Hi Yaroslav,
you may want to create a custom GraphStage in that case that waits for the
first data to arrive and then prepend the extra-data. Afterwards you can
change the state of the GraphStage to forward messages 1-to-1.
Johannes
On Tuesday, September 20, 2016 at 4:00:23 PM UTC+2, Yaroslav Klymko wrote:
>
> Basically I'd like to prepend something, but at the moment first
> ByteString received, I mean that prepended value should not be in the
> stream in case of connection failure.
>
> On Tuesday, September 20, 2016 at 1:44:56 PM UTC+3, Johannes Rudolph wrote:
>>
>> Hi Yaroslav,
>>
>> no worries, this is a good question. It depends a bit on what kind of
>> logic you want to trigger. If you just want to do something, you can use
>> `mapMaterializedValue` to do something with the `OutgoingConnection` object
>> before materialization is complete.
>>
>> If you want to prepend some bytes to be output to the connection, you can
>> do it like this:
>>
>> Flow[ByteString]
>> .prepend(Source.single(ByteString("hello connection"))) // or any other
>> source
>> .via(Tcp(system).outgoingConnection(???, ???))
>>
>> More complex behavior can be built e.g. by wrapping the complete
>> connection flow with a custom GraphStage that would be able to receive all
>> kinds of signals.
>>
>> HTH
>> Johannes
>>
>>
>>
>> On Thursday, September 15, 2016 at 12:32:02 PM UTC+2, Yaroslav Klymko
>> wrote:
>>>
>>> Either my question is silly or there is no easy answer.
>>>
>>> On Saturday, September 10, 2016 at 3:57:33 PM UTC+3, Yaroslav Klymko
>>> wrote:
>>>>
>>>> Hi guys,
>>>>
>>>> I'm trying to figure out on how to trigger some logic at the moment TCP
>>>> connection established, and preferably *before traffic goes*
>>>> Initial code looks like this:
>>>>
>>>>
>>>> Tcp(system).outgoingConnection(???, ???).join(flow).runWith(source, sink)
>>>>
>>>>
>>>>
>>>> As far as I can see I need to access Future[OutgoingConnection]
>>>>
>>>>
>>>> val outgoingConnection: Flow[ByteString, ByteString,
>>>> Future[OutgoingConnection]] = Tcp(system).outgoingConnection(???, ???)
>>>>
>>>>
>>>>
>>>> So far I came to:
>>>>
>>>>
>>>> val (_, connected: Future[Tcp.OutgoingConnection], _) =
>>>> Source.fromGraph(source).viaMat(connection)(Keep.both).toMat(sink)(Keep.both).run()
>>>>
>>>>
>>>>
>>>> Question 1: how to guarantee my code performed before first ByteString
>>>> came?
>>>> Question 2: is there better solution
>>>> Question 3: how to prepend connection as first event in the flow of
>>>> ByteStrings ?
>>>>
>>>>
--
>>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>> Check the FAQ:
>>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user
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