按块读取和写入文件块

Question

我正在开发一个文件加密程序。我正在使用下面的功能来加密文件 直到我意识到它不适合大的；因为它将所有文件内容读入内存。现在，我需要创建一个可以分块读取和写入文件内容的函数。我该怎么做？

private fun encryptFile(file: File) {
   val originalData = file.readBytes()
   val encryptData = encrypt(originalData)
   encryptData?.run {
       file.writeBytes(this)
   }
}

Answer 1

您的加密功能显然不能保持这种状态。它必须成为一个包装 InputStream 或 OutputStream 的东西，然后它就相当琐碎了。

请注意，手动加密几乎 100% 保证您会搞砸，而且加密流已经存在。你有什么理由重新发明轮子并注册通过重新发明你不应该做的事情来破坏安全性？

Answer 2

看看代码。 OP

    // ...
StringBuilder sb = new StringBuilder(); 
String line;
while ((line = inputStream.readLine()) != null) {
    sb.append(line);

    // if enough content is read, extract the chunk
    while (sb.length() >= chunkSize) {

        String c = sb.substring(0, chunkSize);
        // do something with the string

        // add the remaining content to the next chunk
        sb = new StringBuilder(sb.substring(chunkSize));
    }
}
// thats the last chunk
String c = sb.toString();
// do something with the string

编辑：如何使用 Chilkat 库 link to download a Chillkat lib

加密文件块的代码示例

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {

CkCrypt2 crypt = new CkCrypt2();

crypt.put_CryptAlgorithm("aes");
crypt.put_CipherMode("cbc");
crypt.put_KeyLength(128);

crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex");
crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");

String fileToEncrypt = "qa_data/hamlet.xml";
CkFileAccess facIn = new CkFileAccess();
boolean success = facIn.OpenForRead(fileToEncrypt);
if (success != true) {
    System.out.println("Failed to open file that is to be encrytped.");
    return;
    }

String outputEncryptedFile = "qa_output/hamlet.enc";
CkFileAccess facOutEnc = new CkFileAccess();
success = facOutEnc.OpenForWrite(outputEncryptedFile);
if (success != true) {
    System.out.println("Failed to encrypted output file.");
    return;
    }

// Let's encrypt in 10000 byte chunks.
int chunkSize = 10000;
int numChunks = facIn.GetNumBlocks(chunkSize);

crypt.put_FirstChunk(true);
crypt.put_LastChunk(false);

CkBinData bd = new CkBinData();

int i = 0;
while (i < numChunks) {
    i = i+1;
    if (i == numChunks) {
        crypt.put_LastChunk(true);
        }

    // Read the next chunk from the file.
    // The last chunk will be whatever amount remains in the file..
    bd.Clear();
    facIn.FileReadBd(chunkSize,bd);

    // Encrypt.
    crypt.EncryptBd(bd);

    // Write the encrypted chunk to the output file.
    facOutEnc.FileWriteBd(bd,0,0);

    crypt.put_FirstChunk(false);
    }

// Make sure both FirstChunk and LastChunk are restored to true after
// encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
// will produce unexpected results.
crypt.put_FirstChunk(true);
crypt.put_LastChunk(true);

facIn.FileClose();
facOutEnc.FileClose();

// Decrypt the encrypted output file in a single call using CBC mode:
String decryptedFile = "qa_output/hamlet_dec.xml";
success = crypt.CkDecryptFile(outputEncryptedFile,decryptedFile);
// Assume success for the example..

// Compare the contents of the decrypted file with the original file:
boolean bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile);
System.out.println("bSame = " + bSame);
  }
}