Improve Gson and JsonParser trailing data handling

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

@@ -38,7 +38,6 @@
 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;
@@ -983,8 +982,7 @@ public <T> T fromJson(String json, Type typeOfT) throws JsonSyntaxException {
    */
   public <T> T fromJson(Reader json, Class<T> classOfT) throws JsonSyntaxException, JsonIOException {
     JsonReader jsonReader = newJsonReader(json);
-    Object object = fromJson(jsonReader, classOfT);
-    assertFullConsumption(object, jsonReader);
+    Object object = fromJson(jsonReader, classOfT, true);
     return Primitives.wrap(classOfT).cast(object);
   }
 
@@ -1013,49 +1011,29 @@ public <T> T fromJson(Reader json, Class<T> classOfT) throws JsonSyntaxException
   @SuppressWarnings("unchecked")
   public <T> T fromJson(Reader json, Type typeOfT) throws JsonIOException, JsonSyntaxException {
     JsonReader jsonReader = newJsonReader(json);
-    T object = (T) fromJson(jsonReader, typeOfT);
-    assertFullConsumption(object, jsonReader);
+    T object = (T) 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);
-    }
-  }
-
   /**
-   * Reads the next JSON value from {@code reader} and convert it to an object
-   * of type {@code typeOfT}. Returns {@code null}, if the {@code reader} is at EOF.
-   * Since Type is not parameterized by T, this method is type unsafe and should be used carefully.
-   *
-   * <p>Unlike the other {@code fromJson} methods, no exception is thrown if the JSON data has
-   * multiple top-level JSON elements, or if there is trailing data.
-   *
-   * <p>The JSON data is parsed in {@linkplain JsonReader#setLenient(boolean) lenient mode},
-   * regardless of the lenient mode setting of the provided reader. The lenient mode setting
-   * of the reader is restored once this method returns.
-   *
-   * @throws JsonIOException if there was a problem writing to the Reader
-   * @throws JsonSyntaxException if json is not a valid representation for an object of type
+   * @param requireEndDocument whether there must not be any trailing data after
+   *    the first read JSON element
    */
-  @SuppressWarnings("unchecked")
-  public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, JsonSyntaxException {
+  private <T> T fromJson(JsonReader reader, Type typeOfT, boolean requireEndDocument) throws JsonIOException, JsonSyntaxException {
     boolean isEmpty = true;
     boolean oldLenient = reader.isLenient();
     reader.setLenient(true);
     try {
       reader.peek();
       isEmpty = false;
+      @SuppressWarnings("unchecked") // this is not actually safe
       TypeToken<T> typeToken = (TypeToken<T>) TypeToken.get(typeOfT);
       TypeAdapter<T> typeAdapter = getAdapter(typeToken);
       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) {
       /*
@@ -1080,6 +1058,25 @@ public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, J
     }
   }
 
+  /**
+   * Reads the next JSON value from {@code reader} and convert it to an object
+   * of type {@code typeOfT}. Returns {@code null}, if the {@code reader} is at EOF.
+   * Since Type is not parameterized by T, this method is type unsafe and should be used carefully.
+   *
+   * <p>Unlike the other {@code fromJson} methods, no exception is thrown if the JSON data has
+   * multiple top-level JSON elements, or if there is trailing data.
+   *
+   * <p>The JSON data is parsed in {@linkplain JsonReader#setLenient(boolean) lenient mode},
+   * regardless of the lenient mode setting of the provided reader. The lenient mode setting
+   * of the reader is restored once this method returns.
+   *
+   * @throws JsonIOException if there was a problem writing to the Reader
+   * @throws JsonSyntaxException if json is not a valid representation for an object of type
+   */
+  public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, JsonSyntaxException {
+    return fromJson(reader, typeOfT, false);
+  }
+
   /**
    * This method deserializes the Json read from the specified parse tree into an object of the
    * specified type. It is not suitable to use if the specified class is a generic type since it

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;
 
@@ -46,7 +43,7 @@ public JsonParser() {}
    * @return a parse tree of {@link JsonElement}s corresponding to the specified JSON
    * @throws JsonParseException if the specified text is not valid JSON
    */
-  public static JsonElement parseString(String json) throws JsonSyntaxException {
+  public static JsonElement parseString(String json) throws JsonParseException {
     return parseReader(new StringReader(json));
   }
 
@@ -62,20 +59,25 @@ public static JsonElement parseString(String json) throws JsonSyntaxException {
    * @throws JsonParseException if there is an IOException or if the specified
    *     text is not valid JSON
    */
-  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);
     }
   }
 
@@ -91,19 +93,8 @@ public static JsonElement parseReader(Reader reader) throws JsonIOException, Jso
    * @throws JsonParseException if there is an IOException or if the specified
    *     text is not valid JSON
    */
-  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

@@ -23,6 +23,7 @@
 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;
@@ -39,13 +40,22 @@ private Streams() {
 
