.NET Core Api-基于请求值的自定义JSON解析器

问题描述

我希望我的API发出的所有OkObjectResult响应都通过我拥有的自定义JSON解析器运行。解析器依赖于一些特定于请求的数据，即用户的角色。它实际上类似于控制器上的Authorize属性，但用于从API传递到UI的数据传输对象。

我可以通过AddJsonOptions在"配置服务"中添加解析程序，但它无权访问那里的该用户信息。

如何将基于请求的值传递给此解析程序？我看到的是某种自定义中间件，还是其他什么？

作为示例，如果我有一个带有一些自定义属性修饰符的对象，如下所示：

public class TestObject
{
    public String Field1 => "NoRestrictions";
    [RequireRoleView("Admin")]
    public String Field2 => "ViewRequiresAdmin";
}

并使用不同的角色调用我的自定义序列化程序，如下所示：

var test = new TestObject();
var userRoles = GetRoles(); // "User" for the sake of this example
var outputJson = JsonConvert.SerializeObject(test,
                    new JsonSerializerSettings {
                        ContractResolver = new MyCustomResolver(userRoles)
                    });

然后输出JSON将跳过用户无法访问的任何内容，如下所示：

{
    "Field1":"NoRestrictions",
    // Note the absence of Field2, since it has [RequireRoleView("Admin")]
}

推荐答案

假设您有一个自定义的RequireRoleViewAttribute：

[AttributeUsageAttribute(AttributeTargets.All, Inherited = true, AllowMultiple = true)]
public class RequireRoleViewAttribute : Attribute
{

    public string Role;

    public RequireRoleViewAttribute(string role){
        this.Role = role;
    }
}

您可以在自定义解析程序中注入IServiceProvider：

public class RoleBasedContractResolver : DefaultContractResolver
{
    public IServiceProvider ServiceProvider { get; }
    public RoleBasedContractResolver( IServiceProvider sp)
    {
        this.ServiceProvider = sp;
    }

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var contextAccessor = this.ServiceProvider.GetRequiredService<IHttpContextAccessor>() ;
        var context = contextAccessor.HttpContext;
        var user = context.User;

       // if you're using the Identity, you can get the userManager :
       var userManager = context.RequestServices.GetRequiredService<UserManager<IdentityUser>>();

       // ...
    }
}

这样我们就可以随心所欲地得到HttpContext和User。如果您使用的是标识，还可以获取UserManager服务和角色。

现在我们可以按照@dbc's advice来控制ShouldSerialize：

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var contextAccessor = this.ServiceProvider.GetRequiredService<IHttpContextAccessor>() ;
        var context = contextAccessor.HttpContext;
        var user = context.User;

        // if you use the Identitiy, you can get the usermanager
        //UserManager<IdentityUser>
        var userManager = context.RequestServices.GetRequiredService<UserManager<IdentityUser>>();

        JsonProperty property = base.CreateProperty(member, memberSerialization);

        // get the attributes
        var attrs=member.GetCustomAttributes<RequireRoleViewAttribute>();

        // if no [RequireResoveView] decorated, always serialize it
        if(attrs.Count()==0) {
            property.ShouldDeserialize = instance => true;
            return property;
        }

        // custom your logic to dertermine wether should serialize the property
        // I just use check if it can statisify any the condition :
        var roles = this.GetIdentityUserRolesAsync(context,userManager).Result;
        property.ShouldSerialize = instance => {
            var resource = new { /* any you need  */ };
            return attrs.Any(attr => {
                var rolename = attr.Role;
                return roles.Any(r => r == rolename ) ;
            }) ? true : false;
        };
        return property;
    }

函数GetIdentityUserRolesAsync这里是使用当前HttpContext和UserManger服务检索角色的帮助器方法：

private async Task<IList<string>> GetIdentityUserRolesAsync(HttpContext context, UserManager<IdentityUser> userManager)
{
    var rolesCached= context.Items["__userRoles__"];
    if( rolesCached != null){
        return (IList<string>) rolesCached;
    }
    var identityUser = await userManager.GetUserAsync(context.User);
    var roles = await userManager.GetRolesAsync(identityUser);
    context.Items["__userRoles__"] = roles;
    return roles;
}

如何注入IServiceProvider详细说明：

诀窍在于如何使用IServiceProvider配置默认MvcJwtOptions。

不配置JsonOptions人：

services.AddMvc().
    .AddJsonOptions(o =>{
        // o.
    });

，因为它不允许我们添加IServiceProvider参数。

我们可以自定义MvcJsonOptions的子类：

// in .NET 3.1 and above, change this from MvcJsonOptions to MvcNewtonsoftJsonOptions
public class MyMvcJsonOptionsWrapper : IConfigureOptions<MvcJsonOptions>
{
    IServiceProvider ServiceProvider;
    public MyMvcJsonOptionsWrapper(IServiceProvider serviceProvider)
    {
        this.ServiceProvider = serviceProvider;
    }
    public void Configure(MvcJsonOptions options)
    {
        options.SerializerSettings.ContractResolver =new RoleBasedContractResolver(ServiceProvider);
    }
}

并通过以下方式注册服务：

services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();

// don't forget to add the IHttpContextAccessor
// in .NET 3.1 and above, change this from MvcJsonOptions to MvcNewtonsoftJsonOptions
services.AddTransient<IConfigureOptions<MvcJsonOptions>,MyMvcJsonOptionsWrapper>();

测试用例：

假设您有一个自定义POCO：

public class TestObject
{
    public string Field1 => "NoRestrictions";

    [RequireRoleView("Admin")]
    public string Field2 => "ViewRequiresAdmin";

    [RequireRoleView("HR"),RequireRoleView("OP")]
    public string Field3 => "ViewRequiresHROrOP";

    [RequireRoleView("IT"), RequireRoleView("HR")]
    public string Field4 => "ViewRequiresITOrHR";

    [RequireRoleView("IT"), RequireRoleView("OP")]
    public string Field5 => "ViewRequiresITOrOP";
}

且当前用户有角色：Admin和HR：

结果为：

{"Field1":"NoRestrictions","Field2":"ViewRequiresAdmin","Field3":"ViewRequiresHROrOP","Field4":"ViewRequiresITOrHR"}

动作方法测试截图：

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