我正在编写一项服务，旨在供多个调用者使用，包括无法接收或解析 XML 或 JSON 的调用者。
我知道使用原始流从服务响应返回 HTML 是可能的，但我希望能够根据传递的 Accepts-Type 标头返回 XML、JSON 或 HTML 之一客户。
我可以使用单独的 URL 来做到这一点，但这正在替换已经具有良好定义的 API 层的系统。
有没有这样做的例子，或者有谁知道管道的哪些部分需要扩展？
（附录）：我已经了解 AutomaticFormatSelection 并已启用它，但我想从一个端点支持所有三种（或更多）格式（HTML、JSON、XML 等）。
【问题讨论】：
是的，这是可能的。但是您需要创建一个新的消息格式化程序，它知道如何在 CLR 类型（操作响应）和 HTML 页面之间进行转换。最简单的方法是将原始格式化程序包装在新格式化程序中，因此当您收到对带有 Accept: text/html 的请求的响应时，您使用您的逻辑，但对于其他请求，您使用原始格式化程序。
不过，格式化程序无法访问传入的请求，因此我们也可以使用消息检查器来提供它。
下面的代码显示了这种格式化程序/检查器对的一种可能实现。
public class StackOverflow_10519075
{
[DataContract(Name = "Person", Namespace = "")]
public class Person
{
[DataMember]
public string Name { get; set; }
[DataMember]
public int Age { get; set; }
}
[ServiceContract]
public interface ITest
{
[WebGet]
Person GetPerson();
}
public class Service : ITest
{
public Person GetPerson()
{
return new Person { Name = "John Doe", Age = 33 };
}
}
public class MyHtmlAwareFormatter : IDispatchMessageFormatter
{
IDispatchMessageFormatter original;
public MyHtmlAwareFormatter(IDispatchMessageFormatter original)
{
this.original = original;
}
public void DeserializeRequest(Message message, object[] parameters)
{
this.original.DeserializeRequest(message, parameters);
}
public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result)
{
MyUseHtmlExtension useHtml = OperationContext.Current.Extensions.Find<MyUseHtmlExtension>();
if (useHtml != null && useHtml.UseHtmlResponse)
{
StringBuilder sb = new StringBuilder();
sb.AppendLine("<html><head><title>Result of " + useHtml.OperationName + "</title></head>");
sb.AppendLine("<body><h1>Result of " + useHtml.OperationName + "</h1>");
sb.AppendLine("<p><b>" + result.GetType().FullName + "</b></p>");
sb.AppendLine("<ul>");
foreach (var prop in result.GetType().GetProperties())
{
string line = string.Format("{0}: {1}", prop.Name, prop.GetValue(result, null));
sb.AppendLine("<li>" + line + "</li>");
}
sb.AppendLine("</ul></body></html>");
byte[] bytes = Encoding.UTF8.GetBytes(sb.ToString());
Message reply = Message.CreateMessage(messageVersion, null, new RawBodyWriter(bytes));
reply.Properties.Add(WebBodyFormatMessageProperty.Name, new WebBodyFormatMessageProperty(WebContentFormat.Raw));
HttpResponseMessageProperty httpResp = new HttpResponseMessageProperty();
reply.Properties.Add(HttpResponseMessageProperty.Name, httpResp);
httpResp.Headers[HttpResponseHeader.ContentType] = "text/html";
return reply;
}
else
{
return original.SerializeReply(messageVersion, parameters, result);
}
}
class RawBodyWriter : BodyWriter
{
private byte[] bytes;
public RawBodyWriter(byte[] bytes)
: base(true)
{
this.bytes = bytes;
}
protected override void OnWriteBodyContents(XmlDictionaryWriter writer)
{
writer.WriteStartElement("Binary");
writer.WriteBase64(this.bytes, 0, this.bytes.Length);
writer.WriteEndElement();
}
}
}
public class MyHtmlAwareInspector : IDispatchMessageInspector
{
public object AfterReceiveRequest(ref Message request, IClientChannel channel, InstanceContext instanceContext)
{
HttpRequestMessageProperty httpRequest = (HttpRequestMessageProperty)request.Properties[HttpRequestMessageProperty.Name];
string accept = httpRequest.Headers[HttpRequestHeader.Accept];
string operationName = request.Properties[WebHttpDispatchOperationSelector.HttpOperationNamePropertyName] as string;
if (accept == "text/html")
{
OperationContext.Current.Extensions.Add(new MyUseHtmlExtension { UseHtmlResponse = true, OperationName = operationName });
}
return null;
}
public void BeforeSendReply(ref Message reply, object correlationState)
{
}
}
class MyUseHtmlExtension : IExtension<OperationContext>
{
public void Attach(OperationContext owner) { }
public void Detach(OperationContext owner) { }
public bool UseHtmlResponse { get; set; }
public string OperationName { get; set; }
}
public class MyHtmlAwareEndpointBehavior : IEndpointBehavior
{
public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
{
}
public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
{
}
public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
{
endpointDispatcher.DispatchRuntime.MessageInspectors.Add(new MyHtmlAwareInspector());
foreach (DispatchOperation operation in endpointDispatcher.DispatchRuntime.Operations)
{
operation.Formatter = new MyHtmlAwareFormatter(operation.Formatter);
}
}
public void Validate(ServiceEndpoint endpoint)
{
}
}
public static void Test()
{
string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
var endpoint = host.AddServiceEndpoint(typeof(ITest), new WebHttpBinding(), "");
endpoint.Behaviors.Add(new WebHttpBehavior { AutomaticFormatSelectionEnabled = true });
endpoint.Behaviors.Add(new MyHtmlAwareEndpointBehavior());
host.Open();
Console.WriteLine("Host opened");
WebClient c;
c = new WebClient();
c.Headers[HttpRequestHeader.Accept] = "application/json";
Console.WriteLine(c.DownloadString(baseAddress + "/GetPerson"));
Console.WriteLine();
c = new WebClient();
c.Headers[HttpRequestHeader.Accept] = "text/xml";
Console.WriteLine(c.DownloadString(baseAddress + "/GetPerson"));
Console.WriteLine();
c = new WebClient();
c.Headers[HttpRequestHeader.Accept] = "text/html";
Console.WriteLine(c.DownloadString(baseAddress + "/GetPerson"));
Console.WriteLine();
Console.Write("Press ENTER to close the host");
Console.ReadLine();
host.Close();
}
}
【讨论】：