webdav: return 409 for PUT without parent collection

Aligning with the WebDAV RFC specification,
changes the server response for PUT operations that would
create a resource without an existing parent collection
from HTTP 404 Not Found to HTTP 409 Conflict.

RFC RFC4918, section 9.7.1

Fixes golang/go#67150

Change-Id: I5ce6c5ea147a6a450ef5ae2e0077eb0dce409743
Reviewed-on: https://go-review.googlesource.com/c/net/+/583055
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>

webdav/webdav.go

@@ -267,6 +267,9 @@ func (h *Handler) handlePut(w http.ResponseWriter, r *http.Request) (status int,
 
 	f, err := h.FileSystem.OpenFile(ctx, reqPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
+		if os.IsNotExist(err) {
+			return http.StatusConflict, err
+		}
 		return http.StatusNotFound, err
 	}
 	_, copyErr := io.Copy(f, r.Body)

webdav/webdav_test.go

@@ -347,3 +347,63 @@ func TestFilenameEscape(t *testing.T) {
 		}
 	}
 }
+
+func TestPutRequest(t *testing.T) {
+	h := &Handler{
+		FileSystem: NewMemFS(),
+		LockSystem: NewMemLS(),
+	}
+	srv := httptest.NewServer(h)
+	defer srv.Close()
+
+	do := func(method, urlStr string, body string) (*http.Response, error) {
+		bodyReader := strings.NewReader(body)
+		req, err := http.NewRequest(method, urlStr, bodyReader)
+		if err != nil {
+			return nil, err
+		}
+		res, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return nil, err
+		}
+		return res, nil
+	}
+
+	testCases := []struct {
+		name      string
+		urlPrefix string
+		want      int
+	}{{
+		name:      "put",
+		urlPrefix: "/res",
+		want:      http.StatusCreated,
+	}, {
+		name:      "put_utf8_segment",
+		urlPrefix: "/res-%e2%82%ac",
+		want:      http.StatusCreated,
+	}, {
+		name:      "put_empty_segment",
+		urlPrefix: "",
+		want:      http.StatusNotFound,
+	}, {
+		name:      "put_root_segment",
+		urlPrefix: "/",
+		want:      http.StatusNotFound,
+	}, {
+		name:      "put_no_parent [RFC4918:S9.7.1]",
+		urlPrefix: "/409me/noparent.txt",
+		want:      http.StatusConflict,
+	}}
+
+	for _, tc := range testCases {
+		urlStr := srv.URL + tc.urlPrefix
+		res, err := do("PUT", urlStr, "ABC\n")
+		if err != nil {
+			t.Errorf("name=%q: PUT: %v", tc.name, err)
+			continue
+		}
+		if res.StatusCode != tc.want {
+			t.Errorf("name=%q: got status code %d, want %d", tc.name, res.StatusCode, tc.want)
+		}
+	}
+}