// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This file declares a HttpTransactionFactory implementation that can be
// layered on top of another HttpTransactionFactory to add HTTP caching.  The
// caching logic follows RFC 2616 (any exceptions are called out in the code).
//
// The HttpCache takes a disk_cache::Backend as a parameter, and uses that for
// the cache storage.
//
// See HttpTransactionFactory and HttpTransaction for more details.

#ifndef NET_HTTP_HTTP_CACHE_H_
#define NET_HTTP_HTTP_CACHE_H_

#include <list>
#include <map>
#include <set>
#include <string>

#include "base/basictypes.h"
#include "base/containers/hash_tables.h"
#include "base/files/file_path.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/non_thread_safe.h"
#include "base/time/clock.h"
#include "base/time/time.h"
#include "net/base/cache_type.h"
#include "net/base/completion_callback.h"
#include "net/base/load_states.h"
#include "net/base/net_export.h"
#include "net/base/request_priority.h"
#include "net/http/http_network_session.h"
#include "net/http/http_transaction_factory.h"

class GURL;

namespace base {
class SingleThreadTaskRunner;
}  // namespace base

namespace disk_cache {
class Backend;
class Entry;
}  // namespace disk_cache

namespace net {

class CertVerifier;
class ChannelIDService;
class DiskBasedCertCache;
class HostResolver;
class HttpAuthHandlerFactory;
class HttpNetworkSession;
class HttpResponseInfo;
class HttpServerProperties;
class IOBuffer;
class NetLog;
class NetworkDelegate;
class ProxyService;
class SSLConfigService;
class TransportSecurityState;
class ViewCacheHelper;
struct HttpRequestInfo;

class NET_EXPORT HttpCache : public HttpTransactionFactory,
                             NON_EXPORTED_BASE(public base::NonThreadSafe) {
 public:
  // The cache mode of operation.
  enum Mode {
    // Normal mode just behaves like a standard web cache.
    NORMAL = 0,
    // Disables reads and writes from the cache.
    // Equivalent to setting LOAD_DISABLE_CACHE on every request.
    DISABLE
  };

  // A BackendFactory creates a backend object to be used by the HttpCache.
  class NET_EXPORT BackendFactory {
   public:
    virtual ~BackendFactory() {}

    // The actual method to build the backend. Returns a net error code. If
    // ERR_IO_PENDING is returned, the |callback| will be notified when the
    // operation completes, and |backend| must remain valid until the
    // notification arrives.
    // The implementation must not access the factory object after invoking the
    // |callback| because the object can be deleted from within the callback.
    virtual int CreateBackend(NetLog* net_log,
                              scoped_ptr<disk_cache::Backend>* backend,
                              const CompletionCallback& callback) = 0;
  };

  // A default backend factory for the common use cases.
  class NET_EXPORT DefaultBackend : public BackendFactory {
   public:
    // |path| is the destination for any files used by the backend, and
    // |thread| is the thread where disk operations should take place. If
    // |max_bytes| is  zero, a default value will be calculated automatically.
    DefaultBackend(CacheType type,
                   BackendType backend_type,
                   const base::FilePath& path,
                   int max_bytes,
                   const scoped_refptr<base::SingleThreadTaskRunner>& thread);
    ~DefaultBackend() override;

    // Returns a factory for an in-memory cache.
    static BackendFactory* InMemory(int max_bytes);

    // BackendFactory implementation.
    int CreateBackend(NetLog* net_log,
                      scoped_ptr<disk_cache::Backend>* backend,
                      const CompletionCallback& callback) override;

   private:
    CacheType type_;
    BackendType backend_type_;
    const base::FilePath path_;
    int max_bytes_;
    scoped_refptr<base::SingleThreadTaskRunner> thread_;
  };

  // The number of minutes after a resource is prefetched that it can be used
  // again without validation.
  static const int kPrefetchReuseMins = 5;

  // The disk cache is initialized lazily (by CreateTransaction) in this case.
  // The HttpCache takes ownership of the |backend_factory|.
  HttpCache(const HttpNetworkSession::Params& params,
            BackendFactory* backend_factory);

  // The disk cache is initialized lazily (by CreateTransaction) in this case.
  // Provide an existing HttpNetworkSession, the cache can construct a
  // network layer with a shared HttpNetworkSession in order for multiple
  // network layers to share information (e.g. authentication data). The
  // HttpCache takes ownership of the |backend_factory|.
  HttpCache(HttpNetworkSession* session, BackendFactory* backend_factory);

