Sebastian Hagedorn Hagedorn at
Fri Nov 16 17:17:23 EST 2007

-- Ken Murchison <murch at> is rumored to have mumbled on 16. 
November 2007 16:55:27 -0500 regarding RE: Bingo!:

> It looks like it timed out properly, correct?

Exactly. So the non-SSL code path is not affected, but SSL gets stuck. The 
manpage for SSL_read says:

       "If the underlying BIO is blocking, SSL_read() will only return, once
       the read operation has been finished or an error occurred, except 
       a renegotiation take place, in which case a SSL_ERROR_WANT_READ may
       occur.  This behaviour can be controlled with the SSL_MODE_AUTO_RETRY
       flag of the SSL_CTX_set_mode(3) call.

       If the underlying BIO is non-blocking, SSL_read() will also return 
       the underlying BIO could not satisfy the needs of SSL_read() to con-
       tinue the operation. In this case a call to SSL_get_error(3) with the
       return value of SSL_read() will yield SSL_ERROR_WANT_READ or
       SSL_ERROR_WANT_WRITE. As at any time a re-negotiation is possible, a
       call to SSL_read() can also cause write operations! The calling 
       then must repeat the call after taking appropriate action to satisfy
       the needs of SSL_read(). The action depends on the underlying BIO. 
       using a non-blocking socket, nothing is to be done, but select() can 
       used to check for the required condition. When using a buffering BIO,
       like a BIO pair, data must be written into or retrieved out of the 
       before being able to continue."

I haven't yet found what BIO stands for According to Wikipedia it's "an 
abstraction library used by OpenSSL to handle communication of various 
kinds, including files and sockets, both secure and not".

I'm not sure what to make of that. I would assume that we've got a blocking 
BIO, because it is - d'oh - blocking. But I don't see how you influence 
what kind of BIO you use.
Sebastian Hagedorn - Postmaster - RZKR-R1 (Flachbau), Zimmer 18
Zentrum für angewandte Informatik - Universitätsweiter Service RRZK
Universität zu Köln / Cologne University - Tel. +49-221-478-5587
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