EXIF.cs

using System;
using System.Collections.Generic;
using System.IO;
using Waher.Content.Images.Exif;
using Waher.Runtime.Inventory;
 
namespace Waher.Content.Images
{
    public static class EXIF
    {
        private static readonly Dictionary<int, ExifTagName> names = GetNames();
 
        private static Dictionary<int, ExifTagName> GetNames()
        {
            Dictionary<int, ExifTagName> Names = new Dictionary<int, ExifTagName>();
 
            foreach (ExifTagName Value in Enum.GetValues(typeof(ExifTagName)))
                Names[(int)Value] = Value;
 
            return Names;
        }
 
        public static bool TryParse(byte[] ExifData, out ExifTag[] Tags)
        {
            ExifReader Reader = new ExifReader(ExifData);
            List<ExifTag> List = new List<ExifTag>();
 
            Tags = null;
 
            // EXIF identifier
            if (Reader.NextASCIIString() != "Exif")
                return false;
 
            // Padding
            if (Reader.NextByte() < 0)
                return false;
 
            // Byte order
            int RefPos = Reader.Position;
            int i = Reader.NextSHORT();
 
            switch (i)
            {
                case 0x4949:
                    Reader.BigEndian = false;
                    break;
 
                case 0x4d4d:
                    Reader.BigEndian = true;
                    break;
 
                default:
                    return false;
            }
 
            if (Reader.NextSHORT() != 0x2a)
                return false;
 
            // IFD 0 offset
            uint? Offset = Reader.NextLONG();
            if (!Offset.HasValue)
                return false;
 
            int Pos = RefPos + (int)Offset.Value;
            if (Pos < Reader.Position || Pos >= Reader.Length)
                return false;
 
            Reader.Position = Pos;
 
            do
            {
                int NrRecords = Reader.NextSHORT();
                if (NrRecords < 0)
                    return false;
 
                while (NrRecords > 0)
                {
                    int TagID = Reader.NextSHORT();
                    if (TagID < 0)
                        return false;
 
                    if (!names.TryGetValue(TagID, out ExifTagName Name))
                        Name = ExifTagName.Unknown;
 
                    int Type = Reader.NextSHORT();
                    if (Type < 0)
                        return false;
 
                    uint? Count = Reader.NextLONG();
                    if (!Count.HasValue)
                        return false;
 
                    int ElementSize;
                    int NrElements = (int)Count.Value;
 
                    switch ((ExifTagType)Type)
                    {
                        case ExifTagType.ASCII:
                            ElementSize = 1;
                            NrElements = 1;
                            break;
 
                        case ExifTagType.BYTE:
                        case ExifTagType.UNDEFINED:
                        default:
                            ElementSize = 1;
                            break;
 
                        case ExifTagType.SHORT:
                            ElementSize = 2;
                            break;
 
                        case ExifTagType.LONG:
                        case ExifTagType.SLONG:
                            ElementSize = 4;
                            break;
 
                        case ExifTagType.RATIONAL:
                        case ExifTagType.SRATIONAL:
                            ElementSize = 8;
                            break;
                    }
 
                    int RecSize = (int)(Count.Value * ElementSize);
                    int PosBak;
                    int j;
 
                    if (RecSize <= 4)
                        PosBak = Reader.Position + 4;
                    else
                    {
                        uint? ValueOffset = Reader.NextLONG();
                        if (!ValueOffset.HasValue || RefPos + ValueOffset.Value > Reader.Length)
                            return false;
 
                        PosBak = Reader.Position;
                        Reader.Position = RefPos + (int)ValueOffset.Value;
                    }
 
                    switch ((ExifTagType)Type)
                    {
                        case ExifTagType.BYTE:
                            if (NrElements == 1)
                            {
                                i = Reader.NextByte();
                                if (i < 0)
                                    return false;
                                
                                List.Add(new ExifTypedTag<byte>(TagID, Name, (byte)i));
                            }
                            else
                            {
                                byte[] Items = new byte[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    i = Reader.NextByte();
                                    if (i < 0)
                                        return false;
 
                                    Items[j] = (byte)i;
                                }
 
                                List.Add(new ExifTypedTag<byte[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.ASCII:
                            string AsciiValue = Reader.NextASCIIString();
                            List.Add(new ExifAsciiTag(TagID, Name, AsciiValue));
                            break;
 
                        case ExifTagType.SHORT:
                            if (NrElements == 1)
                            {
                                i = Reader.NextSHORT();
                                if (i < 0)
                                    return false;
 
                                List.Add(new ExifTypedTag<ushort>(TagID, Name, (ushort)i));
                            }
                            else
                            {
                                ushort[] Items = new ushort[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    i = Reader.NextSHORT();
                                    if (i < 0)
                                        return false;
 
                                    Items[j] = (ushort)i;
                                }
 
                                List.Add(new ExifTypedTag<ushort[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.LONG:
                            uint? u;
 
                            if (NrElements == 1)
                            {
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                List.Add(new ExifTypedTag<uint>(TagID, Name, u.Value));
                            }
                            else
                            {
                                uint[] Items = new uint[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    Items[j] = u.Value;
                                }
 
