95 lines
3.2 KiB
C#
95 lines
3.2 KiB
C#
using System;
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using System.Diagnostics;
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using Newtonsoft.Json;
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namespace Tapeti.Default
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{
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/// <inheritdoc />
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/// <summary>
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/// Converts an <see cref="T:System.Enum" /> to and from its name string value. If an unknown string value is encountered
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/// it will translate to 0xDEADBEEF (-559038737) so it can be gracefully handled.
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/// If you copy this value as-is to another message and try to send it, this converter will throw an exception.
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/// This converter is far simpler than the default StringEnumConverter, it assumes both sides use the same
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/// enum and therefore skips the naming strategy.
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/// </summary>
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public class FallbackStringEnumConverter : JsonConverter
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{
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private readonly int invalidEnumValue;
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/// <inheritdoc />
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public FallbackStringEnumConverter()
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{
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unchecked { invalidEnumValue = (int)0xDEADBEEF; }
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}
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/// <inheritdoc />
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public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
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{
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if (value == null)
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{
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writer.WriteNull();
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return;
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}
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if ((int) value == invalidEnumValue)
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throw new ArgumentException("Enum value was an unknown string value in an incoming message and can not be published in an outgoing message as-is");
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var outputValue = Enum.GetName(value.GetType(), value);
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writer.WriteValue(outputValue);
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}
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/// <inheritdoc />
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public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
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{
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var isNullable = IsNullableType(objectType);
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if (reader.TokenType == JsonToken.Null)
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{
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if (!isNullable)
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throw new JsonSerializationException($"Cannot convert null value to {objectType}");
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return null;
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}
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var actualType = isNullable ? Nullable.GetUnderlyingType(objectType) : objectType;
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Debug.Assert(actualType != null, nameof(actualType) + " != null");
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if (reader.TokenType != JsonToken.String)
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throw new JsonSerializationException($"Unexpected token {reader.TokenType} when parsing enum");
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var enumText = reader.Value?.ToString() ?? "";
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if (enumText == string.Empty && isNullable)
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return null;
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try
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{
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return Enum.Parse(actualType, enumText);
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}
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catch (ArgumentException)
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{
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return Enum.ToObject(actualType, invalidEnumValue);
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}
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}
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/// <inheritdoc />
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public override bool CanConvert(Type objectType)
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{
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var actualType = IsNullableType(objectType) ? Nullable.GetUnderlyingType(objectType) : objectType;
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return actualType?.IsEnum ?? false;
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}
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private static bool IsNullableType(Type t)
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{
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if (t == null)
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throw new ArgumentNullException(nameof(t));
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return t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>);
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}
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}
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}
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