/**
    * Copyright 2005-2012 The Kuali Foundation
    *
    * Licensed under the Educational Community License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.opensource.org/licenses/ecl2.php
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.kuali.rice.ksb.security;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.security.GeneralSecurityException;
  import java.security.Signature;
  
  import javax.servlet.ServletInputStream;
  
  /**
   * An InputStream which decorates another InputStream with a wrapper that verifies the digital signature
   * of the data after the last piece of data is read.  The digital signature to verify against is
   * passed into the constructor of this stream.
   * 
   * @author Kuali Rice Team (rice.collab@kuali.org)
   */
  public class SignatureVerifyingInputStream extends ServletInputStream {
  
  	private byte[] digitalSignature;
  	private Signature signature;
  	private InputStream wrappedInputStream;
  	
  	public SignatureVerifyingInputStream(byte[] digitalSignature, Signature signature, InputStream wrappedInputStream) {
  		this.digitalSignature = digitalSignature;
  		this.signature = signature;
  		this.wrappedInputStream = wrappedInputStream;
  	}
  
  	@Override
  	public synchronized int read() throws IOException {
  		int data = this.wrappedInputStream.read();
  		try {
  			if (data == -1) {
  				verifySignature();
  			} else {
  			    this.signature.update((byte)data);
  			}
  		} catch (GeneralSecurityException e) {
  			IOException exception = new IOException("Error processing digital signature.");
  			exception.initCause(e);
  			throw exception;
  		}
  		return data;
  	}
  	
  	protected void verifySignature() throws IOException, GeneralSecurityException {
  		boolean verifies = this.signature.verify(this.digitalSignature);
  		if (!verifies) {
  			throw new IOException("The digital signature could not be successfully verified!");
  		}
  	}
  
  }