feat: improve fallback detection check

This commit updates fallback-related checks and refactors the code used
for checking references to publication resources.

The following checks are introduced or updated:

- `RSC-032` (new): reports foreign resources with no fallback used in
  content documents. Replaces `MED-001`, `MED-002`, and `CSS-010`
- `MED-003` now reports when an `img` element child of a `picture` element
  is not a core media type.
- `MED-001` is suppressed. It was used to report a video `poster` attribute
  did not reference a core image media type. It is now reported as `RSC-032`.
- `MED-002` is suppressed. It was used to report HTML elements referencing
  foreign resources without fallback. It is now reported as `RSC-032`.
- `CSS-010` is suppressed. It was used to report references to foreign
  stylesheets with no fallback. It is now reported as `RSC-032`.
- `OPF_040` is now reported when the `fallback` attribute of a package
  document `item` element does not points to an existing ID. This was
  previously implemented as a Schematron check (`RSC-005`) in EPUB 3.x.
- `OPF-013` is now a warning. It is reported when a MIME type declared
  inline in content (for instance with an HTML `type` attribute) does
  not match the MIME type declared in the package document.

The code is refactored as follows:
- the reference/resource registry functionality of the `XRefChecker`
  class is extracted to new top-level classes in the (new) package
  `org.w3c.epubcheck.references`.
  - `Resource` represents a publication resource
  - `ResourceRegistry` is a registry of `Resource` instances
  - `Reference` represents a reference (URL) used anywhere in content
  - `ReferenceRegistry` is a registry of `Reference` instances
  - `XRefChecker` is renamed to `ResourceReferencesChecker`.
  - `ValidationContext` contains optional references to `ResourceRegistry`
    and `ReferenceRegistry`.
  - fallback chain resolution is now done in a new `FallbackChainResolver`
    class, when building `OPFItem` instances from the builders created
    when parsing the package document.
  - `XMLHandler` has convenience methods used to register references
    to the `ReferenceRegistry`.

Fix #1304, Fix #1298.

src/main/java/com/adobe/epubcheck/api/EpubCheck.java

@@ -32,7 +32,7 @@
 
 import org.w3c.epubcheck.constants.MIMEType;
 import org.w3c.epubcheck.core.Checker;
-import org.w3c.epubcheck.url.URLUtils;
+import org.w3c.epubcheck.util.url.URLUtils;
 
 import com.adobe.epubcheck.messages.MessageId;
 import com.adobe.epubcheck.ocf.OCFChecker;

src/main/java/com/adobe/epubcheck/css/CSSHandler.java

@@ -19,16 +19,15 @@
 import org.idpf.epubcheck.util.css.CssGrammar.CssSelector;
 import org.idpf.epubcheck.util.css.CssGrammar.CssURI;
 import org.idpf.epubcheck.util.css.CssLocation;
-import org.w3c.epubcheck.url.URLChecker;
+import org.w3c.epubcheck.core.references.URLChecker;
+import org.w3c.epubcheck.core.references.Reference;
 
