tls_content_peek
ssret = tls_content_peek(s->s3->rcontent, buf, len);
ssret = tls_content_peek(s->s3->rcontent, buf, len);
return tls_content_peek(rl->rcontent, buf, n);
ssize_t tls_content_peek(struct tls_content *content, uint8_t *buf, size_t n);