Fallback to default image loading if loader returns nil

README.md

@@ -46,7 +46,7 @@ This gem parses the given HTML and layouts the following elements in a vertical
 
 All other elements are ignored, their content is added to the parent element. With a few exceptions, no CSS is processed. One exception is the `width` property of `img`, `td` and `th`, which may contain values in `cm`, `mm`, `px`, `pt`, `%` or `auto`. Another exception is the `rgb` or `cmyk` properties of the Prawn-specific `color` tag.
 
-If no explicit loader is given (see above), images are loaded from `http(s)` addresses or may be contained in the `src` attribute as base64 encoded data URIs. Prawn only supports `PNG` and `JPG`.
+If no explicit loader is given (see below), images are loaded from `http(s)` addresses or may be contained in the `src` attribute as base64 encoded data URIs. Prawn only supports `PNG` and `JPG`.
 
 ## Example
 
@@ -95,7 +95,7 @@ Beside these options handled by Prawn / prawn-table, the following values may be
   - `:placeholder`
     - `:too_large`: If the list content does not fit into the current bounding box, this text/callable is rendered instead. Defaults to '[list content too large]'.
 - `:image`
-  - `:loader`: A callable that accepts the `src` attribute as an argument an returns a value understood by Prawn's `image` method. Loads `http(s)` URLs and base64 encoded data URIs by default.
+  - `:loader`: A callable that accepts the `src` attribute as an argument an returns a value understood by Prawn's `image` method (e.g. an `IO` object). If no loader is configured or if it returns `nil`, `http(s)` URLs and base64 encoded data URIs are loaded.
   - `:placeholder`: If an image is not supported, this text/callable is rendered instead. Defaults to '[unsupported image]'.
 - `:iframe`
   - `:placeholder`: If the HTML contains IFrames, this text/callable is rendered instead.

lib/prawn/markup/processor/images.rb

@@ -57,10 +57,14 @@ def image_properties(src)
       end
 
       def load_image(src)
+        custom_load_image(src) ||
+          decode_base64_image(src) ||
+          load_remote_image(src)
+      end
+
+      def custom_load_image(src)
         if options[:image] && options[:image][:loader]
           options[:image][:loader].call(src)
-        else
-          decode_base64_image(src) || load_remote_image(src)
         end
       end
 

spec/prawn/markup/processor/images_spec.rb

@@ -72,10 +72,24 @@
   end
 
   context 'with custom loader' do
-    let(:options) { { image: { loader: ->(src) { "spec/fixtures/#{src}" } } } }
+    let(:loader) do
+      ->(src) do
+        match = src.match(/^fix:(.*?)$/)
+        "spec/fixtures/#{match[1]}" if match
+      end
+    end
+
+    let(:options) { { image: { loader: loader } } }
 
     it 'render image with custom loader' do
-      processor.parse('<p>hello</p><img src="logo.png"><p>world</p>')
+      processor.parse('<p>hello</p><img src="fix:logo.png"><p>world</p>')
+
+      expect(left_positions).to eq([left, left])
+      expect(top_positions).to eq([top, top - line - LOGO_DIMENSION.last - p_gap - 5].map(&:round))
+    end
+
+    it 'falls back to default if loader returns nil' do
+      processor.parse("<p>hello</p><img src=\"#{encode_image('logo.png')}\"><p>world</p>")
 
       expect(left_positions).to eq([left, left])
       expect(top_positions).to eq([top, top - line - LOGO_DIMENSION.last - p_gap - 5].map(&:round))