[jira] [Created] (DAFFODIL-2502) Parse must behave properly for reading data from TCP sockets

["Mike Beckerle (Jira)" <ji...@apache.org>]

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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