Mike Beckerle created DAFFODIL-2502:
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Summary: Parse must behave properly for reading data from TCP
sockets
Key: DAFFODIL-2502
URL: https://issues.apache.org/jira/browse/DAFFODIL-2502
Project: Daffodil
Issue Type: Bug
Components: API, Back End
Affects Versions: 3.0.0
Reporter: Mike Beckerle
Daffodil assumes the input streams are like files - reads are always blocking
for either 1 or more bytes of data, or End-of-data.
People want to use Daffodil to read data from TCP/IP sockets. These can return
0 bytes from a read because there is no data available, but that does NOT mean
the end of data. It's just a temporary condition. More data may come along.
Daffodil's InputSourceDataInputStream is wrapped around a regular Java input
stream, and enables us to support incoming messages which do not conform to
byte-boundaries.
The problem is that there's no way for users to wrap an
InputSourceDataInputStream around a TCP/IP socket, and have it behave properly
when a read() call temporarily says 0 bytes available.
Obviously we don't want to sit in a tight loop just retrying the read until we
get either some bytes or end-of-data.
The right API here is that if the read() of the underlying java stream returns
0 bytes, that a hook function supplied by the API user is called.
One obvious thing a user can do is put a call to Thread.yield() in the hook.
(That might even want to be the default behavior if they supply no hook.) Then
if they have a separate thread parsing the data with daffodil, that thread will
at least yield the CPU, i.e., behave politely in a multi-threaded world.
More advanced usage could start a Daffodil parse using co-routines, returning
control to the caller when the parse must pause due to read() of the Java input
stream returning 0 bytes.
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