Add backwards compatibility for old names of OpenSSL functions

libraries/networking/src/WebRTCOpenSSLCompatibility.cpp

@@ -0,0 +1,77 @@
+//
+//  WebRTCOpenSSLCompatibility.cpp
+//  libraries/networking/src
+//
+//  Created by Dale Glass on 25/05/2022
+//  Copyright 2022 Vircadia contributors.
+//
+//  Distributed under the Apache License, Version 2.0.
+//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
+//
+
+
+
+#include <openssl/opensslv.h>
+
+/*
+ * Starting at OpenSSL 3.0, the names for some of the functions changed.
+ *
+ * This breaks WebRTC. We have a problem:
+ *
+ * WebRTC is a pain to build and has its own build environment. Rather than building it
+ * locally we provide a prebuilt binary. Said binary is generated against some Google-provided
+ * chroot of Debian, so for the most part the result is independent of what you build it
+ * on anyway.
+ *
+ * WebRTC prefers to build and use its own BoringSSL. But we use OpenSSL, and symbol
+ * names collide between what comes from the BoringSSL linked into webrtc, and our
+ * system library.
+ *
+ * Therefore, we use the option to link WebRTC against the system OpenSSL. However,
+ * starting on OpenSSL 3.0, some symbols were renamed. Backwards compatibility is kept
+ * through #defines in the OpenSSL headers, but of course this has no effect on compiled
+ * code. We have a WebRTC that calls SSL_get_peer_certificate, but the new OpenSSL now calls
+ * this SSL_get1_peer_certificate.
+ *
+ * New distros using OpenSSL 3.0 now have problems.
+ *
+ *
+ * We have these possible solutions:
+ *
+ * 1. Have an OpenSSL 3.0 build of WebRTC, and choose which we need. Possible, but a bit painful
+ * while OpenSSL 1.x is still in use.
+ *
+ * 2. Follow the recommendation here:
+ * https://stackoverflow.com/questions/71107066/how-to-integrate-part-of-webrtc-as-a-static-dynamic-library-with-the-existing
+ * and create a wrapper for WebRTC to make sure the library only exposes a minimal interface and stops
+ * conflicting with other things. Then it can be built with BoringSSL and not bother anything else.
+ *
+ * 3. Try to hack around the issue, which is what we do here, by just providing compatibility wrappers
+ * for the missing functions. This is a very simple solution that should work perfectly fine for
+ * the time being, so long binary compatibility hasn't been broken somewhere.
+ */
+#if defined(OPENSSL_VERSION_MAJOR) && OPENSSL_VERSION_MAJOR >= 3
+
+#include <openssl/ssl.h>
+
+// These are defined in the OpenSSL headers as aliases for the new names.
+// We have to get rid of them so that we can make actual functions with such names.
+#undef SSL_get_peer_certificate
+#undef EVP_MD_size
+#undef EVP_MD_type
+
+extern "C" {
+    X509 *SSL_get_peer_certificate(const SSL *ssl) {
+        return SSL_get1_peer_certificate(ssl);
+    }
+
+    int EVP_MD_size(const EVP_MD *md) {
+        return EVP_MD_get_size(md);
+    }
+
+    int EVP_MD_type(const EVP_MD *md) {
+        return EVP_MD_get_type(md);
+    }
+}
+
+#endif