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https://issues.apache.org/jira/browse/DAFFODIL-2502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17330439#comment-17330439
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Steve Lawrence commented on DAFFODIL-2502:
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The Javadoc for the read function in both DataInputStream and InputStream says:
{quote}This method blocks until input data is available, end of file is
detected, or an exception is thrown.
{color:#172b4d}If {color}{{len}}{color:#172b4d} is zero, then no bytes are read
and {color}{{0}}{color:#172b4d} is returned; otherwise, there is an attempt to
read at least one byte. If no byte is available because the stream is at end of
file, the value {color}{{-1}}{color:#172b4d} is returned; otherwise, at least
one byte is read and stored into {color}{{b}}{color:#172b4d}.{color}
{quote}
Daffodil never passes in 0 as the len parameter, so read should always block
until at least one byte is available and return, or return -1 for end of file.
Seems to me the case of getting zero bytes should never happen with the
arguments Daffodil passes to read, and either there's a bug in Daffodil where
we are passing in zero as the length field, or something isn't following the
InputStream API.
> 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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