http_fetcher.h

// 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 CHROMEOS_PLATFORM_UPDATE_ENGINE_HTTP_FETCHER_H__
#define CHROMEOS_PLATFORM_UPDATE_ENGINE_HTTP_FETCHER_H__

#include <deque>
#include <string>
#include <vector>

#include <base/basictypes.h>
#include <base/logging.h>
#include <glib.h>
#include <google/protobuf/stubs/common.h>

#include "update_engine/proxy_resolver.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:
  // |proxy_resolver| is the resolver that will be consulted for proxy
  // settings. It may be null, in which case direct connections will
  // be used. Does not take ownership of the resolver.
  explicit HttpFetcher(ProxyResolver* proxy_resolver)
      : post_data_set_(false),
        http_response_code_(0),
        delegate_(NULL),
        proxies_(1, kNoProxy),
        proxy_resolver_(proxy_resolver),
        no_resolver_idle_id_(0),
        callback_(NULL) {}
  virtual ~HttpFetcher();

  void set_delegate(HttpFetcherDelegate* delegate) { delegate_ = delegate; }
  HttpFetcherDelegate* delegate() const { return delegate_; }
  int http_response_code() const { return http_response_code_; }

  // 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);

  // Proxy methods to set the proxies, then to pop them off.
  // Returns true on success.
  bool ResolveProxiesForUrl(const std::string& url,
                            google::protobuf::Closure* callback);
  
  void SetProxies(const std::deque<std::string>& proxies) {
    proxies_ = proxies;
  }
  const std::string& GetCurrentProxy() const {
    return proxies_.front();
  }
  bool HasProxy() const { return !proxies_.empty(); }
  void PopProxy() { proxies_.pop_front(); }

  // Downloading should resume from this offset
  virtual void SetOffset(off_t offset) = 0;

  // Begins the transfer to the specified URL. This fetcher instance should not
  // be destroyed until either TransferComplete, or TransferTerminated is
  // called.
  virtual void BeginTransfer(const std::string& url) = 0;

  // Aborts the transfer. The transfer may not abort right away -- delegate's
  // TransferTerminated() will be called when the transfer is actually done.
  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;

  // These two function are overloaded in LibcurlHttp fetcher to speed
  // testing.
  virtual void set_idle_seconds(int seconds) {}
  virtual void set_retry_seconds(int seconds) {}

  ProxyResolver* proxy_resolver() const { return proxy_resolver_; }

  // These are used for testing:
  virtual void SetConnectionAsExpensive(bool is_expensive) {}
  virtual void SetBuildType(bool is_official) {}

 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 server's HTTP response code from the last transfer. This
  // field should be set to 0 when a new transfer is initiated, and
  // set to the response code when the transfer is complete.
  int http_response_code_;

  // The delegate; may be NULL.
  HttpFetcherDelegate* delegate_;

  // Proxy servers
  std::deque<std::string> proxies_;

  ProxyResolver* const proxy_resolver_;

  // The ID of the idle callback, used when we have no proxy resolver.
  guint no_resolver_idle_id_;

  // Callback for when we are resolving proxies
  google::protobuf::Closure* callback_;

 private:
  // Callback from the proxy resolver
  void ProxiesResolved(const std::deque<std::string>& proxies);
  static void StaticProxiesResolved(const std::deque<std::string>& proxies,
                                    void* data) {
    reinterpret_cast<HttpFetcher*>(data)->ProxiesResolved(proxies);
  }
   
  DISALLOW_COPY_AND_ASSIGN(HttpFetcher);
};

// Interface for delegates
class HttpFetcherDelegate {
 public:
  // Called every time bytes are received.
  virtual void ReceivedBytes(HttpFetcher* fetcher,
                             const char* bytes,
                             int length) = 0;

  // Called if the fetcher seeks to a particular offset.
  virtual void SeekToOffset(off_t offset) {}

  // When a transfer has completed, exactly one of these two methods will be
  // called. TransferTerminated is called when the transfer has been aborted
  // through TerminateTransfer. TransferComplete is called in all other
  // situations. It's OK to destroy the |fetcher| object in this callback.
  virtual void TransferComplete(HttpFetcher* fetcher, bool successful) = 0;
  virtual void TransferTerminated(HttpFetcher* fetcher) {}
};

}  // namespace chromeos_update_engine

#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_HTTP_FETCHER_H__