To iterate over sys::InStream contents until EOF I have to write old-fashioned loops like this:

while (in.peek != null)
{
  byte := in.read
  //do something with the byte
}

I think having eachByte and eachChar methods in sys::InStream would follow Fantom's API style and make iterating over stream contents more pretty and convenient.

If you want to handle all the stream contents, then for performance reasons it makes sense to read into some buffer. I would suggest implementing it similar to guava ByteProcessor, which in java looks like this:

interface ByteProcessor {
  processBytes(byte[] buf, int off, int len)
}

readBytes(ByteProcessor processor)

And it can be also implemented for sys::File, sys::Buf, etc.

Fantom's streams are buffered by default.

It might be nice for consistency, but that seems like a pretty odd use case. Of all the I/O work I've done, I've never actually wanted to iterate byte by byte or char by char. Can you maybe explain the use case more?

I had to implement percent encoding because I didn't find it in language API (seems like using API you can encode query or uri but not just any string and I needed it). The implementation looks like this:

static Str percentEncode(Str str)
{
  result := StrBuf()

  bytes := str.toBuf
  while (bytes.peek != null)
  {
    byte := bytes.read
    if (byte.isAlphaNum || byte == '-' || byte == '.' || byte == '_' || byte == '~')
    {
      result.addChar(byte)
    }
    else
    {
      result.addChar('%').add(byte.toHex(2).upper)
    }
  }

  return result.toStr
}

As a data point, I've written character by charater looping for parsing input a few times in the last 10 years.