1. The MTU is effective, with the certificate being split into two DTLS records to comply with the limit.
2. The issue occurs when using BIO_get_mem_data, which retrieves all DTLS packets in a single call, even though each is smaller than the MTU.
3. An alternative callback is available for using BIO_new with BIO_s_mem.
4. Improvements to the MTU setting were made, including adding the DTLS_set_link_mtu function and removing the SSL_set_max_send_fragment function.
5. The handshake process was refined, calling SSL_do_handshake only after ICE completion, and using SSL_read to handle handshake messages.
6. The session close code was improved to enable immediate closure upon receiving an SSL CloseNotify or fatal message.
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Co-authored-by: chundonglinlin <chundonglinlin@163.com>
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