base/path_service.h

   1 // Copyright (c) 2011 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 #pragma once
   8
   9 #include <string>
  10
  11 #include "base/base_api.h"
  12 #include "base/base_paths.h"
  13 #include "build/build_config.h"
  14
  15 class FilePath;
  16
  17 // The path service is a global table mapping keys to file system paths.  It is
  18 // OK to use this service from multiple threads.
  19 //
  20 class BASE_API PathService {
  21  public:
  22   // Retrieves a path to a special directory or file and places it into the
  23   // string pointed to by 'path'. If you ask for a directory it is guaranteed
  24   // to NOT have a path separator at the end. For example, "c:\windows\temp"
  25   // Directories are also guaranteed to exist when this function succeeds.
  26   //
  27   // Returns true if the directory or file was successfully retrieved. On
  28   // failure, 'path' will not be changed.
  29   static bool Get(int key, FilePath* path);
  30
  31   // Overrides the path to a special directory or file.  This cannot be used to
  32   // change the value of DIR_CURRENT, but that should be obvious.  Also, if the
  33   // path specifies a directory that does not exist, the directory will be
  34   // created by this method.  This method returns true if successful.
  35   //
  36   // If the given path is relative, then it will be resolved against
  37   // DIR_CURRENT.
  38   //
  39   // WARNING: Consumers of PathService::Get may expect paths to be constant
  40   // over the lifetime of the app, so this method should be used with caution.
  41   static bool Override(int key, const FilePath& path);
  42
  43   // To extend the set of supported keys, you can register a path provider,
  44   // which is just a function mirroring PathService::Get.  The ProviderFunc
  45   // returns false if it cannot provide a non-empty path for the given key.
  46   // Otherwise, true is returned.
  47   //
  48   // WARNING: This function could be called on any thread from which the
  49   // PathService is used, so a the ProviderFunc MUST BE THREADSAFE.
  50   //
  51   typedef bool (*ProviderFunc)(int, FilePath*);
  52
  53   // Call to register a path provider.  You must specify the range "[key_start,
  54   // key_end)" of supported path keys.
  55   static void RegisterProvider(ProviderFunc provider,
  56                                int key_start,
  57                                int key_end);
  58  private:
  59   static bool GetFromCache(int key, FilePath* path);
  60   static bool GetFromOverrides(int key, FilePath* path);
  61   static void AddToCache(int key, const FilePath& path);
  62 };
  63
  64 #endif  // BASE_PATH_SERVICE_H_