Possible new architecture for resolving WebDAV paths

[jwodder]

WIP design document for a new code architecture

• Rename DandiDav to Dav

• Give Dav a register(name: &Component, handler: Box<dyn DavHandler>, description: &str) -> Result<(), DuplicateNameError> method for registering a handler for a WebDAV hierarchy to serve under /{name}/

  • description is used as the "Type" value for the hierarchy in the root HTML view
  • As an alternative to boxing, the type of handler could instead be an enum using enum dispatch.

• Add a DavHandler trait with the following methods:

  • get_resource(&self, path: Vec<Component>) -> Result<DavResource, DavError>
  • get_resource_with_children(&self, path: Vec<Component>) -> Result<DavResourceWithChildren, DavError>

  Note that path may be empty (i.e., when a client requests /{name}/), and so PurePath cannot be used here.

  Note that these methods will be async, which may have implications for boxability of trait objects; cf. https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html.

• Add a DandiDav struct implementing DavHandler for serving resources under /dandisets/; move all code specific to /dandisets/ here

  • This struct will implement resolution of paths under /dandisets/, currently implemented by the current DandiDav type via DavPath

• Add a ZarrMan struct implementing DavHandler for serving resources under /zarrs/

• Idea: The internal implementations of the DavHandler types could traverse their hierarchies as follows:

  • Locations in a handler's hierarchy are represented by an enum with variants for different depths & similar (cf. DavPath and zarrman::ReqPath)

  • The handler instantiates a location enum with the root variant and then applies each component in path in turn by calling an into_child(self, name: Component) -> Result<Self, DavError> method

    • This method returns Err if it can be easily determined (sans IO) that the path so far is invalid/does not exist

  • Details for the final location are then retrieved based on the location enum's final state

• Whose responsibility is it to prepend the /{name}/ component to hrefs in responses?

  • If the DavHandlers don't prepend it, what would the paths of their root collections be? None?
  • Give DavResource[WithChildren] a prepend_path(&mut self, path: &PureDirPath) method for calling by Dav after delegating to a handler?
  • Idea: Make name(&self) -> &'static str a method of DavHandler, and make it the DavHandlers' responsibility to prepend the name
    • This will be more reasonable if enum dispatch is used instead of boxing.

[yarikoptic]

what is the motivation/goal?

[jwodder]

@yarikoptic Cleaner code, separation of concerns, better ability to add more "top-level" services like /dandisets/ and /zarrs/ in the future, etc.