Introduce BufferReader and eliminate a bunch of allocations

MetadataExtractor/Formats/Apple/BplistReader.cs

@@ -43,7 +43,7 @@ public static PropertyListResults Parse(byte[] bplist)
 
         Trailer trailer = ReadTrailer();
 
-        SequentialByteArrayReader reader = new(bplist, baseIndex: checked((int)(trailer.OffsetTableOffset + trailer.TopObject)));
+        var reader = new BufferReader(bplist.AsSpan(checked((int)(trailer.OffsetTableOffset + trailer.TopObject))), isBigEndian: true);
 
         int[] offsets = new int[(int)trailer.NumObjects];
 
@@ -63,7 +63,7 @@ public static PropertyListResults Parse(byte[] bplist)
 
         for (int i = 0; i < offsets.Length; i++)
         {
-            reader = new SequentialByteArrayReader(bplist, offsets[i]);
+            reader = new BufferReader(bplist.AsSpan(offsets[i]), isBigEndian: true);
 
             byte b = reader.GetByte();
 
@@ -73,13 +73,13 @@ public static PropertyListResults Parse(byte[] bplist)
             object obj = objectFormat switch
             {
                 // dict
-                0x0D => HandleDict(marker),
+                0x0D => HandleDict(ref reader, marker),
                 // string (ASCII)
                 0x05 => reader.GetString(bytesRequested: marker & 0x0F, Encoding.ASCII),
                 // data
-                0x04 => HandleData(marker),
+                0x04 => HandleData(ref reader, marker),
                 // int
-                0x01 => HandleInt(marker),
+                0x01 => HandleInt(ref reader, marker),
                 // unknown
                 _ => throw new NotSupportedException($"Unsupported object format {objectFormat:X2}.")
             };
@@ -91,10 +91,10 @@ public static PropertyListResults Parse(byte[] bplist)
 
         Trailer ReadTrailer()
         {
-            SequentialByteArrayReader reader = new(bplist, bplist.Length - Trailer.SizeBytes);
+            var reader = new BufferReader(bplist.AsSpan(bplist.Length - Trailer.SizeBytes), isBigEndian: true);
 
             // Skip 5-byte unused values, 1-byte sort version.
-            reader.Skip(6);
+            reader.Advance(6);
 
             return new Trailer
             {
@@ -106,7 +106,7 @@ Trailer ReadTrailer()
             };
         }
 
-        object HandleInt(byte marker)
+        static object HandleInt(ref BufferReader reader, byte marker)
         {
             return marker switch
             {
@@ -118,7 +118,7 @@ object HandleInt(byte marker)
             };
         }
 
-        Dictionary<byte, byte> HandleDict(byte count)
+        static Dictionary<byte, byte> HandleDict(ref BufferReader reader, byte count)
         {
             var keyRefs = new byte[count];
 
@@ -137,7 +137,7 @@ Dictionary<byte, byte> HandleDict(byte count)
             return map;
         }
 
-        object HandleData(byte marker)
+        object HandleData(ref BufferReader reader, byte marker)
         {
             int byteCount = marker;
 

MetadataExtractor/Formats/Exif/makernotes/OlympusCameraSettingsMakernoteDescriptor.cs

@@ -160,30 +160,16 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
                 return null;
 
             var sb = new StringBuilder();
-            switch (values[0])
+            sb.Append(values[0] switch
             {
-                case 0:
-                    sb.Append("Single AF");
-                    break;
-                case 1:
-                    sb.Append("Sequential shooting AF");
-                    break;
-                case 2:
-                    sb.Append("Continuous AF");
-                    break;
-                case 3:
-                    sb.Append("Multi AF");
-                    break;
-                case 4:
-                    sb.Append("Face detect");
-                    break;
-                case 10:
-                    sb.Append("MF");
-                    break;
-                default:
-                    sb.Append("Unknown (" + values[0] + ")");
-                    break;
-            }
+                0 => "Single AF",
+                1 => "Sequential shooting AF",
+                2 => "Continuous AF",
+                3 => "Multi AF",
+                4 => "Face detect",
+                10 => "MF",
+                _ => $"Unknown ({values[0]})"
+            });
 
             if (values.Length > 1)
             {
@@ -231,18 +217,12 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
 
             var sb = new StringBuilder();
 
-            switch (values[0])
+            sb.Append(values[0] switch
             {
-                case 0:
-                    sb.Append("AF not used");
-                    break;
-                case 1:
-                    sb.Append("AF used");
-                    break;
-                default:
-                    sb.Append("Unknown (" + values[0] + ")");
-                    break;
-            }
+                0 => "AF not used",
+                1 => "AF used",
+                _ => $"Unknown ({values[0]})"
+            });
 
             if (values.Length > 1)
                 sb.Append("; " + values[1]);
@@ -385,24 +365,14 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
 
             var sb = new StringBuilder();
 
