clh-kubernetes commented on issue #1039:
URL: https://github.com/apache/arrow-java/issues/1039#issuecomment-3976084167
@ennuite
Thank you for the quick review. I apologize for the confusion regarding the
API method names in my initial description.
The issue is **not** with the API usage itself, but with the internal
implementation logic triggered when FlightClient.Builder.build() is called with
a Domain Socket location on **Linux**.
Since you are on macOS (which uses KQueue, not Epoll), you cannot reproduce
this locally. The bug is strictly specific to the **Epoll native transport**
path on Linux.
**Root Cause Analysis**
I have decompiled flight-core-17.0.0.jar (16 or 18) and identified the exact
line causing the crash inside the FlightClient.Builder.build() method:
// Internal logic inside FlightClient.Builder.build() or related Epoll
initializer
****
**Code: **
case LocationSchemes.GRPC_DOMAIN_SOCKET:
{
// The implementation is platform-specific, so we have to find
the classes at runtime
builder =
NettyChannelBuilder.forAddress(location.toSocketAddress());
try {
try {
// Linux
builder.channelType(
Class.forName("io.netty.channel.epoll.EpollDomainSocketChannel")
.asSubclass(ServerChannel.class));
}
****
// ❌ BUG: This cast is invalid.
// EpollDomainSocketChannel implements 'Channel' (Client), NOT
'ServerChannel'.
Class<? extends ServerChannel> serverClazz =
clazz.asSubclass(ServerChannel.class);
**Why it fails:**
EpollDomainSocketChannel is a **client-side** channel class.
* ServerChannel is the base interface for **server-side** listeners.
* The correct server class would be EpollServerDomainSocketChannel.
* Attempting to cast the client class to ServerChannel throws a
java.lang.ClassCastException at runtime.
**Corrected Reproduction Steps (Linux Required)**
**Environment:**
* OS: Linux (Ubuntu/CentOS/Alpine) - *Must be Linux to trigger Epoll*
* Java: OpenJDK 11+
* Dependency: {{org.apache.arrow:arrow-flight:17.0.0}} (or 18.0.0)
* Native Lib: {{io.netty:netty-transport-native-epoll}} must be on the
classpath.
**Code:**
import org.apache.arrow.flight.FlightClient;
import org.apache.arrow.flight.Location;
public class ReproUdsBug {
public static void main(String[] args) {
// 1. Use the correct public API
Location loc = Location.forGrpcDomainSocket("/tmp/arrow-test.sock");
BufferAllocator allocator = new RootAllocator();
try {
// 2. The crash happens INSIDE this .build() call
FlightClient client =
FlightClient.builder(allocator,loc).build();
System.out.println("Success: Client created.");
} catch (Exception e) {
System.err.println("Error occurred: " +
e.getClass().getSimpleName());
e.printStackTrace();
// Expected Output:
// java.lang.ClassCastException: class
io.netty.channel.epoll.EpollDomainSocketChannel
// cannot be cast to class io.netty.channel.ServerChannel
}
}
}
{code}
**Summary**
* **API Usage**: The user code is correct (using {{forGrpcDomainSocket}} and
{{builder().build()}}).
* **Trigger**: Calling {{.build()}} with a Domain Socket location on Linux.
* **Defect**: Internal reflection logic incorrectly casts a Client Channel
class to a Server Channel interface.
* **Regression**: Works in v15.0.0, broken in v16.0.0+.
Could you please verify this on a Linux environment or delegate to a team
member with Linux access? The fix should involve correcting the class reference
to {{EpollServerDomainSocketChannel}} (if server logic was intended) or
removing the incorrect cast for client initialization.
Thanks again for your help!
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