1.x: Add Single.onErrorResumeNext(Func)

src/main/java/rx/Single.java

@@ -1432,7 +1432,38 @@ public final Single<T> onErrorReturn(Func1<Throwable, ? extends T> resumeFunctio
      * @see <a href="http://reactivex.io/documentation/operators/catch.html">ReactiveX operators documentation: Catch</a>
      */
     public final Single<T> onErrorResumeNext(Single<? extends T> resumeSingleInCaseOfError) {
-        return new Single<T>(new SingleOperatorOnErrorResumeNextViaSingle<T>(this, resumeSingleInCaseOfError));
+        return new Single<T>(SingleOperatorOnErrorResumeNext.withOther(this, resumeSingleInCaseOfError));
+    }
+
+    /**
+     * Instructs a Single to pass control to another Single rather than invoking
+     * {@link Observer#onError(Throwable)} if it encounters an error.
+     * <p/>
+     * <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/onErrorResumeNext.png" alt="">
+     * <p/>
+     * By default, when a Single encounters an error that prevents it from emitting the expected item to
+     * its {@link Observer}, the Single invokes its Observer's {@code onError} method, and then quits
+     * without invoking any more of its Observer's methods. The {@code onErrorResumeNext} method changes this
+     * behavior. If you pass a function that will return another Single ({@code resumeFunctionInCaseOfError}) to an Single's
+     * {@code onErrorResumeNext} method, if the original Single encounters an error, instead of invoking its
+     * Observer's {@code onError} method, it will instead relinquish control to {@code resumeSingleInCaseOfError} which
+     * will invoke the Observer's {@link Observer#onNext onNext} method if it is able to do so. In such a case,
+     * because no Single necessarily invokes {@code onError}, the Observer may never know that an error
+     * happened.
+     * <p/>
+     * You can use this to prevent errors from propagating or to supply fallback data should errors be
+     * encountered.
+     * <dl>
+     * <dt><b>Scheduler:</b></dt>
+     * <dd>{@code onErrorResumeNext} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     *
+     * @param resumeFunctionInCaseOfError a function that returns a Single that will take control if source Single encounters an error.
+     * @return the original Single, with appropriately modified behavior.
+     * @see <a href="http://reactivex.io/documentation/operators/catch.html">ReactiveX operators documentation: Catch</a>
+     */
+    public final Single<T> onErrorResumeNext(final Func1<Throwable, ? extends Single<? extends T>> resumeFunctionInCaseOfError) {
+        return new Single<T>(SingleOperatorOnErrorResumeNext.withFunction(this, resumeFunctionInCaseOfError));
     }
 
     /**

src/main/java/rx/exceptions/Exceptions.java

@@ -18,6 +18,7 @@
 import java.util.*;
 
 import rx.Observer;
+import rx.SingleSubscriber;
 import rx.annotations.Experimental;
 
 /**
@@ -188,6 +189,7 @@ public static void throwOrReport(Throwable t, Observer<?> o, Object value) {
         Exceptions.throwIfFatal(t);
         o.onError(OnErrorThrowable.addValueAsLastCause(t, value));
     }
+
     /**
      * Forwards a fatal exception or reports it to the given Observer.
      * @param t the exception
@@ -199,4 +201,17 @@ public static void throwOrReport(Throwable t, Observer<?> o) {
         Exceptions.throwIfFatal(t);
         o.onError(t);
     }
+
+    /**
+     * Forwards a fatal exception or reports it to the given Observer.
+     *
+     * @param throwable the exception.
+     * @param subscriber the subscriber to report to.
+     * @since (if this graduates from Experimental/Beta to supported, replace this parenthetical with the release number).
+     */
+    @Experimental
+    public static void throwOrReport(Throwable throwable, SingleSubscriber<?> subscriber) {
+        Exceptions.throwIfFatal(throwable);
+        subscriber.onError(throwable);
+    }
 }

