Support up to 255 levels of nesting. (#349)

Closes: https://github.com/square/moshi/issues/348

moshi/src/main/java/com/squareup/moshi/JsonReader.java

@@ -18,6 +18,7 @@ package com.squareup.moshi;
 import java.io.Closeable;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import javax.annotation.CheckReturnValue;
@@ -176,13 +177,13 @@ import okio.ByteString;
  * of this class are not thread safe.
  */
 public abstract class JsonReader implements Closeable {
-  // The nesting stack. Using a manual array rather than an ArrayList saves 20%. This stack permits
-  // up to 32 levels of nesting including the top-level document. Deeper nesting is prone to trigger
-  // StackOverflowErrors.
+  // The nesting stack. Using a manual array rather than an ArrayList saves 20%. This stack will
+  // grow itself up to 256 levels of nesting including the top-level document. Deeper nesting is
+  // prone to trigger StackOverflowErrors.
   int stackSize = 0;
-  final int[] scopes = new int[32];
-  final String[] pathNames = new String[32];
-  final int[] pathIndices = new int[32];
+  int[] scopes = new int[32];
+  String[] pathNames = new String[32];
+  int[] pathIndices = new int[32];
 
   /** True to accept non-spec compliant JSON. */
   boolean lenient;
@@ -201,8 +202,13 @@ public abstract class JsonReader implements Closeable {
 
   final void pushScope(int newTop) {
     if (stackSize == scopes.length) {
+      if (stackSize == 256) {
         throw new JsonDataException("Nesting too deep at " + getPath());
       }
+      scopes = Arrays.copyOf(scopes, scopes.length * 2);
+      pathNames = Arrays.copyOf(pathNames, pathNames.length * 2);
+      pathIndices = Arrays.copyOf(pathIndices, pathIndices.length * 2);
+    }
     scopes[stackSize++] = newTop;
   }
 

moshi/src/main/java/com/squareup/moshi/JsonUtf8Writer.java

@@ -101,6 +101,7 @@ final class JsonUtf8Writer extends JsonWriter {
    */
   private JsonWriter open(int empty, String openBracket) throws IOException {
     beforeValue();
+    checkStack();
     pushScope(empty);
     pathIndices[stackSize - 1] = 0;
     sink.writeUtf8(openBracket);

moshi/src/main/java/com/squareup/moshi/JsonValueWriter.java

@@ -31,7 +31,7 @@ import static java.lang.Double.POSITIVE_INFINITY;
 
 /** Writes JSON by building a Java object comprising maps, lists, and JSON primitives. */
 final class JsonValueWriter extends JsonWriter {
-  private final Object[] stack = new Object[32];
+  Object[] stack = new Object[32];
   private @Nullable String deferredName;
 
   JsonValueWriter() {
@@ -47,9 +47,7 @@ final class JsonValueWriter extends JsonWriter {
   }
 
   @Override public JsonWriter beginArray() throws IOException {
-    if (stackSize == stack.length) {
-      throw new JsonDataException("Nesting too deep at " + getPath() + ": circular reference?");
-    }
+    checkStack();
     List<Object> list = new ArrayList<>();
     add(list);
     stack[stackSize] = list;
@@ -69,9 +67,7 @@ final class JsonValueWriter extends JsonWriter {
   }
 
   @Override public JsonWriter beginObject() throws IOException {
-    if (stackSize == stack.length) {
-      throw new JsonDataException("Nesting too deep at " + getPath() + ": circular reference?");
-    }
+    checkStack();
     Map<String, Object> map = new LinkedHashTreeMap<>();
     add(map);
     stack[stackSize] = map;

