Manual Pages for UNIX Operating System command usage for man SSL_read

OpenSSL                                        SSL_read(3openssl)



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     SSL_read - read bytes from a TLS/SSL connection.

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      #include 

      int SSL_read(SSL *ssl, void *buf, int num);


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     SSL_read() tries to read nnnnuuuummmm bytes from the specified ssssssssllll
     into the buffer bbbbuuuuffff.

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     If necessary, SSL_read() will negotiate a TLS/SSL session,
     if not already explicitly performed by SSL_connect(3) or
     SSL_accept(3). If the peer requests a re-negotiation, it
     will be performed transparently during the SSL_read()
     operation. The behaviour of SSL_read() depends on the
     underlying BIO.

     For the transparent negotiation to succeed, the ssssssssllll must
     have been initialized to client or server mode. This is
     being done by calling SSL_set_connect_state(3) or
     SSL_set_accept_state() before the first call to an
     SSL_read() or SSL_write(3) function.

     SSL_read() works based on the SSL/TLS records. The data are
     received in records (with a maximum record size of 16kB for
     SSLv3/TLSv1). Only when a record has been completely
     received, it can be processed (decryption and check of
     integrity). Therefore data that was not retrieved at the
     last call of SSL_read() can still be buffered inside the SSL
     layer and will be retrieved on the next call to SSL_read().
     If nnnnuuuummmm is higher than the number of bytes buffered,
     SSL_read() will return with the bytes buffered.  If no more
     bytes are in the buffer, SSL_read() will trigger the
     processing of the next record. Only when the record has been
     received and processed completely, SSL_read() will return
     reporting success. At most the contents of the record will
     be returned. As the size of an SSL/TLS record may exceed the
     maximum packet size of the underlying transport (e.g. TCP),
     it may be necessary to read several packets from the
     transport layer before the record is complete and SSL_read()
     can succeed.

     If the underlying BIO is bbbblllloooocccckkkkiiiinnnngggg, SSL_read() will only
     return, once the read operation has been finished or an
     error occurred, except when 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.



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OpenSSL                                        SSL_read(3openssl)



     If the underlying BIO is nnnnoooonnnn---bbblllloooocccckkkkiiiinnnngggg, SSL_read() will also
     return when the underlying BIO could not satisfy the needs
     of SSL_read() to continue the operation. In this case a call
     to SSL_get_error(3) with the return value of SSL_read() will
     yield SSSSSSSSLLLL_EEEERRRRRRRROOOORRRR_WWWWAAAANNNNTTTT_RRRREEEEAAAADDDD or SSSSSSSSLLLL_EEEERRRRRRRROOOORRRR_WWWWAAAANNNNTTTT_WWWWRRRRIIIITTTTEEEE. As at any
     time a re-negotiation is possible, a call to SSL_read() can
     also cause write operations! The calling process then must
     repeat the call after taking appropriate action to satisfy
     the needs of SSL_read(). The action depends on the
     underlying BIO. When using a non-blocking socket, nothing is
     to be done, but select() can be 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 BIO
     before being able to continue.

     SSL_pending(3) can be used to find out whether there are
     buffered bytes available for immediate retrieval. In this
     case SSL_read() can be called without blocking or actually
     receiving new data from the underlying socket.

WWWWAAAARRRRNNNNIIIINNNNGGGG
     When an SSL_read() operation has to be repeated because of
     SSSSSSSSLLLL_EEEERRRRRRRROOOORRRR_WWWWAAAANNNNTTTT_RRRREEEEAAAADDDD or SSSSSSSSLLLL_EEEERRRRRRRROOOORRRR_WWWWAAAANNNNTTTT_WWWWRRRRIIIITTTTEEEE, it must be
     repeated with the same arguments.

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     The following return values can occur:

     >0  The read operation was successful; the return value is
         the number of bytes actually read from the TLS/SSL
         connection.

     0   The read operation was not successful. The reason may
         either be a clean shutdown due to a "close notify" alert
         sent by the peer (in which case the
         SSL_RECEIVED_SHUTDOWN flag in the ssl shutdown state is
         set (see SSL_shutdown(3), SSL_set_shutdown(3)). It is
         also possible, that the peer simply shut down the
         underlying transport and the shutdown is incomplete.
         Call SSL_get_error() with the return value rrrreeeetttt to find
         out, whether an error occurred or the connection was
         shut down cleanly (SSL_ERROR_ZERO_RETURN).

         SSLv2 (deprecated) does not support a shutdown alert
         protocol, so it can only be detected, whether the
         underlying connection was closed. It cannot be checked,
         whether the closure was initiated by the peer or by
         something else.

     <0  The read operation was not successful, because either an
         error occurred or action must be taken by the calling
         process. Call SSL_get_error() with the return value rrrreeeetttt



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OpenSSL                                        SSL_read(3openssl)



         to find out the reason.

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     SSL_get_error(3), SSL_write(3), SSL_CTX_set_mode(3),
     SSL_CTX_new(3), SSL_connect(3), SSL_accept(3)
     SSL_set_connect_state(3), SSL_pending(3), SSL_shutdown(3),
     SSL_set_shutdown(3), ssl(3), bio(3)
















































1/Aug/2008             Last change: 0.9.8o                      3