Webdav backend incompatible with golang stdlib webdav implementation

[SISheogorath]

I think I found conflict between how the seedvault implementation expects directories to work and how golang handles it:

In this function, you test that directories exist using the HEAD function:

seedvault/core/src/main/java/org/calyxos/seedvault/core/backends/webdav/WebDavHelper.kt

Lines 84 to 103 in 156ffbd

	internal fun DavCollection.ensureFoldersExist(log: KLogger, folders: MutableSet<HttpUrl>) {
	if (location.pathSize <= 2) return
	val parent = location.newBuilder()
	.removePathSegment(location.pathSize - 1)
	.build()
	if (parent in folders) return
	val parentCollection = DavCollection(httpClient, parent)
	try {
	parentCollection.head { response ->
	log.debugLog { "head($parent) = $response" }
	folders.add(parent)
	}
	} catch (e: NotFoundException) {
	log.debugLog { "$parent not found, creating..." }
	parentCollection.mkColCreateMissing { response ->
	log.debugLog { "mkColCreateMissing($parent) = $response" }
	folders.add(parent)
	}
	}
	}

golang doesn't support HEAD requests on directory listings:
https://github.com/golang/net/blob/dfc720dfe0cfc125116068c20efcdcb5e4eab464/webdav/webdav.go#L212

I checked the RFCs RFC4918 and RFC2068 but couldn't find any defintive answer how this should be handled. But there isn't really an answer to this, beyond "Treat GET and HEAD identical". The overall internet also seems undecided how to handle directory requests in webdav. (Here one of the samples I found).

I think the correct way to check for directories would be the usage of PROPFIND with a depth of 0. That would certainly be in line with the RFC4918 section 9.1.

This is an upstream issue for downstream issue GrapheneOS/os-issue-tracker#4558

[grote]

shouldn't be too difficult to change the head request to propfind(depth=0).

[grote]

@martijnboers are you using https://github.com/mholt/caddy-webdav ? If so, it seems that also doesn't support HEAD requests. I am getting 405 from it.

[SISheogorath]

It's based on the same library: https://github.com/mholt/caddy-webdav/blob/42168ba04c9dc2cd228ab8c453dbab27654e52e6/webdav.go#L30

[martijnboers]

Yes I am using that caddy extension, I can setup a non-Go implementation for debugging if that helps. I was looking through the forks but it seems no one has bothered implementing HEAD requests.

[grote]

I am going to submit a PR that removes the HEAD request in favor of PROPFIND. With that it works fine against your caddy server and much much faster than going through SAF and DavX5.