Allow TokenFilter to preserve empty (#729)

nik9000 · web-flow · commit 8bed4d836204 · 2022-01-02T16:41:44.000-08:00
This creates two new method on `TokenFilter` which you can override to decide if empty arrays and objects should be included or excluded. Closes #715
diff --git a/src/main/java/com/fasterxml/jackson/core/filter/FilteringParserDelegate.java b/src/main/java/com/fasterxml/jackson/core/filter/FilteringParserDelegate.java
@@ -273,16 +273,22 @@ public JsonToken nextToken() throws IOException
                     _exposedContext = null;
                     if (ctxt.inArray()) {
                         t = delegate.getCurrentToken();
-// Is this guaranteed to work without further checks?
-//                        if (t != JsonToken.START_ARRAY) {
                         _currToken = t;
+                        if (_currToken == JsonToken.END_ARRAY) {
+                            _headContext = _headContext.getParent();
+                            _itemFilter = _headContext.getFilter();
+                        }
                         return t;
                     }
 
                     // 19-Jul-2021, tatu: [core#700]: following was commented out?!
                     // Almost! Most likely still have the current token;
                     // with the sole exception of FIELD_NAME
                     t = delegate.currentToken();
+                    if (t == JsonToken.END_OBJECT) {
+                        _headContext = _headContext.getParent();
+                        _itemFilter = _headContext.getFilter();
+                    }
                     if (t != JsonToken.FIELD_NAME) {
                         _currToken = t;
                         return t;
@@ -562,12 +568,15 @@ protected final JsonToken _nextToken2() throws IOException
                 continue main_loop;
 
             case ID_END_ARRAY:
-            case ID_END_OBJECT:
                 {
                     boolean returnEnd = _headContext.isStartHandled();
                     f = _headContext.getFilter();
                     if ((f != null) && (f != TokenFilter.INCLUDE_ALL)) {
+                        boolean includeEmpty = f.includeEmptyArray(_headContext.hasCurrentIndex());
                         f.filterFinishArray();
+                        if (includeEmpty) {
+                            return _nextBuffered(_headContext);
+                        }
                     }
                     _headContext = _headContext.getParent();
                     _itemFilter = _headContext.getFilter();
@@ -576,6 +585,23 @@ protected final JsonToken _nextToken2() throws IOException
                     }
                 }
                 continue main_loop;
+            case ID_END_OBJECT:
+                {
+                    boolean returnEnd = _headContext.isStartHandled();
+                    f = _headContext.getFilter();
+                    if ((f != null) && (f != TokenFilter.INCLUDE_ALL)) {
+                        boolean includeEmpty = f.includeEmptyArray(_headContext.hasCurrentName());
+                        f.filterFinishObject();
+                        if (includeEmpty) {
+                            return _nextBuffered(_headContext);
+                        }                    }
+                    _headContext = _headContext.getParent();
+                    _itemFilter = _headContext.getFilter();
+                    if (returnEnd) {
+                        return (_currToken = t);
+                    }
+                }
+                continue main_loop;
 
             case ID_FIELD_NAME:
                 {
@@ -708,13 +734,16 @@ protected final JsonToken _nextTokenWithBuffering(final TokenFilterContext buffR
                 continue main_loop;
 
             case ID_END_ARRAY:
-            case ID_END_OBJECT:
                 {
                     // Unlike with other loops, here we know that content was NOT
                     // included (won't get this far otherwise)
                     f = _headContext.getFilter();
                     if ((f != null) && (f != TokenFilter.INCLUDE_ALL)) {
+                        boolean includeEmpty = f.includeEmptyArray(_headContext.hasCurrentIndex());
                         f.filterFinishArray();
+                        if (includeEmpty) {
+                            return _nextBuffered(buffRoot);
+                        }
                     }
                     boolean gotEnd = (_headContext == buffRoot);
                     boolean returnEnd = gotEnd && _headContext.isStartHandled();
@@ -727,6 +756,33 @@ protected final JsonToken _nextTokenWithBuffering(final TokenFilterContext buffR
                     }
                 }
                 continue main_loop;
+            case ID_END_OBJECT:
+            {
+                // Unlike with other loops, here we know that content was NOT
+                // included (won't get this far otherwise)
+                f = _headContext.getFilter();
+                if ((f != null) && (f != TokenFilter.INCLUDE_ALL)) {
+                    boolean includeEmpty = f.includeEmptyObject(_headContext.hasCurrentName());
+                    f.filterFinishObject();
+                    if (includeEmpty) {
+                        _headContext._currentName = _headContext._parent == null
+                                ? null
+                                : _headContext._parent._currentName;
+                        _headContext._needToHandleName = false;
+                        return _nextBuffered(buffRoot);
+                    }
+                }
+                boolean gotEnd = (_headContext == buffRoot);
+                boolean returnEnd = gotEnd && _headContext.isStartHandled();
+
+                _headContext = _headContext.getParent();
+                _itemFilter = _headContext.getFilter();
+
+                if (returnEnd) {
+                    return t;
+                }
+            }
+            continue main_loop;
 
