Charsets for hex/base64

[Jonas Konrad]

I did not know about the old HexDumpEncoder. It extends an internal 
class `CharacterEncoder` which seems to be pretty similar purpose-wise 
to what I am suggesting with CharsetEncoder. There is also the good old 
`DatatypeConverter.printHexBinary`, though it can't stream.

But this is not really what I mean. The interesting part about doing 
this as a charset is the unified API aspect of it, the fact that you can 
reuse existing code utilizing Charset for hex operations.

- Jonas

On 05/02/2018 11:44 AM, Alan Bateman wrote:
> On 02/05/2018 09:35, Jonas Konrad wrote:
>> Hi,
>>
>> Conceptually, a 'charset' (in java) is a pair of transformations from 
>> bytes to utf-16 code units and vice versa. Could it be useful to have 
>> charset implementations that convert from bytes to the hex (or base64) 
>> representations of those? The idea is as follows:
>>
>> "0a0b0c".getBytes(HexCharset.getInstance()) = new byte[] { 0x0a, 0x0b, 
>> 0x0c }
>> new String(new byte[] { 0x0a, 0x0b, 0x0c }, HexCharset.getInstance()) 
>> = "0a0b0c"
>>
>> The motivation behind this idea is that there are lots of APIs that 
>> provide efficient transformations between chars and bytes using 
>> charsets, but converting to/from hex for debugging is usually more 
>> involved. One example of this is netty ByteBuf.toString ( 
>> https://netty.io/4.0/api/io/netty/buffer/ByteBuf.html#toString-int-int-java.nio.charset.Charset- 
>> ) - it would be really convenient to be able to just plug in a hex 
>> charset to get nice debug output.
>>
>> Of course this is only one example and there are other ways to get hex 
>> output from ByteBuf in netty in particular, but I still think that a 
>> hex charset would be an interesting tool to reuse code. I understand 
>> this is a somewhat dubious use of a Charset, but I'd like to hear 
>> other thoughts on it.
>>
> Have you looked at the Hex API proposed in JDK-8170769? It needs to be 
> dusted off but the last iteration discussed here got to the point where 
> it provides conversion of binary data to/from hex string representation. 
> It also supported both bulk and stream operations.
> 
> -Alan
>