base64.c

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

#include "base64.h"

static const unsigned char base64_table[64] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

unsigned char * base64_encode(const unsigned char *src, size_t len,
                              size_t *out_len)
{
        unsigned char *out, *pos;
        const unsigned char *end, *in;
        size_t olen;
        int line_len;

        olen = len * 4 / 3 + 4; /* 3-byte blocks to 4-byte */
        olen += olen / 72; /* line feeds */
        olen++; /* nul termination */
        out = malloc(olen);
        if (out == NULL)
                return NULL;

        end = src + len;
        in = src;
        pos = out;
        line_len = 0;
        while (end - in >= 3) {
                *pos++ = base64_table[in[0] >> 2];
                *pos++ = base64_table[((in[0] & 0x03) << 4) | (in[1] >> 4)];
                *pos++ = base64_table[((in[1] & 0x0f) << 2) | (in[2] >> 6)];
                *pos++ = base64_table[in[2] & 0x3f];
                in += 3;
                line_len += 4;
                if (line_len >= 72) {
                        *pos++ = '\n';
                        line_len = 0;
                }
        }

        if (end - in) {
                *pos++ = base64_table[in[0] >> 2];
                if (end - in == 1) {
                        *pos++ = base64_table[(in[0] & 0x03) << 4];
                        *pos++ = '=';
                } else {
                        *pos++ = base64_table[((in[0] & 0x03) << 4) |
                                              (in[1] >> 4)];
                        *pos++ = base64_table[(in[1] & 0x0f) << 2];
                }
                *pos++ = '=';
                line_len += 4;
        }

        if (line_len)
                *pos++ = '\n';

        *pos = '\0';
        if (out_len)
                *out_len = pos - out;
        return out;
}


unsigned char * base64_decode(const unsigned char *src, size_t len,
                              size_t *out_len)
{
        unsigned char dtable[256], *out, *pos, in[4], block[4], tmp;
        size_t i, count, olen;

        memset(dtable, 0x80, 256);
        for (i = 0; i < sizeof(base64_table); i++)
                dtable[base64_table[i]] = i;
        dtable['='] = 0;

        count = 0;
        for (i = 0; i < len; i++) {
                if (dtable[src[i]] != 0x80)
                        count++;
        }

        if (count % 4)
                return NULL;

        olen = count / 4 * 3;
        pos = out = malloc(count);
        if (out == NULL)
                return NULL;

        count = 0;
        for (i = 0; i < len; i++) {
                tmp = dtable[src[i]];
                if (tmp == 0x80)
                        continue;

                in[count] = src[i];
                block[count] = tmp;
                count++;
                if (count == 4) {
                        *pos++ = (block[0] << 2) | (block[1] >> 4);
                        *pos++ = (block[1] << 4) | (block[2] >> 2);
                        *pos++ = (block[2] << 6) | block[3];
                        count = 0;
                }
        }

        if (pos > out) {
                if (in[2] == '=')
                        pos -= 2;
                else if (in[3] == '=')
                        pos--;
        }

        *out_len = pos - out;
        return out;
}


#ifdef TEST_MAIN
#include <stdio.h>

int main(int argc, char *argv[])
{
        FILE *f;
        size_t len, elen;
        unsigned char *buf, *e;

        if (argc != 4) {
                printf("Usage: base64 <encode|decode> <in file> <out file>\n");
                return -1;
        }

        f = fopen(argv[2], "r");
        if (f == NULL)
                return -1;
        fseek(f, 0, SEEK_END);
        len = ftell(f);
        fseek(f, 0, SEEK_SET);
        buf = malloc(len);
        if (buf == NULL) {
                fclose(f);
                return -1;
        }
        fread(buf, 1, len, f);
        fclose(f);

        if (strcmp(argv[1], "encode") == 0)
                e = base64_encode(buf, len, &elen);
        else
                e = base64_decode(buf, len, &elen);
        if (e == NULL)
                return -2;
        f = fopen(argv[3], "w");
        if (f == NULL)
                return -3;
        fwrite(e, 1, elen, f);
        fclose(f);
        free(e);

        return 0;
}
#endif /* TEST_MAIN */

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