BIO_set_write_buf_size
r = BIO_set_write_buf_size(bio1, writebuf1);
r = BIO_set_write_buf_size(bio2, writebuf2);
r = BIO_set_write_buf_size(bio1, writebuf1);
r = BIO_set_write_buf_size(bio2, writebuf2);
if (!TEST_true(BIO_set_write_buf_size(bio1, bufsz)))