Charsets for hex/base64

[Vincent Ryan]

FYI here’s the javadoc for a draft of the Hex API that Alan mentioned below:
http://cr.openjdk.java.net/~vinnie/8170769/javadoc.05/api/java.base/java/util/Hex.html

Thanks.


> On 2 May 2018, at 10:55, Jonas Konrad <me at yawk.at> wrote:
> 
> 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