 import com.adobe.epubcheck.api.EPUBLocation;
 import com.adobe.epubcheck.api.Report;
 import com.adobe.epubcheck.messages.MessageId;
 import com.adobe.epubcheck.opf.OPFChecker;
 import com.adobe.epubcheck.opf.OPFChecker30;
 import com.adobe.epubcheck.opf.ValidationContext;
-import com.adobe.epubcheck.opf.XRefChecker;
-import com.adobe.epubcheck.opf.XRefChecker.Type;
 import com.adobe.epubcheck.util.EPUBVersion;
 import com.adobe.epubcheck.util.FeatureEnum;
 import com.adobe.epubcheck.vocab.PackageVocabs;
@@ -42,7 +41,6 @@
 public class CSSHandler implements CssContentHandler, CssErrorHandler
 {
   final ValidationContext context;
-  final XRefChecker xrefChecker;
   final Report report;
   final EPUBVersion version;
   int startingLineNumber = 0; // append to line info from css parser
@@ -69,7 +67,6 @@ public class CSSHandler implements CssContentHandler, CssErrorHandler
   public CSSHandler(ValidationContext context)
   {
     this.context = context;
-    this.xrefChecker = context.xrefChecker.orNull();
     this.report = context.report;
     this.version = context.version;
     this.urlChecker = new URLChecker(context);
@@ -159,7 +156,7 @@ else if (uriOrString.getType() == CssConstruct.Type.STRING)
         }
         if (uri != null)
         {
-          resolveAndRegister(uri, line, col, atRule.toCssString(), Type.GENERIC);
+          resolveAndRegister(uri, line, col, atRule.toCssString(), Reference.Type.GENERIC);
         }
       }
     }
@@ -322,10 +319,10 @@ else if (propertyName.equals("src"))
           if (construct.getType() == CssConstruct.Type.URI)
           {
             URL fontURL = parsedURLs.get(((CssURI) construct).toUriString());
-            if (fontURL != null)
+            if (fontURL != null && context.resourceRegistry.isPresent())
             {
               // check font mimetypes
-              String fontMimeType = xrefChecker.getMimeType(fontURL);
+              String fontMimeType = context.getMimeType(fontURL);
               if (fontMimeType != null)
               {
                 boolean blessed = true;
@@ -367,12 +364,13 @@ private void registerURIs(List<CssConstruct> constructs, int line, int col)
       if (construct.getType() == CssConstruct.Type.URI)
       {
         resolveAndRegister(((CssURI) construct).toUriString(), line, col, construct.toCssString(),
-            inFontFace ? Type.FONT : Type.GENERIC);
+            inFontFace ? Reference.Type.FONT : Reference.Type.GENERIC);
       }
     }
   }
 
-  private void resolveAndRegister(String uriString, int line, int col, String cssContext, Type type)
+  private void resolveAndRegister(String uriString, int line, int col, String cssContext,
+      Reference.Type type)
   {
     if (uriString != null && uriString.trim().length() > 0)
     {
@@ -386,9 +384,9 @@ private void resolveAndRegister(String uriString, int line, int col, String cssC
         URL url = urlChecker.checkURL(uriString, getCorrectedEPUBLocation(line, col, cssContext));
         parsedURLs.put(uriString, url);
 
-        if (url != null)
+        if (url != null && context.referenceRegistry.isPresent())
         {
-          xrefChecker.registerReference(url, type, getCorrectedEPUBLocation(line, col, cssContext));
+          context.referenceRegistry.get().registerReference(url, type, getCorrectedEPUBLocation(line, col, cssContext));
           if (context.isRemote(url))
           {
             detectedProperties.add(ITEM_PROPERTIES.REMOTE_RESOURCES);

src/main/java/com/adobe/epubcheck/dict/SearchKeyMapHandler.java

@@ -1,7 +1,8 @@
 package com.adobe.epubcheck.dict;
 
+import org.w3c.epubcheck.core.references.Reference;
+
 import com.adobe.epubcheck.opf.ValidationContext;
-import com.adobe.epubcheck.opf.XRefChecker.Type;
 import com.adobe.epubcheck.xml.handlers.XMLHandler;
 import com.adobe.epubcheck.xml.model.XMLElement;
 
@@ -39,10 +40,7 @@ else if ("match".equals(name))
   private void processRef()
   {
     URL ref = checkURL(currentElement().getAttribute("href"));
-    if (ref != null && context.xrefChecker.isPresent())
-    {
-      context.xrefChecker.get().registerReference(ref, Type.SEARCH_KEY, location());
-    }
+    registerReference(ref, Reference.Type.SEARCH_KEY);
   }
 
 }

src/main/java/com/adobe/epubcheck/dtbook/DTBookHandler.java

@@ -22,9 +22,10 @@
 
 package com.adobe.epubcheck.dtbook;
 
+import org.w3c.epubcheck.core.references.Reference;
+
 import com.adobe.epubcheck.messages.MessageId;
 import com.adobe.epubcheck.opf.ValidationContext;
-import com.adobe.epubcheck.opf.XRefChecker;
 import com.adobe.epubcheck.util.FeatureEnum;
 import com.adobe.epubcheck.util.URISchemes;
 import com.adobe.epubcheck.xml.handlers.XMLHandler;
@@ -34,12 +35,10 @@
 
 public class DTBookHandler extends XMLHandler
 {
-  private final XRefChecker xrefChecker;
 
   public DTBookHandler(ValidationContext context)
   {
     super(context);
-    this.xrefChecker = context.xrefChecker.get();
   }
 
