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Add backend project that has an improved ResourceContractResolver tha…
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…t generates types of reserved hal properties to help Swagger generators explore types properly
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Laszlo Zold committed Mar 22, 2022
1 parent 254c273 commit 6c9e89c
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Showing 5 changed files with 306 additions and 1 deletion.
22 changes: 22 additions & 0 deletions HalKit.Backend/HalKit.Backend.csproj
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<Project Sdk="Microsoft.NET.Sdk">

<PropertyGroup>
<TargetFramework>netstandard2.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<LangVersion>default</LangVersion>
<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
<PackageProjectUrl>https://github.com/viagogo/HalKit</PackageProjectUrl>
</PropertyGroup>

<ItemGroup>
<PackageReference Include="System.Reflection.Emit" Version="4.7.0" />
<PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
</ItemGroup>

<ItemGroup>
<ProjectReference Include="..\src\HalKit\HalKit.csproj" />
</ItemGroup>

<Import Project="..\Version.props" />
</Project>
80 changes: 80 additions & 0 deletions HalKit.Backend/Json/HalKitTypeBuilder.cs
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using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using Newtonsoft.Json.Serialization;

namespace HalKit.Backend.Json
{
/// <summary>
/// Generates type run-time, based on a sample code found at https://stackoverflow.com/questions/3862226/how-to-dynamically-create-a-class
/// </summary>
public static class HalKitTypeBuilder
{
public static Type CompileResultType(string typeName, IReadOnlyDictionary<string, JsonProperty> properties)
{
var tb = GetTypeBuilder(typeName);
var constructor = tb.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName);

foreach (var field in properties)
{
CreateProperty(tb, field.Key, field.Value.PropertyType);
}

var objectType = tb.CreateTypeInfo().AsType();
return objectType;
}

private static TypeBuilder GetTypeBuilder(string typeName)
{
var an = new AssemblyName("DynamicHalKit");
AssemblyBuilder assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
TypeBuilder tb = moduleBuilder.DefineType(typeName,
TypeAttributes.Public |
TypeAttributes.Class |
TypeAttributes.AutoClass |
TypeAttributes.AnsiClass |
TypeAttributes.BeforeFieldInit |
TypeAttributes.AutoLayout,
null);
return tb;
}

private static void CreateProperty(TypeBuilder tb, string propertyName, Type propertyType)
{
var fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);

var propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
var getPropertyMethodBuilder = tb.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);
var getIl = getPropertyMethodBuilder.GetILGenerator();

getIl.Emit(OpCodes.Ldarg_0);
getIl.Emit(OpCodes.Ldfld, fieldBuilder);
getIl.Emit(OpCodes.Ret);

var setPropertyMethodBuilder =
tb.DefineMethod("set_" + propertyName,
MethodAttributes.Public |
MethodAttributes.SpecialName |
MethodAttributes.HideBySig,
null, new[] { propertyType });

var setIl = setPropertyMethodBuilder.GetILGenerator();
var modifyProperty = setIl.DefineLabel();
var exitSet = setIl.DefineLabel();

setIl.MarkLabel(modifyProperty);
setIl.Emit(OpCodes.Ldarg_0);
setIl.Emit(OpCodes.Ldarg_1);
setIl.Emit(OpCodes.Stfld, fieldBuilder);

setIl.Emit(OpCodes.Nop);
setIl.MarkLabel(exitSet);
setIl.Emit(OpCodes.Ret);

propertyBuilder.SetGetMethod(getPropertyMethodBuilder);
propertyBuilder.SetSetMethod(setPropertyMethodBuilder);
}
}
}
197 changes: 197 additions & 0 deletions HalKit.Backend/Json/TypedResourceContractResolver.cs
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using HalKit.Json;
using HalKit.Models.Response;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Newtonsoft.Json.Serialization;

namespace HalKit.Backend.Json
{
/// <summary>
/// Resolves a <see cref="JsonContract"/> for a given <see cref="Resource"/>.
/// Generates proper type for the reserved JSON properties of "_links" and "_embedded"
/// through reflection so that Swashbuckle.AspNetCore or other tools can properly work out the schema
/// </summary>
public class TypedResourceContractResolver : DefaultContractResolver
{
private static readonly Dictionary<Type, IList<JsonProperty>> ContractPropertiesByType
= new Dictionary<Type, IList<JsonProperty>>();

private readonly JsonSerializerSettings _settings;

/// <summary>
/// Initializes a new instance of the <see cref="TypedResourceContractResolver"/>
/// class.
/// </summary>
public TypedResourceContractResolver(JsonSerializerSettings settings)
{
_settings = settings;
}

protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
var allProperties = base.CreateProperties(type, memberSerialization);
if (!typeof(Resource).GetTypeInfo().IsAssignableFrom(type.GetTypeInfo()))
{
return allProperties;
}

IList<JsonProperty> props;
if (!ContractPropertiesByType.TryGetValue(type, out props))
{
var contractProperties = new List<JsonProperty>();
var embeddedPropertyMap = new Dictionary<string, JsonProperty>();
var linksPropertyMap = new Dictionary<string, JsonProperty>();
foreach (var property in allProperties)
{
var isLinkOrEmbeddedProperty = false;
var attributes = property.AttributeProvider.GetAttributes(false);
foreach (var attribute in attributes)
{
var embeddedAttribute = attribute as EmbeddedAttribute;
if (embeddedAttribute != null)
{
isLinkOrEmbeddedProperty = true;
embeddedPropertyMap.Add(embeddedAttribute.Rel, property);
}

var relAttribute = attribute as RelAttribute;
if (relAttribute != null)
{
isLinkOrEmbeddedProperty = true;
linksPropertyMap.Add(relAttribute.Rel, property);
}
}

