src/cx/buffer.h

/*
 * 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"
#include "string.h"

/**
 * 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 operation 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

/**
 * If this flag is enabled, the buffer will never free its contents regardless of #CX_BUFFER_FREE_CONTENTS.
 *
 * This is useful, for example, when you want to keep a pointer to the data after destroying the buffer.
 */
#define CX_BUFFER_DO_NOT_FREE 0x10

/**
 * 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)


/** 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;
    /** Current position of the buffer. */
    size_t pos;
    /** Current capacity (i.e. maximum size) of the buffer. */
    size_t capacity;
    /** Maximum capacity that this buffer may grow to. */
    size_t max_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 the 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 allocator the allocator this buffer shall use for automatic
 * memory management
 * (if @c NULL, the cxDefaultAllocator will be used)
 * @param space pointer to the memory area, or @c NULL to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @param flags buffer features (see cx_buffer_s.flags)
 * @return zero on success, non-zero if a required allocation failed
 */
CX_EXTERN CX_NONNULL_ARG(1)
int cxBufferInit(CxBuffer *buffer, const CxAllocator *allocator,
        void *space, size_t capacity, int flags);

/**
 * 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_EXTERN CX_NONNULL
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().
 *
 * @param buffer the buffer to deallocate
 * @see cxBufferCreate()
 */
CX_EXTERN
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 the argument for @p space.
 * Then this function will allocate the space and enforce
 * the #CX_BUFFER_FREE_CONTENTS flag.
 *
 * @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 space pointer to the memory area, or @c NULL to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @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_EXTERN CX_MALLOC CX_DEALLOC(cxBufferFree, 1) CX_NODISCARD
CxBuffer *cxBufferCreate(const CxAllocator *allocator, void *space,
                                   size_t capacity, 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.
 * When the 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 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 the parameter type.
 *
 * @attention
 * Security Note: The shifting operation does @em not erase the previously occupied memory cells.
 * But you can do that manually 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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL
int cxBufferSeek(CxBuffer *buffer, off_t offset, int whence);

/**
 * Discards items from the end of the buffer.
 *
 * When the current position points to a byte that gets discarded,
 * the position is set to the buffer size.
 *
 * @param buffer the buffer
 * @param size the size of one item
 * @param nitems the number of items to discard
 * @return the actual number of discarded items
 */
CX_EXTERN CX_NONNULL
size_t cxBufferPop(CxBuffer *buffer, size_t size, size_t nitems);

/**
 * 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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL CX_NODISCARD
bool cxBufferEof(const CxBuffer *buffer);

/**
 * Ensures that the buffer has the required capacity.
 *
 * If the current capacity is not sufficient, the buffer will be extended.
 * If the current capacity is larger, the buffer is shrunk and superfluous
 * content is discarded.
 *
 * This function will reserve no more bytes than requested, in contrast to
 * cxBufferMinimumCapacity(), which may reserve more bytes to improve the
 * number of future necessary reallocations.
 *
 * @param buffer the buffer
 * @param capacity the required capacity for this buffer
 * @retval zero on success
 * @retval non-zero on allocation failure
 * @see cxBufferShrink()
 * @see cxBufferMinimumCapacity()
 */
CX_EXTERN CX_NONNULL
int cxBufferReserve(CxBuffer *buffer, size_t capacity);

/**
 * Limits the buffer's capacity.
 *
 * If the current capacity is already larger, this function fails and returns
 * non-zero.
 *
 * The capacity limit will affect auto-extension features, as well as future
 * calls to cxBufferMinimumCapacity() and cxBufferReserve().
 *
 * @param buffer the buffer
 * @param capacity the maximum allowed capacity for this buffer
 * @retval zero the limit is applied
 * @retval non-zero the new limit is smaller than the current capacity
 * @see cxBufferReserve()
 * @see cxBufferMinimumCapacity()
 */
CX_EXTERN CX_NONNULL
int cxBufferMaximumCapacity(CxBuffer *buffer, size_t capacity);

