Expose content-type/content-encoding etc in the content type

[hypirion]

Hi, thanks for a nice library!

I am using S3.put with the content_type parameter to specify the type of the S3 object I uploaded, and I'd like to retrieve that information somehow. However, head/ls returns content types, and that one doesn't expose the Content-Type stored on the object (it's not in the meta_headers either, I checked).

Would it make sense to add this and other common S3 fields to the content type?

[andersfugmann]

I think it makes perfect sense to extend the content type to include the content type and other useful headers. What other common fields are you thinking of?

[andersfugmann]

Looking further into this, the ListObjects call does not return the content type for each entry (doc). So content type would be empty on each ls. I think the only way to get the content type is though get/head operations (which is actually strange).

I'm cautious not to extend the content type to include too many fields with an option type, but I'll gladly review a PR.

[hypirion]

I'd think people would at least like the API to be symmetric -- currently it's possible to send in content_type, content_encoding and cache_control via put, so I'd assume people would like to be able to retrieve those values as well.

If it makes more sense to you, I can make a head_v2 or something that returns a new type, to avoid polluting the current content type with too many unset values for ls.

[andersfugmann]

Hmm... Having a second version for head would also pollute the namespace - and we would need a solution for get also which I assume will return the same header as for head.

I'm considering two solutions. Extend content type with a optional field pointing to record containing the additional three elements, but that only makes sense if the three are always present (don't really want a record with three optional fields). An alternative could be to just return all headers as an assoc list and provide useful constants to access the fields in this list.

Thoughts.

[hypirion]

I think it'd be just fine to have them all in a headers field. The end result would be the same for me at least.