Re: [Libevent-users] Re: Avoid potential SSL read spinlocks

[Mark Ellzey <mthomas@xxxxxxxxxx>]

On Mon, Nov 14, 2011 at 02:30:32PM -0800, Catalin Patulea wrote:
> This is actually causing an assert in my case :( The key is to get
> SSL_read to return both data (> 0) and EOF (= 0) within the same
> iteration of that (former) while loop. Then the flow looks like this:
> 
> SSL_read() returns N bytes into an iov from evbuffer_reserve_space -
> no run_read_cb yet
> SSL_read() returns 0, which leads into conn_closed(), which queues a
> error_cb(EOF)
> Back in do_read, a read_cb is queued


Not entirely true:

                        int err = SSL_get_error(bev_ssl->ssl, r);
                        print_err(err);
                        switch (err) {
                        case SSL_ERROR_WANT_READ:
                                /* Can't read until underlying has more data. */
                                if (bev_ssl->read_blocked_on_write)
                                        if (clear_rbow(bev_ssl) < 0) 
                                                return -1;
                                break;
                        case SSL_ERROR_WANT_WRITE:                                                                                                                                                    
                                /* This read operation requires a write, and the
                                 * underlying is full */
                                if (!bev_ssl->read_blocked_on_write)
                                        if (set_rbow(bev_ssl) < 0) 
                                                return -1;
                                break;
                        default:
                                conn_closed(bev_ssl, err, r);
                                break;


WANT_READ will trigger when a full record hasn't been processed; My
brain isn't working right now, but it looks as if set_rbow() does the
right thing and waits for the whole record to be read. BUT, I think I
see the issue you trying to explain. 

In one sentence - I think this is the problem:

We cannot schedule or call the readcb UNTIL SSL_read() returns > 0 OR an
error occurs on the socket.


Right?
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