bugfix: Hook the ssl_set_fd function to get FD.

[cfc4n]

This block of logic will be used when wbio's FD is empty.

[ii64]

I think this fallback fd hooks should be optional to make the required symbols uprobe to hook small, or perhaps we could try to use SSL_set_bio instead of SSL_set_{,w,r}fd?

[cfc4n]

SSL_set_bio and SSL_set_{,w,r}fd are not mutually exclusive. Different usage modes and versions of OpenSSL trigger different functions during the HTTPS handshake.

For instance, when OpenSSL is called in a non-BIO mode, then SSL_set{,w,r}fd? comes into play; at this point, hooking the SSL_set_bio function would be ineffective.

However, I cannot provide a definitive conclusion either. If you have expertise in this area and would like to offer better suggestions, your input is welcome.