fix(nc/webdav): MKCOL on a missing parent → 409 (RFC 4918 §9.3.1)

Closes F11.

The NC MKCOL handler previously had `mkdir -p` semantics:
sending MKCOL on /a/b/c/ where neither a nor b exists silently
created both intermediates and returned 201. Sabre/DAV and the
actual NC server both 409 on that — our auto-create deviated.
NC desktop walks ancestors one MKCOL at a time during sync so
nothing real depended on the old behaviour.

Drop the segment-walking creation loop. New flow:
  target exists           → 405
  parent path missing     → 409
  parent ok, target new   → 201

The race-recovery branch for the loop's per-segment create is
also gone — single parent lookup, single create, no window.

Test F11 flipped from pinned-201 to strict 409 and asserts the
intermediate parent was not silently created. F11b and F11c added
as regression guards for the success path and the 'target already
exists' case.

src/interfaces/nextcloud/webdav_handler.rs

@@ -712,7 +712,18 @@ async fn handle_mkcol(
     let folder_service = &state.applications.folder_service;
     let internal_path = nc_to_internal_path(&user.username, subpath)?;
 
-    // If the folder already exists, return 405 per RFC 4918 §9.3.1
+    // RFC 4918 §9.3.1:
+    //   - target already exists                                → 405 Method Not Allowed
+    //   - parent collection of the target does NOT exist       → 409 Conflict
+    //   - parent exists and target does not                    → 201 Created
+    //
+    // Previous behaviour effectively performed `mkdir -p` and returned
+    // 201 even when intermediate ancestors were missing. Sabre/DAV and
+    // the actual NC server both return 409 here, so the legacy
+    // auto-create deviated from the reference implementation. NC desktop
+    // walks ancestors one MKCOL at a time anyway, so dropping the
+    // auto-create doesn't break real clients.
+
     if folder_service
         .get_folder_by_path(&internal_path)
         .await
@@ -724,56 +735,37 @@ async fn handle_mkcol(
             .unwrap());
     }
 
-    // Collect path segments that need to be created (walk from root to leaf)
     let segments: Vec<&str> = subpath.split('/').filter(|s| !s.is_empty()).collect();
+    if segments.is_empty() {
+        return Err(AppError::bad_request("MKCOL on the user root is not allowed"));
+    }
+    let (target_name, parent_segments) = segments.split_last().expect("checked non-empty above");
 
     let user_root = nc_to_internal_path(&user.username, "")?;
-    let mut current_path = user_root.clone();
+    let parent_path = if parent_segments.is_empty() {
-    let mut parent_id = folder_service
+        user_root.clone()
-        .get_folder_by_path(&user_root)
+    } else {
-        .await
+        format!("{}/{}", user_root, parent_segments.join("/"))
-        .map_err(|_| AppError::not_found("User root folder not found"))?
+    };
-        .id
-        .clone();
 
-    for segment in &segments {
+    let parent_folder = match folder_service.get_folder_by_path(&parent_path).await {
-        current_path = format!("{}/{}", current_path, segment);
+        Ok(folder) => folder,
-        match folder_service.get_folder_by_path(&current_path).await {
+        Err(_) => {
-            Ok(existing) => {
+            return Ok(Response::builder()
-                parent_id = existing.id.clone();
+                .status(StatusCode::CONFLICT)
-            }
+                .body(Body::empty())
-            Err(_) => {
+                .unwrap());
-                let dto = CreateFolderDto {
-                    name: segment.to_string(),
-                    parent_id: Some(parent_id.clone()),
-                };
-                match folder_service.create_folder_with_perms(dto, user.id).await {
-                    Ok(created) => {
-                        parent_id = created.id.clone();
-                    }
-                    Err(e)
-                        if e.message.contains("already exists")
-                            || e.message.contains("Already Exists") =>
-                    {
-                        // Race condition — folder created concurrently
-                        let folder = folder_service
-                            .get_folder_by_path(&current_path)
-                            .await
-                            .map_err(|_| {
-                                AppError::internal_error("Folder exists but cannot be found")
-                            })?;
-                        parent_id = folder.id.clone();
-                    }
-                    Err(e) => {
-                        return Err(AppError::internal_error(format!(
-                            "Failed to create folder: {}",
-                            e
-                        )));
-                    }
-                }
-            }
         }
-    }
+    };
+
+    let dto = CreateFolderDto {
+        name: target_name.to_string(),
+        parent_id: Some(parent_folder.id.clone()),
+    };
+    folder_service
+        .create_folder_with_perms(dto, user.id)
+        .await
+        .map_err(|e| AppError::internal_error(format!("Failed to create folder: {}", e)))?;
 
