Close InputStream wrapped into IO - scala

Question

I'm using IO (cats/scalaz does not matter). And I want to use bracket to close InputStream after I'm done with it. The problem is that I'm reading gzipped files. Here is what I tried:
I (Incorrect).
val io1 = IO(Files.newInputStream(Paths.get("/tmp/file")))
val io2 = io1.map(is => new GZIPInputStream(is))
val io3 = io2.bracket{_ =>
IO(println("use"))
//empty usage
}{ is =>
println("close")
IO(is.close())
}
This is incorrect because of if /tmp/file is a broken zip-file with invalid magic we will never reach "resource release" bracket.
II (Incorrect).
val io1 = IO(Files.newInputStream(Paths.get("/tmp/file")))
val io3 = io1.bracket{is =>
val gzis = new GZIPInputStream(is)
IO(println("use"))
//empty usage
}{ is =>
println("close")
IO(is.close())
}
This is incorrect because we are closing the underlying stream, but not the GzipInputStream so we may end up losing some buffered data inside.
In java I could simply do this without flushing:
var is: InputStream = null
try{
is = Files.newInputStream(Paths.get("/tmp/file"))
is = new GZIPInputStream(is)
//use
} finally {
if(is ne null)
is.close()
}
Can you suggest some approach for dealing with GzipInputStream?

Answer 1

It is not a problem to call close on input stream several times, so you can close InputStream and GZIPInputStream separatelly.
In Java it is common to let try with resources hanlde both streams
try (InputStream is = Files.newInputStream(Paths.get("/tmp/file"));
GZIPInputStream gzis = new GZIPInputStream(is)){
//use gzis
}
// both streams are closed in implicit finaly clause
You can translate this approach to IO brackets
val io1 = IO(Files.newInputStream(Paths.get("/tmp/file")))
val io2 = io1.bracket { is =>
IO(new GZIPInputStream(is)).bracket { gzis =>
IO(println("using gzis"))
}(gzis => IO(gzis.close()))
}(is => IO(is.close()))
To awoid nested brackets you can use Resource
def openFile(path: Path) = Resource(IO {
val is = Files.newInputStream(path)
(is, IO(is.close()))
})
def openGZIP(is: InputStream) = Resource(IO {
val gzis = new GZIPInputStream(is)
(gzis, IO(gzis.close()))
})
val gzip: Resource[IO, GZIPInputStream] = for {
is <- openFile(Paths.get("/tmp/file"))
gzis <- openGZIP(is)
} yield gzis
gzip.use {
gzis => IO(println("using gzis"))
}