// This doesn't have a Rel or Embedded attribute so it's just a normal property
if (!isLinkOrEmbeddedProperty)
{
contractProperties.Add(property);
}
}

if (linksPropertyMap.Any())
{
contractProperties.Add(CreateReservedHalJsonProperty(type, "_links", linksPropertyMap));
}

if (embeddedPropertyMap.Any())
{
contractProperties.Add(CreateReservedHalJsonProperty(type, "_embedded", embeddedPropertyMap));
}

if (!ContractPropertiesByType.TryGetValue(type, out props))
{
lock (ContractPropertiesByType)
{
if (!ContractPropertiesByType.TryGetValue(type, out props))
{
ContractPropertiesByType.Add(type, contractProperties);
props = contractProperties;
}
}
}
}
return props;
}

private JsonProperty CreateReservedHalJsonProperty(
Type type,
string name,
IReadOnlyDictionary<string, JsonProperty> propertyMap)
{
return new JsonProperty
{
PropertyName = name,
PropertyType = HalKitTypeBuilder.CompileResultType($"{type.Name}{name}", propertyMap),
ValueProvider = new ReservedHalPropertyValueProvider(_settings, propertyMap),
NullValueHandling = NullValueHandling.Ignore,
Readable = propertyMap.Values.Any(p => p.Readable),
Writable = propertyMap.Values.Any(p => p.Writable),
ShouldSerialize = o => true,
GetIsSpecified = o => true,
SetIsSpecified = null,
Order = int.MaxValue,
};
}

private class ReservedHalPropertyValueProvider : IValueProvider
{
private readonly JsonSerializerSettings _settings;
private readonly IReadOnlyDictionary<string, JsonProperty> _propertyMap;

public ReservedHalPropertyValueProvider(
JsonSerializerSettings settings,
IReadOnlyDictionary<string, JsonProperty> propertyMap)
{
_settings = settings;
_propertyMap = propertyMap;
}

public object GetValue(object target)
{
// Use a SortedDictionary since it just seems "right" for the
// "self" link to be first
var reservedPropertyValue = new SortedDictionary<string, object>(new RelComparer());
foreach (var rel in _propertyMap.Keys)
{
var property = _propertyMap[rel];
var propertyValue = property.ValueProvider.GetValue(target);
if (propertyValue != null)
{
reservedPropertyValue.Add(rel, propertyValue);
}
}

return reservedPropertyValue.Count > 0 ? reservedPropertyValue : null;
}

public void SetValue(object target, object value)
{
var valueDictionary = value as IDictionary<string, object>;
if (valueDictionary == null)
{
return;
}

foreach (var rel in valueDictionary.Keys)
{
JsonProperty property;
if (!_propertyMap.TryGetValue(rel, out property))
{
continue;
}

var serializer = JsonSerializer.Create(_settings);
var propertyJson = valueDictionary[rel] as JToken;
var propertyValue = propertyJson != null
? propertyJson.ToObject(property.PropertyType, serializer)
: null;
property.ValueProvider.SetValue(target, propertyValue);
}
}
}

private class RelComparer : IComparer<string>
{
public int Compare(string rel, string otherRel)
{
const string self = "self";
if (rel == self)
{
return -1;
}

if (otherRel == self)
{
return 1;
}

return string.Compare(rel, otherRel, StringComparison.Ordinal);
}
}
}
}
6 changes: 6 additions & 0 deletions HalKit.sln
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Expand Up @@ -23,6 +23,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Meta", "Meta", "{EC8D73FD-F
Version.props = Version.props
EndProjectSection
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HalKit.Backend", "HalKit.Backend\HalKit.Backend.csproj", "{F018259F-3574-4675-A78C-5D3165039522}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
Expand All @@ -37,6 +39,10 @@ Global
{56D3F770-FD3A-4ADF-A4A0-A5104F5A0012}.Debug|Any CPU.Build.0 = Debug|Any CPU
{56D3F770-FD3A-4ADF-A4A0-A5104F5A0012}.Release|Any CPU.ActiveCfg = Release|Any CPU
{56D3F770-FD3A-4ADF-A4A0-A5104F5A0012}.Release|Any CPU.Build.0 = Release|Any CPU
{F018259F-3574-4675-A78C-5D3165039522}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{F018259F-3574-4675-A78C-5D3165039522}.Debug|Any CPU.Build.0 = Debug|Any CPU
{F018259F-3574-4675-A78C-5D3165039522}.Release|Any CPU.ActiveCfg = Release|Any CPU
{F018259F-3574-4675-A78C-5D3165039522}.Release|Any CPU.Build.0 = Release|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
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2 changes: 1 addition & 1 deletion Version.props
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<Project>
<PropertyGroup>
<VersionPrefix>1.0.3</VersionPrefix>
<VersionPrefix>1.0.4</VersionPrefix>
<VersionSuffix>
</VersionSuffix>
</PropertyGroup>
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