src/ucx/buffer.h

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2017 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
 * 
 * Advanced buffer implementation.
 * 
 * Instances of UcxBuffer can be used to read from or to write to like one
 * would do with a stream. This allows the use of ucx_stream_copy() to copy
 * contents from one buffer to another.
 * 
 * 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
 */

#ifndef UCX_BUFFER_H
#define	UCX_BUFFER_H

#include "ucx.h"
#include <sys/types.h>
#include <stdio.h>

#ifdef	__cplusplus
extern "C" {
#endif

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

/**
 * If this flag is enabled, the buffer will automatically free its contents.
 */
#define UCX_BUFFER_AUTOFREE     0x01

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

/** UCX Buffer. */
typedef struct {
    /** A pointer to the buffer contents. */
    char *space;
    /** 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 #UCX_BUFFER_DEFAULT
     * @see #UCX_BUFFER_AUTOFREE
     * @see #UCX_BUFFER_AUTOEXTEND
     */
    int flags;
} UcxBuffer;

/**
 * Creates a new buffer.
 * 
 * <b>Note:</b> you may provide <code>NULL</code> as argument for
 * <code>space</code>. Then this function will allocate the space and enforce
 * the #UCX_BUFFER_AUTOFREE flag.
 * 
 * @param space pointer to the memory area, or <code>NULL</code> to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @param flags buffer features (see UcxBuffer.flags)
 * @return the new buffer
 */
UcxBuffer *ucx_buffer_new(void *space, size_t capacity, int flags);

/**
 * Destroys a buffer.
 * 
 * If the #UCX_BUFFER_AUTOFREE feature is enabled, the contents of the buffer
 * are also freed.
 * 
 * @param buffer the buffer to destroy
 */
void ucx_buffer_free(UcxBuffer* buffer);

/**
 * Creates a new buffer and fills it with extracted content from another buffer.
 * 
 * <b>Note:</b> the #UCX_BUFFER_AUTOFREE feature is enforced for the new buffer.
 * 
 * @param src the source buffer
 * @param start the start position of extraction
 * @param length the count of bytes to extract (must not be zero)
 * @param flags feature mask for the new buffer
 * @return a new buffer containing the extraction
 */
UcxBuffer* ucx_buffer_extract(UcxBuffer *src,
        size_t start, size_t length, int flags);

/**
 * A shorthand macro for the full extraction of the buffer.
 * 
 * @param src the source buffer
 * @param flags feature mask for the new buffer
 * @return a new buffer with the extracted content
 */
#define ucx_buffer_clone(src,flags) \
    ucx_buffer_extract(src, 0, (src)->capacity, 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 <code>shift</code> 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.
 * 
 * <b>Security note:</b> the shifting operation does <em>not</em> erase the
 * previously occupied memory cells. You can easily do that manually, e.g. by
 * calling <code>memset(buffer->space, 0, shift)</code> for a right shift or
 * <code>memset(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
 */
int ucx_buffer_shift(UcxBuffer* buffer, off_t shift);

/**
 * Shifts the buffer to the right.
 * See ucx_buffer_shift() for details.
 * 
 * @param buffer the buffer
 * @param shift the shift offset
 * @return 0 on success, non-zero if a required auto-extension fails
 * @see ucx_buffer_shift()
 */
int ucx_buffer_shift_right(UcxBuffer* buffer, size_t shift);

/**
 * Shifts the buffer to the left.
 * 
 * See ucx_buffer_shift() for details. Note, however, that this method expects
 * a positive shift offset.
 * 
 * Since a left shift cannot fail due to memory allocation problems, this
 * function always returns zero.
 * 
 * @param buffer the buffer
 * @param shift the shift offset
 * @return always zero
 * @see ucx_buffer_shift()
 */
int ucx_buffer_shift_left(UcxBuffer* buffer, size_t shift);


/**
 * Moves the position of the buffer.
 * 
 * The new position is relative to the <code>whence</code> argument.
 *
 * SEEK_SET marks the start of the buffer.
 * SEEK_CUR marks the current position.
 * SEEK_END marks the end of the buffer.
 * 
 * With an offset of zero, this function sets the buffer position to zero
 * (SEEK_SET), the buffer size (SEEK_END) or leaves the buffer position
 * unchanged (SEEK_CUR).
 * 
 * @param buffer
 * @param offset position offset relative to <code>whence</code>
 * @param whence one of SEEK_SET, SEEK_CUR or SEEK_END
 * @return 0 on success, non-zero if the position is invalid
 *
 */
int ucx_buffer_seek(UcxBuffer *buffer, off_t offset, int whence);

/**
 * Clears the buffer by resetting the position and deleting the data.
 * 
 * The data is deleted by a zeroing it with call to <code>memset()</code>.
 * 
 * @param buffer the buffer to be cleared
 */
#define ucx_buffer_clear(buffer) memset((buffer)->space, 0, (buffer)->size); \
        (buffer)->size = 0; (buffer)->pos = 0;

/**
 * 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.
 */
int ucx_buffer_eof(UcxBuffer *buffer);


/**
 * Extends the capacity of the buffer.
 * 
 * <b>Note:</b> The buffer capacity increased by a power of two. I.e.
 * the buffer capacity is doubled, as long as it would not hold the current
 * content plus the additional required bytes.
 * 
 * <b>Attention:</b> the argument provided is the number of <i>additional</i>
 * bytes the buffer shall hold. It is <b>NOT</b> the total number of bytes the
 * buffer shall hold.
 * 
 * @param buffer the buffer to extend
 * @param additional_bytes the number of additional bytes the buffer shall
 * <i>at least</i> hold
 * @return 0 on success or a non-zero value on failure
 */
int ucx_buffer_extend(UcxBuffer *buffer, size_t additional_bytes);

/**
 * Writes data to a UcxBuffer.
 * 
 * The position of the buffer is increased by the number of bytes written.
 * 
 * @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 UcxBuffer to write to
 * @return the total count of bytes written
 */
size_t ucx_buffer_write(const void *ptr, size_t size, size_t nitems,
        UcxBuffer *buffer);

/**
 * Reads data from a UcxBuffer.
 * 
 * The position of the buffer is increased by the number of bytes read.
 * 
 * @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 UcxBuffer to read from
 * @return the total number of elements read
 */
size_t ucx_buffer_read(void *ptr, size_t size, size_t nitems,
        UcxBuffer *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 #UCX_BUFFER_AUTOEXTEND feature is enabled,
 * the buffer capacity is extended by ucx_buffer_extend(). If the feature is
 * disabled or buffer extension fails, <code>EOF</code> 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 as <code>int</code> value
 * @return the byte that has bean written as <code>int</code> value or
 * <code>EOF</code> when the end of the stream is reached and automatic
 * extension is not enabled or not possible
 */
int ucx_buffer_putc(UcxBuffer *buffer, int c);

/**
 * 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 as <code>int</code> value or <code>EOF</code>, if the
 * end of the buffer is reached
 */
int ucx_buffer_getc(UcxBuffer *buffer);

/**
 * Writes a string to a buffer.
 * 
 * @param buffer the buffer
 * @param str the string
 * @return the number of bytes written
 */
size_t ucx_buffer_puts(UcxBuffer *buffer, const char *str);

/**
 * Returns the complete buffer content as sstr_t.
 * @param buffer the buffer
 * @return the result of <code>sstrn()</code> with the buffer space and size
 * as arguments
 */
#define ucx_buffer_to_sstr(buffer) sstrn((buffer)->space, (buffer)->size)

#ifdef	__cplusplus
}
#endif

#endif	/* UCX_BUFFER_H */