fix: return no remote certificates before the DTLS handshake

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

@@ -69,7 +69,8 @@ JNIEXPORT jobject JNICALL Java_dev_onvoid_webrtc_RTCDtlsTransport_getRemoteCerti
 		auto info = transport->Information();
 		auto certChain = info.remote_ssl_certificates();
 
-		size_t count = certChain->GetSize();
+		// There is no chain before the handshake has received one.
+		size_t count = certChain != nullptr ? certChain->GetSize() : 0;
 
 		jni::JavaArrayList certificates(env, count);
 

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

@@ -64,7 +64,8 @@ public class RTCDtlsTransport extends NativeObject {
 
 	/**
 	 * Returns the certificate chain in use by the remote side, with each
-	 * certificate encoded in PEM format.
+	 * certificate encoded in PEM format. The list is empty until the DTLS
+	 * handshake has received the certificates of the remote side.
 	 *
 	 * @return The certificate chain in use by the remote side.
 	 */

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

@@ -18,7 +18,9 @@
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -127,6 +129,43 @@ public void onError(String error) { }
 				"The replaced observer must not receive further events");
 	}
 
+	@Test
+	void remoteCertificates() {
+		List<RTCCertificatePEM> certificates = transport.getRemoteCertificates();
+
+		assertFalse(certificates.isEmpty());
+
+		for (RTCCertificatePEM certificate : certificates) {
+			assertTrue(certificate.getCertificate().startsWith("-----BEGIN CERTIFICATE-----"));
+		}
+	}
+
+	@Test
+	void remoteCertificatesBeforeHandshake() throws Exception {
+		TestPeerConnection offerer = new TestPeerConnection(factory);
+
+		try {
+			AudioTrackSource audioSource = factory.createAudioSource(new AudioOptions());
+			AudioTrack audioTrack = factory.createAudioTrack("audioTrack", audioSource);
+			RTCRtpSender audioSender = offerer.getPeerConnection()
+					.addTrack(audioTrack, Collections.singletonList("stream1"));
+
+			// Setting the local description creates the transport, which has
+			// no remote certificates before the handshake. Reading them used
+			// to crash the VM.
+			offerer.createOffer();
+
+			RTCDtlsTransport dtlsTransport = audioSender.getTransport();
+			assertNotNull(dtlsTransport);
+			assertEquals(RTCDtlsTransportState.NEW, dtlsTransport.getState());
+
+			assertTrue(dtlsTransport.getRemoteCertificates().isEmpty());
+		}
+		finally {
+			offerer.close();
+		}
+	}
+
 	@Test
 	void observerCanUseRtpSender() throws Exception {
 		// WebRTC reports DTLS states on the network thread, which is also the