I'm trying to port some JVM code to native code, and I need to replicate some `ByteBuffer` code. I'm...

# multiplatform

[eygraber]

I'm trying to port some JVM code to native code, and I need to replicate some ByteBuffer code. I'm using ktor-io but there's something that I'm not doing correctly. Code in 🧵

[eygraber]

Here's what I'm porting:

if (byteBuffer.position() == 0) {
  return;
}
byteBuffer.flip();
try {
  builder.append(decoder.decode(byteBuffer));
} catch (CharacterCodingException e) {
  if (throwOnFailure) {
    throw new IllegalArgumentException(e);
  } else {
    builder.append(INVALID_INPUT_CHARACTER);
  }
} finally {
  // Use the byte buffer to write again.
  byteBuffer.flip();
  byteBuffer.limit(byteBuffer.capacity());
}

[eygraber]

Here's my code (an extension function on Buffer):

if(writePosition == 0) return

resetForRead()

try {
  builder.append(readBytes().decodeToString())
}
catch(e: Exception) {
  if(throwOnFailure) {
    throw IllegalArgumentException(e)
  }
  else {
    builder.append(INVALID_INPUT_CHARACTER)
  }
}
finally {
  reset()
}

[eygraber]

The problem is that a bunch of 0s are showing up when I call readBytes (this is after writing 1 byte to the buffer then calling my function, then writing 3 bytes to the buffer then calling my function, then writing 3 bytes to the buffer then calling my function):

47, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-60, -126, 37, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-32, -95, -128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

[ephemient]

you should probably indicate which Buffer you're using. doesn't seem to be okio.Buffer

[ephemient]

if it's io.ktor.utils.io.core.Buffer, I've no experience with it but resetForRead() doesn't seem to be equivalent to `flip()`: it marks the whole buffer as readable, not just the part up to the write position

[eygraber]

It's ktor's Buffer but my IDE is having issues resolving dependencies, so it's hard to step through it to see how it works.

I'm assuming there's a way to do it with okio.Buffer as well?

[ephemient]

with okio there's usually enough helpers build on (Buffered)Source, (Buffered)Sink, Pipe, etc. that there's no need to work on Buffer directly

[eygraber]

Although looking at the problem again after some sleep I can probably make a simple wrapper around a byte array for this use case.