NodeSeq.Empty is not serializable

[joescii]

It appears that the typical use case of NodeSeq serializes with no problems (I'm speaking of Node, which we can see here is marked as Serializable), but the NodeSeq.Empty surprisingly doesn't. I would expect it to behave like String where the empty string is trivially serializable.

Is there any reason that NodeSeq should not extend Serializable? The offender in the case of NodeSeq.Empty could trivially be marked to extend Serializable here

You can see the behavior below in this console session. Note that java version details are printed at the end. This was run on a MBP running Sierra 10.12.6.

[info] Starting scala interpreter...
[info] 
Welcome to Scala 2.12.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_131).
Type in expressions for evaluation. Or try :help.

scala> import java.io._
import java.io._

scala> import scala.xml.NodeSeq
import scala.xml.NodeSeq

scala>       def serialize(in: Any): Array[Byte] = {
     |         val bos = new ByteArrayOutputStream()
     |         val oos = new ObjectOutputStream(bos)
     |         oos.writeObject(in)
     |         oos.flush()
     |         bos.toByteArray()
     |       }
serialize: (in: Any)Array[Byte]

scala> serialize("joescii")
res0: Array[Byte] = Array(-84, -19, 0, 5, 116, 0, 7, 106, 111, 101, 115, 99, 105, 105)

scala> serialize("")
res3: Array[Byte] = Array(-84, -19, 0, 5, 116, 0, 0)

scala> serialize(<joescii/>)
res1: Array[Byte] = Array(-84, -19, 0, 5, 115, 114, 0, 14, 115, 99, 97, 108, 97, 46, 120, 109, 108, 46, 69, 108, 101, 109, -121, -95, 0, -70, 78, 93, -40, -69, 2, 0, 6, 90, 0, 13, 109, 105, 110, 105, 109, 105, 122, 101, 69, 109, 112, 116, 121, 76, 0, 10, 97, 116, 116, 114, 105, 98, 117, 116, 101, 115, 116, 0, 20, 76, 115, 99, 97, 108, 97, 47, 120, 109, 108, 47, 77, 101, 116, 97, 68, 97, 116, 97, 59, 76, 0, 5, 99, 104, 105, 108, 100, 116, 0, 22, 76, 115, 99, 97, 108, 97, 47, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 47, 83, 101, 113, 59, 76, 0, 5, 108, 97, 98, 101, 108, 116, 0, 18, 76, 106, 97, 118, 97, 47, 108, 97, 110, 103, 47, 83, 116, 114, 105, 110, 103, 59, 76, 0, 6, 112, 114, 101, 102, 105, 120, 113, 0, 126, 0, 3, 76, 0, 5, 115, 99, 111, 112, 101, 11...

scala> val xml = <joescii/>
xml: scala.xml.Elem = <joescii/>

scala> serialize(xml)
res4: Array[Byte] = Array(-84, -19, 0, 5, 115, 114, 0, 14, 115, 99, 97, 108, 97, 46, 120, 109, 108, 46, 69, 108, 101, 109, -121, -95, 0, -70, 78, 93, -40, -69, 2, 0, 6, 90, 0, 13, 109, 105, 110, 105, 109, 105, 122, 101, 69, 109, 112, 116, 121, 76, 0, 10, 97, 116, 116, 114, 105, 98, 117, 116, 101, 115, 116, 0, 20, 76, 115, 99, 97, 108, 97, 47, 120, 109, 108, 47, 77, 101, 116, 97, 68, 97, 116, 97, 59, 76, 0, 5, 99, 104, 105, 108, 100, 116, 0, 22, 76, 115, 99, 97, 108, 97, 47, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 47, 83, 101, 113, 59, 76, 0, 5, 108, 97, 98, 101, 108, 116, 0, 18, 76, 106, 97, 118, 97, 47, 108, 97, 110, 103, 47, 83, 116, 114, 105, 110, 103, 59, 76, 0, 6, 112, 114, 101, 102, 105, 120, 113, 0, 126, 0, 3, 76, 0, 5, 115, 99, 111, 112, 101, 11...

scala> serialize(NodeSeq.Empty)
java.io.NotSerializableException: scala.xml.NodeSeq$$anon$1

  at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1182)
  at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
  at .serialize(<console>:18)
  ... 39 elided

scala> 
descartes:lift-framework joescii$ java -version
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

[SethTisue]

good catch! but please open this issue at https://github.com/scala/scala-xml/issues instead (if it doesn't already exist there)

[som-snytt]

Probably this issue should be opened at https://github.com/scala/scala-xml/issues

There are conceivably issues with xml parsing in the compiler, but this seems to be an implementation issue.

[SethTisue]

jinx

[som-snytt]

oh, I just had a @SethTisue jinx.

Ach, jinx, jinx! double jinx!

[joescii]

Thank you for pointing me to the correct repo. I knew XML was published separately, but after searches failed to find it for me I concluded wrongly that maybe they weren't separate source repos. :)

scala/scala-xml#154