Introduce BufferReader and eliminate a bunch of allocations

MetadataExtractor/Formats/Exif/makernotes/OlympusCameraSettingsMakernoteDescriptor.cs

@@ -367,10 +367,10 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
 
             sb.Append(values[0] switch
             {
-                0 => sb.Append("Off"),
-                3 => sb.Append("TTL"),
-                4 => sb.Append("Auto"),
-                5 => sb.Append("Manual"),
+                0 => "Off",
+                3 => "TTL",
+                4 => "Auto",
+                5 => "Manual",
                 _ => $"Unknown ({values[0]})"
             });
 

MetadataExtractor/Formats/Jpeg/JpegReader.cs

@@ -29,35 +29,45 @@ public JpegDirectory Extract(JpegSegment segment)
             // The value of TagCompressionType is determined by the segment type found
             directory.Set(JpegDirectory.TagCompressionType, (int)segment.Type - (int)JpegSegmentType.Sof0);
 
+            const int JpegHeaderSize = 1 + 2 + 2 + 1;
+
+            if (segment.Span.Length < JpegHeaderSize)
+            {
+                directory.AddError("Insufficient bytes for JPEG segment header.");
+
+                return directory;
+            }
+
             var reader = new BufferReader(segment.Span, isBigEndian: true);
 
-            try
+            directory.Set(JpegDirectory.TagDataPrecision, reader.GetByte());
+            directory.Set(JpegDirectory.TagImageHeight, reader.GetUInt16());
+            directory.Set(JpegDirectory.TagImageWidth, reader.GetUInt16());
+
+            var componentCount = reader.GetByte();
+
+            directory.Set(JpegDirectory.TagNumberOfComponents, componentCount);
+
+            const int JpegComponentSize = 1 + 1 + 1;
+
+            if (reader.Available < componentCount * JpegComponentSize)
             {
-                directory.Set(JpegDirectory.TagDataPrecision, reader.GetByte());
-                directory.Set(JpegDirectory.TagImageHeight, reader.GetUInt16());
-                directory.Set(JpegDirectory.TagImageWidth, reader.GetUInt16());
-
-                var componentCount = reader.GetByte();
-
-                directory.Set(JpegDirectory.TagNumberOfComponents, componentCount);
-
-                // For each component, there are three bytes of data:
-                // 1 - Component ID: 1 = Y, 2 = Cb, 3 = Cr, 4 = I, 5 = Q
-                // 2 - Sampling factors: bit 0-3 vertical, 4-7 horizontal
-                // 3 - Quantization table number
-
-                for (var i = 0; i < componentCount; i++)
-                {
-                    var componentId = reader.GetByte();
-                    var samplingFactorByte = reader.GetByte();
-                    var quantizationTableNumber = reader.GetByte();
-                    var component = new JpegComponent(componentId, samplingFactorByte, quantizationTableNumber);
-                    directory.Set(JpegDirectory.TagComponentData1 + i, component);
-                }
+                directory.AddError("Insufficient bytes for JPEG the requested number of JPEG components.");
+                return directory;
             }
-            catch (IOException ex)
+
+            // For each component, there are three bytes of data:
+            // 1 - Component ID: 1 = Y, 2 = Cb, 3 = Cr, 4 = I, 5 = Q
+            // 2 - Sampling factors: bit 0-3 vertical, 4-7 horizontal
+            // 3 - Quantization table number
+
+            for (var i = 0; i < componentCount; i++)
             {
-                directory.AddError(ex.Message);
+                var componentId = reader.GetByte();
+                var samplingFactorByte = reader.GetByte();
+                var quantizationTableNumber = reader.GetByte();
+                var component = new JpegComponent(componentId, samplingFactorByte, quantizationTableNumber);
+                directory.Set(JpegDirectory.TagComponentData1 + i, component);
             }
 
             return directory;

