Serialize with user-defined functions

BinaryWizard.Tests/BinaryWriterExtensions.cs

@@ -0,0 +1,19 @@
+using System.Text;
+
+namespace BinaryWizard.Tests;
+
+public static class BinaryWriterExtensions {
+    public static void WriteNullTerminatedString(this BinaryWriter writer, string text, Encoding? encoding = null) {
+        encoding ??= Encoding.UTF8;
+
+        if (string.IsNullOrEmpty(text)) {
+            writer.Write("\0"u8);
+
+            return;
+        }
+
+        var textBytes = encoding.GetBytes(text);
+        writer.Write(textBytes);
+        writer.Write(encoding is UnicodeEncoding ? "\0\0"u8 : "\0"u8);
+    }
+}

BinaryWizard.Tests/Samples/Entity.cs

@@ -19,6 +19,6 @@ namespace BinaryWizard.Tests.Samples;
 [BinarySerializable]
 public partial struct Entity {
     public int Id;
-    // public string Name;
+    public string Name;
     public Vector3 Position;
 }

BinaryWizard.Tests/SerializerTests.cs

@@ -74,7 +74,7 @@ public void Entity_CorrectlySerialized() {
         using var stream = new MemoryStream();
         using (var writer = new BinaryWriter(stream, Encoding.UTF8, leaveOpen: true)) {
             writer.Write(69); // Id
-            // writer.Write("glomdom"); // Name
+            writer.WriteNullTerminatedString("glomdom"); // Name
 
             // Position: Vector3
             writer.Write(1); // X
@@ -88,7 +88,8 @@ public void Entity_CorrectlySerialized() {
 
         var actual = Entity.FromBinary(reader);
         var expected = new Entity {
-            Id = 69, /* Name = "glomdom", */
+            Id = 69,
+            Name = "glomdom",
             Position = new Vector3 {
                 X = 1, Y = 2, Z = 3,
             },

BinaryWizard/Analysis/SymbolExtensions.cs

@@ -44,7 +44,7 @@ internal static string GetBinaryPrimitiveReader(this ITypeSymbol sym, Endianness
     internal static int GetByteSize(this ITypeSymbol primitive) {
         return primitive.SpecialType switch {
             SpecialType.System_Boolean => 1,
-            SpecialType.System_Char => 1,
+            SpecialType.System_Char => 2,
             SpecialType.System_SByte => 1,
             SpecialType.System_Byte => 1,
             SpecialType.System_Int16 => 2,
@@ -53,10 +53,12 @@ internal static int GetByteSize(this ITypeSymbol primitive) {
             SpecialType.System_UInt32 => 4,
             SpecialType.System_Int64 => 8,
             SpecialType.System_UInt64 => 8,
+            SpecialType.System_Single => 4,
+            SpecialType.System_Double => 8,
             SpecialType.System_Decimal => 16,
-            SpecialType.System_Double => 32,
+            SpecialType.System_String => -1,
 
-            _ => throw new InvalidOperationException("Unexpected case encountered."),
+            _ => throw new InvalidOperationException($"Unexpected case encountered for SpecialType: {primitive.SpecialType}"),
         };
     }
 

BinaryWizard/Embedded/SerializeWithAttribute.cs

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2026 glomdom
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System;
+
+namespace BinaryWizard;
+
+[AttributeUsage(AttributeTargets.Field)]
+public sealed class SerializeWithAttribute : Attribute {
+    /// <summary>
+    /// The type of the function to use when serializing the attached field.
+    /// </summary>
+    public Type Function { get; set; }
+
+    public SerializeWithAttribute(Type function) {
+        Function = function;
+    }
+}

