long BIO_set_fd(BIO *b, int fd, long close_flag);
long BIO_get_fd(BIO *b, int *c);
BIO *BIO_new_socket(int sock, int close_flag);
DESCRIPTIONBIO_s_socket() returns the socket BIO method. This is a wrapper round the platform's socket routines.
BIO_read() and BIO_write() read or write the underlying socket. BIO_puts() is supported but BIO_gets() is not.
If the close flag is set then the socket is shut down and closed when the BIO is freed.
BIO_set_fd() sets the socket of BIO b to fd and the close flag to close_flag.
BIO_get_fd() places the socket in c if it is not NULL, it also returns the socket. If c is not NULL it should be of type (int *).
BIO_new_socket() returns a socket BIO using sock and close_flag.
NOTESSocket BIOs also support any relevant functionality of file descriptor BIOs.
The reason for having separate file descriptor and socket BIOs is that on some platforms sockets are not file descriptors and use distinct I/O routines, Windows is one such platform. Any code mixing the two will not work on all platforms.
BIO_set_fd() and BIO_get_fd() are macros.
RETURN VALUESBIO_s_socket() returns the socket BIO method.
BIO_set_fd() always returns 1.
BIO_get_fd() returns the socket or -1 if the BIO has not been initialized.
BIO_new_socket() returns the newly allocated BIO or NULL is an error occurred.