Reject BatchStatement with more than 64K elements

JAVA-229 #fixes

Author: Sylvain Lebresne

driver-core/src/main/java/com/datastax/driver/core/BatchStatement.java

@@ -104,6 +104,10 @@ IdAndValues getIdAndValues() {
      *
      * @param statement the new statement to add.
      * @return this batch statement.
+     *
+     * @throws IllegalStateException if adding the new statement means that this
+     * {@code BatchStatement} has more than 65536 statements (since this is the maximum number
+     * of statements for a BatchStatement allowed by the underlying protocol).
      */
     public BatchStatement add(Statement statement) {
 
@@ -115,6 +119,8 @@ public BatchStatement add(Statement statement) {
                 add(subStatements);
             }
         } else {
+            if (statements.size() >= 0xFFFF)
+                throw new IllegalStateException("Batch statement cannot contain more than " + 0xFFFF + " statements.");
             statements.add(statement);
         }
         return this;

driver-core/src/main/java/com/datastax/driver/core/Requests.java

@@ -256,6 +256,7 @@ public static class Batch extends Message.Request {
         public static final Message.Coder<Batch> coder = new Message.Coder<Batch>() {
             public void encode(Batch msg, ChannelBuffer dest) {
                 int queries = msg.queryOrIdList.size();
+                assert queries <= 0xFFFF;
 
                 dest.writeByte(fromType(msg.type));
                 dest.writeShort(queries);