BinaryWizard/Emission/CodeBuilder.cs

@@ -51,7 +51,22 @@ internal static void Generate(SourceProductionContext spc, ClassSerializationMet
             switch (seg) {
                 case FixedSegment fixedSeg: ProcessFixedSegment(++segmentCount, fixedSeg, bodyBuilder, bodyIndent, meta); break;
                 case DynamicSegment dynSeg: ProcessDynamicSegment(dynSeg, bodyBuilder, bodyIndent, meta); break;
-                case NestedObjectSegment nestedSeg: bodyBuilder.AppendLine($"{bodyIndent}result.{nestedSeg.FieldName} = {nestedSeg.TypeName}.FromBinary(reader);"); break;
+                case NestedObjectSegment nestedSeg:
+                    bodyBuilder.AppendLine($"{bodyIndent}result.{nestedSeg.FieldName} = {nestedSeg.TypeName}.FromBinary(reader);"); break;
+                case DynamicStringSegment stringSeg:
+                    bodyBuilder.AppendLine($$"""
+                                             {{bodyIndent}}{
+                                             {{bodyIndent}}    var stringBytes = new System.Collections.Generic.List<byte>();
+                                             {{bodyIndent}}    while (true) {
+                                             {{bodyIndent}}        byte b = reader.ReadByte();
+                                             {{bodyIndent}}        if (b == 0) break;
+                                             {{bodyIndent}}        stringBytes.Add(b);
+                                             {{bodyIndent}}    }
+                                             {{bodyIndent}}    result.{{stringSeg.Field.Name}} = System.Text.Encoding.UTF8.GetString(stringBytes.ToArray());
+                                             {{bodyIndent}}}
+                                             """);
+
+                    break;
             }
         }
 
@@ -117,7 +132,19 @@ private static void ProcessFixedSegment(int segmentIndex, FixedSegment seg, Stri
                 continue;
             }
 
-            sb.AppendLine($"{indent}result.{field.Name} = {field.TypeModel.Type.GetBinaryPrimitiveReader(meta.Endianness)}({bufName}.Slice({localOffset}, {field.ByteSize}));");
+            if (field.TypeModel.IsString) {
+                sb.AppendLine($$"""
+                                {{indent}}{
+                                {{indent}}    var textSpan = {{bufName}}.Slice({{localOffset}}, {{field.ByteSize}});
+                                {{indent}}    var nullIdx = textSpan.IndexOf((byte)0);
+                                {{indent}}    result.{{field.Name}} = System.Text.Encoding.UTF8.GetString(nullIdx >= 0 ? textSpan.Slice(0, nullIdx) : textSpan);
+                                {{indent}}}
+                                """);
+            } else {
+                sb.AppendLine(
+                    $"{indent}result.{field.Name} = {field.TypeModel.Type.GetBinaryPrimitiveReader(meta.Endianness)}({bufName}.Slice({localOffset}, {field.ByteSize}));"
+                );
+            }
 
             if (field.HasMagic) {
                 var magicStr = field.Magic;

BinaryWizard/Models/TypeModel.cs

@@ -26,6 +26,7 @@ internal sealed record TypeModel {
     internal int? InnerTypeByteSize { get; set; }
     internal bool IsFixedArray => FixedArraySize is not null && InnerType is not null;
     internal bool IsDynamicArray => FixedArraySize is null && InnerType is not null;
+    internal bool IsString => Type.SpecialType == SpecialType.System_String;
 
     internal TypeModel(ITypeSymbol type, int? fixedArraySize = null) {
         Type = type;

BinaryWizard/Segmenting/DynamicStringSegment.cs

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2026 glomdom
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System.Collections.Generic;
+using BinaryWizard.Models;
+
+namespace BinaryWizard.Segmenting;
+
+internal record DynamicStringSegment : Segment {
+    internal FieldDef Field { get; set; }
+
+    internal DynamicStringSegment(FieldDef field) {
+        Field = field;
+    }
+}

BinaryWizard/Segmenting/SegmentManager.cs

@@ -29,13 +29,21 @@ internal sealed class SegmentManager {
 
     internal void AddField(FieldDef field, string? lengthRef = null) {
         if (field.IsDynamic) {
-            if (string.IsNullOrEmpty(lengthRef)) throw new ArgumentNullException(nameof(lengthRef), "Length reference was not provided when field is dynamic");
-
             CommitFixed();
 
-            _segments.Add(new DynamicSegment([field], lengthRef!));
+            if (field.TypeModel.IsString) {
+                _segments.Add(new DynamicStringSegment(field));
+
+                Debug.WriteLine($"Added dynamic string segment for {field.Name}");
+            } else {
+                if (string.IsNullOrEmpty(lengthRef)) {
+                    throw new ArgumentNullException(nameof(lengthRef), $"Length reference was not provided for dynamic array field '{field.Name}'");
+                }
+
+                _segments.Add(new DynamicSegment([field], lengthRef!));
 
-            Debug.WriteLine($"Added dynamic segment for {field.Name} (dep. {lengthRef})");
+                Debug.WriteLine($"Added dynamic segment for {field.Name} (dep. {lengthRef})");
+            }
         } else {
             _currentFields.Add(field);