Support fragment references using $anchor (#500)

* refactor: use meta schema to get fragment ref node

* resolve $anchor instead of $id for fragment ref when meta schema uses it

Author: Whathecode

src/main/java/com/networknt/schema/JsonMetaSchema.java

@@ -361,7 +361,31 @@ public static Builder builder(String uri, JsonMetaSchema blueprint) {
     }
 
     public String readId(JsonNode schemaNode) {
-        JsonNode idNode = schemaNode.get(idKeyword);
+        return readText(schemaNode, idKeyword);
+    }
+
+    public JsonNode getNodeByFragmentRef(String ref, JsonNode node) {
+        boolean supportsAnchor = keywords.containsKey("$anchor");
+        String refName = supportsAnchor ? ref.substring(1) : ref;
+        String fieldToRead = supportsAnchor ? "$anchor" : idKeyword;
+
+        boolean nodeContainsRef = refName.equals(readText(node, fieldToRead));
+        if (nodeContainsRef) {
+            return node;
+        } else {
+            Iterator<JsonNode> children = node.elements();
+            while (children.hasNext()) {
+                JsonNode refNode = getNodeByFragmentRef(ref, children.next());
+                if (refNode != null) {
+                    return refNode;
+                }
+            }
+        }
+        return null;
+    }
+
+    private String readText(JsonNode node, String field) {
+        JsonNode idNode = node.get(field);
         if (idNode == null || !idNode.isTextual()) {
             return null;
         }
@@ -372,10 +396,6 @@ public String getUri() {
         return uri;
     }
 
-    public String getIdKeyword() {
-        return idKeyword;
-    }
-
 
     public JsonValidator newValidator(ValidationContext validationContext, String schemaPath, String keyword /* keyword */, JsonNode schemaNode,
                                       JsonSchema parentSchema, String customMessage) {

src/main/java/com/networknt/schema/JsonSchema.java

@@ -21,7 +21,6 @@
 import java.net.URLDecoder;
 import java.util.Collections;
 import java.util.Comparator;
-import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Map;
@@ -46,8 +45,8 @@
 public class JsonSchema extends BaseJsonValidator {
     private static final Pattern intPattern = Pattern.compile("^[0-9]+$");
     private Map<String, JsonValidator> validators;
-    private final String idKeyword;
     private final ValidationContext validationContext;
+    private final JsonMetaSchema metaSchema;
     private boolean validatorsLoaded = false;
 
     /**
@@ -82,7 +81,7 @@ private JsonSchema(ValidationContext validationContext, String schemaPath, URI c
               validationContext.getConfig() != null && validationContext.getConfig().isFailFast(),
               validationContext.getConfig() != null ? validationContext.getConfig().getApplyDefaultsStrategy() : null);
         this.validationContext = validationContext;
-        this.idKeyword = validationContext.getMetaSchema().getIdKeyword();
+        this.metaSchema = validationContext.getMetaSchema();
         this.currentUri = this.combineCurrentUriWithIds(currentUri, schemaNode);
         if (validationContext.getConfig() != null) {
             if (validationContext.getConfig().isOpenAPI3StyleDiscriminators()) {
@@ -156,7 +155,7 @@ public JsonNode getRefSchemaNode(String ref) {
                 }
             }
         } else if (ref.startsWith("#") && ref.length() > 1) {
-            node = getNodeById(ref, node);
+            node = metaSchema.getNodeByFragmentRef(ref, node);
             if (node == null) {
                 node = handleNullNode(ref, schema);
             }
@@ -180,29 +179,6 @@ private JsonNode handleNullNode(String ref, JsonSchema schema) {
         return null;
     }
 
-    private JsonNode getNodeById(String ref, JsonNode node) {
-        if (nodeContainsRef(ref, node)) {
-            return node;
-        } else {
-            Iterator<JsonNode> children = node.elements();
-            while (children.hasNext()) {
-                JsonNode refNode = getNodeById(ref, children.next());
-                if (refNode != null) {
-                    return refNode;
-                }
-            }
-        }
-        return null;
-    }
-
-    private boolean nodeContainsRef(String ref, JsonNode node) {
-        JsonNode id = node.get(idKeyword);
-        if (id != null) {
-            return ref.equals(id.asText());
-        }
-        return false;
-    }
-
     /**
      * Please note that the key in {@link #validators} map is a schema path. It is
      * used in {@link com.networknt.schema.walk.DefaultKeywordWalkListenerRunner} to derive the keyword.