com.github.isaichkindanila.crypt.lib.file.FileDecryptor Maven / Gradle / Ivy

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Simple Java library for stream ciphers based encryption
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package com.github.isaichkindanila.crypt.lib.file;

import com.github.isaichkindanila.crypt.lib.stream.DecryptedInputStream;
import com.github.isaichkindanila.crypt.lib.stream.IncorrectPasswordException;
import com.github.isaichkindanila.crypt.lib.stream.MalformedStreamHeaderException;
import com.github.isaichkindanila.crypt.lib.stream.UnsupportedCipherException;
import com.github.isaichkindanila.crypt.lib.util.IOUtils;

import java.io.*;
import java.nio.charset.StandardCharsets;

/**
 * Class used to decrypt files encrypted by {@code FileEncryptor}.
 *
 * @see FileEncryptor
 */
@SuppressWarnings("WeakerAccess")
public class FileDecryptor {
    private final IOHandler ioHandler;
    private final InputStream in;
    private final File targetDir;
    private final long total;

    /**
     * Equivalent to {@link #FileDecryptor(InputStream, File, String) FileDecryptor(new FileInputStream(encryptedFile), targetDir, password)}.
     *
     * @param encryptedFile encrypted file
     * @param targetDir     directory where decrypted files will be put
     * @param password      password to be used to decrypt input stream
     * @throws IOException                    if IOException occurs while reading stream header
     * @throws MalformedStreamHeaderException if stream header is malformed
     * @throws UnsupportedCipherException     if the stream was encrypted with cipher which is not supported by this version of Crypt Lib
     * @throws IncorrectPasswordException     if the stream was encrypted with different password
     */
    public FileDecryptor(File encryptedFile, File targetDir, String password) throws IOException {
        this(new FileInputStream(encryptedFile), targetDir, password);
    }

    /**
     * Accepts {@code InputStream} to allow decrypting resources accessed via URL.
     *
     * @param encryptedStream encrypted input stream
     * @param targetDir       directory where decrypted files will be put
     * @param password        password to be used to decrypt input stream
     * @throws IOException                    if IOException occurs while reading stream header
     * @throws MalformedStreamHeaderException if stream header is malformed
     * @throws UnsupportedCipherException     if the stream was encrypted with cipher which is not supported by this version of Crypt Lib
     * @throws IncorrectPasswordException     if the stream was encrypted with different password
     */
    public FileDecryptor(InputStream encryptedStream, File targetDir, String password) throws IOException {
        if (!targetDir.exists() && !targetDir.mkdirs()) {
            throw new FileNotFoundException("directory '" + targetDir.getAbsolutePath() + "' does not exist and cannot be created");
        }

        this.in = new DecryptedInputStream(encryptedStream, password);
        this.targetDir = targetDir;

        ioHandler = new IOHandler();
        total = IOUtils.readLong(in);
    }

    private void decryptFile() throws IOException {
        byte[] pathBytes = IOUtils.readByteArray(in);
        long size = IOUtils.readLong(in);

        String path = new String(pathBytes, StandardCharsets.UTF_8);
        File file = new File(targetDir, path);

        ioHandler.createFile(in, file, size);
    }

    /**
     * Decrypts file passed in constructor.
     *
     * @throws IOException if IOException occurs
     */
    public void decrypt() throws IOException {
        int fileCount = IOUtils.readInt(in);

        for (int i = 0; i < fileCount; i++) {
            decryptFile();
        }

        in.close();
    }

    /**
     * Returns value in range [0, 1] representing decryption progress,
     * where 0 means "not started yet" and 1 means "already finished".
     *
     * @return double value in range [0, 1]
     */
    public double progress() {
        return total == 0 ? 1.0 : 1.0 * ioHandler.done / total;
    }
}