Improve Gson and JsonParser trailing data handling

extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java

@@ -178,6 +178,8 @@ public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType) {
   /**
    * Ensures that this factory will handle not just the given {@code baseType}, but any subtype
    * of that type.
+   *
+   * @return this
    */
   public RuntimeTypeAdapterFactory<T> recognizeSubtypes() {
     this.recognizeSubtypes = true;
@@ -190,6 +192,7 @@ public RuntimeTypeAdapterFactory<T> recognizeSubtypes() {
    *
    * @throws IllegalArgumentException if either {@code type} or {@code label}
    *     have already been registered on this type adapter.
+   * @return this
    */
   public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, String label) {
     if (type == null || label == null) {
@@ -209,6 +212,7 @@ public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, Str
    *
    * @throws IllegalArgumentException if either {@code type} or its simple name
    *     have already been registered on this type adapter.
+   * @return this
    */
   public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
     return registerSubtype(type, type.getSimpleName());

extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java

@@ -19,7 +19,10 @@
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonParseException;
+import com.google.gson.TypeAdapter;
 import com.google.gson.TypeAdapterFactory;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.reflect.TypeToken;
 import junit.framework.TestCase;
 
 public final class RuntimeTypeAdapterFactoryTest extends TestCase {
@@ -191,10 +194,10 @@ public void testSerializeCollidingTypeFieldName() {
   public void testSerializeWrappedNullValue() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class)
         .registerSubtype(CreditCard.class)
-        .registerSubtype(BankTransfer.class);    
+        .registerSubtype(BankTransfer.class);
     Gson gson = new GsonBuilder()
         .registerTypeAdapterFactory(billingAdapter)
-        .create();    
+        .create();
     String serialized = gson.toJson(new BillingInstrumentWrapper(null), BillingInstrumentWrapper.class);
     BillingInstrumentWrapper deserialized = gson.fromJson(serialized, BillingInstrumentWrapper.class);
     assertNull(deserialized.instrument);
@@ -229,4 +232,51 @@ static class BankTransfer extends BillingInstrument {
       this.bankAccount = bankAccount;
     }
   }
+
+  public void testJsonAdapterDelegate() throws Exception {
+    Gson gson = new Gson();
+    Shape shape = new Circle(25);
+    String json = gson.toJson(shape);
+    assertEquals("{\"radius\":25,\"type\":\"CIRCLE\"}", json);
+    shape = gson.fromJson(json, Shape.class);
+    assertEquals(25, ((Circle)shape).radius);
+
+    shape = new Square(15);
+    json = gson.toJson(shape);
+    assertEquals("{\"side\":15,\"type\":\"SQUARE\"}", json);
+    shape = gson.fromJson(json, Shape.class);
+    assertEquals(15, ((Square)shape).side);
+    assertEquals(ShapeType.SQUARE, shape.type);
+  }
+
+  @JsonAdapter(Shape.JsonAdapterFactory.class)
+  static class Shape {
+    final ShapeType type;
+    Shape(ShapeType type) { this.type = type; }
+
+    private static final class JsonAdapterFactory implements TypeAdapterFactory {
+      private static final RuntimeTypeAdapterFactory<Shape> delegate = RuntimeTypeAdapterFactory.of(Shape.class, "type", true)
+          .registerSubtype(Circle.class, ShapeType.CIRCLE.toString())
+          .registerSubtype(Square.class, ShapeType.SQUARE.toString());
+
+      @Override
+      public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+        return delegate.create(gson, type);
+      }
+    }
+  }
+
+  enum ShapeType {
+    SQUARE, CIRCLE
+  }
+
+  private static final class Circle extends Shape {
+    final int radius;
+    Circle(int radius) { super(ShapeType.CIRCLE); this.radius = radius; }
+  }
+
+  private static final class Square extends Shape {
+    final int side;
+    Square(int side) { super(ShapeType.SQUARE); this.side = side; }
+  }
 }

gson/src/main/java/com/google/gson/Gson.java

@@ -39,7 +39,6 @@
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
-import com.google.gson.stream.MalformedJsonException;
 import java.io.EOFException;
 import java.io.IOException;
 import java.io.Reader;
@@ -1119,23 +1118,10 @@ public <T> T fromJson(Reader json, Type typeOfT) throws JsonIOException, JsonSyn
    */
   public <T> T fromJson(Reader json, TypeToken<T> typeOfT) throws JsonIOException, JsonSyntaxException {
     JsonReader jsonReader = newJsonReader(json);
-    T object = fromJson(jsonReader, typeOfT);
-    assertFullConsumption(object, jsonReader);
+    T object = fromJson(jsonReader, typeOfT, true);
     return object;
   }
 
