epee: add SSL support

RPC connections now have optional tranparent SSL.

An optional private key and certificate file can be passed,
using the --{rpc,daemon}-ssl-private-key and
--{rpc,daemon}-ssl-certificate options. Those have as
argument a path to a PEM format private private key and
certificate, respectively.
If not given, a temporary self signed certificate will be used.

SSL can be enabled or disabled using --{rpc}-ssl, which
accepts autodetect (default), disabled or enabled.

Access can be restricted to particular certificates using the
--rpc-ssl-allowed-certificates, which takes a list of
paths to PEM encoded certificates. This can allow a wallet to
connect to only the daemon they think they're connected to,
by forcing SSL and listing the paths to the known good
certificates.

To generate long term certificates:

openssl genrsa -out /tmp/KEY 4096
openssl req -new -key /tmp/KEY -out /tmp/REQ
openssl x509 -req -days 999999 -sha256 -in /tmp/REQ -signkey /tmp/KEY -out /tmp/CERT

/tmp/KEY is the private key, and /tmp/CERT is the certificate,
both in PEM format. /tmp/REQ can be removed. Adjust the last
command to set expiration date, etc, as needed. It doesn't
make a whole lot of sense for monero anyway, since most servers
will run with one time temporary self signed certificates anyway.

SSL support is transparent, so all communication is done on the
existing ports, with SSL autodetection. This means you can start
using an SSL daemon now, but you should not enforce SSL yet or
nothing will talk to you.

contrib/epee/include/net/abstract_tcp_server2.h

@@ -45,6 +45,7 @@
 #include <memory>
 
 #include <boost/asio.hpp>
+#include <boost/asio/ssl.hpp>
 #include <boost/array.hpp>
 #include <boost/noncopyable.hpp>
 #include <boost/shared_ptr.hpp>
@@ -93,12 +94,12 @@ namespace net_utils
 			typename t_protocol_handler::config_type& config, 
 			std::atomic<long> &ref_sock_count,  // the ++/-- counter 
 			std::atomic<long> &sock_number, // the only increasing ++ number generator
-			i_connection_filter * &pfilter
-			,t_connection_type connection_type);
+			i_connection_filter * &pfilter,
+			t_connection_type connection_type,
+			epee::net_utils::ssl_support_t ssl_support,
+			ssl_context_t &ssl_context);
 
     virtual ~connection() noexcept(false);
-    /// Get the socket associated with the connection.
-    boost::asio::ip::tcp::socket& socket();
 
     /// Start the first asynchronous operation for the connection.
     bool start(bool is_income, bool is_multithreaded);
@@ -128,6 +129,10 @@ namespace net_utils
     //------------------------------------------------------
     boost::shared_ptr<connection<t_protocol_handler> > safe_shared_from_this();
     bool shutdown();
+    /// Handle completion of a receive operation.
+    void handle_receive(const boost::system::error_code& e,
+      std::size_t bytes_transferred);
+
     /// Handle completion of a read operation.
     void handle_read(const boost::system::error_code& e,
       std::size_t bytes_transferred);
@@ -145,7 +150,7 @@ namespace net_utils
 
     /// Buffer for incoming data.
     boost::array<char, 8192> buffer_;
-    //boost::array<char, 1024> buffer_;
+    size_t buffer_ssl_init_fill;
 
     t_connection_context context;
     i_connection_filter* &m_pfilter;
@@ -198,8 +203,8 @@ namespace net_utils
     std::map<std::string, t_connection_type> server_type_map;
     void create_server_type_map();
 
-    bool init_server(uint32_t port, const std::string address = "0.0.0.0");
-    bool init_server(const std::string port,  const std::string& address = "0.0.0.0");
+    bool init_server(uint32_t port, const std::string address = "0.0.0.0", epee::net_utils::ssl_support_t ssl_support = epee::net_utils::ssl_support_t::e_ssl_support_autodetect, const std::pair<std::string, std::string> &private_key_and_certificate_path = std::make_pair(std::string(), std::string()), const std::list<std::string> &allowed_certificates = {}, bool allow_any_cert = false);
+    bool init_server(const std::string port,  const std::string& address = "0.0.0.0", epee::net_utils::ssl_support_t ssl_support = epee::net_utils::ssl_support_t::e_ssl_support_autodetect, const std::pair<std::string, std::string> &private_key_and_certificate_path = std::make_pair(std::string(), std::string()), const std::list<std::string> &allowed_certificates = {}, bool allow_any_cert = false);
 
     /// Run the server's io_service loop.
     bool run_server(size_t threads_count, bool wait = true, const boost::thread::attributes& attrs = boost::thread::attributes());
@@ -220,9 +225,9 @@ namespace net_utils
 
     void set_connection_filter(i_connection_filter* pfilter);
 
-    bool connect(const std::string& adr, const std::string& port, uint32_t conn_timeot, t_connection_context& cn, const std::string& bind_ip = "0.0.0.0");
+    bool connect(const std::string& adr, const std::string& port, uint32_t conn_timeot, t_connection_context& cn, const std::string& bind_ip = "0.0.0.0", epee::net_utils::ssl_support_t ssl_support = epee::net_utils::ssl_support_t::e_ssl_support_autodetect);
     template<class t_callback>
-    bool connect_async(const std::string& adr, const std::string& port, uint32_t conn_timeot, const t_callback &cb, const std::string& bind_ip = "0.0.0.0");
+    bool connect_async(const std::string& adr, const std::string& port, uint32_t conn_timeot, const t_callback &cb, const std::string& bind_ip = "0.0.0.0", epee::net_utils::ssl_support_t ssl_support = epee::net_utils::ssl_support_t::e_ssl_support_autodetect);
 
     typename t_protocol_handler::config_type& get_config_object(){return m_config;}
 
@@ -331,6 +336,9 @@ namespace net_utils
     boost::mutex connections_mutex;
     std::set<connection_ptr> connections_;
 
+    ssl_context_t m_ssl_context;
+    std::list<std::string> m_allowed_certificates;
+
   }; // class <>boosted_tcp_server