From d857f8dcb40618fefbe85411a16f9c7b42fb9882 Mon Sep 17 00:00:00 2001
From: Jerry Lee <oldratlee@gmail.com>
Date: Sun, 2 Jun 2024 17:24:38 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20report=20exception=20info=20of=20peek?=
 =?UTF-8?q?=20action,=20errors=20should=20never=20pass=20silently=20?=
 =?UTF-8?q?=F0=9F=92=A3=20=F0=9F=91=80?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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---
 .../cffu/CompletableFutureUtils.java          | 30 ++++++++++++++-----
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/cffu-core/src/main/java/io/foldright/cffu/CompletableFutureUtils.java b/cffu-core/src/main/java/io/foldright/cffu/CompletableFutureUtils.java
index 6d1db59b..20832561 100644
--- a/cffu-core/src/main/java/io/foldright/cffu/CompletableFutureUtils.java
+++ b/cffu-core/src/main/java/io/foldright/cffu/CompletableFutureUtils.java
@@ -10,6 +10,8 @@
 import org.jetbrains.annotations.Contract;
 
 import javax.annotation.ParametersAreNonnullByDefault;
+import java.io.PrintWriter;
+import java.io.StringWriter;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -1252,8 +1254,8 @@ public static <T, U> CompletableFuture<U> applyToEitherSuccessAsync(
      * Peeks the result by executing the given action when given stage completes, returns the given stage.
      * <p>
      * When the given stage is complete, the given action is invoked with the result (or {@code null} if none)
-     * and the exception (or {@code null} if none) of given stage as arguments.
-     * Whether the supplied action throws an exception or not, do <strong>NOT</strong> affect this cffu.
+     * and the exception (or {@code null} if none) of given stage as arguments. Whether the supplied action
+     * throws an exception or not, do <strong>NOT</strong> affect the given CompletableFuture.
      * <p>
      * Unlike method {@link CompletionStage#handle handle} and like method
      * {@link CompletionStage#whenComplete(BiConsumer) whenComplete},
@@ -1269,7 +1271,7 @@ C peek(C cf, BiConsumer<? super T, ? super Throwable> action) {
         requireNonNull(cf, "cf is null");
         requireNonNull(action, "action is null");
 
-        cf.whenComplete(action);
+        cf.whenComplete(action).exceptionally(CompletableFutureUtils::reportExceptionInfoOfPeekAction);
         return cf;
     }
 
@@ -1279,8 +1281,8 @@ C peek(C cf, BiConsumer<? super T, ? super Throwable> action) {
      * returns the given stage.
      * <p>
      * When the given stage is complete, the given action is invoked with the result (or {@code null} if none)
-     * and the exception (or {@code null} if none) of given stage as arguments.
-     * Whether the supplied action throws an exception or not, do <strong>NOT</strong> affect this cffu.
+     * and the exception (or {@code null} if none) of given stage as arguments. Whether the supplied action
+     * throws an exception or not, do <strong>NOT</strong> affect the given CompletableFuture.
      * <p>
      * Unlike method {@link CompletionStage#handle handle} and like method
      * {@link CompletionStage#whenComplete(BiConsumer) whenComplete},
@@ -1301,8 +1303,8 @@ C peekAsync(C cf, BiConsumer<? super T, ? super Throwable> action) {
      * executes the given action using the supplied Executor, returns the given stage.
      * <p>
      * When the given stage is complete, the given action is invoked with the result (or {@code null} if none)
-     * and the exception (or {@code null} if none) of given stage as arguments.
-     * Whether the supplied action throws an exception or not, do <strong>NOT</strong> affect this cffu.
+     * and the exception (or {@code null} if none) of given stage as arguments. Whether the supplied action
+     * throws an exception or not, do <strong>NOT</strong> affect the given CompletableFuture.
      * <p>
      * Unlike method {@link CompletionStage#handle handle} and like method
      * {@link CompletionStage#whenComplete(BiConsumer) whenComplete},
@@ -1319,10 +1321,22 @@ C peekAsync(C cf, BiConsumer<? super T, ? super Throwable> action, Executor exec
         requireNonNull(action, "action is null");
         requireNonNull(executor, "executor is null");
 
-        cf.whenCompleteAsync(action, executor);
+        cf.whenCompleteAsync(action, executor).exceptionally(CompletableFutureUtils::reportExceptionInfoOfPeekAction);
         return cf;
     }
 
+    @Nullable
+    private static <T> T reportExceptionInfoOfPeekAction(Throwable ex) {
+        StringWriter sw = new StringWriter(4096);
+        PrintWriter writer = new PrintWriter(sw);
+
+        writer.println("Unexpected exception occurred in the action of peek:");
+        ex.printStackTrace(writer);
+
+        System.err.println(sw);
+        return null;
+    }
+
     ////////////////////////////////////////////////////////////////////////////////
     //# Backport CF static methods + related enhanced methods
     //  compatibility for low Java versions