How to validate image header in java

Question

I've a web page that that can be used to upload files. Now I need to check if the image file type is of correct type like png,jpg,jpeg,gif

I am using the mimeType that comes with the request ,but if i am loading the .txt file that was renamed to .jpg file then also mime-type it is showing image/jpg,basically i dont want to upload this files.Now I want to be sure that nobody is able to upload a .txt file that was renamed in .jpg/.png....

For reference i am putting piece of code here:

  //storing images into bytearray.

byte[] bFile = baos.toByteArray();

if((bFile [i] & 0xFF) == 0xFF && (bFile[i+1] & 0xFF) == 0xD8 && (bFile[bFile.length -    2] & 0xFF) == 0xFF  && (bFile[bFile.length - 1] & 0xFF) == 0xD9) 
                    {
                       System.out.println("is Image");
                    }

The above line will only check for jpeg type but i want to check for other image header for file extensions Can someone please point out what exactly needs to be done to check for other image types?

Thanks

possible duplicate of [Java validate image header](http://stackoverflow.com/questions/15542775/java-validate-image-header) — user3145373 ツ, Aug 07 '14 at 08:39

score 8 · Answer 1 · edited May 23 '17 at 12:17

I have done something like that:

/**
 * Check if the image is a PNG. The first eight bytes of a PNG file always
 * contain the following (decimal) values: 137 80 78 71 13 10 26 10 / Hex:
 * 89 50 4e 47 0d 0a 1a 0a
 */
public boolean isValidPNG(InputStream is) {
    try {
        byte[] b = new byte[8];
        is.read(b, 0, 8);
        if (Arrays.equals(b, new BigInteger("89504e470d0a1a0a",16).toByteArray())) {
            return true;
        }
    } catch (Exception e) {
        //Ignore
        return false;
    }
    return false;
}

/**
 * Check if the image is a JPEG. JPEG image files begin with FF D8 and end
 * with FF D9
 */
public boolean isValidJPEG(InputStream is, int size) {
    try {
        byte[] b = new byte[2];
        is.read(b, 0, 2);
        // check first 2 bytes:
        if ((b[0]&0xff) != 0xff || (b[1]&0xff) != 0xd8) {
            return false;
        }
        // check last 2 bytes:
        is.skip(size-4);
        is.read(b, 0, 2);
        if ((b[0]&0xff) != 0xff || (b[1]&0xff) != 0xd9) {
            return false;
        }
    } catch (Exception e) {
        // Ignore
        return false;
    }
    return true;
}

/** Check if the image is a valid GIF. GIF files start with GIF and 87a or 89a.
 * http://www.onicos.com/staff/iz/formats/gif.html
*/
public boolean isValidGIF(InputStream is) {
    try {
        byte[] b=new byte[6];
        is.read(b, 0, 6);
        //check 1st 3 bytes
        if(b[0]!='G' || b[1]!='I' || b[2]!='F') {
            return false;
        }
        if(b[3]!='8' || !(b[4]=='7' || b[4]=='9') || b[5]!='a') {
            return false;
        }
    } catch(Exception e) {
        // Ignore
        return false;
    }
    return true;
}

There is also a PHP topic with some image headers: PHP : binary image data, checking the image type

Your method isValidPNG helped me, but I had to change something. Somehow the byte array you create from that BigInteger contains 9 bytes, not 8, from which the first is of value zero. I had to chop it off (by wrapping the "wrong" byte array in Arrays.copyOfRange(byteArray, 1, 9). — Benjamin, Nov 04 '17 at 20:15

How to validate image header in java

1 Answers1