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The write() method that is , defined in the class java.io.OutputStream, takes an integer argument intended to be between 0 and argument of type int the value of which must be in the range 0 to 255. Because an int is otherwise designed to store 4 byte numbers, failure to validate user input may lead to unexpected resultsa value of type int could be outside this range, failure to range check can result in the truncation of the higher-order bits of the argument.

The general contract for the write is that () method says that it writes one byte is written to the output stream. The byte to be written is constitutes the eight lowlower-order bits of the argument b. The , passed to the write() method; the 24 high-order bits of b are ignored . Java Specification

Non-Compliant Code Example

(see java.io.OutputStream.write() [API 2014] for more information).

Noncompliant Code Example

This noncompliant The non-compliant code example accepts a value from the user without validating it. If this Any value is greater then 255, it will result in a wrap aroundthat is not in the range of 0 to 255 is truncated. For instance, write(305) will print '1' since the lower order bits of 305 are preserved while the top 24 order bits are lost303) prints / on ASCII-based systems because the lower-order 8 bits of 303 are used while the 24 high-order bits are ignored (303 % 256 = 47, which is the ASCII code for /). That is, the result is the remainder modulo 256 of the absolute value of the inputinput divided by 256.

class console_writeConsoleWrite {
	
  public static void main(String[] args[]) { 
    // Any input value > 255 will result in unexpected output
    System.out.write(Integer.valueOf(args[0]));
    System.out.flush();
  }
}

Compliant Solution (Range-Check Inputs)

This compliant solution prints the corresponding character only if the input integer is in the proper range. If the input is outside the representable range of an int, the Integer.valueOf() method throws a NumberFormatException. If the input can be represented by an int but is outside the range required by write(), this code throws an ArithmeticException.

class FileWrite {
  public static void main(String[] args)
                          throws NumberFormatException, IOException { 
    // Perform range checking  
    int value = Integer.valueOf(args[1]0]);
    if (value < 0 || value > 255) {
      throw new ArithmeticException("Value is out of range");
    }
  
    System.out.write(value);
    System.out.flush(); 
  }
}

Compliant Solution (writeInt())

This compliant solution uses the writeInt() method of the DataOutputStream class, which can output the entire range of values representable as an int:

References

class FileWrite {
  public static void main(String[] args)
                          throws NumberFormatException, IOException { 
    DataOutputStream dos = new DataOutputStream(System.out);
    dos.writeInt(Integer.valueOf(args[0].toString()));
    System.out.flush(); 
  }     
}

Risk Assessment

Using the write() method to output integers outside the range 0 to 255 will result in truncation.

Automated Detection

Automated detection of all uses of the write() method is straightforward. Sound determination of whether the truncating behavior is correct is not feasible in the general case. Heuristic checks could be useful.

Related Guidelines

Bibliography

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Image Added Image Added Image AddedJava I/O, Elliotte Rusty Harold