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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @file buffer.h
 *
 * @brief Advanced buffer implementation.
 *
 * Instances of CxBuffer can be used to read from or to write to like one
 * would do with a stream.
 *
 * Some features for convenient use of the buffer
 * can be enabled. See the documentation of the macro constants for more
 * information.
 *
 * @author Mike Becker
 * @author Olaf Wintermann
 * @copyright 2-Clause BSD License
 */

#ifndef UCX_BUFFER_H
#define UCX_BUFFER_H

#include "common.h"
#include "allocator.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * No buffer features enabled (all flags cleared).
 */
#define CX_BUFFER_DEFAULT 0x00

/**
 * If this flag is enabled, the buffer will automatically free its contents when destroyed.
 *
 * Do NOT set this flag together with #CX_BUFFER_COPY_ON_WRITE. It will be automatically
 * set when the copy-on-write operations is performed.
 */
#define CX_BUFFER_FREE_CONTENTS 0x01

/**
 * If this flag is enabled, the buffer will automatically extend its capacity.
 */
#define CX_BUFFER_AUTO_EXTEND 0x02

/**
 * If this flag is enabled, the buffer will allocate new memory when written to.
 *
 * The current contents of the buffer will be copied to the new memory and the flag
 * will be cleared while the #CX_BUFFER_FREE_CONTENTS flag will be set automatically.
 */
#define CX_BUFFER_COPY_ON_WRITE 0x04

/**
 * If this flag is enabled, the buffer will copy its contents to a new memory area on reallocation.
 *
 * After performing the copy, the flag is automatically cleared.
 * This flag has no effect on buffers which do not have #CX_BUFFER_AUTO_EXTEND set, which is why
 * buffers automatically admit the auto-extend flag when initialized with copy-on-extend enabled.
 */
#define CX_BUFFER_COPY_ON_EXTEND 0x08

/**
 * Function pointer for cxBufferWrite that is compatible with cx_write_func.
 * @see cx_write_func
 */
#define cxBufferWriteFunc  ((cx_write_func) cxBufferWrite)
/**
 * Function pointer for cxBufferRead that is compatible with cx_read_func.
 * @see cx_read_func
 */
#define cxBufferReadFunc  ((cx_read_func) cxBufferRead)

/**
 * Configuration for automatic flushing.
 */
struct cx_buffer_flush_config_s {
    /**
     * The buffer may not extend beyond this threshold before starting to flush.
     *
     * Only used when the buffer uses #CX_BUFFER_AUTO_EXTEND.
     * The threshold will be the maximum capacity the buffer is extended to
     * before flushing.
     */
    size_t threshold;
    /**
     * The block size for the elements to flush.
     */
    size_t blksize;
    /**
     * The maximum number of blocks to flush in one cycle.
     *
     * @attention while it is guaranteed that cxBufferFlush() will not flush
     * more blocks, this is not necessarily the case for cxBufferWrite().
     * After performing a flush cycle, cxBufferWrite() will retry the write
     * operation and potentially trigger another flush cycle, until the
     * flush target accepts no more data.
     */
    size_t blkmax;

    /**
     * The target for write function.
     */
    void *target;

    /**
     * The write-function used for flushing.
     * If NULL, the flushed content gets discarded.
     */
    cx_write_func wfunc;
};

/**
 * Type alias for the flush configuration struct.
 *
 * @code
 * struct cx_buffer_flush_config_s {
 *     size_t threshold;
 *     size_t blksize;
 *     size_t blkmax;
 *     void *target;
 *     cx_write_func wfunc;
 * };
 * @endcode
 */
typedef struct cx_buffer_flush_config_s CxBufferFlushConfig;

/** Structure for the UCX buffer data. */
struct cx_buffer_s {
    /** A pointer to the buffer contents. */
    union {
        /**
         * Data is interpreted as text.
         */
        char *space;
        /**
         * Data is interpreted as binary.
         */
        unsigned char *bytes;
    };
    /** The allocator to use for automatic memory management. */
    const CxAllocator *allocator;
    /**
     * Optional flush configuration
     *
     * @see cxBufferEnableFlushing()
     */
    CxBufferFlushConfig *flush;
    /** Current position of the buffer. */
    size_t pos;
    /** Current capacity (i.e. maximum size) of the buffer. */
    size_t capacity;
    /** Current size of the buffer content. */
    size_t size;
    /**
     * Flag register for buffer features.
     * @see #CX_BUFFER_DEFAULT
     * @see #CX_BUFFER_FREE_CONTENTS
     * @see #CX_BUFFER_AUTO_EXTEND
     * @see #CX_BUFFER_COPY_ON_WRITE
     */
    int flags;
};

