What is a "clogging" input filter?

[Graham Leggett]

Hi all,

Currently mod_ssl doesn't work with the event MPM, as per the following code:

    if (c->clogging_input_filters && !c->aborted) {
        /* Since we have an input filter which 'cloggs' the input stream,
         * like mod_ssl, lets just do the normal read from input filters,
         * like the Worker MPM does.
         */
        apr_atomic_inc32(&clogged_count);
        ap_run_process_connection(c);
        if (cs->pub.state != CONN_STATE_SUSPENDED) {
            cs->pub.state = CONN_STATE_LINGER;
        }
        apr_atomic_dec32(&clogged_count);
    }

Can anyone explain what it means exactly to clog the input stream?

Am I right in understanding that openssl reads ahead, and therefore there may 
not be data for reading when we get to apr_pollset_poll()?

Or is this instead to do with openssl returning SSL_ERROR_WANT_READ during 
SSL_write? (and vice versa)?

Regards,
Graham
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