recover.c

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

typedef uint8_t  BYTE;

int header_is_jpeg(FILE *memcard);
void create_new_outfile(char **outfile, FILE **outptr, int *filename_counter);

int main(int argc, char *argv[])
{
    // check proper usage
    if (argc != 2)
    {
        fprintf(stderr, "usage: ./recover filename\n");
        return 1;
    }

    // keep filenames
    char    *infile = argv[1],
            *outfile = NULL;
    FILE    *inptr = fopen(infile, "r"),
            *outptr = NULL;
    BYTE    *byte_array = malloc(512 * sizeof(BYTE));
    int     filename_counter = 0;

    // program works only with initialized outfile
    outfile = malloc(sizeof("000.jpg") + 1);
    sprintf(outfile, "%03i.jpg", filename_counter);
    outptr = fopen(outfile, "w");

    // check if files open properly
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s\n", infile);
        return 2;
    }

    // skip memory blocks until jpeg header is found
    while (!header_is_jpeg(inptr))
    {
        fseek(inptr, 512, SEEK_CUR);
    }

    if (header_is_jpeg(inptr))
    {
        create_new_outfile(&outfile, &outptr, &filename_counter);
    }

    if (outptr == NULL)
    {
        fprintf(stderr, "Could not write in %s file\n", outfile);
        return 3;
    }

    // only keep reading if block is proper size (512)
    while (fread(outptr, 1, 512, inptr) == 512)
    {
        // rewind seek
        fseek(inptr, -512, SEEK_CUR);

        // read and write 512 bytes, 1 byte at a time
        for(int i = 0, arr_size = sizeof(byte_array); i < arr_size; i++)
        {
            fread(&byte_array[i], 1, 1, inptr);
            fwrite(&byte_array[i], 1, 1, outptr);
        }

        // if next block has a new jpeg header - create new file
        if (header_is_jpeg(inptr))
        {
            create_new_outfile(&outfile, &outptr, &filename_counter);
        }
    }

    // close files
    fclose(inptr);
    fclose(outptr);
    return 0;
}


int header_is_jpeg(FILE *memcard)
{
    BYTE *BLOCKHEADER = malloc(4 * sizeof(BYTE));
    // read first 4 bytes of current memory block
    for (int i = 0; i < 4; i++)
    {
        fread(&BLOCKHEADER[i], 1, 1, memcard);
    }

    // rewind seek back to beginning of block
    fseek(memcard, -4, SEEK_CUR);

    // check if header is the same as JPEG header, return true if it is
    if (BLOCKHEADER[0] == 0xff &&
        BLOCKHEADER[1] == 0xd8 &&
        BLOCKHEADER[2] == 0xff &&
        (BLOCKHEADER[3] & 0xf0) == 0xe0)
    {
        printf("JPEG Header found!\n");
        free(BLOCKHEADER);
        return 1;
    }
    else
    {
        free(BLOCKHEADER);
        return 0;
    }
}

void create_new_outfile(char **outfile, FILE **outptr, int *filename_counter)
{
    // if a file is open - close the old one before creating new one
    if (*outptr != NULL)
    {
        printf("successfuly recovered image: %s\n", *outfile);
        fclose(*outptr);
        free(*outfile);
    }

    // create new output file
    *outfile = malloc(sizeof("000.jpg") + 1);
    sprintf(*outfile, "%03i.jpg", *filename_counter);
    *outptr = fopen(*outfile, "w");
    (*filename_counter)++;
}