/**
 * UCX buffer.
 */
typedef struct cx_buffer_s CxBuffer;

/**
 * Initializes a fresh buffer.
 *
 * You may also provide a read-only @p space, in which case
 * you will need to cast the pointer, and you should set the
 * #CX_BUFFER_COPY_ON_WRITE flag.
 *
 * You need to set the size manually after initialization, if
 * you provide @p space which already contains data.
 *
 * When you specify stack memory as @p space and decide to use
 * the auto-extension feature, you @em must use the
 * #CX_BUFFER_COPY_ON_EXTEND flag, instead of the
 * #CX_BUFFER_AUTO_EXTEND flag.
 *
 * @note You may provide @c NULL as argument for @p space.
 * Then this function will allocate the space and enforce
 * the #CX_BUFFER_FREE_CONTENTS flag. In that case, specifying
 * copy-on-write should be avoided, because the allocated
 * space will be leaking after the copy-on-write operation.
 *
 * @param buffer the buffer to initialize
 * @param space pointer to the memory area, or @c NULL to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @param allocator the allocator this buffer shall use for automatic
 * memory management
 * (if @c NULL, the cxDefaultAllocator will be used)
 * @param flags buffer features (see cx_buffer_s.flags)
 * @return zero on success, non-zero if a required allocation failed
 */
cx_attr_nonnull_arg(1)
cx_attr_export
int cxBufferInit(
        CxBuffer *buffer,
        void *space,
        size_t capacity,
        const CxAllocator *allocator,
        int flags
);

/**
 * Configures the buffer for flushing.
 *
 * Flushing can happen automatically when data is written
 * to the buffer (see cxBufferWrite()) or manually when
 * cxBufferFlush() is called.
 *
 * @param buffer the buffer
 * @param config the flush configuration
 * @retval zero success
 * @retval non-zero failure
 * @see cxBufferFlush()
 * @see cxBufferWrite()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferEnableFlushing(
    CxBuffer *buffer,
    CxBufferFlushConfig config
);

/**
 * Destroys the buffer contents.
 *
 * Has no effect if the #CX_BUFFER_FREE_CONTENTS feature is not enabled.
 * If you want to free the memory of the entire buffer, use cxBufferFree().
 *
 * @param buffer the buffer which contents shall be destroyed
 * @see cxBufferInit()
 */
cx_attr_nonnull
cx_attr_export
void cxBufferDestroy(CxBuffer *buffer);

/**
 * Deallocates the buffer.
 *
 * If the #CX_BUFFER_FREE_CONTENTS feature is enabled, this function also destroys
 * the contents. If you @em only want to destroy the contents, use cxBufferDestroy().
 *
 * @remark As with all free() functions, this accepts @c NULL arguments in which
 * case it does nothing.
 *
 * @param buffer the buffer to deallocate
 * @see cxBufferCreate()
 */
cx_attr_export
void cxBufferFree(CxBuffer *buffer);

/**
 * Allocates and initializes a fresh buffer.
 *
 * You may also provide a read-only @p space, in which case
 * you will need to cast the pointer, and you should set the
 * #CX_BUFFER_COPY_ON_WRITE flag.
 * When you specify stack memory as @p space and decide to use
 * the auto-extension feature, you @em must use the
 * #CX_BUFFER_COPY_ON_EXTEND flag, instead of the
 * #CX_BUFFER_AUTO_EXTEND flag.
 *
 * @note You may provide @c NULL as argument for @p space.
 * Then this function will allocate the space and enforce
 * the #CX_BUFFER_FREE_CONTENTS flag.
 *
 * @param space pointer to the memory area, or @c NULL to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @param allocator the allocator to use for allocating the structure and the automatic
 * memory management within the buffer
 * (if @c NULL, the cxDefaultAllocator will be used)
 * @param flags buffer features (see cx_buffer_s.flags)
 * @return a pointer to the buffer on success, @c NULL if a required allocation failed
 */
cx_attr_malloc
cx_attr_dealloc(cxBufferFree, 1)
cx_attr_nodiscard
cx_attr_export
CxBuffer *cxBufferCreate(
        void *space,
        size_t capacity,
        const CxAllocator *allocator,
        int flags
);