                                List.Add(new ExifTypedTag<uint[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.RATIONAL:
                            if (NrElements == 1)
                            {
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                uint NumeratorValue = u.Value;
 
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                uint DenominatorValue = u.Value;
                                List.Add(new ExifTypedTag<Rational>(TagID, Name, new Rational(NumeratorValue, DenominatorValue)));
                            }
                            else
                            {
                                Rational[] Items = new Rational[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    uint NumeratorValue = u.Value;
 
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    uint DenominatorValue = u.Value;
 
                                    Items[j] = new Rational(NumeratorValue, DenominatorValue);
                                }
 
                                List.Add(new ExifTypedTag<Rational[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.UNDEFINED:
                            if (NrElements == 1)
                            {
                                i = Reader.NextByte();
                                if (i < 0)
                                    return false;
 
                                List.Add(new ExifTypedTag<byte>(TagID, Name, (byte)i));
                            }
                            else
                            {
                                byte[] Items = new byte[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    i = Reader.NextByte();
                                    if (i < 0)
                                        return false;
 
                                    Items[j] = (byte)i;
                                }
 
                                List.Add(new ExifTypedTag<byte[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.SLONG:
                            if (NrElements == 1)
                            {
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                List.Add(new ExifTypedTag<int>(TagID, Name, (int)u.Value));
                            }
                            else
                            {
                                int[] Items = new int[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    Items[j] = (int)u.Value;
                                }
 
                                List.Add(new ExifTypedTag<int[]>(TagID, Name, Items));
                            }
                            break;
 
                        case ExifTagType.SRATIONAL:
                            if (NrElements == 1)
                            {
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                int NumeratorValue = (int)u.Value;
 
                                u = Reader.NextLONG();
                                if (!u.HasValue)
                                    return false;
 
                                int DenominatorValue = (int)u.Value;
                                List.Add(new ExifTypedTag<SignedRational>(TagID, Name, new SignedRational(NumeratorValue, DenominatorValue)));
                            }
                            else
                            {
                                SignedRational[] Items = new SignedRational[NrElements];
 
                                for (j = 0; j < NrElements; j++)
                                {
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    int NumeratorValue = (int)u.Value;
 
                                    u = Reader.NextLONG();
                                    if (!u.HasValue)
                                        return false;
 
                                    int DenominatorValue = (int)u.Value;
 
                                    Items[j] = new SignedRational(NumeratorValue, DenominatorValue);
                                }
 
                                List.Add(new ExifTypedTag<SignedRational[]>(TagID, Name, Items));
                            }
                            break;
                    }
 
                    Reader.Position = PosBak;
                    NrRecords--;
                }
 
                // Next IFD offset
                Offset = Reader.NextLONG();
                if (!Offset.HasValue)
                    return false;
 
                if (Offset.Value == 0)
                    break;
 
                Pos = RefPos + (int)Offset.Value;
                if (Pos < Reader.Position || Pos >= Reader.Length)
                    return false;
 
                Reader.Position = Pos;
            }
            while (true);
 
            Tags = List.ToArray();
            return true;
        }
 
        public static bool TryExtractFromJPeg(string FileName, out ExifTag[] Tags)
        {
            using (FileStream fs = File.OpenRead(FileName))
            {
                return TryExtractFromJPeg(fs, out Tags);
            }
        }
 
        public static bool TryExtractFromJPeg(byte[] Image, out ExifTag[] Tags)
        {
            using (MemoryStream ms = new MemoryStream(Image))
            {
                return TryExtractFromJPeg(ms, out Tags);
            }
        }
 
        public static bool TryExtractFromJPeg(Stream Image, out ExifTag[] Tags)
        {
            Tags = null;
 
            if (Image.ReadByte() != 0xff)
                return false;
 
            if (Image.ReadByte() != 0xd8)
                return false;
 
            byte[] Buf = null;
 
            do
            {
                if (!TryReadWord(Image, out ushort TagID))
                    return false;
 
                if (!TryReadWord(Image, out ushort Len) || Len < 2)
                    return false;
 
                Len -= 2;
 
                switch (TagID)
                {
                    case 0xffe1:    //APP1
                        Buf = new byte[Len];
 
                        if (Image.TryReadAll(Buf, 0, Len) != Len)
                            return false;
 
                        return TryParse(Buf, out Tags);
 
                    default:
                        if (Image.CanSeek)
                            Image.Seek(Len, SeekOrigin.Current);
                        else
                        {
                            if (Buf is null || Buf.Length < Len)
                                Buf = new byte[Len];
 
                            if (Image.TryReadAll(Buf, 0, Len) != Len)
                                return false;
                        }
                        break;
                }
            }
            while (true);
        }
 
        private static bool TryReadWord(Stream Input, out ushort w)
        {
            int i = Input.ReadByte();
            if (i < 0)
            {
                w = 0;
                return false;
            }
 
            w = (byte)i;
 
            i = Input.ReadByte();
            if (i < 0)
                return false;
 
            w <<= 8;
            w |= (byte)i;
 
            return true;
        }
 
    }
}