   /**
    * 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

@@ -62,7 +62,7 @@ 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 (value.isJsonNull()) {
       return null;
     }
@@ -162,5 +162,5 @@ private final class GsonContextImpl implements JsonSerializationContext, JsonDes
     @Override public <R> R deserialize(JsonElement json, Type typeOfT) throws JsonParseException {
       return (R) gson.fromJson(json, typeOfT);
     }
-  };
+  }
 }

gson/src/test/java/com/google/gson/GsonTest.java

@@ -16,11 +16,15 @@
 
 package com.google.gson;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
 import com.google.gson.internal.Excluder;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
 import com.google.gson.stream.MalformedJsonException;
 import java.io.IOException;
+import java.io.Reader;
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.lang.reflect.Field;
@@ -29,14 +33,14 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
-import junit.framework.TestCase;
+import org.junit.Test;
 
 /**
  * Unit tests for {@link Gson}.
  *
  * @author Ryan Harter
  */
-public final class GsonTest extends TestCase {
+public final class GsonTest {
 
   private static final Excluder CUSTOM_EXCLUDER = Excluder.DEFAULT
       .excludeFieldsWithoutExposeAnnotation()
@@ -51,6 +55,7 @@ public final class GsonTest extends TestCase {
   private static final ToNumberStrategy CUSTOM_OBJECT_TO_NUMBER_STRATEGY = ToNumberPolicy.DOUBLE;
   private static final ToNumberStrategy CUSTOM_NUMBER_TO_NUMBER_STRATEGY = ToNumberPolicy.LAZILY_PARSED_NUMBER;
 
+  @Test
   public void testOverridesDefaultExcluder() {
     Gson gson = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
@@ -66,6 +71,7 @@ public void testOverridesDefaultExcluder() {
     assertEquals(false, gson.htmlSafe());
   }
 
+  @Test
   public void testClonedTypeAdapterFactoryListsAreIndependent() {
     Gson original = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
@@ -89,6 +95,7 @@ private static final class TestTypeAdapter extends TypeAdapter<Object> {
     @Override public Object read(JsonReader in) throws IOException { return null; }
   }
 
+  @Test
   public void testNewJsonWriter_Default() throws IOException {
     StringWriter writer = new StringWriter();
     JsonWriter jsonWriter = new Gson().newJsonWriter(writer);
@@ -111,6 +118,7 @@ public void testNewJsonWriter_Default() throws IOException {
     assertEquals("{\"\\u003ctest2\":true}", writer.toString());
   }
 
+  @Test
   public void testNewJsonWriter_Custom() throws IOException {
     StringWriter writer = new StringWriter();
     JsonWriter jsonWriter = new GsonBuilder()
@@ -135,6 +143,7 @@ public void testNewJsonWriter_Custom() throws IOException {
     assertEquals(")]}'\n{\n  \"test\": null,\n  \"<test2\": true\n}1", writer.toString());
   }
 
+  @Test
   public void testNewJsonReader_Default() throws IOException {
     String json = "test"; // String without quotes
     JsonReader jsonReader = new Gson().newJsonReader(new StringReader(json));
@@ -146,6 +155,7 @@ public void testNewJsonReader_Default() throws IOException {
     jsonReader.close();
   }
 
+  @Test
   public void testNewJsonReader_Custom() throws IOException {
     String json = "test"; // String without quotes
     JsonReader jsonReader = new GsonBuilder()
@@ -155,4 +165,46 @@ public void testNewJsonReader_Custom() throws IOException {
     assertEquals("test", jsonReader.nextString());
     jsonReader.close();
   }
+
+  @Test
+  public void testFromJson_Reader_MultipleTopLevel() {
+    Gson gson = new Gson();
+    Reader reader = new StringReader("{}1");
+    try {
+      gson.fromJson(reader, Object.class);
+      fail();
+    } catch (JsonSyntaxException expected) {
+      assertEquals("JSON document was not fully consumed.", expected.getMessage());
+    }
+  }
+
+  @Test
+  public void testFromJson_Reader_MultipleTopLevel_Null() {
+    Gson gson = new Gson();
+    Reader reader = new StringReader("null[]");
+    try {
+      gson.fromJson(reader, Object.class);
+      fail();
+    } catch (JsonSyntaxException expected) {
+      assertEquals("JSON document was not fully consumed.", expected.getMessage());
+    }
+  }
+
+  @Test
+  public void testFromJson_JsonReader_MultipleTopLevel() {
+    Gson gson = new Gson();
+    String json = "{}1";
+    JsonReader jsonReader = new JsonReader(new StringReader(json));
+    Object object = gson.fromJson(jsonReader, Object.class);
+    assertEquals(Collections.emptyMap(), object);
+
+    object = gson.fromJson(jsonReader, Integer.class);
+    assertEquals(1, object);
+
+    try {
+      gson.fromJson(jsonReader, Object.class);
+      fail();
+    } catch (JsonSyntaxException expected) {
+    }
+  }
 }