extract to UserTokenCallProxy

Author: kanat

src/main/java/io/getstream/chat/java/services/framework/DefaultClient.java

@@ -158,31 +158,7 @@ public <TService> TService create(Class<TService> svcClass) {
     return (TService) java.lang.reflect.Proxy.newProxyInstance(
       svcClass.getClassLoader(),
       new Class<?>[] { svcClass },
-      (proxy, method, args) -> {
-        Object result = method.invoke(service, args);
-        
-        // If the result is a Call, wrap it to add the tag
-        if (result instanceof retrofit2.Call) {
-          retrofit2.Call<?> originalCall = (retrofit2.Call<?>) result;
-          retrofit2.Call<?> clonedCall = originalCall.clone();
-          
-          try {
-            // Retrofit's OkHttpCall has a rawCall field
-            var newRequest = originalCall.request().newBuilder().tag(UserToken.class, token).build();
-            okhttp3.Call newOkHttpCall = okHttpClient.newCall(newRequest);
-            
-            java.lang.reflect.Field rawCallField = clonedCall.getClass().getDeclaredField("rawCall");
-            rawCallField.setAccessible(true);
-            rawCallField.set(clonedCall, newOkHttpCall);
-            
-            return clonedCall;
-          } catch (Exception e) {
-            throw new RuntimeException("Failed to modify call", e);
-          }
-        }
-        
-        return result;
-      }
+      new UserTokenCallProxy(okHttpClient, service, token)
     );
   }
 

src/main/java/io/getstream/chat/java/services/framework/UserTokenCallProxy.java

@@ -0,0 +1,78 @@
+package io.getstream.chat.java.services.framework;
+
+import okhttp3.Call;
+import okhttp3.Request;
+import org.jetbrains.annotations.NotNull;
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+
+/**
+ * Dynamic proxy that intercepts Retrofit service calls and injects UserToken
+ * into the request by modifying the internal rawCall field via reflection.
+ * 
+ * This approach allows per-call authentication without creating multiple OkHttpClient
+ * instances, making it suitable for multi-tenant systems with thousands of users.
+ */
+class UserTokenCallProxy implements InvocationHandler {
+  private static volatile Field rawCallField;
+  
+  private final Call.Factory callFactory;
+  private final Object delegate;
+  private final UserToken token;
+
+  UserTokenCallProxy(@NotNull Call.Factory callFactory, @NotNull Object delegate, @NotNull UserToken token) {
+    this.callFactory = callFactory;
+    this.delegate = delegate;
+    this.token = token;
+  }
+  
+  @Override
+  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+    Object result = method.invoke(delegate, args);
+    
+    // If the result is a Retrofit Call, inject the user token
+    if (result instanceof retrofit2.Call) {
+      return injectTokenIntoCall((retrofit2.Call<?>) result);
+    }
+    
+    return result;
+  }
+  
+  private retrofit2.Call<?> injectTokenIntoCall(retrofit2.Call<?> originalCall) {
+    retrofit2.Call<?> clonedCall = originalCall.clone();
+    
+    try {
+      // Cache field lookup for performance (double-checked locking)
+      if (rawCallField == null) {
+        synchronized (UserTokenCallProxy.class) {
+          if (rawCallField == null) {
+            rawCallField = clonedCall.getClass().getDeclaredField("rawCall");
+            rawCallField.setAccessible(true);
+          }
+        }
+      }
+      
+      // Create new request with token tag
+      Request newRequest = originalCall.request().newBuilder()
+        .tag(UserToken.class, token)
+        .build();
+      
+      // Create new OkHttp call with modified request
+      okhttp3.Call newOkHttpCall = callFactory.newCall(newRequest);
+      
+      // Inject the new call into the cloned Retrofit call
+      rawCallField.set(clonedCall, newOkHttpCall);
+      
+      return clonedCall;
+    } catch (NoSuchFieldException e) {
+      // If Retrofit's internal structure changes, provide clear error message
+      throw new RuntimeException(
+        "Retrofit internal structure changed. Field 'rawCall' not found in " + 
+        clonedCall.getClass().getName() + ". Update client implementation.", e);
+    } catch (IllegalAccessException e) {
+      throw new RuntimeException("Failed to inject token into call", e);
+    }
+  }
+}
+