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Noncompliant Code Example

This noncompliant code example corrupts the data when string contains characters that are not representable in the specified charset.

// Corrupts data on errors
public static byte[] toCodePage(String charset, String string)
  throws UnsupportedEncodingException {
  return string.getBytes(charset);
}
 
// Fails to detect corrupt data
public static String fromCodePage(String charset, byte[] bytes)
  throws UnsupportedEncodingException {
  return new String(bytes, charset);
}

Compliant Solution

The java.nio.charset.CharsetEncoder class can transform a sequence of 16-bit Unicode characters into a sequence of bytes in a specific charset, while the java.nio.charset.CharacterDecoder class can reverse the procedure [API 2006].

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public static byte[] toCodePage(String charset, String string)
  throws IOException {
   
  Charset cs = Charset.forName(charset);
  CharsetEncoder coder = cs.newEncoder();
  ByteBuffer bytebuf = coder.encode(CharBuffer.wrap(string));
  byte[] bytes = new byte[bytebuf.limit()];
  bytebuf.get(bytes);
  return bytes;
}

Noncompliant Code Example

This noncompliant code example attempts to append a string to a text file in the specified encoding. This is erroneous because the String may contain unrepresentable characters.

// Corrupts data on errors
public static void toFile(String charset, String filename,
                        String string) throws IOException {
   
  FileOutputStream stream = new FileOutputStream(filename, true);
  OutputStreamWriter writer = new OutputStreamWriter(stream, charset);
  writer.write(string, 0, string.length());
  writer.close();
}

Compliant Solution

This compliant solution uses the CharsetEncoder class to perform the required function.

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Use the FileInputStream and InputStreamReader objects to read back the data from the file. InputStreamReader accepts a optional CharsetDecoder argument, which must be the same as that previously used for writing to the file.

Exceptions

STR03-EX0: Binary data that is expected to be a valid string may be read and converted to a string. How to perform this operation securely is explained in rule STR04-J. Use compatible character encodings when communicating string data between processes. 

Risk Assessment

Attempting to read a byte array containing binary data as if it were character data can produce erroneous results.

Related Guidelines

Bibliography