             case ID_FIELD_NAME:
                 {
diff --git a/src/main/java/com/fasterxml/jackson/core/filter/TokenFilter.java b/src/main/java/com/fasterxml/jackson/core/filter/TokenFilter.java
@@ -432,6 +432,14 @@ public boolean includeEmbeddedValue(Object value) {
         return _includeScalar();
     }
 
+    public boolean includeEmptyArray(boolean contentsFiltered) {
+        return false;
+    }
+
+    public boolean includeEmptyObject(boolean contentsFiltered) {
+        return false;
+    }
+
     /*
     /**********************************************************
     /* Overrides
diff --git a/src/main/java/com/fasterxml/jackson/core/filter/TokenFilterContext.java b/src/main/java/com/fasterxml/jackson/core/filter/TokenFilterContext.java
@@ -233,6 +233,16 @@ public TokenFilterContext closeArray(JsonGenerator gen) throws IOException
     {
         if (_startHandled) {
             gen.writeEndArray();
+        } else {
+            if ((_filter != null) && (_filter != TokenFilter.INCLUDE_ALL)) {
+                if (_filter.includeEmptyArray(hasCurrentIndex())) {
+                    if (_parent != null) {
+                        _parent._writePath(gen);
+                    }
+                    gen.writeStartArray();
+                    gen.writeEndArray();
+                }
+            }
         }
         if ((_filter != null) && (_filter != TokenFilter.INCLUDE_ALL)) {
             _filter.filterFinishArray();
@@ -244,6 +254,16 @@ public TokenFilterContext closeObject(JsonGenerator gen) throws IOException
     {
         if (_startHandled) {
             gen.writeEndObject();
+        } else {
+            if ((_filter != null) && (_filter != TokenFilter.INCLUDE_ALL)) {
+                if (_filter.includeEmptyObject(hasCurrentName())) {
+                    if (_parent != null) {
+                        _parent._writePath(gen);
+                    }
+                    gen.writeStartObject();
+                    gen.writeEndObject();
+                }
+            }
         }
         if ((_filter != null) && (_filter != TokenFilter.INCLUDE_ALL)) {
             _filter.filterFinishObject();
diff --git a/src/test/java/com/fasterxml/jackson/core/BaseTest.java b/src/test/java/com/fasterxml/jackson/core/BaseTest.java
@@ -451,11 +451,15 @@ protected String readAndWrite(JsonFactory f, JsonParser p) throws IOException
         g.disable(JsonGenerator.Feature.AUTO_CLOSE_JSON_CONTENT);
         try {
             while (p.nextToken() != null) {
+                System.err.println(p.currentToken() + "  " + p.currentName() + "  " + p.currentValue());
                 g.copyCurrentEvent(p);
             }
         } catch (IOException e) {
             g.flush();
-            fail("Unexpected problem during `readAndWrite`. Output so far: '"+sw+"'; problem: "+e);
+            throw new AssertionError(
+                    "Unexpected problem during `readAndWrite`. Output so far: '" +
+                            sw + "'; problem: " + e.getMessage(),
+                    e);
         }
         p.close();
         g.close();
diff --git a/src/test/java/com/fasterxml/jackson/core/filter/BasicGeneratorFilteringTest.java b/src/test/java/com/fasterxml/jackson/core/filter/BasicGeneratorFilteringTest.java
diff --git a/src/test/java/com/fasterxml/jackson/core/filter/BasicParserFilteringTest.java b/src/test/java/com/fasterxml/jackson/core/filter/BasicParserFilteringTest.java