moshi/src/main/java/com/squareup/moshi/JsonWriter.java

@@ -18,6 +18,7 @@ package com.squareup.moshi;
 import java.io.Closeable;
 import java.io.Flushable;
 import java.io.IOException;
+import java.util.Arrays;
 import javax.annotation.CheckReturnValue;
 import javax.annotation.Nullable;
 import okio.BufferedSink;
@@ -121,13 +122,13 @@ import static com.squareup.moshi.JsonScope.NONEMPTY_OBJECT;
  * malformed JSON string will fail with an {@link IllegalStateException}.
  */
 public abstract class JsonWriter implements Closeable, Flushable {
-  // The nesting stack. Using a manual array rather than an ArrayList saves 20%. This stack permits
-  // up to 32 levels of nesting including the top-level document. Deeper nesting is prone to trigger
-  // StackOverflowErrors.
+  // The nesting stack. Using a manual array rather than an ArrayList saves 20%. This stack will
+  // grow itself up to 256 levels of nesting including the top-level document. Deeper nesting is
+  // prone to trigger StackOverflowErrors.
   int stackSize = 0;
-  final int[] scopes = new int[32];
-  final String[] pathNames = new String[32];
-  final int[] pathIndices = new int[32];
+  int[] scopes = new int[32];
+  String[] pathNames = new String[32];
+  int[] pathIndices = new int[32];
 
   /**
    * A string containing a full set of spaces for a single level of indentation, or null for no
@@ -155,10 +156,26 @@ public abstract class JsonWriter implements Closeable, Flushable {
     return scopes[stackSize - 1];
   }
 
-  final void pushScope(int newTop) {
-    if (stackSize == scopes.length) {
+  /** Before pushing a value on the stack this confirms that the stack has capacity. */
+  final boolean checkStack() {
+    if (stackSize != scopes.length) return false;
+
+    if (stackSize == 256) {
       throw new JsonDataException("Nesting too deep at " + getPath() + ": circular reference?");
     }
+
+    scopes = Arrays.copyOf(scopes, scopes.length * 2);
+    pathNames = Arrays.copyOf(pathNames, pathNames.length * 2);
+    pathIndices = Arrays.copyOf(pathIndices, pathIndices.length * 2);
+    if (this instanceof JsonValueWriter) {
+      ((JsonValueWriter) this).stack =
+          Arrays.copyOf(((JsonValueWriter) this).stack, ((JsonValueWriter) this).stack.length * 2);
+    }
+
+    return true;
+  }
+
+  final void pushScope(int newTop) {
     scopes[stackSize++] = newTop;
   }
 

moshi/src/test/java/com/squareup/moshi/JsonUtf8ReaderTest.java

@@ -1023,17 +1023,15 @@ public final class JsonUtf8ReaderTest {
   }
 
   @Test public void tooDeeplyNestedArrays() throws IOException {
-    JsonReader reader = newReader(
-        "[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]");
-    for (int i = 0; i < 31; i++) {
+    JsonReader reader = newReader(repeat("[", 256) + repeat("]", 256));
+    for (int i = 0; i < 255; i++) {
       reader.beginArray();
     }
     try {
       reader.beginArray();
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $[0][0][0][0][0][0][0][0][0][0][0][0][0]"
-          + "[0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0]");
+      assertThat(expected).hasMessage("Nesting too deep at $" + repeat("[0]", 255));
     }
   }
 
@@ -1041,12 +1039,12 @@ public final class JsonUtf8ReaderTest {
     // Build a JSON document structured like {"a":{"a":{"a":{"a":true}}}}, but 31 levels deep.
     String array = "{\"a\":%s}";
     String json = "true";
-    for (int i = 0; i < 32; i++) {
+    for (int i = 0; i < 256; i++) {
       json = String.format(array, json);
     }
 
