MirBSD manpage: BIO_get_retry_BIO(3), BIO_get_retry_reason(3), BIO_retry_type(3), BIO_should_io_special(3), BIO_should_read(3), BIO_should_retry(3), BIO_should_write(3)

BIO_SHOULD_RETRY(3)          OpenSSL          BIO_SHOULD_RETRY(3)


     BIO_should_retry, BIO_should_read, BIO_should_write,
     BIO_should_io_special, BIO_retry_type, BIO_should_retry,
     BIO_get_retry_BIO, BIO_get_retry_reason - BIO retry func-


      #include <openssl/bio.h>

      #define BIO_should_read(a)             ((a)->flags & BIO_FLAGS_READ)
      #define BIO_should_write(a)            ((a)->flags & BIO_FLAGS_WRITE)
      #define BIO_should_io_special(a)       ((a)->flags & BIO_FLAGS_IO_SPECIAL)
      #define BIO_retry_type(a)              ((a)->flags & BIO_FLAGS_RWS)
      #define BIO_should_retry(a)            ((a)->flags & BIO_FLAGS_SHOULD_RETRY)

      #define BIO_FLAGS_READ         0x01
      #define BIO_FLAGS_WRITE        0x02
      #define BIO_FLAGS_IO_SPECIAL   0x04
      #define BIO_FLAGS_SHOULD_RETRY 0x08

      BIO *  BIO_get_retry_BIO(BIO *bio, int *reason);
      int    BIO_get_retry_reason(BIO *bio);


     These functions determine why a BIO is not able to read or
     write data. They will typically be called after a failed
     BIO_read() or BIO_write() call.

     BIO_should_retry() is true if the call that produced this
     condition should then be retried at a later time.

     If BIO_should_retry() is false then the cause is an error

     BIO_should_read() is true if the cause of the condition is
     that a BIO needs to read data.

     BIO_should_write() is true if the cause of the condition is
     that a BIO needs to read data.

     BIO_should_io_special() is true if some "special" condition,
     that is a reason other than reading or writing is the cause
     of the condition.

     BIO_get_retry_reason() returns a mask of the cause of a
     retry condition consisting of the values BIO_FLAGS_READ,
     types will only set one of these.

     BIO_get_retry_BIO() determines the precise reason for the
     special condition, it returns the BIO that caused this

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BIO_SHOULD_RETRY(3)          OpenSSL          BIO_SHOULD_RETRY(3)

     condition and if reason is not NULL it contains the reason
     code. The meaning of the reason code and the action that
     should be taken depends on the type of BIO that resulted in
     this condition.

     BIO_get_retry_reason() returns the reason for a special con-
     dition if passed the relevant BIO, for example as returned
     by BIO_get_retry_BIO().


     If BIO_should_retry() returns false then the precise "error
     condition" depends on the BIO type that caused it and the
     return code of the BIO operation. For example if a call to
     BIO_read() on a socket BIO returns 0 and BIO_should_retry()
     is false then the cause will be that the connection closed.
     A similar condition on a file BIO will mean that it has
     reached EOF. Some BIO types may place additional information
     on the error queue. For more details see the individual BIO
     type manual pages.

     If the underlying I/O structure is in a blocking mode almost
     all current BIO types will not request a retry, because the
     underlying I/O calls will not. If the application knows that
     the BIO type will never signal a retry then it need not call
     BIO_should_retry() after a failed BIO I/O call. This is typ-
     ically done with file BIOs.

     SSL BIOs are the only current exception to this rule: they
     can request a retry even if the underlying I/O structure is
     blocking, if a handshake occurs during a call to BIO_read().
     An application can retry the failed call immediately or
     avoid this situation by setting SSL_MODE_AUTO_RETRY on the
     underlying SSL structure.

     While an application may retry a failed non blocking call
     immediately this is likely to be very inefficient because
     the call will fail repeatedly until data can be processed or
     is available. An application will normally wait until the
     necessary condition is satisfied. How this is done depends
     on the underlying I/O structure.

     For example if the cause is ultimately a socket and
     BIO_should_read() is true then a call to select() may be
     made to wait until data is available and then retry the BIO
     operation. By combining the retry conditions of several non
     blocking BIOs in a single select() call it is possible to
     service several BIOs in a single thread, though the perfor-
     mance may be poor if SSL BIOs are present because long
     delays can occur during the initial handshake process.

     It is possible for a BIO to block indefinitely if the under-
     lying I/O structure cannot process or return any data. This

MirBSD #10-current         2005-02-05                           2

BIO_SHOULD_RETRY(3)          OpenSSL          BIO_SHOULD_RETRY(3)

     depends on the behaviour of the platforms I/O functions.
     This is often not desirable: one solution is to use non
     blocking I/O and use a timeout on the select() (or
     equivalent) call.


     The OpenSSL ASN1 functions cannot gracefully deal with non
     blocking I/O: that is they cannot retry after a partial read
     or write. This is usually worked around by only passing the
     relevant data to ASN1 functions when the entire structure
     can be read or written.



MirBSD #10-current         2005-02-05                           3

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