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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

  * \version 3.0

  * \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.

  */

 #define CX_BUFFER_FREE_CONTENTS 0x01

 /**

  * If this flag is enabled, the buffer will automatically extends its capacity.

  */

 #define CX_BUFFER_AUTO_EXTEND 0x02

 /** Structure for the UCX buffer data. */

 typedef struct {

     /** 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. */

     CxAllocator const *allocator;

     /** 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;

     /**

      * The buffer may not extend beyond this threshold before starting to flush.

      * Default is \c SIZE_MAX (flushing disabled when auto extension is enabled).

      */

     size_t flush_threshold;

     /**

      * The block size for the elements to flush.

      * Default is 4096 bytes.

      */

     size_t flush_blksize;

     /**

      * The maximum number of blocks to flush in one cycle.

      * Zero disables flushing entirely (this is the default).

      * Set this to \c SIZE_MAX to flush the entire buffer.

      *

      * @attention if the maximum number of blocks multiplied with the block size

      * is smaller than the expected contents written to this buffer within one write

      * operation, multiple flush cycles are performed after that write.

      * That means the total number of blocks flushed after one write to this buffer may

      * be larger than \c flush_blkmax.

      */

     size_t flush_blkmax;

     /**

      * The write function used for flushing.

      * If NULL, the flushed content gets discarded.

      */

     cx_write_func flush_func;

     /**

      * The target for \c flush_func.

      */

     void *flush_target;

     /**

      * Flag register for buffer features.

      * @see #CX_BUFFER_DEFAULT

      * @see #CX_BUFFER_FREE_CONTENTS

      * @see #CX_BUFFER_AUTO_EXTEND

      */

     int flags;

 } cx_buffer_s;

 /**

  * UCX buffer.

  */

 typedef cx_buffer_s CxBuffer;

 /**

  * Initializes a fresh buffer.

  *

  * \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 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 default heap allocator will be used.

  * @param flags buffer features (see cx_buffer_s.flags)

  * @return zero on success, non-zero if a required allocation failed

  */

 __attribute__((__nonnull__(1)))

 int cxBufferInit(

         CxBuffer *buffer,

         void *space,

         size_t capacity,

         CxAllocator const *allocator,

         int flags

 );

 /**

  * Destroys the buffer contents.

  *

  * Has no effect if the #CX_BUFFER_FREE_CONTENTS feature is not enabled.

  *

  * @param buffer the buffer which contents shall be destroyed

  */

 __attribute__((__nonnull__))

 void cxBufferDestroy(CxBuffer *buffer);

 /**

  * 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)

  * @return 0 on success, non-zero if a required auto-extension fails

  */

 __attribute__((__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

  * @return 0 on success, non-zero if a required auto-extension fails

  * @see cxBufferShift()

  */

 __attribute__((__nonnull__))

 int cxBufferShiftRight(

         CxBuffer *buffer,

         size_t shift

 );

 /**

  * Shifts the buffer to the left.

  * See cxBufferShift() for details.

  *

  * \note Since a left shift cannot fail due to memory allocation problems, this

  * function always returns zero.

  *

  * @param buffer the buffer

  * @param shift the positive shift offset

  * @return always zero

  * @see cxBufferShift()

  */

 __attribute__((__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

  * @return 0 on success, non-zero if the position is invalid

  *

  */

 __attribute__((__nonnull__))

 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().

  *

  * @param buffer the buffer to be cleared

  */

 __attribute__((__nonnull__))

 void cxBufferClear(CxBuffer *buffer);

 /**

  * Tests, if the buffer position has exceeded the buffer capacity.

  *

  * @param buffer the buffer to test

  * @return non-zero, if the current buffer position has exceeded the last

  * available byte of the buffer.

  */

 __attribute__((__nonnull__))

 int cxBufferEof(CxBuffer const *buffer);

 /**

  * Ensures that the buffer has a minimum capacity.

  *

  * If the current capacity is not sufficient, the buffer will be extended.

  *

  * @param buffer the buffer

  * @param capacity the minimum required capacity for this buffer

  * @return 0 on success or a non-zero value on failure

  */

 __attribute__((__nonnull__))

 int cxBufferMinimumCapacity(

         CxBuffer *buffer,

         size_t capacity

 );

 /**

  * Writes data to a CxBuffer.

  *

  * 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.

  * The number returned by this function is the total number of elements that

  * could be written during the process. It does not necessarily mean that those

  * elements are still in this buffer, because some of them could have also be

  * flushed already.

  *

  * If automatic flushing is not enabled, the position of the buffer is increased

  * by the number of bytes written.

  *

  * \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

  */

 __attribute__((__nonnull__))

 size_t cxBufferWrite(

         void const *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

  */

 __attribute__((__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 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.

  *

  * @param buffer the buffer to write to

  * @param c the character to write

  * @return the byte that has bean written or \c EOF when the end of the stream is

  * reached and automatic extension is not enabled or not possible

  */

 __attribute__((__nonnull__))

 int cxBufferPut(

         CxBuffer *buffer,

         int c

 );

 /**

  * Writes a string to a buffer.

  *

  * @param buffer the buffer

  * @param str the zero-terminated string

  * @return the number of bytes written

  */

 __attribute__((__nonnull__))

 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

  */

 __attribute__((__nonnull__))

 int cxBufferGet(CxBuffer *buffer);

 #ifdef __cplusplus

 }

 #endif

 #endif // UCX_BUFFER_H