diff --git a/common/proxy_resolver.h b/common/proxy_resolver.h
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+//
+// Copyright (C) 2010 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef UPDATE_ENGINE_COMMON_PROXY_RESOLVER_H_
+#define UPDATE_ENGINE_COMMON_PROXY_RESOLVER_H_
+
+#include <deque>
+#include <string>
+
+#include <base/logging.h>
+#include <brillo/message_loops/message_loop.h>
+
+#include "update_engine/common/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 base::Callback<void(const std::deque<std::string>& proxies)>
+    ProxiesResolvedFn;
+
+// An id that identifies a proxy request. Used to cancel an ongoing request
+// before the callback is called.
+typedef brillo::MessageLoop::TaskId ProxyRequestId;
+
+// A constant identifying an invalid ProxyRequestId.
+extern const ProxyRequestId kProxyRequestIdNull;
+
+class ProxyResolver {
+ public:
+  ProxyResolver() {}
+  virtual ~ProxyResolver() {}
+
+  // Finds proxies for the given URL and returns them via the callback.
+  // Returns the id of the pending request on success or kProxyRequestIdNull
+  // otherwise.
+  virtual ProxyRequestId GetProxiesForUrl(
+      const std::string& url, const ProxiesResolvedFn& callback) = 0;
+
+  // Cancel the proxy resolution request initiated by GetProxiesForUrl(). The
+  // |request| value must be the one provided by GetProxiesForUrl().
+  virtual bool CancelProxyRequest(ProxyRequestId request) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ProxyResolver);
+};
+
+// Always says to not use a proxy
+class DirectProxyResolver : public ProxyResolver {
+ public:
+  DirectProxyResolver() = default;
+  ~DirectProxyResolver() override;
+  ProxyRequestId GetProxiesForUrl(const std::string& url,
+                                  const ProxiesResolvedFn& callback) override;
+  bool CancelProxyRequest(ProxyRequestId request) override;
+
+  // Set the number of direct (non-) proxies to be returned by resolver.
+  // The default value is 1; higher numbers are currently used in testing.
+  inline void set_num_proxies(size_t num_proxies) {
+    num_proxies_ = num_proxies;
+  }
+
+ private:
+  // The ID of the main loop callback.
+  brillo::MessageLoop::TaskId idle_callback_id_{
+      brillo::MessageLoop::kTaskIdNull};
+
+  // Number of direct proxies to return on resolved list; currently used for
+  // testing.
+  size_t num_proxies_{1};
+
+  // The MainLoop callback, from here we return to the client.
+  void ReturnCallback(const ProxiesResolvedFn& callback);
+  DISALLOW_COPY_AND_ASSIGN(DirectProxyResolver);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_PROXY_RESOLVER_H_