base/path_service.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_PATH_SERVICE_H_
   6 #define BASE_PATH_SERVICE_H_
   7
   8 #include <string>
   9
  10 #include "base/base_export.h"
  11 #include "base/base_paths.h"
  12 #include "build/build_config.h"
  13
  14 class FilePath;
  15
  16 // The path service is a global table mapping keys to file system paths.  It is
  17 // OK to use this service from multiple threads.
  18 //
  19 class BASE_EXPORT PathService {
  20  public:
  21   // Retrieves a path to a special directory or file and places it into the
  22   // string pointed to by 'path'. If you ask for a directory it is guaranteed
  23   // to NOT have a path separator at the end. For example, "c:\windows\temp"
  24   // Directories are also guaranteed to exist when this function succeeds.
  25   //
  26   // Returns true if the directory or file was successfully retrieved. On
  27   // failure, 'path' will not be changed.
  28   static bool Get(int key, FilePath* path);
  29
  30   // Overrides the path to a special directory or file.  This cannot be used to
  31   // change the value of DIR_CURRENT, but that should be obvious.  Also, if the
  32   // path specifies a directory that does not exist, the directory will be
  33   // created by this method.  This method returns true if successful.
  34   //
  35   // If the given path is relative, then it will be resolved against
  36   // DIR_CURRENT.
  37   //
  38   // WARNING: Consumers of PathService::Get may expect paths to be constant
  39   // over the lifetime of the app, so this method should be used with caution.
  40   static bool Override(int key, const FilePath& path);
  41
  42   // This function does the same as PathService::Override but it takes an extra
  43   // parameter |create| which guides whether the directory to be overriden must
  44   // be created in case it doesn't exist already.
  45   static bool OverrideAndCreateIfNeeded(int key,
  46                                         const FilePath& path,
  47                                         bool create);
  48
  49   // To extend the set of supported keys, you can register a path provider,
  50   // which is just a function mirroring PathService::Get.  The ProviderFunc
  51   // returns false if it cannot provide a non-empty path for the given key.
  52   // Otherwise, true is returned.
  53   //
  54   // WARNING: This function could be called on any thread from which the
  55   // PathService is used, so a the ProviderFunc MUST BE THREADSAFE.
  56   //
  57   typedef bool (*ProviderFunc)(int, FilePath*);
  58
  59   // Call to register a path provider.  You must specify the range "[key_start,
  60   // key_end)" of supported path keys.
  61   static void RegisterProvider(ProviderFunc provider,
  62                                int key_start,
  63                                int key_end);
  64  private:
  65   static bool GetFromCache(int key, FilePath* path);
  66   static bool GetFromOverrides(int key, FilePath* path);
  67   static void AddToCache(int key, const FilePath& path);
  68 };
  69
  70 #endif  // BASE_PATH_SERVICE_H_