fix: report rejected synchronous data channel sends

webrtc-jni/src/main/cpp/src/JNI_RTCDataChannel.cpp

@@ -19,6 +19,7 @@
 #include "JavaEnums.h"
 #include "JavaError.h"
 #include "JavaRef.h"
+#include "JavaRuntimeException.h"
 #include "JavaString.h"
 #include "JavaUtils.h"
 
@@ -174,7 +175,9 @@ JNIEXPORT void JNICALL Java_dev_onvoid_webrtc_RTCDataChannel_sendDirectBuffer
 
 		webrtc::CopyOnWriteBuffer data(address, static_cast<size_t>(bufferLength));
 
-		channel->Send(webrtc::DataBuffer(data, static_cast<bool>(isBinary)));
+		if (!channel->Send(webrtc::DataBuffer(data, static_cast<bool>(isBinary)))) {
+			env->Throw(jni::JavaRuntimeException(env, "Data channel rejected the send"));
+		}
 	}
 	else {
 		env->Throw(jni::JavaError(env, "Non-direct buffer provided"));
@@ -195,7 +198,9 @@ JNIEXPORT void JNICALL Java_dev_onvoid_webrtc_RTCDataChannel_sendByteArrayBuffer
 	env->ReleaseByteArrayElements(jBufferArray, arrayPtr, JNI_ABORT);
 
 	try {
-		channel->Send(webrtc::DataBuffer(data, static_cast<bool>(isBinary)));
+		if (!channel->Send(webrtc::DataBuffer(data, static_cast<bool>(isBinary)))) {
+			env->Throw(jni::JavaRuntimeException(env, "Data channel rejected the send"));
+		}
 	}
 	catch (...) {
 		ThrowCxxJavaException(env);

webrtc/src/main/java/dev/onvoid/webrtc/RTCDataChannel.java

@@ -150,8 +150,8 @@ private RTCDataChannel() {
 	 *
 	 * @param buffer The buffer to be queued for transmission.
 	 *
-	 * @throws Exception If queuing data is not possible because not enough
-	 *                   buffer space is available.
+	 * @throws Exception If the native channel rejects the send, for example
+	 *                   because it is not open or its send buffer is full.
 	 */
 	public void send(RTCDataChannelBuffer buffer) throws Exception {
 		ByteBuffer data = buffer.data;

webrtc/src/test/java/dev/onvoid/webrtc/RTCDataChannelSendRejectionTests.java

@@ -0,0 +1,52 @@
+package dev.onvoid.webrtc;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.nio.ByteBuffer;
+
+import org.junit.jupiter.api.Test;
+
+class RTCDataChannelSendRejectionTests extends TestBase {
+
+	@Test
+	void rejectsHeapBufferBeforeOpen() {
+		assertRejected(ByteBuffer.allocate(8), false);
+	}
+
+	@Test
+	void rejectsDirectBufferBeforeOpen() {
+		assertRejected(ByteBuffer.allocateDirect(8), false);
+	}
+
+	@Test
+	void rejectsHeapBufferAfterClose() {
+		assertRejected(ByteBuffer.allocate(8), true);
+	}
+
+	@Test
+	void rejectsDirectBufferAfterClose() {
+		assertRejected(ByteBuffer.allocateDirect(8), true);
+	}
+
+	private void assertRejected(ByteBuffer data, boolean closed) {
+		RTCPeerConnection peer = factory.createPeerConnection(
+				new RTCConfiguration(), candidate -> { });
+		RTCDataChannel channel = peer.createDataChannel("send", new RTCDataChannelInit());
+
+		try {
+			if (closed) {
+				channel.close();
+			}
+			assertEquals(closed ? RTCDataChannelState.CLOSED : RTCDataChannelState.CONNECTING,
+					channel.getState());
+			RuntimeException error = assertThrows(RuntimeException.class,
+					() -> channel.send(new RTCDataChannelBuffer(data, true)));
+			assertEquals("Data channel rejected the send", error.getMessage());
+		}
+		finally {
+			peer.close();
+			channel.dispose();
+		}
+	}
+}