FileTypes.cs

FileTypeDetermination.cs

public FormContentType getFormContentType(Stream dataStream)
{
    if (IsTiff(dataStream))
    {
        return FormContentType.Tiff;
    }
    else if (IsPDF(dataStream))
    {
        return FormContentType.Pdf;
    }
    else if (IsPNG(dataStream))
    {
        return FormContentType.Png;
    }
    else if (IsJpeg(dataStream))
    {
        return FormContentType.Jpeg;
    }

    return FormContentType.Json;
}

private bool IsTiff(Stream stream)
{
    stream.Seek(0, SeekOrigin.Begin);

    // TIFF must be at least 8 bytes long.
    if (stream.Length < 8)
        return false;

    // First two bytes are either II or MM, II Intel little-endian or MM Motorola big-endian
    byte[] header = new byte[2];
    stream.Read(header, 0, header.Length);
    if (header[0] != header[1] || (header[0] != 0x49 && header[0] != 0x4d))
        return false;

    // Work out which endian type the file is then read the next two bytes which
    // should be 4 and 2.
    bool isIntel = header[0] == 0x49;
    byte[] t = new byte[2];
    stream.Read(t, 0, 2);
    ushort mN = isIntel ? t[0] : t[1];

    stream.Seek(0, SeekOrigin.Begin);
    if (mN != 42)
        return false;
    return true;
}

private bool IsPDF(Stream stream)
{
    // PDF's begin with the byteSeq, but it may appear anywhere within the first 1024 bytes.
    stream.Seek(0, SeekOrigin.Begin);
    var byteSeq = new byte[] { 0x25, 0x50, 0x44, 0x46 };

    byte[] buffer = new byte[stream.Length >= 1024 ? 1024 : stream.Length];
    int bytesRead;
    do
    {
        bytesRead = stream.Read(buffer, 0, 1024);
    } while (bytesRead < buffer.Length);

    var counter = 0;
    do
    {
        if (buffer.Skip(counter).Take(byteSeq.Length).SequenceEqual(byteSeq))
            return true;
    } while (++counter <= buffer.Length);

    stream.Seek(0, SeekOrigin.Begin);
    return false;
}

private bool IsPNG(Stream stream)
{
    // Should always just be the first 8 bytes.
    var byteSeq = new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };

    stream.Seek(0, SeekOrigin.Begin);

    byte[] buffer = new byte[byteSeq.Length];
    stream.Read(buffer, 0, buffer.Length);

    return buffer.SequenceEqual(byteSeq);
}

private bool IsJpeg(Stream stream)
{
    // JPEG container is marked with a 3-byte sequence, extended kinds of JPEG
    // are further into the header.
    var byteSeq = new byte[] { 0xFF, 0xD8, 0xFF };

    stream.Seek(0, SeekOrigin.Begin);

    byte[] buffer = new byte[byteSeq.Length];
    stream.Read(buffer, 0, buffer.Length);

    return buffer.SequenceEqual(byteSeq);
}