Mbed OS Reference | FileHandle.h Source File

 /* mbed Microcontroller Library
  * Copyright (c) 2017-2019 ARM Limited
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 #ifndef MBED_FILEHANDLE_H
 #define MBED_FILEHANDLE_H
 
 typedef int FILEHANDLE;
 
 #include <cstdio>
 #include "platform/Callback.h"
 #include "platform/mbed_poll.h"
 #include "platform/platform.h"
 #include "platform/NonCopyable.h"
 
 namespace mbed {
 
 /**
  * \defgroup platform_FileHandle FileHandle functions
  * \ingroup platform-public-api-file
  * @{
  */
 
 
 /** Class FileHandle
  *
  *  An abstract interface that represents operations on a file-like
  *  object. The core functions are read, write and seek, but only
  *  a subset of these operations can be provided.
  *
  *  @note to create a file, @see File
  *  @note Synchronization level: Set by subclass
  */
 class FileHandle : private NonCopyable<FileHandle> {
 public:
     virtual ~FileHandle() = default;
 
     /** Read the contents of a file into a buffer
      *
      *  Devices acting as FileHandles should follow POSIX semantics:
      *
      *  * if no data is available, and nonblocking set, return -EAGAIN
      *  * if no data is available, and blocking set, wait until some data is available
      *  * If any data is available, call returns immediately
      *
      *  @param buffer   The buffer to read in to
      *  @param size     The number of bytes to read
      *  @return         The number of bytes read, 0 at end of file, negative error on failure
      */
     virtual ssize_t read(void *buffer, size_t size) = 0;
 
     /** Write the contents of a buffer to a file
      *
      *  Devices acting as FileHandles should follow POSIX semantics:
      *
      * * if blocking, block until all data is written
      * * if no data can be written, and nonblocking set, return -EAGAIN
      * * if some data can be written, and nonblocking set, write partial
      *
      *  @param buffer   The buffer to write from
      *  @param size     The number of bytes to write
      *  @return         The number of bytes written, negative error on failure
      */
     virtual ssize_t write(const void *buffer, size_t size) = 0;
 
     /** Move the file position to a given offset from from a given location
      *
      *  @param offset   The offset from whence to move to
      *  @param whence   The start of where to seek
      *      SEEK_SET to start from beginning of file,
      *      SEEK_CUR to start from current position in file,
      *      SEEK_END to start from end of file
      *  @return         The new offset of the file, negative error code on failure
      */
     virtual off_t seek(off_t offset, int whence = SEEK_SET) = 0;
 
     /** Close a file
      *
      *  @return         0 on success, negative error code on failure
      */
     virtual int close() = 0;
 
     /** Flush any buffers associated with the file
      *
      *  @return         0 on success, negative error code on failure
      */
     virtual int sync()
     {
         return 0;
     }
 
     /** Check if the file in an interactive terminal device
      *
      *  @return         True if the file is a terminal
      *  @return         False if the file is not a terminal
      *  @return         Negative error code on failure
      */
     virtual int isatty()
     {
         return false;
     }
 
     /** Get the file position of the file
      *
      *  @note This is equivalent to seek(0, SEEK_CUR)
      *
      *  @return         The current offset in the file, negative error code on failure
      */
     virtual off_t tell()
     {
         return seek(0, SEEK_CUR);
     }
 
     /** Rewind the file position to the beginning of the file
      *
      *  @note This is equivalent to seek(0, SEEK_SET)
      */
     virtual void rewind()
     {
         seek(0, SEEK_SET);
     }
 
     /** Get the size of the file
      *
      *  @return         Size of the file in bytes
      */
     virtual off_t size();
 
     /** Truncate or extend a file.
      *
      * The file's length is set to the specified value. The seek pointer is
      * not changed. If the file is extended, the extended area appears as if
      * it were zero-filled.
      *
      *  @param length   The requested new length for the file
      *
      *  @return         Zero on success, negative error code on failure
      */
     virtual int truncate(off_t length)
     {
         return -EINVAL;
     }
 
     /** Set blocking or nonblocking mode of the file operation like read/write.
      *  Definition depends on the subclass implementing FileHandle.
      *  The default is blocking.
      *
      *  @param blocking     true for blocking mode, false for nonblocking mode.
      *
      *  @return             0 on success
      *  @return             Negative error code on failure
      */
     virtual int set_blocking(bool blocking)
     {
         return blocking ? 0 : -ENOTTY;
     }
 
     /** Check current blocking or nonblocking mode for file operations.
      *
      *  @return             true for blocking mode, false for nonblocking mode.
      */
     virtual bool is_blocking() const
     {
         return true;
     }
 
     /** Enable or disable input
      *
      * Control enabling of device for input. This is primarily intended
      * for temporary power-saving; the overall ability of the device to operate for
      * input and/or output may be fixed at creation time, but this call can
      * allow input to be temporarily disabled to permit power saving without
      * losing device state.
      *
      *  @param enabled      true to enable input, false to disable.
      *
      *  @return             0 on success
      *  @return             Negative error code on failure
      */
     virtual int enable_input(bool enabled)
     {
         return -EINVAL;
     }
 
     /** Enable or disable output
      *
      * Control enabling of device for output. This is primarily intended
      * for temporary power-saving; the overall ability of the device to operate for
      * input and/or output may be fixed at creation time, but this call can
      * allow output to be temporarily disabled to permit power saving without
      * losing device state.
      *
      *  @param enabled      true to enable output, false to disable.
      *
      *  @return             0 on success
      *  @return             Negative error code on failure
      */
     virtual int enable_output(bool enabled)
     {
         return -EINVAL;
     }
 
     /** Check for poll event flags
      * You can use or ignore the input parameter. You can return all events
      * or check just the events listed in events.
      * Call is nonblocking - returns instantaneous state of events.
      * Whenever an event occurs, the derived class should call the sigio() callback).
      *
      * @param events        bitmask of poll events we're interested in - POLLIN/POLLOUT etc.
      *
      * @returns             bitmask of poll events that have occurred.
      */
     virtual short poll(short events) const
     {
         // Possible default for real files
         return POLLIN | POLLOUT;
     }
 
     /** Definition depends on the subclass implementing FileHandle.
      *  For example, if the FileHandle is of type Stream, writable() could return
      *  true when there is ample buffer space available for write() calls.
      *
      * @returns             true if the FileHandle is writable.
      */
     bool writable() const
     {
         return poll(POLLOUT) & POLLOUT;
     }
 
     /** Definition depends on the subclass implementing FileHandle.
      *  For example, if the FileHandle is of type Stream, readable() could return
      *  true when there is something available to read.
      *
      *  @returns            true when there is something available to read.
      */
     bool readable() const
     {
         return poll(POLLIN) & POLLIN;
     }
 
     /** Register a callback on state change of the file.
      *
      *  The specified callback will be called on state changes such as when
      *  the file can be written to or read from.
      *
      *  The callback may be called in an interrupt context and should not
      *  perform expensive operations.
      *
      *  Note! This is not intended as an attach-like asynchronous API, but rather
      *  as a building block for constructing such functionality.
      *
      *  The exact timing of when the registered function
      *  is called is not guaranteed and is susceptible to change. It should be used
      *  as a cue to make read/write/poll calls to find the current state.
      *
      *  @param func     Function to call on state change
      */
     virtual void sigio(Callback<void()> func)
     {
         //Default for real files. Do nothing for real files.
     }
 };
 
 /**@}*/
 
 } // namespace mbed
 
 #endif
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