FILE-like buffer system for memory

buffer.c

//
//  buffer.c
//
//  Created by Homework User on 10/20/18.
//  Copyright © 2018 JackMacWindows. All rights reserved.
//

#include "buffer.h"
#include <stdlib.h>
#include <string.h>

uint64_t buf_tell(buffer_t * buffer) {
    return buffer->offset;
}

int buf_seek(buffer_t * buffer, uint64_t pos, int mode) {
    if (mode == 0) {
        if (pos > buffer->size) return -1;
        buffer->size = pos;
        return 0;
    } else if (mode == 1) {
        if (buffer->offset + pos > buffer->size) return -1;
        buffer->offset += pos;
        return 0;
    } else if (mode == 2) {
        if (buffer->size - pos < 0) return -1;
        buffer->offset = buffer->size - pos;
        return 0;
    } else return 1;
}

uint64_t buf_read_u64(buffer_t * buffer) {
    buffer->offset += 8;
    return ((uint64_t*)(&buffer->data[buffer->offset-8]))[0];
}
uint32_t buf_read_u32(buffer_t * buffer) {
    buffer->offset += 4;
    return ((uint32_t*)(&buffer->data[buffer->offset-4]))[0];
}
uint16_t buf_read_u16(buffer_t * buffer) {
    buffer->offset += 2;
    return ((uint16_t*)(&buffer->data[buffer->offset-2]))[0];
}
uint8_t buf_read_u8(buffer_t * buffer) {
    buffer->offset += 1;
    return ((uint8_t*)(&buffer->data[buffer->offset-1]))[0];
}
long buf_read_long(buffer_t * buffer) {
    buffer->offset += sizeof(long);
    return ((long*)(&buffer->data[buffer->offset-sizeof(long)]))[0];
}
const char * buf_read_str(buffer_t * buffer) {
    return (const char *)buf_read_buf(buffer, strlen((const char *)&buffer->data[buffer->offset])+1);
}
uint8_t * buf_read_buf(buffer_t * buffer, uint64_t size) {
    uint8_t * buf = (uint8_t*)malloc(size);
    memcpy(buf, &buffer->data[buffer->offset], size);
    buffer->offset += size;
    return buf;
}

void buf_write_u64(buffer_t * buffer, uint64_t num) {
    ((uint64_t*)(&buffer->data[buffer->offset]))[0] = num;
    buffer->offset += 8;
}
void buf_write_u32(buffer_t * buffer, uint32_t num) {
    ((uint32_t*)(&buffer->data[buffer->offset]))[0] = num;
    buffer->offset += 4;
}
void buf_write_u16(buffer_t * buffer, uint16_t num) {
    ((uint16_t*)(&buffer->data[buffer->offset]))[0] = num;
    buffer->offset += 2;
}
void buf_write_u8(buffer_t * buffer, uint8_t num) {
    buffer->data[buffer->offset] = num;
    buffer->offset++;
}
void buf_write_long(buffer_t * buffer, long num) {
    ((long*)(&buffer->data[buffer->offset]))[0] = num;
    buffer->offset += sizeof(long);
}
void buf_write_buf(buffer_t * buffer, uint8_t * buf, uint64_t size) {
    memcpy(&buffer->data[buffer->offset], buf, size);
    buffer->offset += size;
}
void buf_write_str(buffer_t * buffer, const char * str) {
    buf_write_buf(buffer, (uint8_t*)str, strlen(str)+1);
}

buffer.h

//
//  buffer.h
//
//  Created by Homework User on 10/20/18.
//  Copyright © 2018 JackMacWindows. All rights reserved.
//

#ifndef buffer_h
#define buffer_h

#include <stdint.h>

#ifndef SEEK_SET
#define SEEK_SET        0       /* set file offset to offset */
#endif
#ifndef SEEK_CUR
#define SEEK_CUR        1       /* set file offset to current plus offset */
#endif
#ifndef SEEK_END
#define SEEK_END        2       /* set file offset to EOF plus offset */
#endif

typedef struct {
    uint64_t offset;
    uint64_t size;
    uint8_t * data;
} buffer_t;

extern uint64_t buf_tell(buffer_t * buffer);
extern int buf_seek(buffer_t * buffer, uint64_t pos, int mode);

extern uint64_t buf_read_u64(buffer_t * buffer);
extern uint32_t buf_read_u32(buffer_t * buffer);
extern uint16_t buf_read_u16(buffer_t * buffer);
extern uint8_t buf_read_u8(buffer_t * buffer);
extern long buf_read_long(buffer_t * buffer);
extern const char * buf_read_str(buffer_t * buffer);
extern uint8_t * buf_read_buf(buffer_t * buffer, uint64_t size);

extern void buf_write_u64(buffer_t * buffer, uint64_t num);
extern void buf_write_u32(buffer_t * buffer, uint32_t num);
extern void buf_write_u16(buffer_t * buffer, uint16_t num);
extern void buf_write_u8(buffer_t * buffer, uint8_t num);
extern void buf_write_long(buffer_t * buffer, long num);
extern void buf_write_str(buffer_t * buffer, const char * str);
extern void buf_write_buf(buffer_t * buffer, uint8_t * buf, uint64_t size);

#endif /* buffer_h */