mbed-os/platform/FileHandle.h

/* mbed Microcontroller Library
 * Copyright (c) 2017 ARM Limited
 *
 * 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 "Callback.h"
#include "platform/mbed_poll.h"
#include "platform/platform.h"

namespace mbed {
/** \addtogroup platform */


/** 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
 *  @ingroup platform
 */
class FileHandle {
public:
    virtual ~FileHandle() {}

    /** Read the contents of a file into a buffer
     *
     *  Devices acting as FileHandles should follow POSIX semantics:
     *
     *  * if no data is available, and non-blocking set return -EAGAIN
     *  * if no data is available, and blocking set, wait until 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
     *
     *  @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();

    /** Move the file position to a given offset from a given location.
     *
     *  @param offset The offset from whence to move to
     *  @param whence SEEK_SET for the start of the file, SEEK_CUR for the
     *   current file position, or SEEK_END for the end of the file.
     *
     *  @returns
     *    new file position on success,
     *    -1 on failure or unsupported
     */
    MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::seek")
    virtual off_t lseek(off_t offset, int whence)
    {
        return seek(offset, whence);
    }

    /** Flush any buffers associated with the FileHandle, ensuring it
     *  is up to date on disk
     *
     *  @returns
     *    0 on success or un-needed,
     *   -1 on error
     */
    MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::sync")
    virtual int fsync()
    {
        return sync();
    }

    /** Find the length of the file
     *
     *  @returns
     *   Length of the file
     */
    MBED_DEPRECATED_SINCE("mbed-os-5.4", "Replaced by FileHandle::size")
    virtual off_t flen()
    {
        return size();
    }

    /** Set blocking or non-blocking mode of the file operation like read/write.
     *  Definition depends upon the subclass implementing FileHandle.
     *  The default is blocking.
     *
     *  @param blocking true for blocking mode, false for non-blocking mode.
     */
    virtual int set_blocking(bool blocking)
    {
        return -1;
    }

    /** Check for poll event flags
     * The input parameter can be used or ignored - the could always return all events,
     * or could check just the events listed in events.
     * Call is non-blocking - 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;
    }

    /** Returns true if the FileHandle is writable.
     *  Definition depends upon 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.
     */
    bool writable() const
    {
        return poll(POLLOUT) & POLLOUT;
    }

    /** Returns true if the FileHandle is readable.
     *  Definition depends upon the subclass implementing FileHandle.
     *  For example, if the FileHandle is of type Stream, readable() could return
     *  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 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.
    }
};

/** Not a member function
 *  This call is equivalent to posix fdopen().
 *  Returns a pointer to std::FILE.
 *  It associates a Stream to an already opened file descriptor (FileHandle)
 *
 *  @param fh, a pointer to an opened file descriptor
 *  @param mode, operation upon the file descriptor, e.g., 'wb+'*/

std::FILE *fdopen(FileHandle *fh, const char *mode);

} // namespace mbed

#endif