fix: dc:source element caused a NullPointerException

The checks related to the HTML `source` element were run regardless of
the element namespace, and with lack of protective coding. This caused
an NPE when the markup contained `dc:source` elements.

This commit fixes the situation by:
- only applying `OPSHandler30` checks for the elements in the target
  namespace
- returning early when the `source` element preconditions aren't met,
  as these preconditions are checked by schema

Fix #1514

src/main/java/com/adobe/epubcheck/ops/OPSHandler30.java

@@ -334,109 +334,127 @@ public void startElement()
     processSectioning();
 
     String name = e.getName();
-    if (name.equals("html"))
-    {
-      vocabs = VocabUtil.parsePrefixDeclaration(
-          e.getAttributeNS(EpubConstants.EpubTypeNamespaceUri, "prefix"), RESERVED_VOCABS,
-          KNOWN_VOCAB_URIS, DEFAULT_VOCAB_URIS, report, location());
-    }
-    else if (EpubConstants.HtmlNamespaceUri.equals(e.getNamespace()) && name.equals("meta"))
-    {
-      processMeta();
-    }
-    else if (name.equals("form"))
-    {
-      requiredProperties.add(ITEM_PROPERTIES.SCRIPTED);
-    }
-    else if (name.equals("link"))
-    {
-      processLink();
-    }
-    else if (name.equals("math"))
+    if (EpubConstants.HtmlNamespaceUri.equals(e.getNamespace()))
     {
-      requiredProperties.add(ITEM_PROPERTIES.MATHML);
-      inMathML = true;
-      hasAltorAnnotation = (null != e.getAttribute("alttext"));
-      String altimg = e.getAttribute("altimg");
-      if (altimg != null)
+      if (name.equals("html"))
+      {
+        vocabs = VocabUtil.parsePrefixDeclaration(
+            e.getAttributeNS(EpubConstants.EpubTypeNamespaceUri, "prefix"), RESERVED_VOCABS,
+            KNOWN_VOCAB_URIS, DEFAULT_VOCAB_URIS, report, location());
+      }
+      else if (name.equals("meta"))
+      {
+        processMeta();
+      }
+      else if (name.equals("form"))
       {
-        super.checkImage(null, "altimg");
+        requiredProperties.add(ITEM_PROPERTIES.SCRIPTED);
+      }
+      else if (name.equals("link"))
+      {
+        processLink();
       }
 
-    }
-    else if (name.equals("svg"))
-    {
-      processSVG();
-    }
-    else if (EpubConstants.EpubTypeNamespaceUri.equals(e.getNamespace()) && name.equals("switch"))
-    {
-      requiredProperties.add(ITEM_PROPERTIES.SWITCH);
-    }
-    else if (name.equals("audio"))
-    {
-      startMediaElement();
-    }
-    else if (name.equals("video"))
-    {
-      processVideo();
-      startMediaElement();
-    }
-    else if (name.equals("figure"))
-    {
-      processFigure();
-    }
-    else if (name.equals("table"))
-    {
-      processTable();
-    }
-    else if (name.equals("track"))
-    {
-      startTrack();
-    }
-    else if (name.equals("a"))
-    {
-      anchorNeedsText = true;
-      processAnchor(e);
-    }
-    else if (name.equals("annotation-xml"))
-    {
-      hasAltorAnnotation = true;
-    }
-    else if (name.equals("input"))
-    {
-      startInput();
-    }
-    else if (name.equals("picture"))
-    {
-      inPicture = true;
-    }
-    else if (name.equals("source"))
-    {
-      if ("picture".equals(e.getParent().getName()))
+      else if (name.equals("audio"))
       {
-        checkImage(null, null);
+        startMediaElement();
       }
-      else // audio or video source
+      else if (name.equals("video"))
       {
-        startMediaSource();
+        processVideo();
+        startMediaElement();
+      }
+      else if (name.equals("figure"))
+      {
+        processFigure();
+      }
+      else if (name.equals("table"))
+      {
+        processTable();
+      }
+      else if (name.equals("track"))
+      {
+        startTrack();
+      }
+      else if (name.equals("a"))
+      {
+        anchorNeedsText = true;
+        processAnchor(e);
+      }
+      else if (name.equals("input"))
+      {
+        startInput();
+      }
+      else if (name.equals("picture"))
+      {
+        inPicture = true;
+      }
+      else if (name.equals("source"))
+      {
+        if ("picture".equals(e.getParent().getName()))
+        {
+          checkImage(null, null);
+        }
+        else // audio or video source
+        {
+          startMediaSource();
+        }
+      }
+      else if (name.equals("embed"))
+      {
+        startEmbed();
+      }
+      else if (name.equals("blockquote") || name.equals("q") || name.equals("ins")
+          || name.equals("del"))
+      {
+        checkCiteAttribute();
       }
     }
-    else if ("http://www.w3.org/2000/svg".equals(e.getNamespace()) && name.equals("title"))
-    {
-      hasLabel = true;
-    }
-    else if ("http://www.w3.org/2000/svg".equals(e.getNamespace()) && name.equals("text"))
+    else if ("http://www.w3.org/1998/Math/MathML".equals(e.getNamespace()))
     {
-      hasLabel = true;
+      if (name.equals("math"))
+      {
+        requiredProperties.add(ITEM_PROPERTIES.MATHML);
+        inMathML = true;
+        hasAltorAnnotation = (null != e.getAttribute("alttext"));
+        String altimg = e.getAttribute("altimg");
+        if (altimg != null)
+        {
+          super.checkImage(null, "altimg");
+        }
+
+      }
+      else if (name.equals("annotation-xml"))
+      {
+        hasAltorAnnotation = true;
+      }
     }
-    else if (name.equals("embed"))
+    else if ("http://www.w3.org/2000/svg".equals(e.getNamespace()))
     {
-      startEmbed();
+      if (name.equals("svg"))
+      {
+        processSVG();
+      }
+      else if (name.equals("a"))
+      {
+        anchorNeedsText = true;
+        processAnchor(e);
+      }
+      else if (name.equals("title"))
+      {
+        hasLabel = true;
+      }
+      else if (name.equals("text"))
+      {
+        hasLabel = true;
+      }
     }
-    else if (name.equals("blockquote") || name.equals("q") || name.equals("ins")
-        || name.equals("del"))
+    else if (EpubConstants.EpubTypeNamespaceUri.equals(e.getNamespace()))
     {
-      checkCiteAttribute();
+      if (name.equals("switch"))
+      {
+        requiredProperties.add(ITEM_PROPERTIES.SWITCH);
+      }
     }
 