/**
 * Shifts the contents of the buffer by the given offset.
 *
 * If the offset is positive, the contents are shifted to the right.
 * If auto extension is enabled, the buffer grows, if necessary.
 * In case the auto extension fails, this function returns a non-zero value and
 * no contents are changed.
 * If auto extension is disabled, the contents that do not fit into the buffer
 * are discarded.
 *
 * If the offset is negative, the contents are shifted to the left where the
 * first @p shift bytes are discarded.
 * The new size of the buffer is the old size minus the absolute shift value.
 * If this value is larger than the buffer size, the buffer is emptied (but
 * not cleared, see the security note below).
 *
 * The buffer position gets shifted alongside with the content but is kept
 * within the boundaries of the buffer.
 *
 * @note For situations where @c off_t is not large enough, there are specialized cxBufferShiftLeft() and
 * cxBufferShiftRight() functions using a @c size_t as parameter type.
 *
 * @attention
 * Security Note: The shifting operation does @em not erase the previously occupied memory cells.
 * But you can easily do that manually, e.g. by calling
 * <code>memset(buffer->bytes, 0, shift)</code> for a right shift or
 * <code>memset(buffer->bytes + buffer->size, 0, buffer->capacity - buffer->size)</code>
 * for a left shift.
 *
 * @param buffer the buffer
 * @param shift the shift offset (negative means left shift)
 * @retval zero success
 * @retval non-zero if a required auto-extension or copy-on-write fails
 * @see cxBufferShiftLeft()
 * @see cxBufferShiftRight()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferShift(
        CxBuffer *buffer,
        off_t shift
);

/**
 * Shifts the buffer to the right.
 * See cxBufferShift() for details.
 *
 * @param buffer the buffer
 * @param shift the shift offset
 * @retval zero success
 * @retval non-zero if a required auto-extension or copy-on-write fails
 * @see cxBufferShift()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferShiftRight(
        CxBuffer *buffer,
        size_t shift
);

/**
 * Shifts the buffer to the left.
 * See cxBufferShift() for details.
 *
 * @param buffer the buffer
 * @param shift the positive shift offset
 * @retval zero success
 * @retval non-zero if the buffer uses copy-on-write and the allocation fails
 * @see cxBufferShift()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferShiftLeft(
        CxBuffer *buffer,
        size_t shift
);


/**
 * Moves the position of the buffer.
 *
 * The new position is relative to the @p whence argument.
 *
 * @li @c SEEK_SET marks the start of the buffer.
 * @li @c SEEK_CUR marks the current position.
 * @li @c SEEK_END marks the end of the buffer.
 *
 * With an offset of zero, this function sets the buffer position to zero
 * (@c SEEK_SET), the buffer size (@c SEEK_END) or leaves the buffer position
 * unchanged (@c SEEK_CUR).
 *
 * @param buffer the buffer
 * @param offset position offset relative to @p whence
 * @param whence one of @c SEEK_SET, @c SEEK_CUR or @c SEEK_END
 * @retval zero success
 * @retval non-zero if the position is invalid
 *
 */
cx_attr_nonnull
cx_attr_export
int cxBufferSeek(
        CxBuffer *buffer,
        off_t offset,
        int whence
);

/**
 * Clears the buffer by resetting the position and deleting the data.
 *
 * The data is deleted by zeroing it with a call to memset().
 * If you do not need that, you can use the faster cxBufferReset().
 *
 * @note If the #CX_BUFFER_COPY_ON_WRITE flag is set, this function
 * will not erase the data and behave exactly as cxBufferReset().
 *
 * @param buffer the buffer to be cleared
 * @see cxBufferReset()
 */
cx_attr_nonnull
cx_attr_export
void cxBufferClear(CxBuffer *buffer);

/**
 * Resets the buffer by resetting the position and size to zero.
 *
 * The data in the buffer is not deleted. If you need a safe
 * reset of the buffer, use cxBufferClear().
 *
 * @param buffer the buffer to be cleared
 * @see cxBufferClear()
 */
cx_attr_nonnull
cx_attr_export
void cxBufferReset(CxBuffer *buffer);

