goshs: WebDAV listener ignores --read-only, --upload-only, and --no-delete mode flags

When goshs is launched with WebDAV enabled (-w), the mode-restriction flags --read-only, --upload-only, and --no-delete are enforced only on the primary HTTP port. The WebDAV port is wired straight to golang.org/x/net/webdav.Handler with no equivalent guard, so an authenticated WebDAV client can PUT, DELETE, MKCOL, MOVE, and COPY despite the operator's stated intent.

httpserver/server.go:207-238 — the WebDAV mux registers only IPWhitelistMiddleware, ServerHeaderMiddleware, and optionally BasicAuthMiddleware. There is no fs.ReadOnly || fs.UploadOnly || fs.NoDelete check on the WebDAV path. The HTTP mux in the same file (lines 134-204) does check these flags on every state-changing route.

• Integrity — --read-only and --no-delete are silently downgraded to "no protection" on the WebDAV port. Any WebDAV client (curl, cadaver, Windows Explorer, Finder) can overwrite/delete files.
• Confidentiality — --upload-only is also bypassed: WebDAV GET/PROPFIND still return file contents.
• Trust — operators using goshs -w -ro -d /srv/case-files -b reviewer:pw to deliver engagement artifacts believe the directory is immutable. It isn't.

Add a small http.HandlerFunc in front of wdHandler that maps WebDAV verbs to the existing mode flags:

 1wdGuard := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 2    switch r.Method {
 3    case http.MethodPut, "MKCOL", "MOVE", "COPY":
 4        if fs.ReadOnly || fs.UploadOnly { http.Error(w, "read-only", 403); return }
 5    case http.MethodDelete:
 6        if fs.ReadOnly || fs.UploadOnly || fs.NoDelete { http.Error(w, "delete disabled", 403); return }
 7    case http.MethodGet, "PROPFIND", "HEAD":
 8        if fs.UploadOnly { http.Error(w, "upload-only", 403); return }
 9    }
10    wdHandler.ServeHTTP(w, r)
11})

Add regression tests in integration/functions.go covering each mode flag × each WebDAV verb.

Reporter: Nishant Verma. Reproduced live against goshs v2.0.9 (commit 8fc1e91) on 2026-05-27.