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+Notes on Thrift/SSL
+
+Author: Ping Li <pingli@facebook.com>
+
+1. Scope
+
+   This SSL only supports blocking mode socket I/O. It can only be used with
+   TSimpleServer, TThreadedServer, and TThreadPoolServer.
+
+2. Implementation
+
+   There're two main classes TSSLSocketFactory and TSSLSocket. Instances of
+   TSSLSocket are always created from TSSLSocketFactory.
+
+   PosixSSLThreadFactory creates PosixSSLThread. The only difference from the
+   PthreadThread type is that it cleanups OpenSSL error queue upon exiting
+   the thread. Ideally, OpenSSL APIs should only be called from PosixSSLThread.
+
+3. How to use SSL APIs
+
+   // This is for demo. In real code, typically only one TSSLSocketFactory
+   // instance is needed.
+   shared_ptr<TSSLSocketFactory> getSSLSocketFactory() {
+     shared_ptr<TSSLSocketFactory> factory(new TSSLSocketFactory());
+     // client: load trusted certificates
+     factory->loadTrustedCertificates("my-trusted-ca-certificates.pem");
+     // client: optionally set your own access manager, otherwise,
+     //         the default client access manager will be loaded.
+
+     factory->loadCertificate("my-certificate-signed-by-ca.pem");
+     factory->loadPrivateKey("my-private-key.pem");
+     // server: optionally setup access manager
+     // shared_ptr<AccessManager> accessManager(new MyAccessManager);
+     // factory->access(acessManager);
+     ...
+   }
+
+   // client code sample
+   shared_ptr<TSSLSocketFactory> factory = getSSLScoketFactory();
+   shared_ptr<TSocket> socket = factory.createSocket(host, port);
+   shared_ptr<TBufferedTransport> transport(new TBufferedTransport(socket));
+   ...
+
+   // server code sample
+   shared_ptr<TSSLSocketFactory> factory = getSSLSocketFactory();
+   shared_ptr<TSSLServerSocket> socket(new TSSLServerSocket(port, factory));
+   shared_ptr<TTransportFactory> transportFactory(new TBufferedTransportFactory));
+   ...
+
+4. AccessManager
+
+   AccessManager defines a callback interface. It has three callback methods:
+
+   (a) Decision verify(const sockaddr_storage& sa);
+   (b) Decision verify(const string& host, const char* name, int size);
+   (c) Decision verify(const sockaddr_storage& sa, const char* data, int size);
+
+   After SSL handshake completes, additional checks are conducted. Application
+   is given the chance to decide whether or not to continue the conversation
+   with the remote. Application is inqueried through the above three "verify"
+   method. They are called at different points of the verification process.
+
+   Decisions can be one of ALLOW, DENY, and SKIP. ALLOW and DENY means the
+   conversation should be continued or disconnected, respectively. ALLOW and
+   DENY decision stops the verification process. SKIP means there's no decision
+   based on the given input, continue the verification process.
+
+   First, (a) is called with the remote IP. It is called once at the beginning.
+   "sa" is the IP address of the remote peer.
+
+   Then, the certificate of remote peer is loaded. SubjectAltName extensions
+   are extracted and sent to application for verification. When a DNS
+   subjectAltName field is extracted, (b) is called. When an IP subjectAltName
+   field is extracted, (c) is called.
+
+   The "host" in (b) is the value from TSocket::getHost() if this is a client
+   side socket, or TScoket::getPeerHost() if this is a server side socket. The
+   reason is client side socket initiates the connection. TSocket::getHost()
+   is the remote host name. On server side, the remote host name is unknown
+   unless it's retrieved through TSocket::getPeerHost(). Either way, "host"
+   should be the remote host name. Keep in mind, if TSocket::getPeerHost()
+   failed, it would return the remote host name in numeric format.
+
+   If all subjectAltName extensions were "skipped", the common name field would
+   be checked. It is sent to application through (c), where "sa" is the remote
+   IP address. "data" is the IP address extracted from subjectAltName IP
+   extension, and "size" is the length of the extension data.
+
+   If any of the above "verify" methods returned a decision ALLOW or DENY, the
+   verification process would be stopped.
+
+   If any of the above "verify" methods returned SKIP, that decision would be
+   ignored and the verification process would move on till the last item is
+   examined. At that point, if there's still no decision, the connection is
+   terminated.
+
+   Thread safety, an access manager should not store state information if it's
+   to be used by many SSL sockets.
+
+5. SIGPIPE signal
+
+   Applications running OpenSSL over network connections may crash if SIGPIPE
+   is not ignored. This happens when they receive a connection reset by remote
+   peer exception, which somehow triggers a SIGPIPE signal. If not handled,
+   this signal would kill the application.
+
+6. How to run test client/server in SSL mode
+
+   The server expects the followings from the current working directory,
+   - "server-certificate.pem"
+   - "server-private-key.pem"
+
+   The client loads "trusted-ca-certificate.pem" from current directory.
+
+   The file names are hard coded in the source code. You need to create these
+   certificates before you can run the test code in SSL mode. Make sure at least
+   one of the followings is included in "server-certificate.pem",
+   - subjectAltName, DNS localhost
+   - subjectAltName, IP  127.0.0.1
+   - common name,    localhost
+
+   Run,
+   - "./test_server --ssl" to start server
+   - "./test_client --ssl" to run client
+
+   If "-h <host>" is used to run client, the above "localhost" in the above
+   server-certificate.pem has to be replaced with that host name.
+
+7. TSSLSocketFactory::randomize()
+
+   The default implementation of OpenSSLSocketFactory::randomize() simply calls
+   OpenSSL's RAND_poll() when OpenSSL library is first initialized.
+
+   The PRNG seed is key to the application security. This method should be
+   overriden if it's not strong enough for you.