[undertow-dev] output buffering

[Nate]

On Wed, Jun 17, 2020 at 1:02 AM Stuart Douglas <sdouglas at redhat.com> wrote:

> Is there a way I can know when the client has received all the data, even
>> if it is buffered at the system level?
>>
>
> If you call flush() on the OutputStream is won't return until the client
> has recieved and acked the data AFAIK.
>

Alright, I tried this:

System.out.println("start");
PooledByteBuffer poolBuffer =
exchange.getConnection().getByteBufferPool().getArrayBackedPool().allocate();
byte[] buffer = poolBuffer.getBuffer().array(); // buffer.length is 16KB.
exchange.startBlocking();
OutputStream output = exchange.getOutputStream();
try (var input = new FileInputStream(file)) {
    while (true) {
        int count = input.read(buffer);
        if (count == -1) break;
        output.flush(); // Before write() to avoid flushing a closed
OutputStream.
        output.write(buffer, 0, count);
    }
}
exchange.endExchange();
System.out.println("end");

When I hit the URL, I see "start" and "end" printed immediately in the
server log even though the curl download takes much, much longer at 10
bytes/sec.

That was on Debian. Next I tried the same on Windows 10 and there I see
only "start" while the download is in progress. That is true even if I
remove the flush.

So it seems it is something specific about Debian or its configuration. Any
idea what is happening, or other ideas on how I can know when the client
has really received the data?

Cheers,
-Nate
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