src/buffer.c

/*
 * 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.
 */

#include "cx/buffer.h"
#include "cx/utils.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>

int cxBufferInit(
        CxBuffer *buffer,
        void *space,
        size_t capacity,
        CxAllocator const *allocator,
        int flags
) {
    buffer->allocator = allocator;
    buffer->flags = flags;
    if (!space) {
        buffer->bytes = cxMalloc(allocator, capacity);
        if (buffer->bytes == NULL) {
            return 1;
        }
        buffer->flags |= CX_BUFFER_FREE_CONTENTS;
    } else {
        buffer->bytes = space;
    }
    buffer->capacity = capacity;
    buffer->size = 0;
    buffer->pos = 0;

    buffer->flush_func = NULL;
    buffer->flush_blkmax = 0;
    buffer->flush_blksize = 4096;
    buffer->flush_threshold = SIZE_MAX;

    return 0;
}

void cxBufferDestroy(CxBuffer *buffer) {
    if ((buffer->flags & CX_BUFFER_FREE_CONTENTS) == CX_BUFFER_FREE_CONTENTS) {
        cxFree(buffer->allocator, buffer->bytes);
    }
}

int cxBufferSeek(
        CxBuffer *buffer,
        off_t offset,
        int whence
) {
    size_t npos;
    switch (whence) {
        case SEEK_CUR:
            npos = buffer->pos;
            break;
        case SEEK_END:
            npos = buffer->size;
            break;
        case SEEK_SET:
            npos = 0;
            break;
        default:
            return -1;
    }

    size_t opos = npos;
    npos += offset;

    if ((offset > 0 && npos < opos) || (offset < 0 && npos > opos)) {
        return -1;
    }

    if (npos >= buffer->size) {
        return -1;
    } else {
        buffer->pos = npos;
        return 0;
    }

}

void cxBufferClear(CxBuffer *buffer) {
    memset(buffer->bytes, 0, buffer->size);
    buffer->size = 0;
    buffer->pos = 0;
}

int cxBufferEof(CxBuffer const *buffer) {
    return buffer->pos >= buffer->size;
}

int cxBufferMinimumCapacity(
        CxBuffer *buffer,
        size_t newcap
) {
    if (newcap <= buffer->capacity) {
        return 0;
    }

    if (cxReallocate(buffer->allocator,
                     (void **) &buffer->bytes, newcap) == 0) {
        buffer->capacity = newcap;
        return 0;
    } else {
        return -1;
    }
}

size_t cxBufferWrite(
        void const *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
) {
    // TODO: optimize for special case size == nitems == 1
    size_t len;
    if (cx_szmul(size, nitems, &len)) {
        return 0;
    }
    size_t required = buffer->pos + len;
    if (buffer->pos > required) {
        return 0;
    }

    bool perform_flush = false;
    if (required > buffer->capacity) {
        if ((buffer->flags & CX_BUFFER_AUTO_EXTEND) == CX_BUFFER_AUTO_EXTEND && required) {
            if (buffer->flush_blkmax > 0 && required > buffer->flush_threshold) {
                perform_flush = true;
            } else {
                if (cxBufferMinimumCapacity(buffer, required)) {
                    return 0;
                }
            }
        } else {
            if (buffer->flush_blkmax > 0) {
                perform_flush = true;
            } else {
                // truncate data to be written, if we can neither extend nor flush
                len = buffer->capacity - buffer->pos;
                if (size > 1) {
                    // TODO: this is bugged - it would only discard one element and not as many as required
                    len -= len % size;
                    nitems = len / size;
                }
            }
        }
    }

    if (len == 0) {
        return len;
    }

    if (perform_flush) {
        // TODO: implement flushing
        // (1) determine how many bytes to flush (use flushmax = blkmax * blksize)
        // (2) if len is larger than the number computed in (1) we need more flush cycles, compute how many
        // (3) determine how many bytes from the buffer shall be flushed
        // (4) if something remains in the buffer, shift the buffer to the left
        // (4a) if buffer was shifted, append the new data to the buffer
        // (4b) if the buffer was flushed entirely AND the new data also fits into flushmax,
        //      directly write the new data to the flush sink
        return 0; // remove this after implementation
    } else {
        memcpy(buffer->bytes + buffer->pos, ptr, len);
        buffer->pos += len;
        if (buffer->pos > buffer->size) {
            buffer->size = buffer->pos;
        }
    }

    return nitems;
}

int cxBufferPut(
        CxBuffer *buffer,
        int c
) {
    c &= 0xFF;
    unsigned char const ch = c;
    if (cxBufferWrite(&ch, 1, 1, buffer) == 1) {
        return c;
    } else {
        return EOF;
    }
}

size_t cxBufferPutString(
        CxBuffer *buffer,
        const char *str
) {
    return cxBufferWrite(str, 1, strlen(str), buffer);
}

size_t cxBufferRead(
        void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
) {
    size_t len;
    if (cx_szmul(size, nitems, &len)) {
        return 0;
    }
    if (buffer->pos + len > buffer->size) {
        len = buffer->size - buffer->pos;
        if (size > 1) len -= len % size;
    }

    if (len <= 0) {
        return len;
    }

    memcpy(ptr, buffer->bytes + buffer->pos, len);
    buffer->pos += len;

    return len / size;
}

int cxBufferGet(CxBuffer *buffer) {
    if (cxBufferEof(buffer)) {
        return EOF;
    } else {
        int c = buffer->bytes[buffer->pos];
        buffer->pos++;
        return c;
    }
}

int cxBufferShiftLeft(
        CxBuffer *buffer,
        size_t shift
) {
    if (shift >= buffer->size) {
        buffer->pos = buffer->size = 0;
    } else {
        memmove(buffer->bytes, buffer->bytes + shift, buffer->size - shift);
        buffer->size -= shift;

        if (buffer->pos >= shift) {
            buffer->pos -= shift;
        } else {
            buffer->pos = 0;
        }
    }
    return 0;
}

int cxBufferShiftRight(
        CxBuffer *buffer,
        size_t shift
) {
    size_t req_capacity = buffer->size + shift;
    size_t movebytes;

    // auto extend buffer, if required and enabled
    if (buffer->capacity < req_capacity) {
        if ((buffer->flags & CX_BUFFER_AUTO_EXTEND) == CX_BUFFER_AUTO_EXTEND) {
            if (cxBufferMinimumCapacity(buffer, req_capacity)) {
                return 1;
            }
            movebytes = buffer->size;
        } else {
            movebytes = buffer->capacity - shift;
        }
    } else {
        movebytes = buffer->size;
    }

    memmove(buffer->bytes + shift, buffer->bytes, movebytes);
    buffer->size = shift + movebytes;

    buffer->pos += shift;
    if (buffer->pos > buffer->size) {
        buffer->pos = buffer->size;
    }

    return 0;
}

int cxBufferShift(
        CxBuffer *buffer,
        off_t shift
) {
    if (shift < 0) {
        return cxBufferShiftLeft(buffer, (size_t) (-shift));
    } else if (shift > 0) {
        return cxBufferShiftRight(buffer, (size_t) shift);
    } else {
        return 0;
    }
}