+ uint8_t buffer[len];
+ size_t outlen;
+ return chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen);
+}
+
+// Receive incoming data, datagram version.
+static bool sptps_receive_data_datagram(sptps_t *s, const uint8_t *data, size_t len) {
+ if(len < (s->instate ? 21 : 5)) {
+ return error(s, EIO, "Received short packet");
+ }
+
+ uint32_t seqno;
+ memcpy(&seqno, data, 4);
+ seqno = ntohl(seqno);
+ data += 4;
+ len -= 4;
+
+ if(!s->instate) {
+ if(seqno != s->inseqno) {
+ return error(s, EIO, "Invalid packet seqno: %d != %d", seqno, s->inseqno);
+ }
+