WCF 專題系列（三）：深入尋址 Part 3 — 訊息篩選引擎核心機制

訊息篩選引擎架構

WCF 接收訊息時，透過訊息篩選引擎決定目標端點。核心兩大組件：

• 篩選器：MessageFilter 抽象基類，判斷訊息是否匹配條件
• 篩選器表：IMessageFilterTable<TFilterData>，儲存篩選器鍵值對，支援優先級

每個 EndpointDispatcher 持有兩個篩選器：地址篩選器（檢查 To 標頭與尋址標頭）與契約篩選器（檢查 Action 標頭）。

內建五大篩選器

篩選器運作示範

var actionFilter1 = new ActionMessageFilter("Add", "Sub");
var actionFilter2 = new ActionMessageFilter("Mul");
var addrFilter1 = new EndpointAddressMessageFilter(new EndpointAddress("https://localhost:8887/Calculator"));
var addrFilter2 = new EndpointAddressMessageFilter(new EndpointAddress("https://www.cnblogs.com/terrylee"));

var msg = Message.CreateMessage(MessageVersion.Soap12WSAddressing10, "myBody");
msg.Headers.Action = "Add";
msg.Headers.To = new Uri("https://localhost:8887/Calculator");

Console.WriteLine(actionFilter1.Match(msg)); // True
Console.WriteLine(actionFilter2.Match(msg)); // False
Console.WriteLine(addrFilter1.Match(msg));   // True
Console.WriteLine(addrFilter2.Match(msg));   // False

SOAP 訊息實際內容：

<s:Envelope ...>
  <s:Header>
    <a:To>https://localhost:8887/Calculator</a:To>
    <a:Action>Add</a:Action>
  </s:Header>
  <s:Body></s:Body>
</s:Envelope>

篩選器表內部機制

依篩選器型別分桶存儲，新增時自動分配預設優先級：

篩選器條件建構後不可變，需建立新實例替換。

服務層級控制：AddressFilterMode

ServiceBehavior 屬性 AddressFilterMode 三選一：

• Exact（預設）：EndpointAddressMessageFilter
• Prefix：PrefixEndpointAddressMessageFilter
• Any：MatchAllMessageFilter

[ServiceBehavior(AddressFilterMode = AddressFilterMode.Prefix)]
public class CalculatorService : ICalculator { ... }

驗證 EndpointDispatcher 實際篩選器

foreach (var cd in host.ChannelDispatchers)
    foreach (var ed in cd.Endpoints)
        Console.WriteLine($"AddrFilter: {ed.AddressFilter} | ContractFilter: {ed.ContractFilter}");

總結

訊息篩選引擎是 WCF 訊息分派核心，內建篩選器涵蓋常見需求，AddressFilterMode 提供服務級快速切換，自訂篩選器（下篇主題）則支援任意複雜路由邏輯。