  // Initialize the cache from its component parts. The lifetime of the
  // |network_layer| and |backend_factory| are managed by the HttpCache and
  // will be destroyed using |delete| when the HttpCache is destroyed.
  HttpCache(HttpTransactionFactory* network_layer,
            NetLog* net_log,
            BackendFactory* backend_factory);

  ~HttpCache() override;

  HttpTransactionFactory* network_layer() { return network_layer_.get(); }

  DiskBasedCertCache* cert_cache() const { return cert_cache_.get(); }

  // Retrieves the cache backend for this HttpCache instance. If the backend
  // is not initialized yet, this method will initialize it. The return value is
  // a network error code, and it could be ERR_IO_PENDING, in which case the
  // |callback| will be notified when the operation completes. The pointer that
  // receives the |backend| must remain valid until the operation completes.
  int GetBackend(disk_cache::Backend** backend,
                 const CompletionCallback& callback);

  // Returns the current backend (can be NULL).
  disk_cache::Backend* GetCurrentBackend() const;

  // Given a header data blob, convert it to a response info object.
  static bool ParseResponseInfo(const char* data, int len,
                                HttpResponseInfo* response_info,
                                bool* response_truncated);

  // Writes |buf_len| bytes of metadata stored in |buf| to the cache entry
  // referenced by |url|, as long as the entry's |expected_response_time| has
  // not changed. This method returns without blocking, and the operation will
  // be performed asynchronously without any completion notification.
  void WriteMetadata(const GURL& url,
                     RequestPriority priority,
                     base::Time expected_response_time,
                     IOBuffer* buf,
                     int buf_len);

  // Get/Set the cache's mode.
  void set_mode(Mode value) { mode_ = value; }
  Mode mode() { return mode_; }

  // Get/Set the cache's clock. These are public only for testing.
  void SetClockForTesting(scoped_ptr<base::Clock> clock) {
    clock_.reset(clock.release());
  }
  base::Clock* clock() const { return clock_.get(); }

  // Close currently active sockets so that fresh page loads will not use any
  // recycled connections.  For sockets currently in use, they may not close
  // immediately, but they will not be reusable. This is for debugging.
  void CloseAllConnections();

  // Close all idle connections. Will close all sockets not in active use.
  void CloseIdleConnections();

  // Called whenever an external cache in the system reuses the resource
  // referred to by |url| and |http_method|.
  void OnExternalCacheHit(const GURL& url, const std::string& http_method);

  // Causes all transactions created after this point to effectively bypass
  // the cache lock whenever there is lock contention.
  void BypassLockForTest() {
    bypass_lock_for_test_ = true;
  }

  // Causes all transactions created after this point to generate a failure
  // when attempting to conditionalize a network request.
  void FailConditionalizationForTest() {
    fail_conditionalization_for_test_ = true;
  }

  bool use_stale_while_revalidate() const {
    return use_stale_while_revalidate_;
  }

  // Enable stale_while_revalidate functionality for testing purposes.
  void set_use_stale_while_revalidate_for_testing(
      bool use_stale_while_revalidate) {
    use_stale_while_revalidate_ = use_stale_while_revalidate;
  }

  // HttpTransactionFactory implementation:
  int CreateTransaction(RequestPriority priority,
                        scoped_ptr<HttpTransaction>* trans) override;
  HttpCache* GetCache() override;
  HttpNetworkSession* GetSession() override;

  base::WeakPtr<HttpCache> GetWeakPtr() { return weak_factory_.GetWeakPtr(); }

  // Resets the network layer to allow for tests that probe
  // network changes (e.g. host unreachable).  The old network layer is
  // returned to allow for filter patterns that only intercept
  // some creation requests.  Note ownership exchange.
  scoped_ptr<HttpTransactionFactory>
      SetHttpNetworkTransactionFactoryForTesting(
          scoped_ptr<HttpTransactionFactory> new_network_layer);

 private:
  // Types --------------------------------------------------------------------

  // Disk cache entry data indices.
  enum {
    kResponseInfoIndex = 0,
    kResponseContentIndex,
    kMetadataIndex,