/**
 * Tests, if the buffer position has exceeded the buffer size.
 *
 * @param buffer the buffer to test
 * @retval true if the current buffer position has exceeded the last
 * byte of the buffer's contents
 * @retval false otherwise
 */
cx_attr_nonnull
cx_attr_nodiscard
cx_attr_export
bool cxBufferEof(const CxBuffer *buffer);


/**
 * Ensures that the buffer has a minimum capacity.
 *
 * If the current capacity is not sufficient, the buffer will be extended.
 *
 * The new capacity will be a power of two until the system's page size is reached.
 * Then, the new capacity will be a multiple of the page size.
 *
 * @param buffer the buffer
 * @param capacity the minimum required capacity for this buffer
 * @retval zero the capacity was already sufficient or successfully increased
 * @retval non-zero on allocation failure
 * @see cxBufferShrink()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferMinimumCapacity(
        CxBuffer *buffer,
        size_t capacity
);

/**
 * Shrinks the capacity of the buffer to fit its current size.
 *
 * If @p reserve is larger than zero, the buffer is shrunk to its size plus
 * the number of reserved bytes.
 *
 * If the current capacity is not larger than the size plus the reserved bytes,
 * nothing happens.
 *
 * If the #CX_BUFFER_COPY_ON_WRITE or #CX_BUFFER_COPY_ON_EXTEND flag is set,
 * this function does nothing.
 *
 * @param buffer the buffer
 * @param reserve the number of bytes that shall remain reserved
 * @see cxBufferMinimumCapacity()
 */
cx_attr_nonnull
cx_attr_export
void cxBufferShrink(
        CxBuffer *buffer,
        size_t reserve
);

/**
 * Writes data to a CxBuffer.
 *
 * If automatic flushing is not enabled, the data is simply written into the
 * buffer at the current position and the position of the buffer is increased
 * by the number of bytes written.
 *
 * If flushing is enabled and the buffer needs to flush, the data is flushed to
 * the target until the target signals that it cannot take more data by
 * returning zero via the respective write function. In that case, the remaining
 * data in this buffer is shifted to the beginning of this buffer so that the
 * newly available space can be used to append as much data as possible.
 *
 * This function only stops writing more elements, when the flush target and this
 * buffer are both incapable of taking more data or all data has been written.
 *
 * If, after flushing, the number of items that shall be written still exceeds
 * the capacity or flush threshold, this function tries to write all items directly
 * to the flush target, if possible.
 *
 * The number returned by this function is the number of elements from
 * @c ptr that could be written to either the flush target or the buffer
 * (so it does not include the number of items that had been already in the buffer
 * in were flushed during the process).
 *
 * @attention
 * When @p size is larger than one and the contents of the buffer are not aligned
 * with @p size, flushing stops after all complete items have been flushed, leaving
 * the mis-aligned part in the buffer.
 * Afterward, this function only writes as many items as possible to the buffer.
 *
 * @note The signature is compatible with the fwrite() family of functions.
 *
 * @param ptr a pointer to the memory area containing the bytes to be written
 * @param size the length of one element
 * @param nitems the element count
 * @param buffer the CxBuffer to write to
 * @return the total count of elements written
 * @see cxBufferAppend()
 * @see cxBufferRead()
 */
cx_attr_nonnull
cx_attr_export
size_t cxBufferWrite(
        const void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
);

/**
 * Appends data to a CxBuffer.
 *
 * The data is always appended to current data within the buffer,
 * regardless of the current position.
 * This is especially useful when the buffer is primarily meant for reading
 * while additional data is added to the buffer occasionally.
 * Consequently, the position of the buffer is unchanged after this operation.
 *
 * @note The signature is compatible with the fwrite() family of functions.
 *
 * @param ptr a pointer to the memory area containing the bytes to be written
 * @param size the length of one element
 * @param nitems the element count
 * @param buffer the CxBuffer to write to
 * @return the total count of elements written
 * @see cxBufferWrite()
 * @see cxBufferRead()
 */
cx_attr_nonnull
cx_attr_export
size_t cxBufferAppend(
        const void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
);

