Allow width and height attributes for img tags

reader/sanitizer/sanitizer.go

@@ -113,6 +113,10 @@ func sanitizeAttributes(baseURL, tagName string, attributes []html.Attribute) ([
 			value = sanitizeSrcsetAttr(baseURL, value)
 		}
 
+		if tagName == "img" && (attribute.Key == "width" || attribute.Key == "height") && !isPositiveInteger(value) {
+			continue
+		}
+
 		if isExternalResourceAttribute(attribute.Key) {
 			if tagName == "iframe" {
 				if isValidIframeSource(baseURL, attribute.Val) {
@@ -350,7 +354,7 @@ func isValidIframeSource(baseURL, src string) bool {
 
 func getTagAllowList() map[string][]string {
 	whitelist := make(map[string][]string)
-	whitelist["img"] = []string{"alt", "title", "src", "srcset", "sizes"}
+	whitelist["img"] = []string{"alt", "title", "src", "srcset", "sizes", "width", "height"}
 	whitelist["picture"] = []string{}
 	whitelist["audio"] = []string{"src"}
 	whitelist["video"] = []string{"poster", "height", "width", "src"}
@@ -511,3 +515,10 @@ func isValidDataAttribute(value string) bool {
 	}
 	return false
 }
+
+func isPositiveInteger(value string) bool {
+	if number, err := strconv.Atoi(value); err == nil {
+		return number > 0
+	}
+	return false
+}

reader/sanitizer/sanitizer_test.go

@@ -15,6 +15,26 @@ func TestValidInput(t *testing.T) {
 	}
 }
 
+func TestImgWithWidthAndHeightAttribute(t *testing.T) {
+	input := `<img src="https://example.org/image.png" width="10" height="20">`
+	expected := `<img src="https://example.org/image.png" width="10" height="20" loading="lazy">`
+	output := Sanitize("http://example.org/", input)
+
+	if output != expected {
+		t.Errorf(`Wrong output: %s`, output)
+	}
+}
+
+func TestImgWithIncorrectWidthAndHeightAttribute(t *testing.T) {
+	input := `<img src="https://example.org/image.png" width="10px" height="20px">`
+	expected := `<img src="https://example.org/image.png" loading="lazy">`
+	output := Sanitize("http://example.org/", input)
+
+	if output != expected {
+		t.Errorf(`Wrong output: %s`, output)
+	}
+}
+
 func TestImgWithTextDataURL(t *testing.T) {
 	input := `<img src="data:text/plain;base64,SGVsbG8sIFdvcmxkIQ==" alt="Example">`
 	expected := ``
@@ -57,7 +77,7 @@ func TestSourceWithSrcsetAndMedia(t *testing.T) {
 
 func TestMediumImgWithSrcset(t *testing.T) {
 	input := `<img alt="Image for post" class="t u v ef aj" src="https://miro.medium.com/max/5460/1*aJ9JibWDqO81qMfNtqgqrw.jpeg" srcset="https://miro.medium.com/max/552/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 276w, https://miro.medium.com/max/1000/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 500w" sizes="500px" width="2730" height="3407">`
-	expected := `<img alt="Image for post" src="https://miro.medium.com/max/5460/1*aJ9JibWDqO81qMfNtqgqrw.jpeg" srcset="https://miro.medium.com/max/552/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 276w, https://miro.medium.com/max/1000/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 500w" sizes="500px" loading="lazy">`
+	expected := `<img alt="Image for post" src="https://miro.medium.com/max/5460/1*aJ9JibWDqO81qMfNtqgqrw.jpeg" srcset="https://miro.medium.com/max/552/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 276w, https://miro.medium.com/max/1000/1*aJ9JibWDqO81qMfNtqgqrw.jpeg 500w" sizes="500px" width="2730" height="3407" loading="lazy">`
 	output := Sanitize("http://example.org/", input)
 
 	if output != expected {