Further reduce memory usage of JsonPointer (wrt #818) (#820)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/core/JsonPointer.java

@@ -65,9 +65,17 @@ public class JsonPointer implements Serializable
     /**
      * We will retain representation of the pointer, as a String,
      * so that {@link #toString} should be as efficient as possible.
+     *<p>
+     * NOTE: starting with 2.14, there is no accompanying
+     * {@link #_asStringOffset} that MUST be considered with this String;
      */
     protected final String _asString;
 
+    /**
+     * @since 2.14
+     */
+    protected final int _asStringOffset;
+    
     protected final String _matchingPropertyName;
 
     protected final int _matchingElementIndex;
@@ -88,21 +96,26 @@ protected JsonPointer() {
         _matchingPropertyName = null;
         _matchingElementIndex = -1;
         _asString = "";
+        _asStringOffset = 0;
     }
 
     // Constructor used for creating non-empty Segments
-    protected JsonPointer(String fullString, String segment, JsonPointer next) {
+    protected JsonPointer(String fullString, int fullStringOffset,
+            String segment, JsonPointer next)
+    {
         _asString = fullString;
+        _asStringOffset = fullStringOffset;
         _nextSegment = next;
         // Ok; may always be a property
         _matchingPropertyName = segment;
         // but could be an index, if parsable
         _matchingElementIndex = _parseIndex(segment);
     }
 
-    // @since 2.5
-    protected JsonPointer(String fullString, String segment, int matchIndex, JsonPointer next) {
+    protected JsonPointer(String fullString, int fullStringOffset,
+            String segment, int matchIndex, JsonPointer next) {
         _asString = fullString;
+        _asStringOffset = fullStringOffset;
         _nextSegment = next;
         _matchingPropertyName = segment;
         _matchingElementIndex = matchIndex;
@@ -199,11 +212,11 @@ public static JsonPointer forPath(JsonStreamContext context,
                 if (seg == null) { // is this legal?
                     seg = "";
                 }
-                tail = new JsonPointer(_fullPath(tail, seg), seg, tail);
+                tail = new JsonPointer(_fullPath(tail, seg), 0, seg, tail);
             } else if (context.inArray() || includeRoot) {
                 int ix = context.getCurrentIndex();
                 String ixStr = String.valueOf(ix);
-                tail = new JsonPointer(_fullPath(tail, ixStr), ixStr, ix, tail);
+                tail = new JsonPointer(_fullPath(tail, ixStr), 0, ixStr, ix, tail);
             }
             // NOTE: this effectively drops ROOT node(s); should have 1 such node,
             // as the last one, but we don't have to care (probably some paths have
@@ -517,7 +530,13 @@ public JsonPointer head() {
     /**********************************************************
      */
 
-    @Override public String toString() { return _asString; }
+    @Override public String toString() {
+        if (_asStringOffset <= 0) {
+            return _asString;
+        }
+        return _asString.substring(_asStringOffset);
+    }
+
     @Override public int hashCode() { return _asString.hashCode(); }
 
     @Override public boolean equals(Object o) {
@@ -563,21 +582,21 @@ private final static int _parseIndex(String str) {
         return NumberInput.parseInt(str);
     }
 
-    protected static JsonPointer _parseTail(String fullPath)
+    protected static JsonPointer _parseTail(final String fullPath)
     {
         PointerParent parent = null;
 
         // first char is the contextual slash, skip
         int i = 1;
-        int end = fullPath.length();
+        final int end = fullPath.length();
+        int startOffset = 0;
 
         while (i < end) {
             char c = fullPath.charAt(i);
             if (c == '/') { // common case, got a segment
-                parent = new PointerParent(parent, fullPath, fullPath.substring(1, i));
-                fullPath = fullPath.substring(i);
-                i = 1;
-                end = fullPath.length();
+                parent = new PointerParent(parent, startOffset, fullPath.substring(startOffset + 1, i));
+                startOffset = i;
+                ++i;
                 continue;
             }
             ++i;
@@ -591,10 +610,9 @@ protected static JsonPointer _parseTail(String fullPath)
                 if (i < 0) { // end!
                     return _buildPath(fullPath, segment, parent);
                 }
-                parent = new PointerParent(parent, fullPath, segment);
-                fullPath = fullPath.substring(i);
-                i = 1;
-                end = fullPath.length();
+                parent = new PointerParent(parent, startOffset, segment);
+                startOffset = i;
+                ++i;
                 continue;
             }
             // otherwise, loop on
@@ -603,11 +621,11 @@ protected static JsonPointer _parseTail(String fullPath)
         return _buildPath(fullPath, fullPath.substring(1), parent);
     }
 
