p>A return value of 0 indicates a non-fatal error. This could (for example) be because of nonblocking IO, or some invalid message having been received from a peer. Errors may be placed on the OpenSSL error queue with further information if appropriate. Typically user code is expected to retry the call to DTLSv1_listen() in the event of a non-fatal error.</p>

<p>A return value of &lt;0 indicates a fatal error. This could (for example) be because of a failure to allocate sufficient memory for the operation.<