Illegal seek for FileIO.fromPath with named pipe

[johanandren]

It seems to be not working for me (tried with mulitple versions):

java.io.IOException: Illegal seek
        at java.base/sun.nio.ch.FileDispatcherImpl.seek0(Native Method)
        at java.base/sun.nio.ch.FileDispatcherImpl.seek(FileDispatcherImpl.java:78)
        at java.base/sun.nio.ch.FileChannelImpl.position(FileChannelImpl.java:361)
        at akka.stream.impl.io.FileSource$$anon$1.preStart(IOSources.scala:80)
        at akka.stream.impl.fusing.GraphInterpreter.init(GraphInterpreter.scala:295)
        at akka.stream.impl.fusing.GraphInterpreterShell.init(ActorGraphInterpreter.scala:557)
        at akka.stream.impl.fusing.ActorGraphInterpreter.tryInit(ActorGraphInterpreter.scala:679)
        at akka.stream.impl.fusing.ActorGraphInterpreter.preStart(ActorGraphInterpreter.scala:727)
        at akka.actor.Actor.aroundPreStart(Actor.scala:528)
        at akka.actor.Actor.aroundPreStart$(Actor.scala:528)
        at akka.stream.impl.fusing.ActorGraphInterpreter.aroundPreStart(ActorGraphInterpreter.scala:670)
        at akka.actor.ActorCell.create(ActorCell.scala:652)
        at akka.actor.ActorCell.invokeAll$1(ActorCell.scala:523)
        at akka.actor.ActorCell.systemInvoke(ActorCell.scala:545)
        at akka.dispatch.Mailbox.processAllSystemMessages(Mailbox.scala:283)
        at akka.dispatch.Mailbox.run(Mailbox.scala:224)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:834)```

Originally posted by @syspulse in #25328 (comment)

[johanandren]

If you can share a reproducer or clear steps to reproduce that would be useful @syspulse

[syspulse]

# uname -a
Linux  5.15.0-79-generic #86~20.04.2-Ubuntu SMP Mon Jul 17 23:27:17 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
# mkfifo /tmp/pipe

ammonite (Ammonite Repl 2.5.4 (Scala 2.13.8 Java 11.0.5)):

import $ivy.`com.typesafe.akka::akka-stream:2.6.19`
import akka.stream._
import akka.stream.scaladsl._
import java.nio.file.{Paths, Files}
import akka.actor.ActorSystem
implicit val as = ActorSystem("Pipe")
implicit val ec = scala.concurrent.ExecutionContext.global
val f = FileIO.fromPath(Paths.get("/tmp/pipe")).to(Sink.foreach{println}).run()

Push data:

echo "1" >/tmp/pipe

[ERROR] [09/27/2023 11:51:00.173] [Pipe-akka.actor.default-blocking-io-dispatcher-8] [akka://Pipe/system/Materializers/StreamSupervisor-0/flow-0-1-fileSource] Error during preStart in [akka.stream.impl.io.FileSource$$anon$2-fileSource]: Nicht erlaubter Seek
java.io.IOException: Nicht erlaubter Seek
        at java.base/sun.nio.ch.FileDispatcherImpl.seek0(Native Method)
        at java.base/sun.nio.ch.FileDispatcherImpl.seek(FileDispatcherImpl.java:78)
        at java.base/sun.nio.ch.FileChannelImpl.position(FileChannelImpl.java:361)
        at akka.stream.impl.io.FileSource$$anon$2.preStart(IOSources.scala:74)
        at akka.stream.impl.fusing.GraphInterpreter.init(GraphInterpreter.scala:306)
        at akka.stream.impl.fusing.GraphInterpreterShell.init(ActorGraphInterpreter.scala:619)
        at akka.stream.impl.fusing.ActorGraphInterpreter.tryInit(ActorGraphInterpreter.scala:727)
        at akka.stream.impl.fusing.ActorGraphInterpreter.preStart(ActorGraphInterpreter.scala:776)
        at akka.actor.Actor.aroundPreStart(Actor.scala:548)
        at akka.actor.Actor.aroundPreStart$(Actor.scala:548)
        at akka.stream.impl.fusing.ActorGraphInterpreter.aroundPreStart(ActorGraphInterpreter.scala:716)
        at akka.actor.ActorCell.create(ActorCell.scala:644)
        at akka.actor.ActorCell.invokeAll$1(ActorCell.scala:514)
        at akka.actor.ActorCell.systemInvoke(ActorCell.scala:536)
        at akka.dispatch.Mailbox.processAllSystemMessages(Mailbox.scala:295)
        at akka.dispatch.Mailbox.run(Mailbox.scala:230)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:834)

[johanandren]

In the FileSource we always read with a position, but that is not supported at all with fifos, additionally, opening a fifo with FileChannel.open will block the thread until there is a write on the other side.

I think we should detect fifos passed to it and fail early saying it is not supported. To stream from a fifo there would need to be a special stream source, but this is the first time I have seen anyone talking about it so it is unlikely to be something we add in core akka streams.

[johanandren]

For the record a workaround would be to consume the fifo with a FileInputStream and adapt to stream using StreamConverters.fromInputStream (which expects and handles that the interactions are blocking)