/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache 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.apache.org/licenses/LICENSE-2.0
 *
 * 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 freemarker.template.utility;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.List;

import freemarker.template.TemplateModelException;

Gives FreeMarker the the ability to execute external commands. Will fork
a process, and inline anything that process sends to stdout in the template.
Based on a patch submitted by Peter Molettiere.
BE CAREFUL! this tag, depending on use, may allow you
to set something up so that users of your web
application could run arbitrary code on your server.
This can only happen if you allow unchecked GET/POST
submissions to be used as the command string in the
exec tag.
Usage:

From java:
SimpleHash root = new SimpleHash();
root.put( "exec", new freemarker.template.utility.Execute() );
...

From your FreeMarker template:
The following is executed:
${exec( "/usr/bin/ls" )}
...

/**
 * <p>Gives FreeMarker the the ability to execute external commands. Will fork
 * a process, and inline anything that process sends to stdout in the template.
 * Based on a patch submitted by Peter Molettiere.</p>
 *
 * <p>BE CAREFUL! this tag, depending on use, may allow you
 * to set something up so that users of your web
 * application could run arbitrary code on your server.
 * This can only happen if you allow unchecked GET/POST
 * submissions to be used as the command string in the
 * exec tag.</p>
 *
 * <p>Usage:<br>
 * From java:</p>
 * <pre>
 * SimpleHash root = new SimpleHash();
 *
 * root.put( "exec", new freemarker.template.utility.Execute() );
 *
 * ...
 * </pre>
 *
 * <p>From your FreeMarker template:</p>
 * <pre>
 *
 * The following is executed:
 * ${exec( "/usr/bin/ls" )}
 *
 * ...
 * </pre>
 */
public class Execute implements freemarker.template.TemplateMethodModel {

    private final static int OUTPUT_BUFFER_SIZE = 1024;

    
Executes a method call.
Params:
arguments – a List of String objects containing the values
of the arguments passed to the method.
Returns:
the TemplateModel produced by the method, or null./**
     * Executes a method call.
     *
     * @param arguments a <tt>List</tt> of <tt>String</tt> objects containing the values
     * of the arguments passed to the method.
     * @return the <tt>TemplateModel</tt> produced by the method, or null.
     */
    public Object exec (List arguments) throws TemplateModelException {
        String aExecute;
        StringBuilder    aOutputBuffer = new StringBuilder();

        if ( arguments.size() < 1 ) {
            throw new TemplateModelException( "Need an argument to execute" );
        }

        aExecute = (String) (arguments.get(0));

        try {
            Process exec = Runtime.getRuntime().exec( aExecute );

            // stdout from the process comes in here
            InputStream execOut = exec.getInputStream();
            try {
                Reader execReader = new InputStreamReader( execOut );
    
                char[] buffer = new char[ OUTPUT_BUFFER_SIZE ];
                int bytes_read = execReader.read( buffer );
                while ( bytes_read > 0 ) {
                    aOutputBuffer.append( buffer, 0, bytes_read );
                    bytes_read = execReader.read( buffer );
                }
            } finally {
                execOut.close();
            }
        } catch ( IOException ioe ) {
            throw new TemplateModelException( ioe.getMessage() );
        }
        return aOutputBuffer.toString();
    }
}