ppapi/cpp/file_io.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 PPAPI_CPP_FILE_IO_H_
   6 #define PPAPI_CPP_FILE_IO_H_
   7
   8 #include "ppapi/c/pp_time.h"
   9 #include "ppapi/cpp/completion_callback.h"
  10 #include "ppapi/cpp/resource.h"
  11
  12 /// @file
  13 /// This file defines the API to create a file i/o object.
  14
  15 struct PP_FileInfo;
  16
  17 namespace pp {
  18
  19 class FileRef;
  20 class InstanceHandle;
  21
  22 /// The <code>FileIO</code> class represents a regular file.
  23 class FileIO : public Resource {
  24  public:
  25   /// Default constructor for creating an is_null() <code>FileIO</code>
  26   /// object.
  27   FileIO();
  28
  29   /// A constructor used to create a <code>FileIO</code> and associate it with
  30   /// the provided <code>Instance</code>.
  31   ///
  32   /// @param[in] instance The instance with which this resource will be
  33   /// associated.
  34   explicit FileIO(const InstanceHandle& instance);
  35
  36   /// The copy constructor for <code>FileIO</code>.
  37   ///
  38   /// @param[in] other A reference to a <code>FileIO</code>.
  39   FileIO(const FileIO& other);
  40
  41   /// Open() opens the specified regular file for I/O according to the given
  42   /// open flags, which is a bit-mask of the PP_FileOpenFlags values.  Upon
  43   /// success, the corresponding file is classified as "in use" by this FileIO
  44   /// object until such time as the FileIO object is closed or destroyed.
  45   ///
  46   /// @param[in] file_ref A <code>PP_Resource</code> corresponding to a file
  47   /// reference.
  48   ///
  49   /// @param[in] open_flags A bit-mask of the <code>PP_FileOpenFlags</code>
  50   /// values. Valid values are:
  51   ///  - PP_FILEOPENFLAG_READ
  52   ///  - PP_FILEOPENFLAG_WRITE
  53   ///  - PP_FILEOPENFLAG_CREATE
  54   ///  - PP_FILEOPENFLAG_TRUNCATE
  55   ///  - PP_FILEOPENFLAG_EXCLUSIVE
  56   /// See <code>PP_FileOpenFlags</code> in <code>ppb_file_io.h</code> for more
  57   /// details on these flags.
  58   ///
  59   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
  60   /// completion of Open().
  61   ///
  62   /// @return An int32_t containing an error code from
  63   /// <code>pp_errors.h</code>.
  64   int32_t Open(const FileRef& file_ref,
  65                int32_t open_flags,
  66                const CompletionCallback& cc);
  67
  68   /// Query() queries info about the file opened by this FileIO object. This
  69   /// function will fail if the FileIO object has not been opened.
  70   ///
  71   /// @param[in] result_buf The <code>PP_FileInfo</code> structure representing
  72   /// all information about the file.
  73   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
  74   /// completion of Query().
  75   ///
  76   /// @return An int32_t containing an error code from
  77   /// <code>pp_errors.h</code>.
  78   int32_t Query(PP_FileInfo* result_buf,
  79                 const CompletionCallback& cc);
  80
  81   /// Touch() Updates time stamps for the file opened by this FileIO object.
  82   /// This function will fail if the FileIO object has not been opened.
  83   ///
  84   /// @param[in] last_access_time The last time the FileIO was accessed.
  85   /// @param[in] last_modified_time The last time the FileIO was modified.
  86   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
  87   /// completion of Touch().
  88   ///
  89   /// @return An int32_t containing an error code from
  90   /// <code>pp_errors.h</code>.
  91   int32_t Touch(PP_Time last_access_time,
  92                 PP_Time last_modified_time,
  93                 const CompletionCallback& cc);
  94
  95   /// Reads from an offset in the file.
  96   ///
  97   /// The size of the buffer must be large enough to hold the specified number
  98   /// of bytes to read.  This function might perform a partial read, meaning
  99   /// that all the requested bytes might not be returned, even if the end of the
 100   /// file has not been reached.
 101   ///
 102   /// This function reads into a buffer that the caller supplies. This buffer
 103   /// must remain valid as long as the FileIO resource is alive. If you use
 104   /// a completion callback factory and it goes out of scope, it will not issue
 105   /// the callback on your class, BUT the callback factory can NOT cancel
 106   /// the request from the browser's perspective. This means that the browser
 107   /// will still try to write to your buffer even if the callback factory is
 108   /// destroyed!
 109   ///
 110   /// So you must ensure that your buffer outlives the FileIO resource. If you
 111   /// have one class and use the FileIO resource exclusively from that class
 112   /// and never make any copies, this will be fine: the resource will be
 113   /// destroyed when your class is. But keep in mind that copying a pp::FileIO
 114   /// object just creates a second reference to the original resource. For
 115   /// example, if you have a function like this:
 116   ///   pp::FileIO MyClass::GetFileIO();
 117   /// where a copy of your FileIO resource could outlive your class, the
 118   /// callback will still be pending when your class goes out of scope, creating
 119   /// the possibility of writing into invalid memory. So it's recommended to
 120   /// keep your FileIO resource and any output buffers tightly controlled in
 121   /// the same scope.
