SSL_read failing with SSL_ERROR_SYSCALL error

Question

We have implemented tls using openssl. While downloading larger data from server getting SSL_ERROR_SYSCALL error after receiving the some data. For smaller files I am not getting this error, able to download without any error. ERR_get_error() is showing zero for larger files.

We are using linux and c++ framework. How to find reason for the failure? What could be the reason for failure? kindly provide your suggestions.

Answer 1

SSL_ERROR_SYSCALL indicates that some problem happened with the underlying I/O (Should be TCP in this case). So, you can try checking with errno.

OpenSSL help says:

SSL_ERROR_SYSCALL

Some I/O error occurred. The OpenSSL error queue may contain more information on the error. If the error queue is empty (i.e. ERR_get_error() returns 0), ret can be used to find out more about the error: If ret == 0, an EOF was observed that violates the protocol. If ret == -1, the underlying BIO reported an I/O error (for socket I/O on Unix systems, consult errno for details).