return url as AbsPath from WebFile to implement FileInfo

[jmank88]

This PR extends WebFile to implement FileInfo, causing the url to be sent in the abspath header (to be used in subsequent PRs to go-ipfs-cmds and go-ipfs).
Towards ipfs/kubo#6065

[Jorropo]

I don't get where is it use full, I'm working on ipfs/kubo#6065 (like you), personaly I'm close to finish (I'm in trouble with the post run function of add when it is an url because it wait a lot of things that not here.) and I don't need that.
Please can you tell me when is use full please ?

[jmank88]

I'm following the method describe here, which is different than how urlstore works. This PR indirectly adds the url to the abspath header. Then go-ipfs-cmds will need an update to use files.WebFile when it encounters a url path. Then go-ipfs will need an update to set DagBuilderParams.URL from files.FileInfo.AbsPath(). All together those changes enable using urls and also supports --nocopy. It's a small change overall, but it crosses multiple repos and each piece depends on the last.

[Jorropo]

Ok :)

[Stebalien]

@magik6k I think this is the right way to do this but it's kind of weird. Basically, setting AbsPath like this (and tweaking the cmds library to create WebFiles) should make ipfs add --nocopy magically work with URLs. Does that sound right?

[jmank88]

And a third step to set DagBuilderParams.URL to FileInfo.AbsPath() in go-ipfs/core/coreunix/add.go (urlstore manages its own DagBuilderParams directly).
Here is all three pieces ipfs/kubo#6065 (comment)

[magik6k]

LGTM.

(another way to approach this would be to make MultipartReader just send the URL with type like application/x-url, and parse that into WebFiles in MultipartFile, but that's much more involved change to save a bit of bandwidth between client and daemon)