     Ok(Response::builder()
         .status(StatusCode::CREATED)

tests/webdav/test_nc_put_mkcol_blake3.sh

@@ -319,38 +319,43 @@ grep -q '<d:collection/>' <<< "$BODY" \
 pass "F10: MKCOL creates folder, PROPFIND sees it as a collection"
 
 # ─────────────────────────────────────────────────────────────
-# F11 — MKCOL with missing intermediate parent
+# F11 / F11b / F11c — MKCOL parent semantics (RFC 4918 §9.3.1)
 #
-# Pinned current behaviour: OxiCloud's MKCOL auto-creates
+# F11  : missing intermediate parent → 409 Conflict
-# missing intermediate parents (effectively `mkdir -p`
+# F11b : parent exists, target new   → 201 Created (positive case)
-# semantics). Sending MKCOL on `/a/b/c/` where neither `a` nor
+# F11c : target already exists       → 405 Method Not Allowed
-# `b` exists succeeds with 201 — both intermediates are
-# silently created.
 #
-# Strict RFC 4918 §9.3.1 requires 409 Conflict here ("when the
+# Sabre/DAV and the actual NC server both 409 on a missing
-# parent collection does not exist"). NC desktop tolerates
+# intermediate; our previous `mkdir -p` behaviour deviated. NC
-# either behaviour (it always MKCOLs ancestors one at a time
+# desktop walks ancestors one MKCOL at a time during sync so
-# during sync), so the auto-create behaviour is harmless in
+# nothing real breaks from dropping the auto-create.
-# practice — but if you ever want strict mode, the fix lives
-# in `interfaces/nextcloud/webdav_handler.rs::handle_mkcol`:
-# look up the parent path before creating; 409 if missing.
 # ─────────────────────────────────────────────────────────────
-echo "  F11: MKCOL with missing parent (pinned: auto-creates parents, RFC-4918 would 409)"
+echo "  F11: MKCOL with missing intermediate parent → 409"
 STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MKCOL \
     "$NC_FILES_BASE/f11-nonexistent-parent/inner/")
-case "$STATUS" in
+[[ "$STATUS" == "409" ]] \
-    201)
+    || fail "F11: expected 409 Conflict for MKCOL with missing parent, got $STATUS"
-        pass "F11: MKCOL auto-created intermediate parents (201) — pinned current behaviour"
+# The non-existent parent must NOT have been auto-created either.
-        ;;
+[[ "$(nc_status_propfind_depth0 "$NC_FILES_BASE/f11-nonexistent-parent/")" == "404" ]] \
-    409)
+    || fail "F11: intermediate parent was silently created — auto-create still happening"
-        fail "F11: server now returns 409 (RFC-4918 strict). Bug? Improvement? — review and update pin to strict assertion."
+pass "F11: MKCOL with missing parent → 409, parent not silently created"
-        ;;
+
-    *)
+echo "  F11b: MKCOL with existing parent + new target → 201"
-        fail "F11: unexpected status $STATUS"
+nc_curl -o /dev/null -X MKCOL "$NC_FILES_BASE/f11b-parent/" > /dev/null
-        ;;
+STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MKCOL \
-esac
+    "$NC_FILES_BASE/f11b-parent/child/")
-# Cleanup the auto-created parent so subsequent tests don't see it.
+[[ "$STATUS" == "201" ]] \
-nc_curl -o /dev/null -X DELETE "$NC_FILES_BASE/f11-nonexistent-parent/" > /dev/null 2>&1 || true
+    || fail "F11b: expected 201 Created for MKCOL with existing parent, got $STATUS"
+[[ "$(nc_status_propfind_depth0 "$NC_FILES_BASE/f11b-parent/child/")" == "207" ]] \
+    || fail "F11b: target collection not visible via PROPFIND after MKCOL"
+pass "F11b: MKCOL with existing parent → 201, target reachable"
+
+echo "  F11c: MKCOL with target that already exists → 405"
+STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MKCOL \
+    "$NC_FILES_BASE/f11b-parent/child/")
+[[ "$STATUS" == "405" ]] \
+    || fail "F11c: expected 405 Method Not Allowed for MKCOL on existing collection, got $STATUS"
+pass "F11c: MKCOL on existing target → 405"
 
 # ─────────────────────────────────────────────────────────────
 # F12 — MKCOL on existing folder → 405