   @Override
@@ -51,11 +50,15 @@ public void startElement()
     if (ns.equals("http://www.daisy.org/z3986/2005/dtbook/"))
     {
       // Register IDs
-      xrefChecker.registerID(e.getAttribute("id"), XRefChecker.Type.GENERIC, location());
+      if (context.resourceRegistry.isPresent())
+      {
+        context.resourceRegistry.get().registerID(e.getAttribute("id"), Reference.Type.GENERIC,
+            location().url);
+      }
 
       // Check cross-references (link@href | a@href | img@src)
       URL url = null;
-      XRefChecker.Type type = XRefChecker.Type.GENERIC;
+      Reference.Type type = Reference.Type.GENERIC;
       /*
        * This section checks to see if the references used are registered
        * schema-types and whether they point to external resources. The
@@ -68,8 +71,9 @@ public void startElement()
 
         if (url != null && "true".equals(e.getAttribute("external")))
         {
-          //FIXME 2022 check that external attribute is set for remote URLs
-          if (context.isRemote(url)) {
+          // FIXME 2022 check that external attribute is set for remote URLs
+          if (context.isRemote(url))
+          {
             report.info(path, FeatureEnum.REFERENCE, url.toString());
             if (!URISchemes.contains(url.scheme()))
             {
@@ -86,12 +90,12 @@ else if (name.equals("link"))
       else if (name.equals("img"))
       {
         url = checkURL(e.getAttribute("src"));
-        type = XRefChecker.Type.IMAGE;
+        type = Reference.Type.IMAGE;
       }
 
       if (url != null)
       {
-        xrefChecker.registerReference(url, type, location());
+        registerReference(url, type);
         if (context.isRemote(url))
         {
           report.info(path, FeatureEnum.REFERENCE, url.toString());

src/main/java/com/adobe/epubcheck/messages/DefaultSeverities.java

@@ -144,8 +144,8 @@ private void initialize()
     severities.put(MessageId.HTM_058, Severity.ERROR);
 
     // Media
-    severities.put(MessageId.MED_001, Severity.ERROR);
-    severities.put(MessageId.MED_002, Severity.ERROR);
+    severities.put(MessageId.MED_001, Severity.SUPPRESSED);
+    severities.put(MessageId.MED_002, Severity.SUPPRESSED);
     severities.put(MessageId.MED_003, Severity.ERROR);
     severities.put(MessageId.MED_004, Severity.ERROR);
     severities.put(MessageId.MED_005, Severity.ERROR);
@@ -205,7 +205,7 @@ private void initialize()
     severities.put(MessageId.OPF_010, Severity.ERROR);
     severities.put(MessageId.OPF_011, Severity.ERROR);
     severities.put(MessageId.OPF_012, Severity.ERROR);
-    severities.put(MessageId.OPF_013, Severity.ERROR);
+    severities.put(MessageId.OPF_013, Severity.WARNING);
     severities.put(MessageId.OPF_014, Severity.ERROR);
     severities.put(MessageId.OPF_015, Severity.ERROR);
     severities.put(MessageId.OPF_016, Severity.ERROR);
@@ -348,6 +348,7 @@ private void initialize()
     severities.put(MessageId.RSC_029, Severity.ERROR);
     severities.put(MessageId.RSC_030, Severity.ERROR);
     severities.put(MessageId.RSC_031, Severity.WARNING);
+    severities.put(MessageId.RSC_032, Severity.ERROR);
 
     // Scripting
     severities.put(MessageId.SCP_001, Severity.SUPPRESSED); // checking scripts is out of scope

src/main/java/com/adobe/epubcheck/messages/MessageId.java

@@ -342,6 +342,7 @@ public enum MessageId implements Comparable<MessageId>
   RSC_029("RSC-029"),
   RSC_030("RSC-030"),
   RSC_031("RSC-031"),
+  RSC_032("RSC-032"),
 
   // Messages relating to scripting
   SCP_001("SCP-001"),

src/main/java/com/adobe/epubcheck/nav/NavHandler.java

@@ -3,9 +3,10 @@
 import java.util.EnumSet;
 import java.util.Set;
 
