Allow font-size 0, handle different initial font-size values

DEVSIX-9614, DEVSIX-3591

Author: vitali-pr

src/main/java/com/itextpdf/html2pdf/css/apply/util/FontStyleApplierUtil.java

@@ -89,11 +89,9 @@ private FontStyleApplierUtil() {
      */
     public static void applyFontStyles(Map<String, String> cssProps, ProcessorContext context,
             IStylesContainer stylesContainer, IPropertyContainer element) {
-        float em = CssDimensionParsingUtils.parseAbsoluteLength(cssProps.get(CssConstants.FONT_SIZE));
-        float rem = context.getCssContext().getRootFontSize();
-        if (em != 0) {
-            element.setProperty(Property.FONT_SIZE, UnitValue.createPointValue(em));
-        }
+        final float em = CssDimensionParsingUtils.parseAbsoluteLength(cssProps.get(CssConstants.FONT_SIZE));
+        final float rem = context.getCssContext().getRootFontSize();
+        element.setProperty(Property.FONT_SIZE, UnitValue.createPointValue(em));
 
         if (cssProps.get(CssConstants.FONT_FAMILY) != null) {
             // TODO DEVSIX-2534

src/main/java/com/itextpdf/html2pdf/css/resolve/DefaultCssResolver.java

@@ -224,7 +224,19 @@ private Map<String, String> resolveStyles(INode element, CssContext context) {
             // Format to 4 decimal places to prevent differences between Java and C#
             elementStyles.put(CssConstants.FONT_SIZE, DecimalFormatUtil.formatNumber(absoluteFontSize, "0.####") + CssConstants.PT);
         } else {
-            elementStyles.put(CssConstants.FONT_SIZE, Float.toString(CssDimensionParsingUtils.parseAbsoluteFontSize(elementFontSize)) + CssConstants.PT);
+            float fontSize;
+            if (CssTypesValidationUtils.isInitialOrInheritOrUnset(elementFontSize)) {
+                // font-size is inheritable property so we can always process initial/inherit/unset identically
+                if (parentFontSizeStr == null) {
+                    fontSize = CssDimensionParsingUtils.parseAbsoluteFontSize(
+                            CssDefaults.getDefaultValue(CssConstants.FONT_SIZE));
+                } else {
+                    fontSize = CssDimensionParsingUtils.parseAbsoluteLength(parentFontSizeStr);
+                }
+            } else {
+                fontSize = CssDimensionParsingUtils.parseAbsoluteFontSize(elementFontSize);
+            }
+            elementStyles.put(CssConstants.FONT_SIZE, Float.toString(fontSize) + CssConstants.PT);
         }
 
         // Update root font size

src/test/java/com/itextpdf/html2pdf/HtmlConverterPdfUA1UA2Test.java

@@ -371,6 +371,16 @@ public void emptyTableDataCellTest(PdfUAConformance conformance) throws IOExcept
         convertToUaAndCheckCompliance(conformance, sourceHtml, destinationPdf, cmpPdf, null, true, null);
     }
 
+    @ParameterizedTest
+    @MethodSource("conformanceLevels")
+    public void zeroFontSizeTest(PdfUAConformance conformance) throws IOException, InterruptedException {
+        String sourceHtml = SOURCE_FOLDER + "zeroFontSize.html";
+
+        String cmpPdf = SOURCE_FOLDER + "cmp_zeroFontSizeUa" + conformance.getPart() + ".pdf";
+        String destinationPdf = DESTINATION_FOLDER + "zeroFontSizeUa" + conformance.getPart() + ".pdf";
+        convertToUaAndCheckCompliance(conformance, sourceHtml, destinationPdf, cmpPdf, null, true, null);
+    }
+
     @Test
     public void duplicateConformanceLevelAAndUAThrows() {
         ConverterProperties converterProperties = new ConverterProperties();

src/test/java/com/itextpdf/html2pdf/css/FontSizeTest.java

@@ -72,4 +72,25 @@ public void spacesInFontSizeValueTest() throws IOException, InterruptedException
     public void defaultFontDiffFontSizeSpanTest() throws IOException, InterruptedException {
         convertToPdfAndCompare("defaultFontDiffFontSizeSpan", sourceFolder, destinationFolder);
     }
+
+    @Test
+    @LogMessages(messages = {
+            @LogMessage(messageTemplate = StyledXmlParserLogMessageConstant.INVALID_CSS_PROPERTY_DECLARATION)
+    })
+    public void inheritedFontSizeTest() throws IOException, InterruptedException {
+        convertToPdfAndCompare("inheritedFontSize", sourceFolder, destinationFolder);
+    }
+
+    @Test
+    public void nestingTagsFontSizeTest() throws IOException, InterruptedException {
+        convertToPdfAndCompare("nestingTagsFontSize", sourceFolder, destinationFolder);
+    }
+
+    @Test
+    @LogMessages(messages = {
+            @LogMessage(messageTemplate = StyledXmlParserLogMessageConstant.INVALID_CSS_PROPERTY_DECLARATION, count = 2)
+    })
+    public void garbageFontSizeTest() throws IOException, InterruptedException {
+        convertToPdfAndCompare("garbageFontSize", sourceFolder, destinationFolder);
+    }
 }

src/test/resources/com/itextpdf/html2pdf/HtmlConverterPdfUA1UA2Test/cmp_zeroFontSizeUa1.pdf

@@ -0,0 +1,8 @@
+<html>
+<head>
+<meta charset="utf-8"/>
+<body>
+<p style="font-size: 9pt;font-family: Arial; line-height: 14pt;">Some Text.</p>
+<p style="font-size: 0px;font-family: Arial;">text2</p>
+</body>
+</html>