    // Must remain at the end of the enum.
    kNumCacheEntryDataIndices
  };

  class MetadataWriter;
  class QuicServerInfoFactoryAdaptor;
  class Transaction;
  class WorkItem;
  friend class Transaction;
  friend class ViewCacheHelper;
  struct PendingOp;  // Info for an entry under construction.
  class AsyncValidation;  // Encapsulates a single async revalidation.

  typedef std::list<Transaction*> TransactionList;
  typedef std::list<WorkItem*> WorkItemList;
  typedef std::map<std::string, AsyncValidation*> AsyncValidationMap;

  struct ActiveEntry {
    explicit ActiveEntry(disk_cache::Entry* entry);
    ~ActiveEntry();

    disk_cache::Entry* disk_entry;
    Transaction*       writer;
    TransactionList    readers;
    TransactionList    pending_queue;
    bool               will_process_pending_queue;
    bool               doomed;
  };

  typedef base::hash_map<std::string, ActiveEntry*> ActiveEntriesMap;
  typedef base::hash_map<std::string, PendingOp*> PendingOpsMap;
  typedef std::set<ActiveEntry*> ActiveEntriesSet;
  typedef base::hash_map<std::string, int> PlaybackCacheMap;

  // Methods ------------------------------------------------------------------

  // Creates the |backend| object and notifies the |callback| when the operation
  // completes. Returns an error code.
  int CreateBackend(disk_cache::Backend** backend,
                    const CompletionCallback& callback);

  // Makes sure that the backend creation is complete before allowing the
  // provided transaction to use the object. Returns an error code.  |trans|
  // will be notified via its IO callback if this method returns ERR_IO_PENDING.
  // The transaction is free to use the backend directly at any time after
  // receiving the notification.
  int GetBackendForTransaction(Transaction* trans);

  // Generates the cache key for this request.
  std::string GenerateCacheKey(const HttpRequestInfo*);

  // Dooms the entry selected by |key|, if it is currently in the list of active
  // entries.
  void DoomActiveEntry(const std::string& key);

  // Dooms the entry selected by |key|. |trans| will be notified via its IO
  // callback if this method returns ERR_IO_PENDING. The entry can be
  // currently in use or not.
  int DoomEntry(const std::string& key, Transaction* trans);

  // Dooms the entry selected by |key|. |trans| will be notified via its IO
  // callback if this method returns ERR_IO_PENDING. The entry should not
  // be currently in use.
  int AsyncDoomEntry(const std::string& key, Transaction* trans);

  // Dooms the entry associated with a GET for a given |url|.
  void DoomMainEntryForUrl(const GURL& url);

  // Closes a previously doomed entry.
  void FinalizeDoomedEntry(ActiveEntry* entry);

  // Returns an entry that is currently in use and not doomed, or NULL.
  ActiveEntry* FindActiveEntry(const std::string& key);

  // Creates a new ActiveEntry and starts tracking it. |disk_entry| is the disk
  // cache entry.
  ActiveEntry* ActivateEntry(disk_cache::Entry* disk_entry);

  // Deletes an ActiveEntry.
  void DeactivateEntry(ActiveEntry* entry);

  // Deletes an ActiveEntry using an exhaustive search.
  void SlowDeactivateEntry(ActiveEntry* entry);

  // Returns the PendingOp for the desired |key|. If an entry is not under
  // construction already, a new PendingOp structure is created.
  PendingOp* GetPendingOp(const std::string& key);

  // Deletes a PendingOp.
  void DeletePendingOp(PendingOp* pending_op);

  // Opens the disk cache entry associated with |key|, returning an ActiveEntry
  // in |*entry|. |trans| will be notified via its IO callback if this method
  // returns ERR_IO_PENDING.
  int OpenEntry(const std::string& key, ActiveEntry** entry,
                Transaction* trans);

  // Creates the disk cache entry associated with |key|, returning an
  // ActiveEntry in |*entry|. |trans| will be notified via its IO callback if
  // this method returns ERR_IO_PENDING.
  int CreateEntry(const std::string& key, ActiveEntry** entry,
                  Transaction* trans);

  // Destroys an ActiveEntry (active or doomed).
  void DestroyEntry(ActiveEntry* entry);

  // Adds a transaction to an ActiveEntry. If this method returns ERR_IO_PENDING
  // the transaction will be notified about completion via its IO callback. This
  // method returns ERR_CACHE_RACE to signal the transaction that it cannot be
  // added to the provided entry, and it should retry the process with another
  // one (in this case, the entry is no longer valid).
  int AddTransactionToEntry(ActiveEntry* entry, Transaction* trans);

