Fix PMTU discovery via datagram SPTPS.

In send_sptps_data(), the len variable contains the length of the whole
datagram that needs to be sent to the peer, including the overhead from SPTPS
itself.

diff --git a/src/net_packet.c b/src/net_packet.c
index 012085e..ecdcfe2 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -767,7 +767,7 @@ bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
 
        /* Send it via TCP if it is a handshake packet, TCPOnly is in use, or this packet is larger than the MTU. */
 
-       if(type >= SPTPS_HANDSHAKE || ((myself->options | to->options) & OPTION_TCPONLY) || (type != PKT_PROBE && len > to->minmtu)) {
+       if(type >= SPTPS_HANDSHAKE || ((myself->options | to->options) & OPTION_TCPONLY) || (type != PKT_PROBE && (len - SPTPS_DATAGRAM_OVERHEAD) > to->minmtu)) {
                char buf[len * 4 / 3 + 5];
                b64encode(data, buf, len);
                /* If no valid key is known yet, send the packets using ANS_KEY requests,
@@ -792,6 +792,8 @@ bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
 
        if(sendto(listen_socket[sock].udp.fd, data, len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
                if(sockmsgsize(sockerrno)) {
+                       // Compensate for SPTPS overhead
+                       len -= SPTPS_DATAGRAM_OVERHEAD;
                        if(to->maxmtu >= len)
                                to->maxmtu = len - 1;
                        if(to->mtu >= len)

diff --git a/src/sptps.h b/src/sptps.h
index 3f8d29c..efca2b3 100644 (file)
--- a/src/sptps.h
+++ b/src/sptps.h
@@ -39,6 +39,9 @@
 #define SPTPS_SIG 3           // Waiting for a SIGnature record
 #define SPTPS_ACK 4           // Waiting for an ACKnowledgement record
 
+// Overhead for datagrams
+#define SPTPS_DATAGRAM_OVERHEAD 21
+
 typedef bool (*send_data_t)(void *handle, uint8_t type, const char *data, size_t len);
 typedef bool (*receive_record_t)(void *handle, uint8_t type, const char *data, uint16_t len);