx2/src/RxConvert.kt

@@ -5,6 +5,7 @@
 package kotlinx.coroutines.rx2
 
 import io.reactivex.*
+import io.reactivex.disposables.Disposable
 import kotlinx.coroutines.*
 import kotlinx.coroutines.channels.*
 import kotlinx.coroutines.flow.*
@@ -77,6 +78,31 @@ public fun <T : Any> ReceiveChannel<T>.asObservable(context: CoroutineContext):
         send(t)
 }
 
+/**
+ * Transforms given cold [ObservableSource] into cold [Flow].
+ *
+ * The resulting flow is _cold_, which means that [ObservableSource.subscribe] is called every time a terminal operator
+ * is applied to the resulting flow.
+ *
+ * A channel with the [default][Channel.BUFFERED] buffer size is used. Use the [buffer] operator on the
+ * resulting flow to specify a user-defined value and to control what happens when data is produced faster
+ * than consumed, i.e. to control the back-pressure behavior. Check [callbackFlow] for more details.
+ */
+@ExperimentalCoroutinesApi
+public fun <T: Any> ObservableSource<T>.asFlow(): Flow<T> = callbackFlow {
+
+    var disposable: Disposable? = null
+
+    val observer = object : Observer<T> {
+        override fun onComplete() { close() }
+        override fun onSubscribe(d: Disposable) { disposable = d }
+        override fun onNext(t: T) { sendBlocking(t) }
+        override fun onError(e: Throwable) { close(e) }
+    }
+    subscribe(observer)
+    awaitClose { disposable?.dispose() }
+}
+
 /**
  * Converts the given flow to a cold observable.
  * The original flow is cancelled when the observable subscriber is disposed.

reactive/kotlinx-coroutines-rx2/test/ObservableAsFlowTest.kt

@@ -0,0 +1,162 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.rx2
+
+import io.reactivex.Observable
+import io.reactivex.subjects.PublishSubject
+import kotlinx.coroutines.*
+import kotlinx.coroutines.channels.*
+import kotlinx.coroutines.flow.*
+import kotlin.test.*
+
+class ObservableAsFlowTest : TestBase() {
+    @Test
+    fun testCancellation() = runTest {
+        var onNext = 0
+        var onCancelled = 0
+        var onError = 0
+
+        val source = rxObservable(currentDispatcher()) {
+            coroutineContext[Job]?.invokeOnCompletion {
+                if (it is CancellationException) ++onCancelled
+            }
+
+            repeat(100) {
+                send(it)
+            }
+        }
+
+        source.asFlow().launchIn(CoroutineScope(Dispatchers.Unconfined)) {
+            onEach {
+                ++onNext
+                throw RuntimeException()
+            }
+            catch<Throwable> {
+                ++onError
+            }
+        }.join()
+
+
+        assertEquals(1, onNext)
+        assertEquals(1, onError)
+        assertEquals(1, onCancelled)
+    }
+
+    @Test
+    fun testImmediateCollection() {
+        val source = PublishSubject.create<Int>()
+        val flow = source.asFlow()
+        GlobalScope.launch(Dispatchers.Unconfined) {
+            expect(1)
+            flow.collect { expect(it) }
+            expect(6)
+        }
+        expect(2)
+        source.onNext(3)
+        expect(4)
+        source.onNext(5)
+        source.onComplete()
+        finish(7)
+    }
+
+    @Test
+    fun testOnErrorCancellation() {
+        val source = PublishSubject.create<Int>()
+        val flow = source.asFlow()
+        val exception = RuntimeException()
+        GlobalScope.launch(Dispatchers.Unconfined) {
+            try {
+                expect(1)
+                flow.collect { expect(it) }
+                expectUnreached()
+            }
+            catch (e: Exception) {
+                assertSame(exception, e.cause)
+                expect(5)
+            }
+            expect(6)
+        }
+        expect(2)
+        source.onNext(3)
+        expect(4)
+        source.onError(exception)
+        finish(7)
+    }
+
+    @Test
+    fun testUnsubscribeOnCollectionException() {
+        val source = PublishSubject.create<Int>()
+        val flow = source.asFlow()
+        val exception = RuntimeException()
+        GlobalScope.launch(Dispatchers.Unconfined) {
+            try {
+                expect(1)
+                flow.collect {
+                    expect(it)
+                    if (it == 3) throw exception
+                }
+                expectUnreached()
+            }
+            catch (e: Exception) {
+                assertSame(exception, e.cause)
+                expect(4)
+            }
+            expect(5)
+        }
+        expect(2)
+        assertTrue(source.hasObservers())
+        source.onNext(3)
+        assertFalse(source.hasObservers())
+        finish(6)
+    }
+
+    @Test
+    fun testBufferUnlimited() = runTest {
+        val source = rxObservable(currentDispatcher()) {
+            expect(1); send(10)
+            expect(2); send(11)
+            expect(3); send(12)
+            expect(4); send(13)
+            expect(5); send(14)
+            expect(6); send(15)
+            expect(7); send(16)
+            expect(8); send(17)
+            expect(9)
+        }
+        source.asFlow().buffer(Channel.UNLIMITED).collect { expect(it) }
+        finish(18)
+    }
+
+    @Test
+    fun testConflated() = runTest {
+        val source = Observable.range(1, 5)
+        val list = source.asFlow().conflate().toList()
+        assertEquals(listOf(1, 5), list)
+    }
+
+    @Test
+    fun testLongRange() = runTest {
+        val source = Observable.range(1, 10_000)
+        val count = source.asFlow().count()
+        assertEquals(10_000, count)
+    }
+
+    @Test
+    fun testProduce() = runTest {
+        val source = Observable.range(0, 10)
+        val flow = source.asFlow()
+        check((0..9).toList(), flow.produceIn(this))
+        check((0..9).toList(), flow.buffer(Channel.UNLIMITED).produceIn(this))
+        check((0..9).toList(), flow.buffer(2).produceIn(this))
+        check((0..9).toList(), flow.buffer(0).produceIn(this))
+        check(listOf(0, 9), flow.conflate().produceIn(this))
+    }
+
+    private suspend fun check(expected: List<Int>, channel: ReceiveChannel<Int>) {
+        val result = ArrayList<Int>(10)
+        channel.consumeEach { result.add(it) }
+        assertEquals(expected, result)
+    }
+}