Fix epoll spliceTo file descriptor with offset (netty#9369)

Motivation

The AbstractEpollStreamChannel::spliceTo(FileDescriptor, ...) methods
take an offset parameter but this was effectively ignored due to what
looks like a typo in the corresponding JNI function impl. Instead it
would always use the file's own native offset.

Modification

- Fix typo in netty_epoll_native_splice0() and offset accounting in
AbstractEpollStreamChannel::SpliceFdTask.
- Modify unit test to include an invocation of the public spliceTo
method using non-zero offset.

Result

spliceTo FD methods work as expected when an offset is provided.

transport-native-epoll/src/main/c/netty_epoll_native.c

@@ -385,7 +385,7 @@ static jint netty_epoll_native_splice0(JNIEnv* env, jclass clazz, jint fd, jlong
     loff_t off_out = (loff_t) offOut;
 
     loff_t* p_off_in = off_in >= 0 ? &off_in : NULL;
-    loff_t* p_off_out = off_in >= 0 ? &off_out : NULL;
+    loff_t* p_off_out = off_out >= 0 ? &off_out : NULL;
 
     do {
        res = splice(fd, p_off_in, fdOut, p_off_out, (size_t) len, SPLICE_F_NONBLOCK | SPLICE_F_MOVE);

transport-native-epoll/src/main/java/io/netty/channel/epoll/AbstractEpollStreamChannel.java

@@ -205,7 +205,7 @@ public final ChannelFuture spliceTo(final FileDescriptor ch, final int offset, f
     public final ChannelFuture spliceTo(final FileDescriptor ch, final int offset, final int len,
                                         final ChannelPromise promise) {
         checkPositiveOrZero(len, "len");
-        checkPositiveOrZero(offset, "offser");
+        checkPositiveOrZero(offset, "offset");
         if (config().getEpollMode() != EpollMode.LEVEL_TRIGGERED) {
             throw new IllegalStateException("spliceTo() supported only when using " + EpollMode.LEVEL_TRIGGERED);
         }
@@ -977,7 +977,7 @@ public boolean spliceOut() throws Exception {
     private final class SpliceFdTask extends SpliceInTask {
         private final FileDescriptor fd;
         private final ChannelPromise promise;
-        private final int offset;
+        private int offset;
 
         SpliceFdTask(FileDescriptor fd, int offset, int len, ChannelPromise promise) {
             super(len, promise);
@@ -1007,6 +1007,7 @@ public boolean spliceIn(RecvByteBufAllocator.Handle handle) {
                         }
                         do {
                             int splicedOut = Native.splice(pipeIn.intValue(), -1, fd.intValue(), offset, splicedIn);
+                            offset += splicedOut;
                             splicedIn -= splicedOut;
                         } while (splicedIn > 0);
                         if (len == 0) {

transport-native-epoll/src/test/java/io/netty/channel/epoll/EpollSpliceTest.java

@@ -189,7 +189,7 @@ public void operationComplete(ChannelFuture future) throws Exception {
         }
     }
 
-    @Test
+    @Test(timeout = 10000)
     public void spliceToFile() throws Throwable {
         EventLoopGroup group = new EpollEventLoopGroup(1);
         File file = File.createTempFile("netty-splice", null);
@@ -215,7 +215,7 @@ public void spliceToFile() throws Throwable {
             i += length;
         }
 
-        while (sh.future == null || !sh.future.isDone()) {
+        while (sh.future2 == null || !sh.future2.isDone() || !sh.future.isDone()) {
             if (sh.exception.get() != null) {
                 break;
             }
@@ -291,22 +291,22 @@ public void exceptionCaught(ChannelHandlerContext ctx,
     private static class SpliceHandler extends ChannelInboundHandlerAdapter {
         private final File file;
 
-        volatile Channel channel;
         volatile ChannelFuture future;
+        volatile ChannelFuture future2;
         final AtomicReference<Throwable> exception = new AtomicReference<Throwable>();
 
         SpliceHandler(File file) {
             this.file = file;
         }
 
         @Override
-        public void channelActive(ChannelHandlerContext ctx)
-                throws Exception {
-            channel = ctx.channel();
+        public void channelActive(ChannelHandlerContext ctx) throws Exception {
             final EpollSocketChannel ch = (EpollSocketChannel) ctx.channel();
             final FileDescriptor fd = FileDescriptor.from(file);
 
-            future = ch.spliceTo(fd, 0, data.length);
+            // splice two halves separately to test starting offset
+            future = ch.spliceTo(fd, 0, data.length / 2);
+            future2 = ch.spliceTo(fd, data.length / 2, data.length / 2);
         }
 
         @Override