-  private static void assertFullConsumption(Object obj, JsonReader reader) {
-    try {
-      if (obj != null && reader.peek() != JsonToken.END_DOCUMENT) {
-        throw new JsonSyntaxException("JSON document was not fully consumed.");
-      }
-    } catch (MalformedJsonException e) {
-      throw new JsonSyntaxException(e);
-    } catch (IOException e) {
-      throw new JsonIOException(e);
-    }
-  }
-
   // fromJson(JsonReader, Class) is unfortunately missing and cannot be added now without breaking
   // source compatibility in certain cases, see https://github.com/google/gson/pull/1700#discussion_r973764414
 
@@ -1201,6 +1187,14 @@ public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, J
    * @see #fromJson(JsonReader, Type)
    */
   public <T> T fromJson(JsonReader reader, TypeToken<T> typeOfT) throws JsonIOException, JsonSyntaxException {
+    return fromJson(reader, typeOfT, false);
+  }
+
+  /**
+   * @param requireEndDocument whether there must not be any trailing data after
+   *    the first read JSON element
+   */
+  private <T> T fromJson(JsonReader reader, TypeToken<T> typeOfT, boolean requireEndDocument) throws JsonIOException, JsonSyntaxException {
     boolean isEmpty = true;
     boolean oldLenient = reader.isLenient();
     reader.setLenient(true);
@@ -1209,6 +1203,10 @@ public <T> T fromJson(JsonReader reader, TypeToken<T> typeOfT) throws JsonIOExce
       isEmpty = false;
       TypeAdapter<T> typeAdapter = getAdapter(typeOfT);
       T object = typeAdapter.read(reader);
+
+      if (requireEndDocument && reader.peek() != JsonToken.END_DOCUMENT) {
+        throw new JsonSyntaxException("JSON document was not fully consumed.");
+      }
       return object;
     } catch (EOFException e) {
       /*
@@ -1313,7 +1311,7 @@ public <T> T fromJson(JsonElement json, TypeToken<T> typeOfT) throws JsonSyntaxE
     if (json == null) {
       return null;
     }
-    return fromJson(new JsonTreeReader(json), typeOfT);
+    return fromJson(new JsonTreeReader(json), typeOfT, false);
   }
 
   static class FutureTypeAdapter<T> extends SerializationDelegatingTypeAdapter<T> {

gson/src/main/java/com/google/gson/JsonParser.java

@@ -17,9 +17,6 @@
 
 import com.google.gson.internal.Streams;
 import com.google.gson.stream.JsonReader;
-import com.google.gson.stream.JsonToken;
-import com.google.gson.stream.MalformedJsonException;
-import java.io.IOException;
 import java.io.Reader;
 import java.io.StringReader;
 
@@ -47,7 +44,7 @@ public JsonParser() {}
    * @throws JsonParseException if the specified text is not valid JSON
    * @since 2.8.6
    */
-  public static JsonElement parseString(String json) throws JsonSyntaxException {
+  public static JsonElement parseString(String json) throws JsonParseException {
     return parseReader(new StringReader(json));
   }
 
@@ -64,20 +61,25 @@ public static JsonElement parseString(String json) throws JsonSyntaxException {
    *     text is not valid JSON
    * @since 2.8.6
    */
-  public static JsonElement parseReader(Reader reader) throws JsonIOException, JsonSyntaxException {
+  public static JsonElement parseReader(Reader reader) throws JsonParseException {
+    JsonReader jsonReader = new JsonReader(reader);
+    return parseReader(jsonReader, true);
+  }
+
+  private static JsonElement parseReader(JsonReader reader, boolean requiredEndDocument)
+      throws JsonParseException {
+    boolean lenient = reader.isLenient();
+    reader.setLenient(true);
     try {
-      JsonReader jsonReader = new JsonReader(reader);
-      JsonElement element = parseReader(jsonReader);
-      if (!element.isJsonNull() && jsonReader.peek() != JsonToken.END_DOCUMENT) {
-        throw new JsonSyntaxException("Did not consume the entire document.");
-      }
-      return element;
-    } catch (MalformedJsonException e) {
-      throw new JsonSyntaxException(e);
-    } catch (IOException e) {
-      throw new JsonIOException(e);
+      return Streams.parse(reader, requiredEndDocument);
     } catch (NumberFormatException e) {
       throw new JsonSyntaxException(e);
+    } catch (StackOverflowError e) {
+      throw new JsonParseException("Failed parsing JSON source: " + reader + " to Json", e);
+    } catch (OutOfMemoryError e) {
+      throw new JsonParseException("Failed parsing JSON source: " + reader + " to Json", e);
+    } finally {
+      reader.setLenient(lenient);
     }
   }
 