src/main/java/rx/internal/operators/SingleOperatorOnErrorResumeNext.java

@@ -0,0 +1,65 @@
+package rx.internal.operators;
+
+import rx.Single;
+import rx.SingleSubscriber;
+import rx.exceptions.Exceptions;
+import rx.functions.Func1;
+import rx.plugins.RxJavaPlugins;
+
+public class SingleOperatorOnErrorResumeNext<T> implements Single.OnSubscribe<T> {
+
+    private final Single<? extends T> originalSingle;
+    private final Func1<Throwable, ? extends Single<? extends T>> resumeFunctionInCaseOfError;
+
+    private SingleOperatorOnErrorResumeNext(Single<? extends T> originalSingle, Func1<Throwable, ? extends Single<? extends T>> resumeFunctionInCaseOfError) {
+        if (originalSingle == null) {
+            throw new NullPointerException("originalSingle must not be null");
+        }
+
+        if (resumeFunctionInCaseOfError == null) {
+            throw new NullPointerException("resumeFunctionInCaseOfError must not be null");
+        }
+
+        this.originalSingle = originalSingle;
+        this.resumeFunctionInCaseOfError = resumeFunctionInCaseOfError;
+    }
+
+    public static <T> SingleOperatorOnErrorResumeNext<T> withFunction(Single<? extends T> originalSingle, Func1<Throwable, ? extends Single<? extends T>> resumeFunctionInCaseOfError) {
+        return new SingleOperatorOnErrorResumeNext<T>(originalSingle, resumeFunctionInCaseOfError);
+    }
+
+    public static <T> SingleOperatorOnErrorResumeNext<T> withOther(Single<? extends T> originalSingle, final Single<? extends T> resumeSingleInCaseOfError) {
+        if (resumeSingleInCaseOfError == null) {
+            throw new NullPointerException("resumeSingleInCaseOfError must not be null");
+        }
+
+        return new SingleOperatorOnErrorResumeNext<T>(originalSingle, new Func1<Throwable, Single<? extends T>>() {
+            @Override
+            public Single<? extends T> call(Throwable throwable) {
+                return resumeSingleInCaseOfError;
+            }
+        });
+    }
+
+    @Override
+    public void call(final SingleSubscriber<? super T> child) {
+        final SingleSubscriber<? super T> parent = new SingleSubscriber<T>() {
+            @Override
+            public void onSuccess(T value) {
+                child.onSuccess(value);
+            }
+
+            @Override
+            public void onError(Throwable error) {
+                try {
+                    resumeFunctionInCaseOfError.call(error).subscribe(child);
+                } catch (Throwable innerError) {
+                    Exceptions.throwOrReport(innerError, child);
+                }
+            }
+        };
+
+        child.add(parent);
+        originalSingle.subscribe(parent);
+    }
+}

src/test/java/rx/SingleTest.java

@@ -1220,13 +1220,59 @@ public void onErrorResumeNextViaSingleShouldPreventNullSingle() {
         try {
             Single
                     .just("value")
-                    .onErrorResumeNext(null);
+                    .onErrorResumeNext((Single<String>) null);
             fail();
         } catch (NullPointerException expected) {
             assertEquals("resumeSingleInCaseOfError must not be null", expected.getMessage());
         }
     }
 
+    @Test
+    public void onErrorResumeNextViaFunctionShouldNotInterruptSuccesfulSingle() {
+        TestSubscriber<String> testSubscriber = new TestSubscriber<String>();
+
+        Single
+                .just("success")
+                .onErrorResumeNext(new Func1<Throwable, Single<? extends String>>() {
+                    @Override
+                    public Single<? extends String> call(Throwable throwable) {
+                        return Single.just("fail");
+                    }
+                })
+                .subscribe(testSubscriber);
+
+        testSubscriber.assertValue("success");
+    }
+
+    @Test
+    public void onErrorResumeNextViaFunctionShouldResumeWithPassedSingleInCaseOfError() {
+        TestSubscriber<String> testSubscriber = new TestSubscriber<String>();
+
+        Single
+                .<String> error(new RuntimeException("test exception"))
+                .onErrorResumeNext(new Func1<Throwable, Single<? extends String>>() {
+                    @Override
+                    public Single<? extends String> call(Throwable throwable) {
+                        return Single.just("fallback");
+                    }
+                })
+                .subscribe(testSubscriber);
+
+        testSubscriber.assertValue("fallback");
+    }
+
+    @Test
+    public void onErrorResumeNextViaFunctionShouldPreventNullFunction() {
+        try {
+            Single
+                    .just("value")
+                    .onErrorResumeNext((Func1<Throwable, ? extends Single<? extends String>>) null);
+            fail();
+        } catch (NullPointerException expected) {
+            assertEquals("resumeFunctionInCaseOfError must not be null", expected.getMessage());
+        }
+    }
+
     @Test(expected = NullPointerException.class)
     public void iterableToArrayShouldThrowNullPointerExceptionIfIterableNull() {
         Single.iterableToArray(null);