MetadataExtractor/Formats/Png/PngMetadataReader.cs

@@ -295,32 +295,50 @@ private static IEnumerable<Directory> ProcessChunk(PngChunk chunk)
             }
             else if (chunkType == PngChunkType.tIME)
             {
-                var reader = new BufferReader(bytes, isBigEndian: true);
-                var year = reader.GetUInt16();
-                var month = reader.GetByte();
-                int day = reader.GetByte();
-                int hour = reader.GetByte();
-                int minute = reader.GetByte();
-                int second = reader.GetByte();
                 var directory = new PngDirectory(PngChunkType.tIME);
-                if (DateUtil.IsValidDate(year, month, day) && DateUtil.IsValidTime(hour, minute, second))
+
+                if (bytes.Length < 2 + 1 + 1 + 1 + 1 + 1)
                 {
-                    var time = new DateTime(year, month, day, hour, minute, second, DateTimeKind.Unspecified);
-                    directory.Set(PngDirectory.TagLastModificationTime, time);
+                    directory.AddError("Insufficient bytes for PNG tIME chunk.");
                 }
                 else
                 {
-                    directory.AddError($"PNG tIME data describes an invalid date/time: year={year} month={month} day={day} hour={hour} minute={minute} second={second}");
+                    var reader = new BufferReader(bytes, isBigEndian: true);
+
+                    var year = reader.GetUInt16();
+                    var month = reader.GetByte();
+                    int day = reader.GetByte();
+                    int hour = reader.GetByte();
+                    int minute = reader.GetByte();
+                    int second = reader.GetByte();
+
+                    if (DateUtil.IsValidDate(year, month, day) && DateUtil.IsValidTime(hour, minute, second))
+                    {
+                        var time = new DateTime(year, month, day, hour, minute, second, DateTimeKind.Unspecified);
+                        directory.Set(PngDirectory.TagLastModificationTime, time);
+                    }
+                    else
+                    {
+                        directory.AddError($"PNG tIME data describes an invalid date/time: year={year} month={month} day={day} hour={hour} minute={minute} second={second}");
+                    }
+                    yield return directory;
                 }
-                yield return directory;
             }
             else if (chunkType == PngChunkType.pHYs)
             {
+                var directory = new PngDirectory(PngChunkType.pHYs);
+
+                if (bytes.Length < 4 + 4 + 1)
+                {
+                    directory.AddError("Insufficient bytes for PNG pHYs chunk.");
+                }
+
                 var reader = new BufferReader(bytes, isBigEndian: true);
+
                 var pixelsPerUnitX = reader.GetInt32();
                 var pixelsPerUnitY = reader.GetInt32();
                 var unitSpecifier = reader.GetSByte();
-                var directory = new PngDirectory(PngChunkType.pHYs);
+
                 directory.Set(PngDirectory.TagPixelsPerUnitX, pixelsPerUnitX);
                 directory.Set(PngDirectory.TagPixelsPerUnitY, pixelsPerUnitY);
                 directory.Set(PngDirectory.TagUnitSpecifier, unitSpecifier);

MetadataExtractor/IO/BufferReader.cs

@@ -21,15 +21,17 @@ public byte GetByte()
 
     public void GetBytes(scoped Span<byte> bytes)
     {
-        Debug.Assert(_position + bytes.Length <= _bytes.Length, "attempted to read past end of data");
+        if (_position + bytes.Length > _bytes.Length)
+            throw new IOException("End of data reached.");
 
         _bytes.Slice(_position, bytes.Length).CopyTo(bytes);
         _position += bytes.Length;
     }
 
     public byte[] GetBytes(int count)
     {
-        Debug.Assert(_position + count <= _bytes.Length, "attempted to read past end of data");
+        if (_position + count > _bytes.Length)
+            throw new IOException("End of data reached.");
 
         var bytes = new byte[count];
 
@@ -43,7 +45,9 @@ public byte[] GetBytes(int count)
     public void Advance(int n)
     {
         Debug.Assert(n >= 0, "n must be zero or greater");
-        Debug.Assert(_position + n <= _bytes.Length, "attempted to advance past end of data");
+
+        if (_position + n > _bytes.Length)
+            throw new IOException("End of data reached.");
 
         _position += n;
     }
@@ -65,14 +69,13 @@ public bool TryAdvance(int n)
 
     public sbyte GetSByte()
     {
-        return unchecked((sbyte)GetByte());
+        return unchecked((sbyte)_bytes[_position++]);
     }
 
     public ushort GetUInt16()
     {
-        Span<byte> bytes = stackalloc byte[2];
-
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 2);
+        _position += 2;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadUInt16BigEndian(bytes)
@@ -81,9 +84,8 @@ public ushort GetUInt16()
 
     public short GetInt16()
     {
-        Span<byte> bytes = stackalloc byte[2];
-
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 2);
+        _position += 2;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadInt16BigEndian(bytes)
@@ -92,9 +94,8 @@ public short GetInt16()
 
     public uint GetUInt32()
     {
-        Span<byte> bytes = stackalloc byte[4];
-
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 4);
+        _position += 4;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadUInt32BigEndian(bytes)
@@ -103,9 +104,8 @@ public uint GetUInt32()
 
     public int GetInt32()
     {
-        Span<byte> bytes = stackalloc byte[4];
-
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 4);
+        _position += 4;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadInt32BigEndian(bytes)
@@ -114,8 +114,8 @@ public int GetInt32()
 
     public long GetInt64()
     {
-        Span<byte> bytes = stackalloc byte[8];
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 8);
+        _position += 8;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadInt64BigEndian(bytes)
@@ -124,8 +124,8 @@ public long GetInt64()
 
     public ulong GetUInt64()
     {
-        Span<byte> bytes = stackalloc byte[8];
-        GetBytes(bytes);
+        var bytes = _bytes.Slice(_position, 8);
+        _position += 8;
 
         return _isBigEndian
             ? BinaryPrimitives.ReadUInt64BigEndian(bytes)