@@ -94,19 +96,8 @@ public static JsonElement parseReader(Reader reader) throws JsonIOException, Jso
    *     text is not valid JSON
    * @since 2.8.6
    */
-  public static JsonElement parseReader(JsonReader reader)
-      throws JsonIOException, JsonSyntaxException {
-    boolean lenient = reader.isLenient();
-    reader.setLenient(true);
-    try {
-      return Streams.parse(reader);
-    } catch (StackOverflowError e) {
-      throw new JsonParseException("Failed parsing JSON source: " + reader + " to Json", e);
-    } catch (OutOfMemoryError e) {
-      throw new JsonParseException("Failed parsing JSON source: " + reader + " to Json", e);
-    } finally {
-      reader.setLenient(lenient);
-    }
+  public static JsonElement parseReader(JsonReader reader) throws JsonParseException {
+    return parseReader(reader, false);
   }
 
   /** @deprecated Use {@link JsonParser#parseString} */

gson/src/main/java/com/google/gson/JsonStreamParser.java

@@ -61,7 +61,7 @@ public final class JsonStreamParser implements Iterator<JsonElement> {
   public JsonStreamParser(String json) {
     this(new StringReader(json));
   }
-  
+
   /**
    * @param reader The data stream containing JSON elements concatenated to each other.
    * @since 1.4
@@ -71,7 +71,7 @@ public JsonStreamParser(Reader reader) {
     parser.setLenient(true);
     lock = new Object();
   }
-  
+
   /**
    * Returns the next available {@link JsonElement} on the reader. Throws a
    * {@link NoSuchElementException} if no element is available.
@@ -86,9 +86,9 @@ public JsonElement next() throws JsonParseException {
     if (!hasNext()) {
       throw new NoSuchElementException();
     }
-    
+
     try {
-      return Streams.parse(parser);
+      return Streams.parse(parser, false);
     } catch (StackOverflowError e) {
       throw new JsonParseException("Failed parsing JSON source to Json", e);
     } catch (OutOfMemoryError e) {

gson/src/main/java/com/google/gson/internal/Streams.java

@@ -20,9 +20,11 @@
 import com.google.gson.JsonIOException;
 import com.google.gson.JsonNull;
 import com.google.gson.JsonParseException;
+import com.google.gson.JsonParser;
 import com.google.gson.JsonSyntaxException;
 import com.google.gson.internal.bind.TypeAdapters;
 import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
 import com.google.gson.stream.MalformedJsonException;
 import java.io.EOFException;
@@ -38,15 +40,40 @@ private Streams() {
     throw new UnsupportedOperationException();
   }
 
+  /**
+   * @deprecated
+   *    This method is declared in an internal Gson class. Use the public API class {@link JsonParser}
+   *    (note that {@code JsonParser} parses JSON in lenient mode), or obtain the {@code TypeAdapter}
+   *    for {@code JsonElement} and use that for parsing:
+   *    <pre>{@code
+   *    TypeAdapter<JsonElement> adapter = gson.getAdapter(JsonElement.class);
+   *    JsonElement element = adapter.read(...);
+   *    }</pre>
+   */
+  // Only keeping this internal method because third-party projects depend on it
+  @Deprecated
+  public static JsonElement parse(JsonReader reader) {
+    return parse(reader, false);
+  }
+
   /**
    * Takes a reader in any state and returns the next value as a JsonElement.
+   *
+   * @param requireEndDocument whether there must not be any trailing data after
+   *    the JsonElement
    */
-  public static JsonElement parse(JsonReader reader) throws JsonParseException {
+  public static JsonElement parse(JsonReader reader, boolean requireEndDocument) throws JsonParseException {
     boolean isEmpty = true;
     try {
       reader.peek();
       isEmpty = false;
-      return TypeAdapters.JSON_ELEMENT.read(reader);
+      JsonElement element = TypeAdapters.JSON_ELEMENT.read(reader);
+
+      if (requireEndDocument && reader.peek() != JsonToken.END_DOCUMENT) {
+        throw new JsonSyntaxException("Did not consume the entire document.");
+      }
+      return element;
+
     } catch (EOFException e) {
       /*
        * For compatibility with JSON 1.5 and earlier, we return a JsonNull for

gson/src/main/java/com/google/gson/internal/bind/TreeTypeAdapter.java

@@ -69,7 +69,7 @@ public TreeTypeAdapter(JsonSerializer<T> serializer, JsonDeserializer<T> deseria
     if (deserializer == null) {
       return delegate().read(in);
     }
-    JsonElement value = Streams.parse(in);
+    JsonElement value = Streams.parse(in, false);
     if (nullSafe && value.isJsonNull()) {
       return null;
     }