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feat: add TcpStackAwareSocketChannel for z/OS TCP/IP stack recovery — GH#4776 #4792

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feat: add TcpStackAwareSocketChannel for z/OS TCP/IP stack recovery — GH#4776 #4792

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5de0b3e
refactor: move isTcpStackRestarted/isRecycledClass to static, add tcp…
balhar-jakub Jul 9, 2026
904c283
feat: add TcpStackAwareSocketChannel wrapper for z/OS TCP/IP recovery…
balhar-jakub Jul 9, 2026
5d653b2
test: add TcpStackAwareSocketChannel unit tests (#4776)
balhar-jakub Jul 9, 2026
fb7e318
fix: disable TcpStackAwareSocketChannel by default
balhar-jakub Jul 10, 2026
208847d
Merge branch 'v3.x.x' into hermes/gh4776
balhar-jakub Aug 20, 2026
0dfba61
fix: address TcpStackAwareSocketChannel review feedback
balhar-jakub Aug 24, 2026
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190 changes: 165 additions & 25 deletions apiml-tomcat-common/src/main/java/org/zowe/apiml/product/web/TomcatAcceptFixConfig.java
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.SelectorProvider;
Expand All @@ -51,11 +52,15 @@ public class TomcatAcceptFixConfig {
@Value("${server.tomcat.retryRebindTimeoutSecs:10}")
int retryRebindTimeoutSecs;

@Value("${apiml.tcpStackAwareSocketChannel.enabled:false}")
boolean tcpStackAwareSocketChannelEnabled;

private static final Field ENDPOINT_FIELD;
private static final Field NIO_SOCKET_FIELD;

private static final MethodHandle IMPL_CLOSE_SELECTABGLE_CHANNEL_HANLE; // NOSONAR
private static final MethodHandle IMPL_CLOSE_SELECTABLE_CHANNEL_HANDLE; // NOSONAR
private static final MethodHandle IMPL_CONFIGURE_BLOCKING; // NOSONAR
private static final String NETWORK_RECYCLED_EXCEPTION_CLASS = "com.ibm.net.NetworkRecycledException";

/**
* To mitigate parallel treatment of socket rebinding
Expand All @@ -69,7 +74,7 @@ public class TomcatAcceptFixConfig {

Method implCloseSelectableChannel = AbstractSelectableChannel.class.getDeclaredMethod("implCloseSelectableChannel");
implCloseSelectableChannel.setAccessible(true); // NOSONAR
IMPL_CLOSE_SELECTABGLE_CHANNEL_HANLE = MethodHandles.lookup().unreflect(implCloseSelectableChannel);
IMPL_CLOSE_SELECTABLE_CHANNEL_HANDLE = MethodHandles.lookup().unreflect(implCloseSelectableChannel);

Method implConfigureBlocking = AbstractSelectableChannel.class.getDeclaredMethod("implConfigureBlocking", boolean.class);
implConfigureBlocking.setAccessible(true); // NOSONAR
Expand Down Expand Up @@ -143,12 +148,32 @@ public void stopping() {
running.set(false);
}

static boolean isRecycledClass(Throwable t) {
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return NETWORK_RECYCLED_EXCEPTION_CLASS.equals(t.getClass().getName());
}

static boolean isTcpStackRestarted(Throwable t) {
if ((t.getMessage() != null) && t.getMessage().contains("EDC5122I")) {
return true;
}

if (isRecycledClass(t)) {
return true;
}

Throwable cause = t.getCause();
if ((cause != null) && (cause != t)) {
return isTcpStackRestarted(cause);
}

return false;
}

/**
* Socket implementation wrapper to handle rebinding on TCP Stack restart
*/
class FixedServerSocketChannel extends ServerSocketChannel {

private static final String NETWORK_RECYCLED_EXCEPTION_CLASS = "com.ibm.net.NetworkRecycledException";

/**
* Wrapper server socket inside
Expand Down Expand Up @@ -181,7 +206,7 @@ class FixedServerSocketChannel extends ServerSocketChannel {
@Override
protected void implCloseSelectableChannel() throws IOException {
try {
IMPL_CLOSE_SELECTABGLE_CHANNEL_HANLE.invoke(socket);
IMPL_CLOSE_SELECTABLE_CHANNEL_HANDLE.invoke(socket);
} catch (IOException | RuntimeException e) {
throw e;
} catch (Throwable t) {
Expand Down Expand Up @@ -249,43 +274,33 @@ private synchronized void rebind(int stateBefore) throws IOException {
}
}

boolean isRecycledClass(Throwable t) {
return NETWORK_RECYCLED_EXCEPTION_CLASS.equals(t.getClass().getName());
}

boolean isTcpStackRestarted(Throwable t) {
if ((t.getMessage() != null) && t.getMessage().contains("EDC5122I")) {
return true;
}

if (isRecycledClass(t)) {
return true;
}

Throwable cause = t.getCause();
if ((cause != null) && (cause != t)) {
return isTcpStackRestarted(cause);
}

