Add a Callbacks function for ALPN

3 files changed, 44 insertions, 14 deletions

diff --git a/src/lib/tls/tls_callbacks.h b/src/lib/tls/tls_callbacks.h
index db1b70693..5c7b21a99 100644
--- a/src/lib/tls/tls_callbacks.h
+++ b/src/lib/tls/tls_callbacks.h
@@ -61,10 +61,26 @@ class BOTAN_DLL Callbacks
 
        /**
        * Optional callback: inspect handshake message
+       * Throw an exception to abort the handshake.
        */       
        virtual void tls_inspect_handshake_msg(const Handshake_Message&) {}
 
        /**
+       * Optional callback for server: choose ALPN protocol
+       * ALPN (RFC 7301) works by the client sending a list of application
+       * protocols it is willing to negotiate. The server then selects which
+       * protocol to use, which is not necessarily even on the list that
+       * the client sent.
+       *
+       * If the empty string is returned from this function the server will
+       * just ignore the client ALPN extension.
+       */
+       virtual std::string tls_server_choose_app_protocol(const std::vector<std::string>& client_protos)
+          {
+          return "";
+          }
+
+       /**
        * Optional callback: debug logging. (not currently used)
        */       
        virtual bool tls_log_debug(const char*) { return false; }
@@ -83,6 +99,7 @@ class BOTAN_DLL Compat_Callbacks final : public Callbacks
       typedef std::function<void (Alert, const byte[], size_t)> alert_cb;
       typedef std::function<bool (const Session&)> handshake_cb;
       typedef std::function<void (const Handshake_Message&)> handshake_msg_cb;
+      typedef std::function<std::string (std::vector<std::string>)> next_protocol_fn;
 
       /**
        * @param output_fn is called with data for the outbound socket
@@ -95,18 +112,21 @@ class BOTAN_DLL Compat_Callbacks final : public Callbacks
        */
        BOTAN_DEPRECATED("Use TLS::Callbacks (virtual interface).")
        Compat_Callbacks(output_fn out, data_cb app_data_cb, alert_cb alert_cb,
-                        handshake_cb hs_cb, handshake_msg_cb hs_msg_cb = nullptr)
+                        handshake_cb hs_cb, handshake_msg_cb hs_msg_cb = nullptr,
+                        next_protocol_fn next_proto = nullptr)
           : m_output_function(out), m_app_data_cb(app_data_cb),
             m_alert_cb(std::bind(alert_cb, std::placeholders::_1, nullptr, 0)),
-            m_hs_cb(hs_cb), m_hs_msg_cb(hs_msg_cb) {}
+            m_hs_cb(hs_cb), m_hs_msg_cb(hs_msg_cb), m_next_proto(next_proto) {}
 
        BOTAN_DEPRECATED("Use TLS::Callbacks (virtual interface).")
        Compat_Callbacks(output_fn out, data_cb app_data_cb,
                         std::function<void (Alert)> alert_cb,
-                        handshake_cb hs_cb, handshake_msg_cb hs_msg_cb = nullptr)
+                        handshake_cb hs_cb,
+                        handshake_msg_cb hs_msg_cb = nullptr,
+                        next_protocol_fn next_proto = nullptr)
           : m_output_function(out), m_app_data_cb(app_data_cb),
             m_alert_cb(alert_cb),
-            m_hs_cb(hs_cb), m_hs_msg_cb(hs_msg_cb) {}
+            m_hs_cb(hs_cb), m_hs_msg_cb(hs_msg_cb), m_next_proto(next_proto) {}
 
        void tls_emit_data(const byte data[], size_t size) override
           {
@@ -136,6 +156,12 @@ class BOTAN_DLL Compat_Callbacks final : public Callbacks
           return m_hs_cb(session);
           }
 
+       std::string tls_server_choose_app_protocol(const std::vector<std::string>& client_protos) override
+          {
+          if(m_next_proto != nullptr) { return m_next_proto(client_protos); }
+          return "";
+          }
+ 
        void tls_inspect_handshake_msg(const Handshake_Message& hmsg) override
           {
           // The handshake message callback is optional so we can
@@ -149,6 +175,7 @@ class BOTAN_DLL Compat_Callbacks final : public Callbacks
          const std::function<void (Alert)> m_alert_cb;
          const handshake_cb m_hs_cb;
          const handshake_msg_cb m_hs_msg_cb;
+         const next_protocol_fn m_next_proto;
    };
 
 }
diff --git a/src/lib/tls/tls_server.cpp b/src/lib/tls/tls_server.cpp
index 5eccec2a7..2e546eab1 100644
--- a/src/lib/tls/tls_server.cpp
+++ b/src/lib/tls/tls_server.cpp
@@ -242,13 +242,11 @@ Server::Server(Callbacks& callbacks,
                Credentials_Manager& creds,
                const Policy& policy,
                RandomNumberGenerator& rng,
-               next_protocol_fn next_proto,
                bool is_datagram,
                size_t io_buf_sz) :
    Channel(callbacks, session_manager, rng, policy,
            is_datagram, io_buf_sz),
-   m_creds(creds),
-   m_choose_next_protocol(next_proto)
+   m_creds(creds)
    {
    }
 
@@ -419,8 +417,16 @@ void Server::process_client_hello_msg(const Handshake_State* active_state,
    catch(...) {}
 
    m_next_protocol = "";
-   if(m_choose_next_protocol && pending_state.client_hello()->supports_alpn())
-      m_next_protocol = m_choose_next_protocol(pending_state.client_hello()->next_protocols());
+   if(pending_state.client_hello()->supports_alpn())
+      {
+      m_next_protocol = callbacks().tls_server_choose_app_protocol(pending_state.client_hello()->next_protocols());
+
+      // if the callback return was empty, fall back to the (deprecated) std::function
+      if(m_next_protocol.empty() && m_choose_next_protocol)
+         {
+         m_next_protocol = m_choose_next_protocol(pending_state.client_hello()->next_protocols());
+         }
+      }
 
    if(resuming)
       {
diff --git a/src/lib/tls/tls_server.h b/src/lib/tls/tls_server.h
index 508dde440..051eda445 100644
--- a/src/lib/tls/tls_server.h
+++ b/src/lib/tls/tls_server.h
@@ -42,9 +42,6 @@ class BOTAN_DLL Server final : public Channel
       *
       * @param rng a random number generator
       *
-      * @param next_proto is called with client's ALPN protocol list
-      *        and returns chosen protocol.
-      *
       * @param is_datagram set to true if this server should expect DTLS
       *        connections. Otherwise TLS connections are expected.
       *
@@ -57,7 +54,6 @@ class BOTAN_DLL Server final : public Channel
              Credentials_Manager& creds,
              const Policy& policy,
              RandomNumberGenerator& rng,
-             next_protocol_fn next_proto = next_protocol_fn(),
              bool is_datagram = false,
              size_t reserved_io_buffer_size = TLS::Server::IO_BUF_DEFAULT_SIZE
          );
@@ -148,9 +144,10 @@ class BOTAN_DLL Server final : public Channel
       Handshake_State* new_handshake_state(Handshake_IO* io) override;
 
       Credentials_Manager& m_creds;
+      std::string m_next_protocol;
 
+      // Set by deprecated constructor, Server calls both this fn and Callbacks version
       next_protocol_fn m_choose_next_protocol;
-      std::string m_next_protocol;
    };
 
 }