+import org.w3c.epubcheck.core.references.Reference;
+
 import com.adobe.epubcheck.messages.MessageId;
 import com.adobe.epubcheck.opf.ValidationContext;
-import com.adobe.epubcheck.opf.XRefChecker;
 import com.adobe.epubcheck.ops.OPSHandler30;
 import com.adobe.epubcheck.util.EpubConstants;
 import com.adobe.epubcheck.util.FeatureEnum;
@@ -78,12 +79,11 @@ public void startElement()
         // cross-reference checker, to be able to check that they are in reading
         // order
         // after all the Content Documents have been parsed
-        else if ((NavType.TOC__PAGE_LIST.contains(currentNavType)) && xrefChecker.isPresent())
+        else if (NavType.TOC__PAGE_LIST.contains(currentNavType))
         {
-          xrefChecker.get().registerReference(url,
-              (currentNavType == NavType.TOC) ? XRefChecker.Type.NAV_TOC_LINK
-                  : XRefChecker.Type.NAV_PAGELIST_LINK,
-              location());
+          registerReference(url,
+              (currentNavType == NavType.TOC) ? Reference.Type.NAV_TOC_LINK
+                  : Reference.Type.NAV_PAGELIST_LINK);
         }
       }
     }

src/main/java/com/adobe/epubcheck/ncx/NCXHandler.java

@@ -22,9 +22,10 @@
 
 package com.adobe.epubcheck.ncx;
 
+import org.w3c.epubcheck.core.references.Reference;
+
 import com.adobe.epubcheck.messages.MessageId;
 import com.adobe.epubcheck.opf.ValidationContext;
-import com.adobe.epubcheck.opf.XRefChecker;
 import com.adobe.epubcheck.util.FeatureEnum;
 import com.adobe.epubcheck.xml.handlers.XMLHandler;
 import com.adobe.epubcheck.xml.model.XMLElement;
@@ -33,14 +34,12 @@
 
 public class NCXHandler extends XMLHandler
 {
-  private final XRefChecker xrefChecker;
   private static final String TEXT = "text"; 
   String uid;
 
   public NCXHandler(ValidationContext context)
   {
     super(context);
-    this.xrefChecker = context.xrefChecker.get();
   }
 
   @Override
@@ -76,7 +75,7 @@ public void startElement()
           {
             report.info(path, FeatureEnum.REFERENCE, srcURL.toString());
           }
-          xrefChecker.registerReference(srcURL, XRefChecker.Type.HYPERLINK, location());
+          registerReference(srcURL, Reference.Type.HYPERLINK);
         }
       }
       else if ("meta".equals(name))

src/main/java/com/adobe/epubcheck/ocf/OCFChecker.java

@@ -48,8 +48,6 @@
 import com.adobe.epubcheck.opf.OPFItem;
 import com.adobe.epubcheck.opf.ValidationContext;
 import com.adobe.epubcheck.opf.ValidationContext.ValidationContextBuilder;
-import com.adobe.epubcheck.opf.XRefChecker;
-import com.adobe.epubcheck.overlay.OverlayTextChecker;
 import com.adobe.epubcheck.util.CheckUtil;
 import com.adobe.epubcheck.util.EPUBVersion;
 import com.adobe.epubcheck.util.FeatureEnum;
@@ -170,8 +168,6 @@ public void check()
 
       opfContext.container(container);
       opfContext.pubTypes(state.getPublicationTypes(packageDoc));
-      opfContext.xrefChecker(new XRefChecker(state.context().build()));
-      opfContext.overlayTextChecker(new OverlayTextChecker());
 
       Checker opfChecker = CheckerFactory.newChecker(opfContext.build());
       assert opfChecker instanceof OPFChecker;

src/main/java/com/adobe/epubcheck/ocf/OCFContainer.java

@@ -7,7 +7,7 @@
 import java.util.Set;
 import java.util.UUID;
 
-import org.w3c.epubcheck.url.URLUtils;
+import org.w3c.epubcheck.util.url.URLUtils;
 
 import com.adobe.epubcheck.ocf.encryption.EncryptionFilter;
 import com.adobe.epubcheck.util.GenericResourceProvider;