OpenSSL BIO and SSL_read

Question

In our client/server application, we use TLS/TCP protocol for messaging. There is a message shift occurs between applications after a while (messages are sent and received in the correct order at the beginning) ie the client sends the 1000th message to the server and receives the response of message 999th. The suspect is on the client side, in which we implement TCP and TLS layers independently ie do not bind TCP socket to SSL object (via SSL_set_fd()) but using BIOs. When the client app gets the response from server (pretty sure that message is processed in the server correctly, client TCP layer receives the message correctly etc.), the message is forwarded to SSL layer. The client app firstly write the message to BIO:

BIO_write (readBio, data, length);

Then in another function of SSL layer, the message is read using SSL_read():

res = SSL_read (ssl, buffer, length);

The read operation is done successfully, but my goal is to check whether there is another record(s) to be read in the BIO. I considered to use the method SSL_pending() but it seems that this one should be used in order to check if there are still bytes in the SAME record. If our suspects are correct, I would like to check if there is another record in the BIO so that all messages are processed without any delay. Can you help me on this topic? Thanks in advance.

Answer 1

SSL_pending tells you if there are data from the current decryted SSL record which got not yet read by SSL_read. BIO_pending can be used to find out if there are already data in the BIO which are not processed by the SSL layer. To find out if the are unread data at the socket level use MSG_PEEK .