 122   ///
 123   /// <strong>Caveat:</strong> This Read() is potentially unsafe if you're using
 124   /// a CompletionCallbackFactory to scope callbacks to the lifetime of your
 125   /// class.  When your class goes out of scope, the callback factory will not
 126   /// actually cancel the callback, but will rather just skip issuing the
 127   /// callback on your class.  This means that if the FileIO object outlives
 128   /// your class (if you made a copy saved somewhere else, for example), then
 129   /// the browser will still try to write into your buffer when the
 130   /// asynchronous read completes, potentially causing a crash.
 131   ///
 132   /// See the other version of Read() which avoids this problem by writing into
 133   /// CompletionCallbackWithOutput, where the output buffer is automatically
 134   /// managed by the callback.
 135   ///
 136   /// @param[in] offset The offset into the file.
 137   /// @param[in] buffer The buffer to hold the specified number of bytes read.
 138   /// @param[in] bytes_to_read The number of bytes to read from
 139   /// <code>offset</code>.
 140   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
 141   /// completion of Read().
 142   ///
 143   /// @return An The number of bytes read an error code from
 144   /// <code>pp_errors.h</code>. If the return value is 0, then end-of-file was
 145   /// reached. It is valid to call Read() multiple times with a completion
 146   /// callback to queue up parallel reads from the file at different offsets.
 147   int32_t Read(int64_t offset,
 148                char* buffer,
 149                int32_t bytes_to_read,
 150                const CompletionCallback& cc);
 151
 152   /// Read() reads from an offset in the file.  A PP_ArrayOutput must be
 153   /// provided so that output will be stored in its allocated buffer.  This
 154   /// function might perform a partial read.
 155   ///
 156   /// @param[in] file_io A <code>PP_Resource</code> corresponding to a file
 157   /// FileIO.
 158   /// @param[in] offset The offset into the file.
 159   /// @param[in] max_read_length The maximum number of bytes to read from
 160   /// <code>offset</code>.
 161   /// @param[in] output A <code>PP_ArrayOutput</code> to hold the output data.
 162   /// @param[in] callback A <code>PP_CompletionCallback</code> to be called upon
 163   /// completion of Read().
 164   ///
 165   /// @return The number of bytes read or an error code from
 166   /// <code>pp_errors.h</code>. If the return value is 0, then end-of-file was
 167   /// reached. It is valid to call Read() multiple times with a completion
 168   /// callback to queue up parallel reads from the file, but pending reads
 169   /// cannot be interleaved with other operations.
 170   int32_t Read(int32_t offset,
 171                int32_t max_read_length,
 172                const CompletionCallbackWithOutput< std::vector<char> >& cc);
 173
 174   /// Write() writes to an offset in the file.  This function might perform a
 175   /// partial write. The FileIO object must have been opened with write access.
 176   ///
 177   /// @param[in] offset The offset into the file.
 178   /// @param[in] buffer The buffer to hold the specified number of bytes read.
 179   /// @param[in] bytes_to_write The number of bytes to write to
 180   /// <code>offset</code>.
 181   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
 182   /// completion of Write().
 183   ///
 184   /// @return An The number of bytes written or an error code from
 185   /// <code>pp_errors.h</code>. If the return value is 0, then end-of-file was
 186   /// reached. It is valid to call Write() multiple times with a completion
 187   /// callback to queue up parallel writes to the file at different offsets.
 188   int32_t Write(int64_t offset,
 189                 const char* buffer,
 190                 int32_t bytes_to_write,
 191                 const CompletionCallback& cc);
 192
 193   /// SetLength() sets the length of the file.  If the file size is extended,
 194   /// then the extended area of the file is zero-filled.  The FileIO object must
 195   /// have been opened with write access.
 196   ///
 197   /// @param[in] length The length of the file to be set.
 198   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
 199   /// completion of SetLength().
 200   ///
 201   /// @return An int32_t containing an error code from
 202   /// <code>pp_errors.h</code>.
 203   int32_t SetLength(int64_t length,
 204                     const CompletionCallback& cc);
 205
 206   /// Flush() flushes changes to disk.  This call can be very expensive!
 207   ///
 208   /// @param[in] cc A <code>CompletionCallback</code> to be called upon
 209   /// completion of Flush().
 210   ///
 211   /// @return An int32_t containing an error code from
 212   /// <code>pp_errors.h</code>.
 213   int32_t Flush(const CompletionCallback& cc);
 214
 215   /// Close() cancels any IO that may be pending, and closes the FileIO object.
 216   /// Any pending callbacks will still run, reporting
 217   /// <code>PP_ERROR_ABORTED</code> if pending IO was interrupted.  It is not
 218   /// valid to call Open() again after a call to this method.
 219   ///
 220   /// <strong>Note:</strong> If the FileIO object is destroyed, and it is still
 221   /// open, then it will be implicitly closed, so you are not required to call
 222   /// Close().
 223   void Close();
 224
 225  private:
 226   struct CallbackData1_0 {
 227     PP_ArrayOutput output;
 228     char* temp_buffer;
 229     PP_CompletionCallback original_callback;
 230   };
 231
 232   // Provide backwards-compatibility for older Read versions. Converts the
 233   // old-style "char*" output buffer of 1.0 to the new "PP_ArrayOutput"
 234   // interface in 1.1.
 235   //
 236   // This takes a heap-allocated CallbackData1_0 struct passed as the user data
 237   // and deletes it when the call completes.
 238   static void CallbackConverter(void* user_data, int32_t result);
 239 };
 240
 241 }  // namespace pp
 242
 243 #endif  // PPAPI_CPP_FILE_IO_H_