-            switch (values[0])
+            sb.Append(values[0] switch
             {
-                case 0:
-                    sb.Append("Off");
-                    break;
-                case 3:
-                    sb.Append("TTL");
-                    break;
-                case 4:
-                    sb.Append("Auto");
-                    break;
-                case 5:
-                    sb.Append("Manual");
-                    break;
-                default:
-                    sb.Append("Unknown (" + values[0] + ")");
-                    break;
-            }
+                0 => "Off",
+                3 => "TTL",
+                4 => "Auto",
+                5 => "Manual",
+                _ => $"Unknown ({values[0]})"
+            });
 
             for (var i = 1; i < values.Length; i++)
                 sb.Append("; ").Append(values[i]);
@@ -692,33 +662,17 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
                 return null;
 
             var sb = new StringBuilder();
-            switch (values[0])
+            sb.Append(values[0] switch
             {
-                case 1:
-                    sb.Append("Vivid");
-                    break;
-                case 2:
-                    sb.Append("Natural");
-                    break;
-                case 3:
-                    sb.Append("Muted");
-                    break;
-                case 4:
-                    sb.Append("Portrait");
-                    break;
-                case 5:
-                    sb.Append("i-Enhance");
-                    break;
-                case 256:
-                    sb.Append("Monotone");
-                    break;
-                case 512:
-                    sb.Append("Sepia");
-                    break;
-                default:
-                    sb.Append("Unknown (").Append(values[0]).Append(')');
-                    break;
-            }
+                1 => "Vivid",
+                2 => "Natural",
+                3 => "Muted",
+                4 => "Portrait",
+                5 => "i-Enhance",
+                256 => "Monotone",
+                512 => "Sepia",
+                _ => $"Unknown ({values[0]})"
+            });
 
             if (values.Length > 1)
                 sb.Append("; ").Append(values[1]);
@@ -822,33 +776,18 @@ public sealed class OlympusCameraSettingsMakernoteDescriptor(OlympusCameraSettin
                     sb.Append("Partial Color " + values[i] + "; ");
                 else if (i == 4)
                 {
-                    switch (values[i])
+                    sb.Append(values[i] switch
                     {
-                        case 0x0000:
-                            sb.Append("No Effect");
-                            break;
-                        case 0x8010:
-                            sb.Append("Star Light");
-                            break;
-                        case 0x8020:
-                            sb.Append("Pin Hole");
-                            break;
-                        case 0x8030:
-                            sb.Append("Frame");
-                            break;
-                        case 0x8040:
-                            sb.Append("Soft Focus");
-                            break;
-                        case 0x8050:
-                            sb.Append("White Edge");
-                            break;
-                        case 0x8060:
-                            sb.Append("B&W");
-                            break;
-                        default:
-                            sb.Append("Unknown (").Append(values[i]).Append(')');
-                            break;
-                    }
+                        0x0000 => "No Effect",
+                        0x8010 => "Star Light",
+                        0x8020 => "Pin Hole",
+                        0x8030 => "Frame",
+                        0x8040 => "Soft Focus",
+                        0x8050 => "White Edge",
+                        0x8060 => "B&W",
+                        _ => $"Unknown ({values[i]})"
+                    });
+
                     sb.Append("; ");
                 }
                 else if (i == 6)

MetadataExtractor/Formats/Exif/makernotes/OlympusMakernoteDirectory.cs

@@ -448,9 +448,9 @@ public override void Set(int tagType, object value)
                 base.Set(tagType, value);
         }
 
-        private void ProcessCameraSettings(byte[] bytes)
+        private void ProcessCameraSettings(ReadOnlySpan<byte> bytes)
         {
-            var reader = new SequentialByteArrayReader(bytes);
+            var reader = new BufferReader(bytes, isBigEndian: true);
             var count = bytes.Length / 4;
 
             for (var i = 0; i < count; i++)

MetadataExtractor/Formats/Flir/FlirReader.cs

@@ -153,8 +153,9 @@ public IEnumerable<Directory> Extract(IndexedReader reader)
                     directory.Set(TagRawValueMedian, reader2.GetUInt16(TagRawValueMedian));
                     directory.Set(TagRawValueRange, reader2.GetUInt16(TagRawValueRange));
 
-                    var dateTimeBytes = reader2.GetBytes(TagDateTimeOriginal, 10);
-                    var dateTimeReader = new SequentialByteArrayReader(dateTimeBytes, isMotorolaByteOrder: false);
+                    Span<byte> dateTimeBytes = stackalloc byte[10];
+                    reader2.GetBytes(TagDateTimeOriginal, dateTimeBytes);
+                    var dateTimeReader = new BufferReader(dateTimeBytes, isBigEndian: false);
                     var tm = dateTimeReader.GetUInt32();
                     var ss = dateTimeReader.GetUInt32() & 0xffff;
                     var tz = dateTimeReader.GetInt16();

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);
 
-            SequentialReader reader = new SequentialByteArrayReader(segment.Bytes);
+            const int JpegHeaderSize = 1 + 2 + 2 + 1;
 
-            try
+            if (segment.Span.Length < JpegHeaderSize)
             {
-                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 segment header.");
+
+                return directory;
             }
-            catch (IOException ex)
+
+            var reader = new BufferReader(segment.Span, isBigEndian: true);
+
+            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.AddError("Insufficient bytes for JPEG the requested number of JPEG components.");
+                return directory;
+            }
+
+            // 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/Photoshop/PhotoshopReader.cs

@@ -53,12 +53,15 @@ public IReadOnlyList<Directory> Extract(SequentialReader reader, int length)
             // http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/#50577409_pgfId-1037504
             var pos = 0;
             int clippingPathCount = 0;
+
+            Span<byte> signature = stackalloc byte[4];
+
             while (pos < length)
             {
                 try
                 {
                     // 4 bytes for the signature ("8BIM", "PHUT", etc.)
-                    var signature = reader.GetString(4, Encoding.UTF8);
+                    reader.GetBytes(signature);
                     pos += 4;
 
                     // 2 bytes for the resource identifier (tag type).
@@ -106,7 +109,7 @@ public IReadOnlyList<Directory> Extract(SequentialReader reader, int length)
                     }
 
                     // Skip any unsupported IRBs
-                    if (signature != "8BIM")
+                    if (!signature.SequenceEqual("8BIM"u8))
                         continue;
 
                     switch (tagType)