Improved support for byte strings

[borman]

Currently working on a serialization library for a format where all strings are byte strings. Thus, I find byte string support requiring some attention.

The proposed changes are:

1. Allow to disassemble Bytes/ByteBuf into underlying representation
2. Add a nice-looking Debug implementation for Bytes/ByteBuf
3. Add methods to construct strings from byte strings via str::from_utf8
4. Add default visit_byte_buf implementation as a fallback to visit_bytes
5. Implement ValueDeserializer for Bytes/ByteBuf
6. Recognize struct field names as byte strings.

[oli-obk]

why not also use Into here?

[borman]

Would conflict with From<T> at line 94:

impl Into<Vec<u8>> for ByteBuf {...}
impl<T> From<T> for ByteBuf where T: Into<Vec<u8>> {...}

src/bytes.rs:100:1: 106:2 error: conflicting implementations for trait `core::convert::From` [E0119]
src/bytes.rs:100 impl<T> From<T> for ByteBuf where T: Into<Vec<u8>> {
src/bytes.rs:101     fn from(bytes: T) -> Self {
src/bytes.rs:102         ByteBuf {
src/bytes.rs:103             bytes: bytes.into(),
src/bytes.rs:104         }
src/bytes.rs:105     }
                 ...
src/bytes.rs:100:1: 106:2 note: conflicting implementation in crate `core`
src/bytes.rs:100 impl<T> From<T> for ByteBuf where T: Into<Vec<u8>> {
src/bytes.rs:101     fn from(bytes: T) -> Self {
src/bytes.rs:102         ByteBuf {
src/bytes.rs:103             bytes: bytes.into(),
src/bytes.rs:104         }
src/bytes.rs:105     }
                 ...

[borman]

I would suggest removing

impl<T> From<T> for ByteBuf where T: Into<Vec<u8>>

in favor of simpler

impl From<Vec<u8>> for ByteBuf

Though that would be a breaking change.

[oli-obk]

does removing the From impl and adding the Into impl work?
Then the From impl is generated in the standard library if I read this correctly.

[borman]

Then the From impl is generated in the standard library if I read this correctly.

Yes, the offending implementation is

impl<T> From<T> for T

http://doc.rust-lang.org/src/core/convert.rs.html#152

[oli-obk]

nope it's that one: http://doc.rust-lang.org/src/core/convert.rs.html#144 ;)

[oli-obk]

what I mean is, you don't need to implement Into, it's generated, since From exists.

[borman]

Well, the message actually mentions From implementations, not Into.

Anyway, committed this change.

[borman]

It would be generated if there was impl From<ByteBuf> for Vec<u8>, not impl From<Vec<u8>> for ByteBuf

[oli-obk]

oh right... I got very confused with all those From and Into... sorry about that

[borman]

Updated; will squash commits after review.

[erickt]

Thanks! I'm prepping for a release, so the WIPs are fine for me right now :)