This parameter is NULL or the pointer to the previous state
for the previous protocol in the case of a protocol change,
for instance from HTTP1 to HTTP2
This way, the new protocol can use the old protocol context.
For instance, HTTP2 mimicks the HTTP1 request, to have a HTTP2
transaction with both request and response
Optional callback a parser can register for applying configuration
to the 'transaction'. Most parsers have a bidirectional tx. For those
parsers that have different types of transaction handling, this new
callback can be used to properly apply the config.
AppLayerTxData is a structure each tx should include that will contain
the common fields the engine needs for tracking logging, detection and
possibly other things.
AppLayerTxConfig will be used by the detection engine to configure
the transaction.
To signal incomplete data, we must return the number of
consumed bytes. When we get a banner and some records, we have
to take into account the number of bytes already consumed by
the banner parsing before reaching an incomplete record.