Hooks for DTLS fragmentation

2 files changed, 32 insertions, 12 deletions

diff --git a/src/tls/tls_handshake_io.cpp b/src/tls/tls_handshake_io.cpp
index 6ff8f71e0..51f04acd6 100644
--- a/src/tls/tls_handshake_io.cpp
+++ b/src/tls/tls_handshake_io.cpp
@@ -258,29 +258,37 @@ Datagram_Handshake_IO::Handshake_Reassembly::message() const
    }
 
 std::vector<byte>
-Datagram_Handshake_IO::format_w_seq(const std::vector<byte>& msg,
-                                    Handshake_Type type,
-                                    u16bit msg_sequence) const
+Datagram_Handshake_IO::format_fragment(const std::vector<byte>& frag,
+                                       Handshake_Type type,
+                                       u16bit msg_len,
+                                       u16bit frag_offset,
+                                       u16bit msg_sequence) const
    {
-   std::vector<byte> send_buf(12 + msg.size());
-
-   const size_t buf_size = msg.size();
+   std::vector<byte> send_buf(12 + frag.size());
 
    send_buf[0] = type;
 
-   store_be24(&send_buf[1], buf_size);
+   store_be24(&send_buf[1], msg_len);
 
    store_be(msg_sequence, &send_buf[4]);
 
-   store_be24(&send_buf[6], 0); // fragment_offset
-   store_be24(&send_buf[9], buf_size); // fragment_length
+   store_be24(&send_buf[6], frag_offset);
+   store_be24(&send_buf[9], frag.size());
 
-   copy_mem(&send_buf[12], &msg[0], msg.size());
+   copy_mem(&send_buf[12], &frag[0], frag.size());
 
    return send_buf;
    }
 
 std::vector<byte>
+Datagram_Handshake_IO::format_w_seq(const std::vector<byte>& msg,
+                                    Handshake_Type type,
+                                    u16bit msg_sequence) const
+   {
+   return format_fragment(msg, type, msg.size(), 0, msg_sequence);
+   }
+
+std::vector<byte>
 Datagram_Handshake_IO::format(const std::vector<byte>& msg,
                               Handshake_Type type) const
    {
@@ -301,8 +309,12 @@ Datagram_Handshake_IO::send(const Handshake_Message& msg)
    const std::vector<byte> no_fragment =
       format_w_seq(msg_bits, msg.type(), m_out_message_seq);
 
-   // FIXME: fragment to mtu size if needed
-   m_writer.send(HANDSHAKE, no_fragment);
+   if(no_fragment.size() <= m_mtu)
+      m_writer.send(HANDSHAKE, no_fragment);
+   else
+      {
+      throw Internal_Error("Fragmentation required");
+      }
 
    m_out_message_seq += 1;
 
diff --git a/src/tls/tls_handshake_io.h b/src/tls/tls_handshake_io.h
index e57f6926d..6b82ed95d 100644
--- a/src/tls/tls_handshake_io.h
+++ b/src/tls/tls_handshake_io.h
@@ -110,6 +110,13 @@ class Datagram_Handshake_IO : public Handshake_IO
       std::pair<Handshake_Type, std::vector<byte>>
          get_next_record(bool expecting_ccs) override;
    private:
+      std::vector<byte> format_fragment(
+         const std::vector<byte>& fragment,
+         Handshake_Type type,
+         u16bit msg_len,
+         u16bit frag_offset,
+         u16bit msg_sequence) const;
+
       std::vector<byte> format_w_seq(
          const std::vector<byte>& handshake_msg,
          Handshake_Type handshake_type,
@@ -142,6 +149,7 @@ class Datagram_Handshake_IO : public Handshake_IO
       std::map<u16bit, Handshake_Reassembly> m_messages;
       std::set<u16bit> m_ccs_epochs;
 
+      u16bit m_mtu = 320;
       u16bit m_in_message_seq = 0;
       u16bit m_out_message_seq = 0;
       Record_Writer& m_writer;