diff --git a/http_fetcher.h b/http_fetcher.h
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+++ b/http_fetcher.h
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+// Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UPDATE_ENGINE_HTTP_FETCHER_H__
+#define UPDATE_ENGINE_HTTP_FETCHER_H__
+
+#include <string>
+#include <glib.h>
+#include "base/basictypes.h"
+
+// This class is a simple wrapper around an HTTP library (libcurl). We can
+// easily mock out this interface for testing.
+
+// Implementations of this class should use asynchronous i/o. They can access
+// the glib main loop to request callbacks when timers or file descriptors
+// change.
+
+namespace chromeos_update_engine {
+
+class HttpFetcherDelegate;
+
+class HttpFetcher {
+ public:
+  HttpFetcher() : delegate_(NULL) {}
+  virtual ~HttpFetcher() {}
+  void set_delegate(HttpFetcherDelegate* delegate) {
+    delegate_ = delegate;
+  }
+  HttpFetcherDelegate* delegate() const {
+    return delegate_;
+  }
+
+  // Optional: Post data to the server. The HttpFetcher should make a copy
+  // of this data and upload it via HTTP POST during the transfer.
+  void SetPostData(const void* data, size_t size) {
+    post_data_set_ = true;
+    post_data_.clear();
+    const char *char_data = reinterpret_cast<const char*>(data);
+    post_data_.insert(post_data_.end(), char_data, char_data + size);
+  }
+
+  // Begins the transfer to the specified URL.
+  virtual void BeginTransfer(const std::string& url) = 0;
+
+  // Aborts the transfer. TransferComplete() will not be called on the
+  // delegate.
+  virtual void TerminateTransfer() = 0;
+
+  // If data is coming in too quickly, you can call Pause() to pause the
+  // transfer. The delegate will not have ReceivedBytes() called while
+  // an HttpFetcher is paused.
+  virtual void Pause() = 0;
+
+  // Used to unpause an HttpFetcher and let the bytes stream in again.
+  // If a delegate is set, ReceivedBytes() may be called on it before
+  // Unpause() returns
+  virtual void Unpause() = 0;
+
+ protected:
+  // The URL we're actively fetching from
+  std::string url_;
+
+  // POST data for the transfer, and whether or not it was ever set
+  bool post_data_set_;
+  std::vector<char> post_data_;
+
+  // The delegate; may be NULL.
+  HttpFetcherDelegate* delegate_;
+ private:
+  DISALLOW_COPY_AND_ASSIGN(HttpFetcher);
+};
+
+// Interface for delegates
+class HttpFetcherDelegate {
+ public:
+  // Called every time bytes are received, even if they are automatically
+  // delivered to an output file.
+  virtual void ReceivedBytes(HttpFetcher* fetcher,
+                             const char* bytes,
+                             int length) = 0;
+
+  // Called when the transfer has completed successfully or been somehow
+  // aborted.
+  virtual void TransferComplete(HttpFetcher* fetcher, bool successful) = 0;
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_HTTP_FETCHER_H__