FileHandle.h

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2017-2019 ARM Limited
00003  * SPDX-License-Identifier: Apache-2.0
00004  *
00005  * Licensed under the Apache License, Version 2.0 (the "License");
00006  * you may not use this file except in compliance with the License.
00007  * You may obtain a copy of the License at
00008  *
00009  *     http://www.apache.org/licenses/LICENSE-2.0
00010  *
00011  * Unless required by applicable law or agreed to in writing, software
00012  * distributed under the License is distributed on an "AS IS" BASIS,
00013  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00014  * See the License for the specific language governing permissions and
00015  * limitations under the License.
00016  */
00017 #ifndef MBED_FILEHANDLE_H
00018 #define MBED_FILEHANDLE_H
00019 
00020 typedef int FILEHANDLE;
00021 
00022 #include <cstdio>
00023 #include "platform/Callback.h"
00024 #include "platform/mbed_poll.h"
00025 #include "platform/platform.h"
00026 #include "platform/NonCopyable.h"
00027 
00028 namespace mbed {
00029 
00030 /**
00031  * \defgroup platform_FileHandle FileHandle functions
00032  * \ingroup platform-public-api-file
00033  * @{
00034  */
00035 
00036 
00037 /** Class FileHandle
00038  *
00039  *  An abstract interface that represents operations on a file-like
00040  *  object. The core functions are read, write and seek, but only
00041  *  a subset of these operations can be provided.
00042  *
00043  *  @note to create a file, @see File
00044  *  @note Synchronization level: Set by subclass
00045  */
00046 class FileHandle : private NonCopyable<FileHandle> {
00047 public:
00048     virtual ~FileHandle() {}
00049 
00050     /** Read the contents of a file into a buffer
00051      *
00052      *  Devices acting as FileHandles should follow POSIX semantics:
00053      *
00054      *  * if no data is available, and nonblocking set, return -EAGAIN
00055      *  * if no data is available, and blocking set, wait until some data is available
00056      *  * If any data is available, call returns immediately
00057      *
00058      *  @param buffer   The buffer to read in to
00059      *  @param size     The number of bytes to read
00060      *  @return         The number of bytes read, 0 at end of file, negative error on failure
00061      */
00062     virtual ssize_t read(void *buffer, size_t size) = 0;
00063 
00064     /** Write the contents of a buffer to a file
00065      *
00066      *  Devices acting as FileHandles should follow POSIX semantics:
00067      *
00068      * * if blocking, block until all data is written
00069      * * if no data can be written, and nonblocking set, return -EAGAIN
00070      * * if some data can be written, and nonblocking set, write partial
00071      *
00072      *  @param buffer   The buffer to write from
00073      *  @param size     The number of bytes to write
00074      *  @return         The number of bytes written, negative error on failure
00075      */
00076     virtual ssize_t write(const void *buffer, size_t size) = 0;
00077 
00078     /** Move the file position to a given offset from from a given location
00079      *
00080      *  @param offset   The offset from whence to move to
00081      *  @param whence   The start of where to seek
00082      *      SEEK_SET to start from beginning of file,
00083      *      SEEK_CUR to start from current position in file,
00084      *      SEEK_END to start from end of file
00085      *  @return         The new offset of the file, negative error code on failure
00086      */
00087     virtual off_t seek(off_t offset, int whence = SEEK_SET) = 0;
00088 
00089     /** Close a file
00090      *
00091      *  @return         0 on success, negative error code on failure
00092      */
00093     virtual int close() = 0;
00094 
00095     /** Flush any buffers associated with the file
00096      *
00097      *  @return         0 on success, negative error code on failure
00098      */
00099     virtual int sync()
00100     {
00101         return 0;
00102     }
00103 
00104     /** Check if the file in an interactive terminal device
00105      *
00106      *  @return         True if the file is a terminal
00107      *  @return         False if the file is not a terminal
00108      *  @return         Negative error code on failure
00109      */
00110     virtual int isatty()
00111     {
00112         return false;
00113     }
00114 
00115     /** Get the file position of the file
00116      *
00117      *  @note This is equivalent to seek(0, SEEK_CUR)
00118      *
00119      *  @return         The current offset in the file, negative error code on failure
00120      */
00121     virtual off_t tell()
00122     {
00123         return seek(0, SEEK_CUR);
00124     }
00125 
00126     /** Rewind the file position to the beginning of the file
00127      *
00128      *  @note This is equivalent to seek(0, SEEK_SET)
00129      */
00130     virtual void rewind()
00131     {
00132         seek(0, SEEK_SET);
00133     }
00134 
00135     /** Get the size of the file
00136      *
00137      *  @return         Size of the file in bytes
00138      */
00139     virtual off_t size();
00140 
00141     /** Truncate or extend a file.
00142      *
00143      * The file's length is set to the specified value. The seek pointer is
00144      * not changed. If the file is extended, the extended area appears as if
00145      * it were zero-filled.
00146      *
00147      *  @param length   The requested new length for the file
00148      *
00149      *  @return         Zero on success, negative error code on failure
00150      */
00151     virtual int truncate(off_t length)
00152     {
00153         return -EINVAL;
00154     }
00155 
00156     /** Move the file position to a given offset from a given location.
00157      *
00158      *  @param offset The offset from whence to move to
00159      *  @param whence SEEK_SET for the start of the file, SEEK_CUR for the
00160      *   current file position, or SEEK_END for the end of the file.
