SSLread(3) OpenSSL SSLread(3)

NAME
       SSLread - read bytes from a TLS/SSL connection.

SYNOPSIS
        #include 

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

DESCRIPTION
       SSLread() tries to read nnuumm bytes from the specified ssssll into the
       buffer bbuuff.

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

       For the transparent negotiation to succeed, the ssssll must have been
       initialized to client or server mode. This is being done by calling
       SSLsetconnectstate(3) or SSLsetacceptstate() before the first
       call to an SSLread() or SSLwrite(3) function.

       SSLread() 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 SSLread() can still be buffered inside the SSL layer and
       will be retrieved on the next call to SSLread(). If nnuumm is higher than
       the number of bytes buffered, SSLread() will return with the bytes
       buffered.  If no more bytes are in the buffer, SSLread() will trigger
       the processing of the next record. Only when the record has been
       received and processed completely, SSLread() 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
       SSLread() can succeed.

       If the underlying BIO is bblloocckkiinngg, SSLread() will only return, once
       the read operation has been finished or an error occurred, except when
       a renegotiation take place, in which case a SSLERRORWANTREAD may
       occur.  This behaviour can be controlled with the SSLMODEAUTORETRY
       flag of the SSLCTXsetmode(3) call.

       If the underlying BIO is nnoonn-bblloocckkiinngg, SSLread() will also return when
       the underlying BIO could not satisfy the needs of SSLread() to
       continue the operation. In this case a call to SSLgeterror(3) with
       the return value of SSLread() will yield SSSSLLEERRRROORRWWAANNTTRREEAADD or
       SSSSLLEERRRROORRWWAANNTTWWRRIITTEE. As at any time a re-negotiation is possible, a
       call to SSLread() can also cause write operations! The calling process
       then must repeat the call after taking appropriate action to satisfy
       the needs of SSLread(). 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.

WWAARRNNIINNGG
       When an SSLread() operation has to be repeated because of
       SSSSLLEERRRROORRWWAANNTTRREEAADD or SSSSLLEERRRROORRWWAANNTTWWRRIITTEE, it must be repeated with
       the same arguments.

RETURN VALUES
       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 SSLRECEIVEDSHUTDOWN flag in the ssl shutdown state
           is set (see SSLshutdown(3), SSLsetshutdown(3)). It is also
           possible, that the peer simply shut down the underlying transport
           and the shutdown is incomplete. Call SSLgeterror() with the
           return value rreett to find out, whether an error occurred or the
           connection was shut down cleanly (SSLERRORZERORETURN).

           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
           SSLgeterror() with the return value rreett to find out the reason.

SEE ALSO
       SSLgeterror(3), SSLwrite(3), SSLCTXsetmode(3), SSLCTXnew(3),
       SSLconnect(3), SSLaccept(3) SSLsetconnectstate(3),
       SSLshutdown(3), SSLsetshutdown(3), ssl(3), bio(3)



0.9.7l                            2001-09-13                       SSLread(3)