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https://issues.apache.org/jira/browse/DAFFODIL-2502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17330478#comment-17330478
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Steve Lawrence commented on DAFFODIL-2502:
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Looking more at how we call read, I think we will even accept a read that
returns zero. When Daffodil reads from an InputSource, it does so because it
requires some amount of bytes before make progress (in fillBucketsToIndex), so
it just keeps calling read until it gets that many bytes or gets an EOF. So
we're just going to be suck in a spin loop waiting for more data if we keep
getting zero. Not particularly efficient, but things should still work. Feels
to me like maybe the InputStream is incorrectly returning EOF when it really
just temporarily doesn't have any data, or isAtEnd stuff is broke.
> 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
> Assignee: Mike Beckerle
> Priority: Major
>
> 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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