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 functions
BIO_should_read(a) ((a)->flags & BIO_FLAGS_READ)
BIO_should_write(a) ((a)->flags & BIO_FLAGS_WRITE)
BIO_should_io_special(a) ((a)->flags & BIO_FLAGS_IO_SPECIAL)
BIO_retry_type(a) ((a)->flags & BIO_FLAGS_RWS)
BIO_should_retry(a) ((a)->flags & BIO_FLAGS_SHOULD_RETRY)
#define BIO_FLAGS_WRITE 0x02
BIO_FLAGS_IO_SPECIAL 0x04 #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
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
BIO_get_retry_reason() returns a mask of the cause of a retry
condition consisting of the values BIO_FLAGS_READ, BIO_FLAGS_WRITE, BIO_FLAGS_IO_SPECIAL though
current BIO 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 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 condition
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 typically 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 performance 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 underlying
I/O structure cannot process or return any data. This 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