/**
 * Performs a single flush-run on the specified buffer.
 *
 * Does nothing when the position in the buffer is zero.
 * Otherwise, the data until the current position minus
 * one is considered for flushing.
 * Note carefully that flushing will never exceed the
 * current @em position, even when the size of the
 * buffer is larger than the current position.
 *
 * One flush run will try to flush @c blkmax many
 * blocks of size @c blksize until either the @p buffer
 * has no more data to flush or the write function
 * used for flushing returns zero.
 *
 * The buffer is shifted left for that many bytes
 * the flush operation has successfully flushed.
 *
 * @par Example 1
 * Assume you have a buffer with size 340 and you are
 * at position 200. The flush configuration is
 * @c blkmax=4 and @c blksize=64 .
 * Assume that the entire flush operation is successful.
 * All 200 bytes on the left hand-side from the current
 * position are written.
 * That means, the size of the buffer is now 140 and the
 * position is zero.
 *
 * @par Example 2
 * Same as Example 1, but now the @c blkmax is 1.
 * The size of the buffer is now 276 and the position is 136.
 *
 * @par Example 3
 * Same as Example 1, but now assume the flush target
 * only accepts 100 bytes before returning zero.
 * That means, the flush operations manages to flush
 * one complete block and one partial block, ending
 * up with a buffer with size 240 and position 100.
 *
 * @remark Just returns zero when flushing was not enabled with
 * cxBufferEnableFlushing().
 *
 * @remark When the buffer uses copy-on-write, the memory
 * is copied first, before attempting any flush.
 * This is, however, considered an erroneous use of the
 * buffer, because it does not make much sense to put
 * readonly data into an UCX buffer for flushing, instead
 * of writing it directly to the target.
 *
 * @param buffer the buffer
 * @return the number of successfully flushed bytes
 * @see cxBufferEnableFlushing()
 */
cx_attr_nonnull
cx_attr_export
size_t cxBufferFlush(CxBuffer *buffer);

/**
 * Reads data from a CxBuffer.
 *
 * The position of the buffer is increased by the number of bytes read.
 *
 * @note The signature is compatible with the fread() family of functions.
 *
 * @param ptr a pointer to the memory area where to store the read data
 * @param size the length of one element
 * @param nitems the element count
 * @param buffer the CxBuffer to read from
 * @return the total number of elements read
 * @see cxBufferWrite()
 * @see cxBufferAppend()
 */
cx_attr_nonnull
cx_attr_export
size_t cxBufferRead(
        void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
);

/**
 * Writes a character to a buffer.
 *
 * The least significant byte of the argument is written to the buffer. If the
 * end of the buffer is reached and #CX_BUFFER_AUTO_EXTEND feature is enabled,
 * the buffer capacity is extended by cxBufferMinimumCapacity(). If the feature
 * is disabled or buffer extension fails, @c EOF is returned.
 *
 * On successful write, the position of the buffer is increased.
 *
 * If you just want to write a null-terminator at the current position, you
 * should use cxBufferTerminate() instead.
 *
 * @param buffer the buffer to write to
 * @param c the character to write
 * @return the byte that has been written or @c EOF when the end of the stream is
 * reached and automatic extension is not enabled or not possible
 * @see cxBufferTerminate()
 */
cx_attr_nonnull
cx_attr_export
int cxBufferPut(
        CxBuffer *buffer,
        int c
);

/**
 * Writes a terminating zero to a buffer at the current position.
 *
 * If successful, sets the size to the current position and advances the position by one.
 *
 * The purpose of this function is to have the written data ready to be used as
 * a C string with the buffer's size being the length of that string.
 *
 * @param buffer the buffer to write to
 * @return zero, if the terminator could be written, non-zero otherwise
 */
cx_attr_nonnull
cx_attr_export
int cxBufferTerminate(CxBuffer *buffer);

/**
 * Writes a string to a buffer.
 *
 * This is a convenience function for <code>cxBufferWrite(str, 1, strlen(str), buffer)</code>.
 *
 * @param buffer the buffer
 * @param str the zero-terminated string
 * @return the number of bytes written
 */
cx_attr_nonnull
cx_attr_cstr_arg(2)
cx_attr_export
size_t cxBufferPutString(
        CxBuffer *buffer,
        const char *str
);

/**
 * Gets a character from a buffer.
 *
 * The current position of the buffer is increased after a successful read.
 *
 * @param buffer the buffer to read from
 * @return the character or @c EOF, if the end of the buffer is reached
 */
cx_attr_nonnull
cx_attr_export
int cxBufferGet(CxBuffer *buffer);

#ifdef __cplusplus
}
#endif

#endif // UCX_BUFFER_H