Add test cases for invalid input

src/main/java/org/json/JSONObject.java

@@ -225,12 +225,19 @@ public class JSONObject {
             throw x.syntaxError("A JSONObject text must begin with '{'");
         }
         for (;;) {
+            char prev = x.getPrevious();
             c = x.nextClean();
             switch (c) {
             case 0:
                 throw x.syntaxError("A JSONObject text must end with '}'");
             case '}':
                 return;
+            case '{':
+            case '[':
+                if(prev=='{') {
+                    throw x.syntaxError("A JSON Object can not directly nest another JSON Object or JSON Array.");
+                }
+                // fall through
             default:
                 x.back();
                 key = x.nextValue().toString();

src/main/java/org/json/JSONTokener.java

@@ -209,6 +209,12 @@ public class JSONTokener {
         this.previous = (char) c;
         return this.previous;
     }
+    
+    /**
+     * Get the last character read from the input or '\0' if nothing has been read yet.
+     * @return the last character read from the input.
+     */
+    protected char getPrevious() { return this.previous;}
 
     /**
      * Increments the internal indexes according to the previous character
@@ -428,10 +434,18 @@ public class JSONTokener {
             return this.nextString(c);
         case '{':
             this.back();
-            return new JSONObject(this);
+            try {
+                return new JSONObject(this);
+            } catch (StackOverflowError e) {
+                throw new JSONException("JSON Array or Object depth too large to process.", e);
+            }
         case '[':
             this.back();
-            return new JSONArray(this);
+            try {
+                return new JSONArray(this);
+            } catch (StackOverflowError e) {
+                throw new JSONException("JSON Array or Object depth too large to process.", e);
+            }
         }
 
         /*