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The MockFtpServer project provides mock/dummy FTP server implementations for testing FTP client code. Two FTP Server implementations are provided, each at a different level of abstraction. FakeFtpServer provides a higher-level abstraction. You define a virtual file system, including directories and files, as well as a set of valid user accounts and credentials. The FakeFtpServer then responds with appropriate replies and reply codes based on that configuration. StubFtpServer, on the other hand, is a lower-level "stub" implementation. You configure the individual FTP server commands to return custom data or reply codes, allowing simulation of either success or failure scenarios. You can also verify expected command invocations.

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/*
 * Copyright 2008 the original author or authors.
 *
 * Licensed 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 org.mockftpserver.fake.command;

import org.mockftpserver.core.command.Command;
import org.mockftpserver.core.command.ReplyCodes;
import org.mockftpserver.core.session.Session;
import org.mockftpserver.core.session.SessionKeys;
import org.mockftpserver.core.util.IoUtil;
import org.mockftpserver.fake.filesystem.FileEntry;
import org.mockftpserver.fake.filesystem.FileSystemEntry;
import org.mockftpserver.fake.filesystem.FileSystemException;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * CommandHandler for the RETR command. Handler logic:
 * 
 * If the user has not logged in, then reply with 530 and terminate
 * If the required pathname parameter is missing, then reply with 501 and terminate
 * If the pathname parameter does not specify a valid, existing filename, then reply with 550 and terminate
 * If the current user does not have read access to the file at the specified path or execute permission to its directory, then reply with 550 and terminate
 * Send an initial reply of 150
 * Send the contents of the named file across the data connection
 * If there is an error reading the file, then reply with 550 and terminate
 * Send a final reply with 226
 * 
 *
 * @author Chris Mair
 */
public class RetrCommandHandler extends AbstractFakeCommandHandler {

    protected void handle(Command command, Session session) {
        verifyLoggedIn(session);
        this.replyCodeForFileSystemException = ReplyCodes.READ_FILE_ERROR;

        String path = getRealPath(session, command.getRequiredParameter(0));
        FileSystemEntry entry = getFileSystem().getEntry(path);
        verifyFileSystemCondition(entry != null, path, "filesystem.doesNotExist");
        verifyFileSystemCondition(!entry.isDirectory(), path, "filesystem.isNotAFile");
        FileEntry fileEntry = (FileEntry) entry;

        // User must have read permission to the file
        verifyReadPermission(session, path);

        // User must have execute permission to the parent directory
        verifyExecutePermission(session, getFileSystem().getParent(path));

        sendReply(session, ReplyCodes.TRANSFER_DATA_INITIAL_OK);
        InputStream input = fileEntry.createInputStream();
        session.openDataConnection();
        byte[] bytes = null;
        try {
            bytes = IoUtil.readBytes(input);
        }
        catch (IOException e) {
            LOG.error("Error reading from file [" + fileEntry.getPath() + "]", e);
            throw new FileSystemException(fileEntry.getPath(), null, e);
        }
        finally {
            try {
                input.close();
            }
            catch (IOException e) {
                LOG.error("Error closing InputStream for file [" + fileEntry.getPath() + "]", e);
            }
        }

        if (isAsciiMode(session)) {
            bytes = convertLfToCrLf(bytes);
        }
        session.sendData(bytes, bytes.length);
        session.closeDataConnection();
        sendReply(session, ReplyCodes.TRANSFER_DATA_FINAL_OK);
    }

    /**
     * Within the specified byte array, replace all LF (\n) that are NOT preceded by a CR (\r) into CRLF (\r\n).
     *
     * @param bytes - the bytes to be converted
     * @return the result of converting LF to CRLF
     */
    protected byte[] convertLfToCrLf(byte[] bytes) {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        char lastChar = ' ';
        for (int i = 0; i < bytes.length; i++) {
            char ch = (char) bytes[i];
            if (ch == '\n' && lastChar != '\r') {
                out.write('\r');
                out.write('\n');
            } else {
                out.write(bytes[i]);
            }
            lastChar = ch;
        }
        return out.toByteArray();
    }

    private boolean isAsciiMode(Session session) {
        // Defaults to true
        return session.getAttribute(SessionKeys.ASCII_TYPE) != Boolean.FALSE;
    }

}