return false;
return TomcatAcceptFixConfig.isTcpStackRestarted(t);
}

public SocketChannel accept() throws IOException {
// obtain current state of rebinding to detection parallel actions
final int stateBefore = state.get();
try {
return socket.accept();
return wrapIfEnabled(socket.accept());
} catch (IOException ioe) {
if (isTcpStackRestarted(ioe)) {
if (TomcatAcceptFixConfig.isTcpStackRestarted(ioe)) {
// the fix solve just one issue about stopped TCP/IP stack
log.debug("The TCP/IP stack was probably restarted. The socket of Tomcat will rebind.");
rebind(stateBefore);
return socket.accept();
return wrapIfEnabled(socket.accept());
}
throw ioe;
}
}

private SocketChannel wrapIfEnabled(SocketChannel socketChannel) {
if (tcpStackAwareSocketChannelEnabled) {
return new TcpStackAwareSocketChannel(socketChannel);
}
return socketChannel;
}

}

/**
Expand All @@ -310,4 +325,129 @@ private interface Overridden {

}

/**
* The list of methods excluded from Lombok @Delegate for TcpStackAwareSocketChannel.
* It contains methods inherited from SocketChannel that must not be delegated and
* read/write/close-related methods that are wrapped explicitly in this class.
*/
private interface ExcludedSocketOps {
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SelectorProvider provider();
boolean isRegistered();
SelectionKey keyFor(Selector sel);
SelectionKey register(Selector sel, int ops, Object att);
SelectionKey register(Selector sel, int ops) throws ClosedChannelException;
boolean isBlocking();
Object blockingLock();
SelectableChannel configureBlocking(boolean block) throws IOException;
void implCloseChannel() throws IOException;
void close() throws IOException;
boolean isOpen();
int validOps();
long read(ByteBuffer[] dsts) throws IOException;
long write(ByteBuffer[] srcs) throws IOException;
int read(ByteBuffer dst) throws IOException;
long read(ByteBuffer[] dsts, int offset, int length) throws IOException;
int write(ByteBuffer src) throws IOException;
long write(ByteBuffer[] srcs, int offset, int length) throws IOException;
void implCloseSelectableChannel() throws IOException;
void implConfigureBlocking(boolean block) throws IOException;

}

/**
* SocketChannel wrapper that detects z/OS TCP/IP stack restarts during I/O operations.
* When EDC5122I or NetworkRecycledException is caught on read/write, the underlying
* socket is closed and the exception is re-thrown so Tomcat can discard the connection.
*/
class TcpStackAwareSocketChannel extends SocketChannel {
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@Delegate(excludes = ExcludedSocketOps.class)
private final SocketChannel delegate;

TcpStackAwareSocketChannel(SocketChannel delegate) {
super(delegate.provider());
this.delegate = delegate;
}

@Override
public int read(ByteBuffer dst) throws IOException {
try {
return delegate.read(dst);
} catch (IOException e) {
if (TomcatAcceptFixConfig.isTcpStackRestarted(e)) {
log.debug("TCP/IP stack restart detected during read on client socket; closing connection", e);
safeClose(delegate);
}
throw e;
}
}

@Override
public long read(ByteBuffer[] dsts, int offset, int length) throws IOException {
try {
return delegate.read(dsts, offset, length);
} catch (IOException e) {
if (TomcatAcceptFixConfig.isTcpStackRestarted(e)) {
log.debug("TCP/IP stack restart detected during scatter read on client socket; closing connection", e);
safeClose(delegate);
}
throw e;
}
}

@Override
public int write(ByteBuffer src) throws IOException {
try {
return delegate.write(src);
} catch (IOException e) {
if (TomcatAcceptFixConfig.isTcpStackRestarted(e)) {
log.debug("TCP/IP stack restart detected during write on client socket; closing connection", e);
safeClose(delegate);
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}
throw e;
}
}

@Override
public long write(ByteBuffer[] srcs, int offset, int length) throws IOException {
try {
return delegate.write(srcs, offset, length);
} catch (IOException e) {
if (TomcatAcceptFixConfig.isTcpStackRestarted(e)) {
log.debug("TCP/IP stack restart detected during scatter write on client socket; closing connection", e);
safeClose(delegate);
}
throw e;
}
}

@Override
protected void implCloseSelectableChannel() throws IOException {
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// SocketChannel.close() is final; it reaches this override through
// AbstractInterruptibleChannel.close().
delegate.close();
}

@Override
protected void implConfigureBlocking(boolean block) throws IOException {
try {
IMPL_CONFIGURE_BLOCKING.invoke(delegate, block);
} catch (IOException | RuntimeException e) {
throw e;
} catch (Throwable t) {
throw new IllegalStateException(t);
}
}

private static void safeClose(SocketChannel ch) {
try {
ch.close();
} catch (IOException e) {
log.trace("Best-effort close of client socket failed", e);
}
}

}

}
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