     processInlineScripts();
@@ -595,10 +613,12 @@ protected void endMediaElement()
   protected void startMediaSource()
   {
     XMLElement elem = currentElement();
-    assert "source".equals(elem.getName())
-        && ("audio".equals(elem.getParent().getName())
-            || "video".equals(elem.getParent().getName()))
-        && elem.getParent().getAttribute("src") == null;
+    assert "source".equals(elem.getName());
+    if (!("audio".equals(elem.getParent().getName())
+        || "video".equals(elem.getParent().getName())))
+    {
+      return; // schema error was reported
+    }
 
     // check the `src` attribute
     URL url = checkResourceURL(elem.getAttribute("src"));

src/test/resources/epub3/06-content-document/content-document-xhtml.feature

@@ -551,6 +551,12 @@ Feature: EPUB 3 — Content Documents — XHTML
 
   #//TODO verify script core media types
 
+  #### source
+
+  Scenario: Verify non-HTML `source` elements are skipped
+    See https://github.com/w3c/epubcheck/issues/1514
+    When checking EPUB 'dc-source-valid'
+    Then no errors or warnings are reported
 
   ####  Style
 

src/test/resources/epub3/06-content-document/files/dc-source-valid/EPUB/content_001.xhtml

@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html xmlns:epub="http://www.idpf.org/2007/ops" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
+	lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<title>Minimal EPUB</title>
+	</head>
+	<body>
+		<h1>Loomings</h1>
+		<p>Call me Ishmael.</p>
+		<svg id="1" width="12cm" height="4cm" viewBox="0 0 1200 400" version="1.1"
+			xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"
+			xmlns:cc="http://web.resource.org/cc/" xmlns:dc="http://purl.org/dc/elements/1.1/">
+			<desc>Example</desc>
+			<metadata>
+				<cc:Work>
+					<dc:source>https://example.com</dc:source>
+				</cc:Work>
+			</metadata>
+		</svg>
+	</body>
+</html>

src/test/resources/epub3/06-content-document/files/dc-source-valid/EPUB/nav.xhtml

@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en" lang="en">
+	<head>
+		<meta charset="utf-8"/>
+		<title>Minimal Nav</title>
+	</head>
+	<body>
+		<nav epub:type="toc">
+			<ol>
+				<li><a href="content_001.xhtml">content 001</a></li>
+			</ol>
+		</nav>
+	</body>
+</html>

src/test/resources/epub3/06-content-document/files/dc-source-valid/EPUB/package.opf

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="q">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="q">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-06-14T00:00:01Z</meta>
+</metadata>
+<manifest>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml" properties="svg"/>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+</spine>
+</package>

src/test/resources/epub3/06-content-document/files/dc-source-valid/META-INF/container.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
+	<rootfiles>
+		<rootfile full-path="EPUB/package.opf" media-type="application/oebps-package+xml"/>
+	</rootfiles>
+</container>

src/test/resources/epub3/06-content-document/files/dc-source-valid/mimetype

@@ -0,0 +1 @@
+application/epub+zip