00161      *
00162      *  @returns
00163      *    new file position on success,
00164      *    -1 on failure or unsupported
00165      *  @deprecated Replaced by `off_t FileHandle::seek(off_t offset, int whence = SEEK_SET)'
00166      *
00167      */
00168     MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::seek")
00169     virtual off_t lseek(off_t offset, int whence)
00170     {
00171         return seek(offset, whence);
00172     }
00173 
00174     /** Flush any buffers associated with the FileHandle, ensuring it
00175      *  is up to date on disk
00176      *
00177      *  @returns
00178      *    0 on success or un-needed,
00179      *   -1 on error
00180      *  @deprecated Replaced by `int FileHandle::sync()'
00181      */
00182     MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::sync")
00183     virtual int fsync()
00184     {
00185         return sync();
00186     }
00187 
00188     /** Find the length of the file
00189      *
00190      *  @returns
00191      *   Length of the file
00192      *  @deprecated Replaced by `off_t FileHandle::size()'
00193      */
00194     MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::size")
00195     virtual off_t flen()
00196     {
00197         return size();
00198     }
00199 
00200     /** Set blocking or nonblocking mode of the file operation like read/write.
00201      *  Definition depends on the subclass implementing FileHandle.
00202      *  The default is blocking.
00203      *
00204      *  @param blocking     true for blocking mode, false for nonblocking mode.
00205      *
00206      *  @return             0 on success
00207      *  @return             Negative error code on failure
00208      */
00209     virtual int set_blocking(bool blocking)
00210     {
00211         return blocking ? 0 : -ENOTTY;
00212     }
00213 
00214     /** Check current blocking or nonblocking mode for file operations.
00215      *
00216      *  @return             true for blocking mode, false for nonblocking mode.
00217      */
00218     virtual bool is_blocking() const
00219     {
00220         return true;
00221     }
00222 
00223     /** Enable or disable input
00224      *
00225      * Control enabling of device for input. This is primarily intended
00226      * for temporary power-saving; the overall ability of the device to operate for
00227      * input and/or output may be fixed at creation time, but this call can
00228      * allow input to be temporarily disabled to permit power saving without
00229      * losing device state.
00230      *
00231      *  @param enabled      true to enable input, false to disable.
00232      *
00233      *  @return             0 on success
00234      *  @return             Negative error code on failure
00235      */
00236     virtual int enable_input(bool enabled)
00237     {
00238         return -EINVAL;
00239     }
00240 
00241     /** Enable or disable output
00242      *
00243      * Control enabling of device for output. This is primarily intended
00244      * for temporary power-saving; the overall ability of the device to operate for
00245      * input and/or output may be fixed at creation time, but this call can
00246      * allow output to be temporarily disabled to permit power saving without
00247      * losing device state.
00248      *
00249      *  @param enabled      true to enable output, false to disable.
00250      *
00251      *  @return             0 on success
00252      *  @return             Negative error code on failure
00253      */
00254     virtual int enable_output(bool enabled)
00255     {
00256         return -EINVAL;
00257     }
00258 
00259     /** Check for poll event flags
00260      * You can use or ignore the input parameter. You can return all events
00261      * or check just the events listed in events.
00262      * Call is nonblocking - returns instantaneous state of events.
00263      * Whenever an event occurs, the derived class should call the sigio() callback).
00264      *
00265      * @param events        bitmask of poll events we're interested in - POLLIN/POLLOUT etc.
00266      *
00267      * @returns             bitmask of poll events that have occurred.
00268      */
00269     virtual short poll(short events) const
00270     {
00271         // Possible default for real files
00272         return POLLIN | POLLOUT;
00273     }
00274 
00275     /** Definition depends on the subclass implementing FileHandle.
00276      *  For example, if the FileHandle is of type Stream, writable() could return
00277      *  true when there is ample buffer space available for write() calls.
00278      *
00279      * @returns             true if the FileHandle is writable.
00280      */
00281     bool writable() const
00282     {
00283         return poll(POLLOUT) & POLLOUT;
00284     }
00285 
00286     /** Definition depends on the subclass implementing FileHandle.
00287      *  For example, if the FileHandle is of type Stream, readable() could return
00288      *  true when there is something available to read.
00289      *
00290      *  @returns            true when there is something available to read.
00291      */
00292     bool readable() const
00293     {
00294         return poll(POLLIN) & POLLIN;
00295     }
00296 
00297     /** Register a callback on state change of the file.
00298      *
00299      *  The specified callback will be called on state changes such as when
00300      *  the file can be written to or read from.
00301      *
00302      *  The callback may be called in an interrupt context and should not
00303      *  perform expensive operations.
00304      *
00305      *  Note! This is not intended as an attach-like asynchronous API, but rather
00306      *  as a building block for constructing such functionality.
00307      *
00308      *  The exact timing of when the registered function
00309      *  is called is not guaranteed and is susceptible to change. It should be used
00310      *  as a cue to make read/write/poll calls to find the current state.
00311      *
00312      *  @param func     Function to call on state change
00313      */
00314     virtual void sigio(Callback<void()> func)
00315     {
00316         //Default for real files. Do nothing for real files.
00317     }
00318 };
00319 
00320 /**@}*/
00321 
00322 } // namespace mbed
00323 
00324 #endif