Implement SSL support for servers and clients

Summary:
This diff implements OpenSSL support in the network stack.
Currently SSL support is only enabled for Bolt connections,
support for RPC connections will be added in another diff.

Reviewers: buda, teon.banek

Reviewed By: buda

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1328

tests/manual/ssl_server.cpp

@@ -0,0 +1,73 @@
+#include <atomic>
+
+#include <gflags/gflags.h>
+#include <glog/logging.h>
+
+#include "communication/server.hpp"
+#include "utils/exceptions.hpp"
+
+DEFINE_string(address, "127.0.0.1", "Server address");
+DEFINE_int32(port, 54321, "Server port");
+DEFINE_string(cert_file, "", "Certificate file to use.");
+DEFINE_string(key_file, "", "Key file to use.");
+DEFINE_string(ca_file, "", "CA file to use.");
+DEFINE_bool(verify_peer, false, "Set to true to verify the peer.");
+
+struct EchoData {
+  std::atomic<bool> alive{true};
+};
+
+class EchoSession {
+ public:
+  EchoSession(EchoData &data, communication::InputStream &input_stream,
+              communication::OutputStream &output_stream)
+      : data_(data),
+        input_stream_(input_stream),
+        output_stream_(output_stream) {}
+
+  void Execute() {
+    if (input_stream_.size() < 2) return;
+    const uint8_t *data = input_stream_.data();
+    uint16_t size = *reinterpret_cast<const uint16_t *>(input_stream_.data());
+    input_stream_.Resize(size + 2);
+    if (input_stream_.size() < size + 2) return;
+    if (size == 0) {
+      LOG(INFO) << "Server received EOF message";
+      data_.alive.store(false);
+      return;
+    }
+    LOG(INFO) << "Server received '"
+              << std::string(reinterpret_cast<const char *>(data + 2), size)
+              << "'";
+    if (!output_stream_.Write(data + 2, size)) {
+      throw utils::BasicException("Output stream write failed!");
+    }
+    input_stream_.Shift(size + 2);
+  }
+
+ private:
+  EchoData &data_;
+  communication::InputStream &input_stream_;
+  communication::OutputStream &output_stream_;
+};
+
+int main(int argc, char **argv) {
+  gflags::ParseCommandLineFlags(&argc, &argv, true);
+  google::InitGoogleLogging(argv[0]);
+
+  communication::Init();
+
+  // Initialize the server.
+  EchoData echo_data;
+  io::network::Endpoint endpoint(FLAGS_address, FLAGS_port);
+  communication::ServerContext context(FLAGS_key_file, FLAGS_cert_file,
+                                       FLAGS_ca_file, FLAGS_verify_peer);
+  communication::Server<EchoSession, EchoData> server(endpoint, echo_data,
+                                                      &context, -1, "SSL", 1);
+
+  while (echo_data.alive) {
+    std::this_thread::sleep_for(std::chrono::milliseconds(100));
+  }
+
+  return 0;
+}