base64_for_utf16le.c

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iconv.h>

char base64decode_lut[] = {
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
    64, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
    64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};

static void base64decode(char *src, char *dest, int len)
{
    int i = 0, slen = strlen(src);

    for (i = 0; i < slen && i < len; i += 4, src += 4) {
        char c1 = base64decode_lut[*(src + 0)],
             c2 = base64decode_lut[*(src + 1)],
             c3 = base64decode_lut[*(src + 2)],
             c4 = base64decode_lut[*(src + 3)];

        *(dest++) = (c1 & 0x3F) << 0x2 | (c2 & 0x30) >> 0x4;
        *(dest++) = (c3 != 64) ? ((c2 & 0xF) << 0x4 | (c3 & 0x3C) >> 0x2) : '\0';
        *(dest++) = (c4 != 64) ? ((c3 & 0x3) << 0x6 | c4 & 0x3F) : '\0';
    }
    *dest = '\0';       // Append terminator
}

static int b64_decode_string(char *source)
{
    iconv_t handle;
    size_t dest_size;
    size_t utf_size;
    char *dest, *d;
    char *utf, *u;

    dest_size = strlen(source);
    d = dest = calloc(dest_size, sizeof(char));
    if (!dest)
        return -ENOMEM;

    base64decode(source, dest, dest_size);

    for (int j = 0; j < dest_size; j++)
        printf("%d: %x\n", j, *((unsigned char *)(dest + j)));

    printf("Decode: %s\n", dest);

    utf_size = dest_size * 4;
    u = utf = malloc(utf_size);
    if (!utf) {
        free(d);
        return -ENOMEM;
    }

    handle = iconv_open("UTF-8", "UTF-16LE");
    if (handle < 0)
        perror("Can't open translation");

    iconv(handle, &dest, &dest_size, &utf, &utf_size);

    iconv_close(handle);

    printf("Decode (UTF-8): %s\n", u);

    free(u);
    free(d);
    return 0;
}

int main()
{
    return b64_decode_string("SABlAGwAbABvAA==");
}