[Swagger] 在Swagger UI 新增自订Header

用Swagger UI 进行测试时，预设是没有Header 可以用，当API 需要用到Header，要自己手动处理一下，让Swagger UI 提供画面让开发人员调试

先定义一个Attribute

[ AttributeUsage ( AttributeTargets . Method, AllowMultiple = true ) ]
public class  HeaderAttribute : Attribute
{
    public string Name {  get ; set ; }

    public string Type {  get ; set ; }

    public object [] EnumValues  {  get ; set ; }

    public bool  Required  {  get ; set ; }

    public object  Default  {  get ; set ; }
}

依照需求，把挂在Action 上

public class  ValuesController : ApiController
{
    [ Header ( Name = "Header1" , Type = "string" , EnumValues = new  object [] { 1 , 2 , 3 } , Default = "2" ) ]
    public IEnumerable < string > Get ()
    {
        return  new [] { "value1" , "value2" } ;
     }
}

实作 IOperationFilter，用来把Action 上面的HeaderAttribute，放到Operation.parameters

public class  HeaderFilter : IOperationFilter
{
    public void  Apply ( Operation  operation, SchemaRegistry  schemaRegistry, ApiDescription  apiDescription )
    {
        var  headers = apiDescription . ActionDescriptor . GetCustomAttributes< HeaderAttribute > () ;
         if ( ! headers . Any () )
        {
            return ;
         }

        if ( operation . parameters == null )
        {
            operation . parameters = new  List < Parameter > () ;
         }

        foreach ( var  header in headers )
        {
            var  parameter = new  Parameter
            {
                name = header . Name,
                @in = "header" ,
                type = header . Type,
                @enum = header . EnumValues? . ToList () ,
                required = header . Required,
                @default = header . Default
             } ;
            operation . parameters . Add ( parameter ) ;
         }
    }
}

在SwaggerConfig.cs 里面套用 

c . OperationFilter< HeaderFilter > ()