反向迭代Akka ByteString

Question

I receive data from a TCP server as ByteString . A message ends with the last byte being 0x03. For every ByteString I receive I need to check if last byte is 0x03. Right now I am calling lastIndexof .

val data : ByteString = ...

if (data.lastIndexOf(0x03) >= 0) {}

But this is inefficient since for most of the message chunks it will traverse all the bytes for no good reason. Is there any way to iterate through the bytes in reverse?

Answer 1

Since ByteString is a Seq you can do

if (data.last == 0x03) {}

But I don't how it's implemented so I can't guarantee that it doesn't traverse the whole thing anyway.

Answer 2

A ByteString is an IndexedSeq , so in constant or near constant time, you should be able to do something like this:

val terminated = data.lastOption.filter(_ == 0x03).getOrElse(false)

Under the hood, this is going to use the apply method to get the length - 1 element. Both length and apply should perform in constant or near constant time according to the IndexedSeq documentation.

Indexed sequences support constant-time or near constant-time element access and length computation