Use constants for header names

[djc]

No description provided.

[tottoto]

Making the header name constant seems reasonable, but making them associated constants for Status doesn't seem like the good place to do so, considering that Status itself is not a header. Rather, given tonic::metadata::GRPC_CONTENT_TYPE is already placed as a header value constant, I feel it seems better to put it in tonic::metadata.

[LucioFranco]

making them associated constants for Status doesn't seem like the good place to do so, considering that Status itself is not a header

I actually don't agree, we convert these headers in Status and its good to encapsulate the encoding portion of these header names within the status.rs. So to me this makes sense. Metadata is much more abstract than specific extraction of headers. In addition, the metadata shouldn't contain the status headers etc that should all be extracted from the Status functions.

[tottoto]

@LucioFranco

making them associated constants for Status doesn't seem like the good place to do so, considering that Status itself is not a header

I actually don't agree, we convert these headers in Status and its good to encapsulate the encoding portion of these header names within the status.rs. So to me this makes sense. Metadata is much more abstract than specific extraction of headers. In addition, the metadata shouldn't contain the status headers etc that should all be extracted from the Status functions.

I understand that the abstraction of metadata is a high level one. Then, I think it's fine to use Status's associated constants, considering that these will be doc(hidden) and will not actually be made into public API.

[djc]

Made them #[doc(hidden)] as requested.