     JsonReader reader = newReader(json);
-    for (int i = 0; i < 31; i++) {
+    for (int i = 0; i < 255; i++) {
       reader.beginObject();
       assertThat(reader.nextName()).isEqualTo("a");
     }
@@ -1054,8 +1052,7 @@ public final class JsonUtf8ReaderTest {
       reader.beginObject();
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage(
-          "Nesting too deep at $.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a");
+      assertThat(expected).hasMessage("Nesting too deep at $" + repeat(".a", 255));
     }
   }
 

moshi/src/test/java/com/squareup/moshi/JsonWriterTest.java

@@ -25,6 +25,7 @@ import org.junit.runners.Parameterized;
 import org.junit.runners.Parameterized.Parameter;
 import org.junit.runners.Parameterized.Parameters;
 
+import static com.squareup.moshi.TestUtil.repeat;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
 import static org.junit.Assume.assumeTrue;
@@ -434,15 +435,15 @@ public final class JsonWriterTest {
 
   @Test public void tooDeepNestingArrays() throws IOException {
     JsonWriter writer = factory.newWriter();
-    for (int i = 0; i < 31; i++) {
+    for (int i = 0; i < 255; i++) {
       writer.beginArray();
     }
     try {
       writer.beginArray();
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $[0][0][0][0][0][0][0][0][0][0][0][0][0]"
-          + "[0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0]: circular reference?");
+      assertThat(expected).hasMessage("Nesting too deep at $"
+          + repeat("[0]", 255) + ": circular reference?");
     }
   }
 
@@ -464,7 +465,7 @@ public final class JsonWriterTest {
 
   @Test public void tooDeepNestingObjects() throws IOException {
     JsonWriter writer = factory.newWriter();
-    for (int i = 0; i < 31; i++) {
+    for (int i = 0; i < 255; i++) {
       writer.beginObject();
       writer.name("a");
     }
@@ -472,8 +473,8 @@ public final class JsonWriterTest {
       writer.beginObject();
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a."
-          + "a.a.a.a.a.a.a.a.a.a.a.a: circular reference?");
+      assertThat(expected).hasMessage("Nesting too deep at $"
+          + repeat(".a", 255) + ": circular reference?");
     }
   }
 

moshi/src/test/java/com/squareup/moshi/MoshiTest.java

@@ -38,6 +38,7 @@ import okio.Buffer;
 import org.junit.Test;
 
 import static com.squareup.moshi.TestUtil.newReader;
+import static com.squareup.moshi.TestUtil.repeat;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
@@ -971,8 +972,8 @@ public final class MoshiTest {
       moshi.adapter(Object.class).toJson(map);
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a."
-          + "a.a.a.a.a.a.a.a.a.a.a.a: circular reference?");
+      assertThat(expected).hasMessage("Nesting too deep at $"
+          + repeat(".a", 255) + ": circular reference?");
     }
   }
 
@@ -984,8 +985,8 @@ public final class MoshiTest {
       moshi.adapter(Object.class).toJson(list);
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $[0][0][0][0][0][0][0][0][0][0][0][0][0]"
-          + "[0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0]: circular reference?");
+      assertThat(expected).hasMessage("Nesting too deep at $"
+          + repeat("[0]", 255) + ": circular reference?");
     }
   }
 
@@ -999,8 +1000,8 @@ public final class MoshiTest {
       moshi.adapter(Object.class).toJson(list);
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Nesting too deep at $[0].a[0].a[0].a[0].a[0].a[0].a[0].a[0]."
-          + "a[0].a[0].a[0].a[0].a[0].a[0].a[0].a[0]: circular reference?");
+      assertThat(expected).hasMessage("Nesting too deep at $[0]"
+          + repeat(".a[0]", 127) + ": circular reference?");
     }
   }
 

moshi/src/test/java/com/squareup/moshi/TestUtil.java

@@ -30,6 +30,14 @@ final class TestUtil {
     return new String(array);
   }
 
+  static String repeat(String s, int count) {
+    StringBuilder result = new StringBuilder(s.length() * count);
+    for (int i = 0; i < count; i++) {
+      result.append(s);
+    }
+    return result.toString();
+  }
+
   private TestUtil() {
     throw new AssertionError("No instances.");
   }