/**
 * Ensures that the buffer has a minimum capacity.
 *
 * If the current capacity is not sufficient, the buffer will be generously
 * 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 cxBufferMaximumCapacity()
 * @see cxBufferReserve()
 * @see cxBufferShrink()
 */
CX_EXTERN CX_NONNULL
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 cxBufferReserve()
 * @see cxBufferMinimumCapacity()
 */
CX_EXTERN CX_NONNULL
void cxBufferShrink(CxBuffer *buffer, size_t reserve);

/**
 * Writes data to a CxBuffer.
 *
 * If auto-extension is enabled, the buffer's capacity is automatically
 * increased when it is not large enough to hold all data.
 * By default, the capacity grows indefinitely, unless limited with
 * cxBufferMaximumCapacity().
 * When auto-extension fails, this function writes no data and returns zero.
 *
 * The position of the buffer is moved alongside the written data.
 *
 * @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_EXTERN CX_NONNULL
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_EXTERN CX_NONNULL
size_t cxBufferAppend(const void *ptr, size_t size,
        size_t nitems, 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_EXTERN CX_NONNULL
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, unless a limit set by
 * cxBufferMaximumCapacity() is reached.
 * If the feature is disabled or the buffer extension fails, @c EOF is returned.
 *
 * On successful writing, 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_EXTERN CX_NONNULL
int cxBufferPut(CxBuffer *buffer, int c);

/**
 * Writes a terminating zero to a buffer at the current position.
 *
 * If successful, also sets the size to the current position and shrinks the buffer.
 *
 * 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
 * @see cxBufferShrink()
 */
CX_EXTERN CX_NONNULL
int cxBufferTerminate(CxBuffer *buffer);

/**
 * Internal function - do not use.
 *
 * @param buffer the buffer
 * @param str the string
 * @return the number of bytes written
 * @see cxBufferPutString()
 */
CX_EXTERN CX_NONNULL
size_t cx_buffer_put_string(CxBuffer *buffer, cxstring str);

/**
 * Writes a string to a buffer with cxBufferWrite().
 *
 * @param buffer (@c CxBuffer*) the buffer
 * @param str (any string) the zero-terminated string
 * @return (@c size_t) the number of bytes written
 * @see cxBufferWrite()
 * @see cx_strcast()
 */
#define cxBufferPutString(buffer, str) cx_buffer_put_string(buffer, cx_strcast(str))

/**
 * Internal function - do not use.
 *
 * @param buffer the buffer
 * @param str the string
 * @return the number of bytes written
 * @see cxBufferPutString()
 */
CX_EXTERN CX_NONNULL
size_t cx_buffer_append_string(CxBuffer *buffer, cxstring str);

/**
 * Appends a string to a buffer with cxBufferAppend().
 *
 * @param buffer (@c CxBuffer*) the buffer
 * @param str (any string) the zero-terminated string
 * @return (@c size_t) the number of bytes written
 * @see cxBufferAppend()
 * @see cx_strcast()
 */
#define cxBufferAppendString(buffer, str) cx_buffer_append_string(buffer, cx_strcast(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_EXTERN CX_NONNULL
int cxBufferGet(CxBuffer *buffer);

/**
 * Gets the data in a buffer as a @c cxstring.
 *
 * @param buffer the buffer
 * @return the data in the buffer interpreted as a @c cxstring
 */
CX_NONNULL CX_INLINE
cxstring cx_bstr(CxBuffer *buffer) {
    return cx_strn(buffer->space, buffer->size);
}

/**
 * Gets the data in a buffer as a @c cxmutstr.
 *
 * @param buffer the buffer
 * @return the data in the buffer interpreted as a @c cxmutstr
 */
CX_NONNULL CX_INLINE
cxmutstr cx_bstr_m(CxBuffer *buffer) {
    return cx_mutstrn(buffer->space, buffer->size);
}

#endif // UCX_BUFFER_H