Extract _scale_url() for overridable scale URL generation

news/199.feature

@@ -0,0 +1,2 @@
+Extract ``_scale_url()`` method on ``ImageScale`` and ``ImageScaling`` for overridable scale URL generation. This allows custom image backends (e.g. Thumbor) to generate direct URLs by overriding a single method.
+@jensens

src/plone/namedfile/scaling.py

@@ -94,7 +94,6 @@ def __init__(self, context, request, **info):
         if self.data is None:
             self.data = getattr(self.context, self.fieldname)
 
-        url = self.context.absolute_url()
         extension = self.data.contentType.split("/")[-1].lower()
         if self.data.contentType == "image/svg+xml":
             extension = "svg"
@@ -103,21 +102,34 @@ def __init__(self, context, request, **info):
         else:
             name = info["fieldname"]
         self.__name__ = f"{name}.{extension}"
-        self.url = f"{url}/@@images/{self.__name__}"
+        self.url = self._scale_url(name, extension)
         self.srcset = info.get("srcset", [])
 
+    def _scale_url(self, uid, extension, base_url=None):
+        """Build the URL for an image scale.
+
+        Override this method to generate custom scale URLs, e.g. for
+        external image services like Thumbor.
+
+        :param uid: The unique scale identifier.
+        :param extension: The file extension (e.g. "jpeg", "png").
+        :param base_url: The base URL of the content object.
+            Defaults to ``self.context.absolute_url()``.
+        :returns: The full URL to the image scale.
+        """
+        if base_url is None:
+            base_url = self.context.absolute_url()
+        return f"{base_url}/@@images/{uid}.{extension}"
+
     def absolute_url(self):
         return self.url
 
     def srcset_attribute(self):
         _srcset_attr = []
         extension = self.data.contentType.split("/")[-1].lower()
         for scale in self.srcset:
-            _srcset_attr.append(
-                "{}/@@images/{}.{} {}x".format(
-                    self.context.absolute_url(), scale["uid"], extension, scale["scale"]
-                )
-            )
+            url = self._scale_url(scale["uid"], extension)
+            _srcset_attr.append(f"{url} {scale['scale']}x")
         srcset_attr = ", ".join(_srcset_attr)
         return srcset_attr
 
@@ -520,6 +532,22 @@ def available_sizes(self):
     def available_sizes(self, value):
         self._sizes = value
 
+    def _scale_url(self, uid, extension, base_url=None):
+        """Build the URL for an image scale.
+
+        Override this method to generate custom scale URLs, e.g. for
+        external image services like Thumbor.
+
+        :param uid: The unique scale identifier.
+        :param extension: The file extension (e.g. "jpeg", "png").
+        :param base_url: The base URL of the content object.
+            Defaults to ``self.context.absolute_url()``.
+        :returns: The full URL to the image scale.
+        """
+        if base_url is None:
+            base_url = self.context.absolute_url()
+        return f"{base_url}/@@images/{uid}.{extension}"
+
     def getImageSize(self, fieldname=None):
         if fieldname is not None:
             try:
@@ -776,9 +804,8 @@ def srcset(
             )
             if scale:
                 extension = scale["mimetype"].split("/")[-1].lower()
-                srcset_urls.append(
-                    f'{self.context.absolute_url()}/@@images/{scale["uid"]}.{extension} {scale["width"]}w'
-                )
+                url = self._scale_url(scale["uid"], extension)
+                srcset_urls.append(f"{url} {scale['width']}w")
 
         # then get the urls of the scales that are smaller than the original
         for width, height in self.available_sizes.values():
@@ -787,9 +814,8 @@ def srcset(
                     fieldname=fieldname, width=width, height=height, mode="scale"
                 )
                 extension = scale["mimetype"].split("/")[-1].lower()
-                srcset_urls.append(
-                    f'{self.context.absolute_url()}/@@images/{scale["uid"]}.{extension} {scale["width"]}w'
-                )
+                url = self._scale_url(scale["uid"], extension)
+                srcset_urls.append(f"{url} {scale['width']}w")
 
         attributes = {}
         if title is _marker:

src/plone/namedfile/tests/test_scaling.py

@@ -814,6 +814,79 @@ def testOversizedHighPixelDensityScale(self):
         self.assertEqual(foo.srcset[0]["scale"], 2)
 
 
+class TestScaleUrl(unittest.TestCase):
+    """Test the _scale_url override mechanism on ImageScale and ImageScaling."""
+
+    layer = PLONE_NAMEDFILE_INTEGRATION_TESTING
+
+    def setUp(self):
+        data = getFile("image.png")
+        item = DummyContent()
+        item.image = MockNamedImage(data, "image/png", "image.png")
+        self.layer["app"]._setOb("item", item)
+        self.item = self.layer["app"].item
+
+    def test_image_scaling_scale_url_default(self):
+        scaling = ImageScaling(self.item, None)
+        url = scaling._scale_url("abc-123", "jpeg")
+        self.assertEqual(url, f"{self.item.absolute_url()}/@@images/abc-123.jpeg")
+
+    def test_image_scaling_scale_url_custom_base(self):
+        scaling = ImageScaling(self.item, None)
+        url = scaling._scale_url("abc-123", "jpeg", base_url="http://example.com")
+        self.assertEqual(url, "http://example.com/@@images/abc-123.jpeg")
+
+    def test_image_scaling_scale_url_override(self):
+        """Subclasses can override _scale_url to produce custom URLs."""
+
+        class CustomScaling(ImageScaling):
+            def _scale_url(self, uid, extension, base_url=None):
+                return f"https://thumbor.example.com/{uid}.{extension}"
+
+        scaling = CustomScaling(self.item, None)
+        url = scaling._scale_url("abc-123", "jpeg")
+        self.assertEqual(url, "https://thumbor.example.com/abc-123.jpeg")
+
+    def test_image_scale_uses_scale_url(self):
+        """ImageScale.url should use _scale_url."""
+        scaling = ImageScaling(self.item, None)
+        scale = scaling.scale("image", width=100, height=100, pre=True)
+        # The url should follow the _scale_url pattern
+        self.assertIn("/@@images/", scale.url)
+        self.assertTrue(scale.url.endswith(".png"))
+
+    def test_image_scale_override(self):
+        """A custom ImageScale subclass can override _scale_url."""
+
+        class CustomImageScale(ImageScale):
+            def _scale_url(self, uid, extension, base_url=None):
+                return f"https://cdn.example.com/{uid}.{extension}"
+
+        class CustomScaling(ImageScaling):
+            _scale_view_class = CustomImageScale
+
+        scaling = CustomScaling(self.item, None)
+        scale = scaling.scale("image", width=100, height=100, pre=True)
+        self.assertTrue(scale.url.startswith("https://cdn.example.com/"))
+
+    def test_srcset_uses_scale_url(self):
+        """ImageScaling.srcset should use _scale_url for srcset URLs."""
+
+        class CustomScaling(ImageScaling):
+            def _scale_url(self, uid, extension, base_url=None):
+                return f"https://thumbor.example.com/{uid}.{extension}"
+
+        scaling = CustomScaling(self.item, None)
+        scaling.available_sizes = {
+            "mini": (200, 65536),
+            "thumb": (128, 128),
+            "tile": (64, 64),
+        }
+        tag = scaling.srcset("image", sizes="100vw", scale_in_src="mini")
+        # The srcset attribute URLs should use the custom _scale_url
+        self.assertIn("https://thumbor.example.com/", tag)
+
+
 class TestImgSrcSet(unittest.TestCase):
 
     layer = PLONE_NAMEDFILE_INTEGRATION_TESTING