如何在使用自定义InputFormatter时使用配置的JSON选项？

Question

我希望用自定义输入格式化程序替换默认的SystemTextJsonInputFormatter，或者作为TextInputFormatter的子类，或者(最好是) SystemTextJsonInputFormatter；最好是后者，尽可能接近内置的ASp.NET核心行为，而不必将代码复制到类中，在新的ASP.NET Core版本对SystemTextJsonInputFormatter进行更改时，需要定期更新。

这里有一些相关信息：

ASP.NET核心Web中的自定义格式化程序

提供如何注册自定义输入格式化程序的示例：

var builder = WebApplication.CreateBuilder(args);
   
builder.Services.AddControllers(options =>
{
    options.InputFormatters.Insert(0, new VcardInputFormatter());
});

但是，我目前也对JSON选项进行了自定义，如下所示：

internal static IServiceCollection ConfigureJsonSerialization(this IServiceCollection services)
{
    services.AddControllers().AddJsonOptions(opts => {
        // Note. some of these settings are defaults, but we ensure they are set as required.
        opts.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
        opts.JsonSerializerOptions.PropertyNameCaseInsensitive = false;
        opts.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;

        // Add our custom converters.
        opts.JsonSerializerOptions.Converters.Add(new DateOnlyJsonConverter());
    });

    return services;
}

opts有一个Microsoft.AspNetCore.Mvc.JsonOptions对象。

当使用内置SystemTextJsonInputFormatter时，这些选项通过其构造函数将其放入格式化程序实例(相关代码似乎在MvcCoreMvcOptionsSetup中)。

我希望在我的自定义输入格式化程序中使用相同的JSON选项，但是无法看到如何在构建时获得JsonOptions (从上面的options.InputFormatters.Insert(0, new VcardInputFormatter());行)。

我将继续查看ASP.NET核心内部，试图找出一种方法，但我想我会在这里要求，以防任何人可以提供一些指导。

谢谢。

Answer 1

一种有点麻烦的方法是简单地从JsonSerializerOptions核心提供的现有SystemTextJsonInputFormatter实例中复制ASP.NET属性，如下所示：

public static class ServiceCollectionExtensions
{
    internal static IServiceCollection ConfigureJsonSerialization(this IServiceCollection services)
    {
        services.AddControllers(
            opts => {
                // Search for an existing instance of SystemTextJsonInputFormatter in the InputFormatters list;
                // this is the instance provided as standard by ASP.NET Core.
                int idx = FindSystemTextJsonInputFormatter(
                    opts.InputFormatters,
                    out SystemTextJsonInputFormatter? sysTextJsonInputFormatter);

                // We expect to find the SystemTextJsonInputFormatter.
                if (sysTextJsonInputFormatter is null)
                    throw new InvalidOperationException("No SystemTextJsonInputFormatter is defined.");

                // We will now create our own input formatter, and swap it in to substitute the
                // SystemTextJsonInputFormatter instance. First we have some objects to setup.

                // Copy the json serializer settings from the existing SystemTextJsonInputFormatter.
                var jsonOptions = new JsonOptions();
                CopyJsonSerializerOptions(
                    jsonOptions.JsonSerializerOptions,
                    sysTextJsonInputFormatter.SerializerOptions);

                // TODO/FIXME: Research how best to get a logger for our input formatter!
                var loggerFactory = LoggerFactory.Create(builder => {
                    builder.AddConsole();
                });
                var logger = loggerFactory.CreateLogger<SystemTextJsonInputFormatter>();

                // Perform the substitution.
                opts.InputFormatters[idx] = new JsonMergePatchInputFormatter(jsonOptions, logger);
            })
            .AddJsonOptions(opts => {
                // Note. some of these settings are defaults, but we ensure they are set as required.
                opts.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
                opts.JsonSerializerOptions.PropertyNameCaseInsensitive = false;
                opts.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;

                // Add our custom converters.
                opts.JsonSerializerOptions.Converters.Add(new DateOnlyJsonConverter());
            });

        return services;
    }

    private static int FindSystemTextJsonInputFormatter(
        FormatterCollection<IInputFormatter> inputFormatters,
        out SystemTextJsonInputFormatter? sysTextJsonInputFormatter)
    {
        // Search for an instance of SystemTextJsonInputFormatter, and store it's index in the InputFormatters list.
        // Note. We expect only one instance at most, but if there is more then one then we simply take the first instance.
        for (int i = 0; i < inputFormatters.Count; i++)
        {
            if (inputFormatters[i] is SystemTextJsonInputFormatter formatter)
            {
                sysTextJsonInputFormatter = formatter;
                return i;
            }
        }

        // Not found.
        sysTextJsonInputFormatter = null;
        return -1;
    }

    private static void CopyJsonSerializerOptions(JsonSerializerOptions targetOptions, JsonSerializerOptions sourceOptions)
    {
        // Notes. A hacky but necessary approach, because we are given a pre-built JsonSerializerOptions object
        // that can't be replaced, therefore we must copy the various setting into it.
        targetOptions.AllowTrailingCommas = sourceOptions.AllowTrailingCommas;
        targetOptions.DefaultBufferSize = sourceOptions.DefaultBufferSize;
        targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;
        targetOptions.DictionaryKeyPolicy = sourceOptions.DictionaryKeyPolicy;
        targetOptions.Encoder = sourceOptions.Encoder;
        targetOptions.IgnoreNullValues = sourceOptions.IgnoreNullValues;
        targetOptions.IgnoreReadOnlyFields = sourceOptions.IgnoreReadOnlyFields;
        targetOptions.IncludeFields = sourceOptions.IncludeFields;
        targetOptions.MaxDepth = sourceOptions.MaxDepth;
        targetOptions.NumberHandling = sourceOptions.NumberHandling;
        targetOptions.PropertyNameCaseInsensitive = sourceOptions.PropertyNameCaseInsensitive;
        targetOptions.PropertyNamingPolicy = sourceOptions.PropertyNamingPolicy;
        targetOptions.ReadCommentHandling = sourceOptions.ReadCommentHandling;
        targetOptions.ReferenceHandler = sourceOptions.ReferenceHandler;
        targetOptions.UnknownTypeHandling = sourceOptions.UnknownTypeHandling;
        targetOptions.WriteIndented = sourceOptions.WriteIndented;
        targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;
        targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;

        // Re-use the same converter instances; this is OK because their current parent
        // SystemTextJsonInputFormatter is about to be discarded.
        targetOptions.Converters.Clear();
        foreach (var jsonConverter in sourceOptions.Converters)
        {
            targetOptions.Converters.Add(jsonConverter);
        }
    }
}

我花了一些时间仔细研究ASP.NET核心源代码和调用堆栈，试图找到一种更好/更干净/更正式的方式，但最终不得不放弃并使用上面的方法。如果有更好的解决办法，请告诉我。