From aec35a56e0d60119fc894302b9b2b61df4fbe4af Mon Sep 17 00:00:00 2001
From: Thimios <thimios.dimopulos@lyrasis.org>
Date: Thu, 16 Jul 2026 19:24:03 +0300
Subject: [PATCH] [fix] avoid infinite loop in Response#isClientAbortException,
 fixes #449.

---
 .../java/org/jruby/rack/ext/Response.java     | 14 ++++--
 src/spec/ruby/jruby/rack/response_spec.rb     | 43 +++++++++++++++++++
 2 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/src/main/java/org/jruby/rack/ext/Response.java b/src/main/java/org/jruby/rack/ext/Response.java
index 8e7d0670a..0a312d4c5 100644
--- a/src/main/java/org/jruby/rack/ext/Response.java
+++ b/src/main/java/org/jruby/rack/ext/Response.java
@@ -615,15 +615,23 @@ private boolean handledAsClientAbort(final Exception ioe) {
         return false;
     }
 
+    /**
+     * How many nested causes {@link #isClientAbortException(Exception)} inspects.
+     * A cause chain is allowed to be cyclic, thus the traversal needs a bound.
+     */
+    private static final int MAX_CAUSE_DEPTH = 20;
+
     // ioe.inspect =~ /(ClientAbortException|EofException|broken pipe)/i
     protected boolean isClientAbortException(final Exception ioe) {
         String error = ioe.toString();
         if ( error.contains("ClientAbortException") ) return true;
         if ( error.contains("EofException") ) return true;
-        while ( true ) {
+        Throwable cause = ioe;
+        for ( int depth = 0; depth < MAX_CAUSE_DEPTH; depth++ ) {
             if ( error.toLowerCase().contains("broken pipe") ) return true;
-            if ( ioe.getCause() == null ) break;
-            error = ioe.getCause().getMessage();
+            cause = cause.getCause();
+            if ( cause == null ) break;
+            error = cause.getMessage();
             if ( error == null ) break;
         }
         return false;
diff --git a/src/spec/ruby/jruby/rack/response_spec.rb b/src/spec/ruby/jruby/rack/response_spec.rb
index a1dd9b5a6..95f745d47 100644
--- a/src/spec/ruby/jruby/rack/response_spec.rb
+++ b/src/spec/ruby/jruby/rack/response_spec.rb
@@ -519,6 +519,49 @@ def flush
       end
     end
 
+    it "raises exceptions with a nested cause that do not look like abort exceptions" do
+      servlet_response = org.jruby.rack.mock.fail.FailingHttpServletResponse.new
+      # e.g. Jetty failing a stalled write: IOException caused by a TimeoutException
+      servlet_response.setFailure java.io.IOException.new(
+        java.util.concurrent.TimeoutException.new('Idle timeout expired: 30000/30000 ms')
+      )
+      begin
+        with_swallow_client_abort do
+          response.write_body new_response_environment(servlet_response)
+        end
+        fail 'IO exception NOT raised!'
+      rescue java.io.IOException => e
+        expect(e.to_s).to match(/idle timeout expired/i)
+      end
+    end
+
+    it "swallows client abort exceptions nested deeper in the cause chain" do
+      servlet_response = org.jruby.rack.mock.fail.FailingHttpServletResponse.new
+      servlet_response.setFailure java.io.IOException.new('write failed',
+        java.io.IOException.new('connection problem', java.io.IOException.new('Broken pipe'))
+      )
+      with_swallow_client_abort do
+        response.write_body new_response_environment(servlet_response)
+      end
+    end
+
+    it "raises (and does not hang) on a cyclic cause chain" do
+      failure = java.io.IOException.new 'write failed'
+      cause = java.io.IOException.new 'nested failure'
+      failure.initCause cause
+      cause.initCause failure
+      servlet_response = org.jruby.rack.mock.fail.FailingHttpServletResponse.new
+      servlet_response.setFailure failure
+      begin
+        with_swallow_client_abort do
+          response.write_body new_response_environment(servlet_response)
+        end
+        fail 'IO exception NOT raised!'
+      rescue java.io.IOException => e
+        expect(e.to_s).to match(/write failed/i)
+      end
+    end
+
     private
 
     def with_dechunk(dechunk = true)