-    private static JsonPointer _buildPath(String fullPath, String segment,
+    private static JsonPointer _buildPath(final String fullPath, String segment,
             PointerParent parent) {
-        JsonPointer curr = new JsonPointer(fullPath, segment, EMPTY);
+        JsonPointer curr = new JsonPointer(fullPath, 0, segment, EMPTY);
         for (; parent != null; parent = parent.parent) {
-            curr = new JsonPointer(parent.fullPath, parent.segment, curr);
+            curr = new JsonPointer(fullPath, parent.fullPathOffset, parent.segment, curr);
         }
         return curr;
     }
@@ -669,7 +687,9 @@ protected JsonPointer _constructHead()
         // and from that, length of suffix to drop
         int suffixLength = last._asString.length();
         JsonPointer next = _nextSegment;
-        return new JsonPointer(_asString.substring(0, _asString.length() - suffixLength), _matchingPropertyName,
+        // !!! TODO 07-Oct-2022, tatu: change to iterative, not recursive
+        return new JsonPointer(_asString.substring(0, _asString.length() - suffixLength), 0,
+                _matchingPropertyName,
                 _matchingElementIndex, next._constructHead(suffixLength, last));
     }
 
@@ -680,7 +700,9 @@ protected JsonPointer _constructHead(int suffixLength, JsonPointer last)
         }
         JsonPointer next = _nextSegment;
         String str = _asString;
-        return new JsonPointer(str.substring(0, str.length() - suffixLength), _matchingPropertyName,
+        // !!! TODO 07-Oct-2022, tatu: change to iterative, not recursive
+        return new JsonPointer(str.substring(0, str.length() - suffixLength), 0,
+                _matchingPropertyName,
                 _matchingElementIndex, next._constructHead(suffixLength, last));
     }
 
@@ -696,12 +718,12 @@ protected JsonPointer _constructHead(int suffixLength, JsonPointer last)
      */
     private static class PointerParent {
         public final PointerParent parent;
-        public final String fullPath;
+        public final int fullPathOffset;
         public final String segment;
 
-        PointerParent(PointerParent pp, String fp, String sgm) {
+        PointerParent(PointerParent pp, int fpo, String sgm) {
             parent = pp;
-            fullPath = fp;
+            fullPathOffset = fpo;
             segment = sgm;
         }
     }

src/test/java/com/fasterxml/jackson/core/fuzz/Fuzz51806JsonPointerParse818Test.java

@@ -7,8 +7,11 @@
 // (reported as [core#818]
 public class Fuzz51806JsonPointerParse818Test extends BaseTest
 {
-    // Before fix, looks like this is enough to cause StackOverflowError
-    private final static int TOO_DEEP_PATH = 10_000;
+    // Before fix, StackOverflowError with 6_000 or so,
+    // and OOME with 20_000.
+    // After fixes will get progressively slower so limit size to
+    // keep test runs from making suite too slow
+    private final static int TOO_DEEP_PATH = 25_000;
 
     // Verify that a very deep/long (by number of segments) JsonPointer
     // may still be parsed ok, for "simple" case (no quoted chars)
@@ -28,6 +31,16 @@ private void _testJsonPointer(String pathExpr)
         assertNotNull(p);
         // But also verify it didn't change
         assertEquals(pathExpr, p.toString());
+
+        // And then verify segment by segment, easiest way is to
+        // check that tail segment is proper substring
+        JsonPointer curr = p;
+
+        while ((curr = curr.tail()) != null) {
+            String act = curr.toString();
+            String exp = pathExpr.substring(pathExpr.length() - act.length());
+            assertEquals(exp, act);
+        }
     }
 
     private String _generatePath(int depth, boolean escaped) {