How to Get Raw File extension from Header in Kotlin

Question

I have a file that extension is unknown. Is there a way to find the type of extension through the file header?

Answer 1

Usage:

GetFileHeader.isPDF(filename)

GetFileHeader Class written in java but you can use it in kotlin

public class GetFileHeader {
    private static final int PDF_MAGIC[] = new int[] { 0x25, 0x50, 0x44, 0x46};
    private static final int DOC1_MAGIC[] = new int[] { 0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1};
    private static final int DOC2_MAGIC[] = new int[] { 0x0d, 0x44, 0x4f, 0x43};
    private static final int DOC3_MAGIC[] = new int[] { 0xcf, 0x11, 0xe0, 0xa1, 0xb1,0x1a, 0xe1, 0x00};
    private static final int DOC4_MAGIC[] = new int[] { 0xdb, 0xa5, 0x2d, 0x00};
    private static final int DOC5_MAGIC[] = new int[] { 0xec, 0xa5, 0xc1, 0x00};
    private static final int DOCX1_MAGIC[] = new int[] { 0x50, 0x4b, 0x03, 0x04};
    private static final int DOCX2_MAGIC[] = new int[] { 0x50, 0x4b, 0x03, 0x04, 0x14, 0x00, 0x06, 0x00};

    public static boolean isPDF(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < PDF_MAGIC.length; ++i) {
                if(ins.read() != PDF_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDoc1(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOC1_MAGIC.length; ++i) {
                if(ins.read() != DOC1_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDoc2(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOC2_MAGIC.length; ++i) {
                if(ins.read() != DOC2_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDoc3(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOC3_MAGIC.length; ++i) {
                if(ins.read() != DOC3_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDoc4(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOC4_MAGIC.length; ++i) {
                if(ins.read() != DOC4_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDoc5(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOC5_MAGIC.length; ++i) {
                if(ins.read() != DOC5_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDocX1(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOCX1_MAGIC.length; ++i) {
                if(ins.read() != DOCX1_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }
    public static boolean isDocX2(File filename) throws Exception {
        FileInputStream ins = new FileInputStream(filename);
        try {
            for(int i = 0; i < DOCX2_MAGIC.length; ++i) {
                if(ins.read() != DOCX2_MAGIC[i]) {
                    return false;
                }
            }
            return true;
        } finally {
            ins.close();
        }
    }

Answer 2

Do you have a good guess? There's not one standard file header that every format uses. Some (like .txt) have no header. The others all have their own custom header. Sometimes even the header isn't enough- there's multiple subheaders for different types of .wav and .bmp files. If you have a guess you can test that guess out using whatever header that format has, but if you don't even have a guess you're not going to get anywhere.

The header of a file isn't metadata, it's just (usually) the first N bytes of the file.