  // Called when the transaction has finished working with this entry. |cancel|
  // is true if the operation was cancelled by the caller instead of running
  // to completion.
  void DoneWithEntry(ActiveEntry* entry, Transaction* trans, bool cancel);

  // Called when the transaction has finished writing to this entry. |success|
  // is false if the cache entry should be deleted.
  void DoneWritingToEntry(ActiveEntry* entry, bool success);

  // Called when the transaction has finished reading from this entry.
  void DoneReadingFromEntry(ActiveEntry* entry, Transaction* trans);

  // Converts the active writer transaction to a reader so that other
  // transactions can start reading from this entry.
  void ConvertWriterToReader(ActiveEntry* entry);

  // Returns the LoadState of the provided pending transaction.
  LoadState GetLoadStateForPendingTransaction(const Transaction* trans);

  // Removes the transaction |trans|, from the pending list of an entry
  // (PendingOp, active or doomed entry).
  void RemovePendingTransaction(Transaction* trans);

  // Removes the transaction |trans|, from the pending list of |entry|.
  bool RemovePendingTransactionFromEntry(ActiveEntry* entry,
                                         Transaction* trans);

  // Removes the transaction |trans|, from the pending list of |pending_op|.
  bool RemovePendingTransactionFromPendingOp(PendingOp* pending_op,
                                             Transaction* trans);

  // Instantiates and sets QUIC server info factory.
  void SetupQuicServerInfoFactory(HttpNetworkSession* session);

  // Resumes processing the pending list of |entry|.
  void ProcessPendingQueue(ActiveEntry* entry);

  // Called by Transaction to perform an asynchronous revalidation. Creates a
  // new independent transaction as a copy of the original.
  void PerformAsyncValidation(const HttpRequestInfo& original_request,
                              const BoundNetLog& net_log);

  // Remove the AsyncValidation with url |url| from the |async_validations_| set
  // and delete it.
  void DeleteAsyncValidation(const std::string& url);

  // Events (called via PostTask) ---------------------------------------------

  void OnProcessPendingQueue(ActiveEntry* entry);

  // Callbacks ----------------------------------------------------------------

  // Processes BackendCallback notifications.
  void OnIOComplete(int result, PendingOp* entry);

  // Helper to conditionally delete |pending_op| if the HttpCache object it
  // is meant for has been deleted.
  //
  // TODO(ajwong): The PendingOp lifetime management is very tricky.  It might
  // be possible to simplify it using either base::Owned() or base::Passed()
  // with the callback.
  static void OnPendingOpComplete(const base::WeakPtr<HttpCache>& cache,
                                  PendingOp* pending_op,
                                  int result);

  // Processes the backend creation notification.
  void OnBackendCreated(int result, PendingOp* pending_op);

  // Variables ----------------------------------------------------------------

  NetLog* net_log_;

  // Used when lazily constructing the disk_cache_.
  scoped_ptr<BackendFactory> backend_factory_;
  bool building_backend_;
  bool bypass_lock_for_test_;
  bool fail_conditionalization_for_test_;

  // true if the implementation of Cache-Control: stale-while-revalidate
  // directive is enabled (either via command-line flag or experiment).
  bool use_stale_while_revalidate_;

  Mode mode_;

  scoped_ptr<QuicServerInfoFactoryAdaptor> quic_server_info_factory_;

  scoped_ptr<HttpTransactionFactory> network_layer_;

  scoped_ptr<disk_cache::Backend> disk_cache_;

  scoped_ptr<DiskBasedCertCache> cert_cache_;

  // The set of active entries indexed by cache key.
  ActiveEntriesMap active_entries_;

  // The set of doomed entries.
  ActiveEntriesSet doomed_entries_;

  // The set of entries "under construction".
  PendingOpsMap pending_ops_;

  scoped_ptr<PlaybackCacheMap> playback_cache_map_;

  // The async validations currently in progress, keyed by URL.
  AsyncValidationMap async_validations_;

  // A clock that can be swapped out for testing.
  scoped_ptr<base::Clock> clock_;

  base::WeakPtrFactory<HttpCache> weak_factory_;

  DISALLOW_COPY_AND_ASSIGN(HttpCache);
};

}  // namespace net

#endif  // NET_HTTP_HTTP_CACHE_H_