diff --git a/proxy_resolver.h b/proxy_resolver.h
index af228d2..53fd920 100644
--- a/proxy_resolver.h
+++ b/proxy_resolver.h
@@ -5,28 +5,39 @@
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_PROXY_RESOLVER_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_PROXY_RESOLVER_H__
 
-#include <base/logging.h>
 
 #include <deque>
 #include <string>
 
+#include <base/logging.h>
+#include <google/protobuf/stubs/common.h>
+
+#include "update_engine/utils.h"
+
 namespace chromeos_update_engine {
 
 extern const char kNoProxy[];
 
+// Callback for a call to GetProxiesForUrl().
+// Resultant proxies are in |out_proxy|. Each will be in one of the
+// following forms:
+// http://<host>[:<port>] - HTTP proxy
+// socks{4,5}://<host>[:<port>] - SOCKS4/5 proxy
+// kNoProxy - no proxy
+typedef void (*ProxiesResolvedFn)(const std::deque<std::string>& proxies,
+                                  void* data);
+
 class ProxyResolver {
  public:
   ProxyResolver() {}
   virtual ~ProxyResolver() {}
 
-  // Stores a list of proxies for a given |url| in |out_proxy|.
-  // Returns true on success. The resultant proxy will be in one of the
-  // following forms:
-  // http://<host>[:<port>] - HTTP proxy
-  // socks{4,5}://<host>[:<port>] - SOCKS4/5 proxy
-  // kNoProxy - no proxy
+  // Finds proxies for the given URL and returns them via the callback.
+  // |data| will be passed to the callback.
+  // Returns true on success.
   virtual bool GetProxiesForUrl(const std::string& url,
-                                std::deque<std::string>* out_proxies) = 0;
+                                ProxiesResolvedFn callback,
+                                void* data) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ProxyResolver);
@@ -35,11 +46,18 @@
 // Always says to not use a proxy
 class DirectProxyResolver : public ProxyResolver {
  public:
-  DirectProxyResolver() {}
+  DirectProxyResolver() : idle_callback_id_(0) {}
+  virtual ~DirectProxyResolver();
   virtual bool GetProxiesForUrl(const std::string& url,
-                                std::deque<std::string>* out_proxies);
+                                ProxiesResolvedFn callback,
+                                void* data);
 
  private:
+  // The ID of the idle main loop callback
+  guint idle_callback_id_;
+
+  // The MainLoop callback, from here we return to the client.
+  void ReturnCallback(ProxiesResolvedFn callback, void* data);
   DISALLOW_COPY_AND_ASSIGN(DirectProxyResolver);
 };