/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

/* $Id: base64.c,v 1.7 2020/09/14 08:40:44 florian Exp $ */

/*! \file */

#include <string.h>

#include <isc/base64.h>
#include <isc/buffer.h>
#include <isc/region.h>
#include <isc/util.h>

#define RETERR(x) do { \
        isc_result_t _r = (x); \
        if (_r != ISC_R_SUCCESS) \
                return (_r); \
        } while (0)

/*@{*/

static const char base64[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
/*@}*/

isc_result_t
isc_base64_totext(isc_region_t *source, int wordlength,
                  const char *wordbreak, isc_buffer_t *target)
{
        char buf[5];
        unsigned int loops = 0;

        if (wordlength < 4)
                wordlength = 4;

        memset(buf, 0, sizeof(buf));
        while (source->length > 2) {
                buf[0] = base64[(source->base[0]>>2)&0x3f];
                buf[1] = base64[((source->base[0]<<4)&0x30)|
                                ((source->base[1]>>4)&0x0f)];
                buf[2] = base64[((source->base[1]<<2)&0x3c)|
                                ((source->base[2]>>6)&0x03)];
                buf[3] = base64[source->base[2]&0x3f];
                RETERR(isc_str_tobuffer(buf, target));
                isc_region_consume(source, 3);

                loops++;
                if (source->length != 0 &&
                    (int)((loops + 1) * 4) >= wordlength)
                {
                        loops = 0;
                        RETERR(isc_str_tobuffer(wordbreak, target));
                }
        }
        if (source->length == 2) {
                buf[0] = base64[(source->base[0]>>2)&0x3f];
                buf[1] = base64[((source->base[0]<<4)&0x30)|
                                ((source->base[1]>>4)&0x0f)];
                buf[2] = base64[((source->base[1]<<2)&0x3c)];
                buf[3] = '=';
                RETERR(isc_str_tobuffer(buf, target));
                isc_region_consume(source, 2);
        } else if (source->length == 1) {
                buf[0] = base64[(source->base[0]>>2)&0x3f];
                buf[1] = base64[((source->base[0]<<4)&0x30)];
                buf[2] = buf[3] = '=';
                RETERR(isc_str_tobuffer(buf, target));
                isc_region_consume(source, 1);
        }
        return (ISC_R_SUCCESS);
}

/*%
 * State of a base64 decoding process in progress.
 */
typedef struct {
        int length;             /*%< Desired length of binary data or -1 */
        isc_buffer_t *target;   /*%< Buffer for resulting binary data */
        int digits;             /*%< Number of buffered base64 digits */
        int seen_end;   /*%< True if "=" end marker seen */
        int val[4];
} base64_decode_ctx_t;

static inline void
base64_decode_init(base64_decode_ctx_t *ctx, int length, isc_buffer_t *target)
{
        ctx->digits = 0;
        ctx->seen_end = 0;
        ctx->length = length;
        ctx->target = target;
}

static inline isc_result_t
base64_decode_char(base64_decode_ctx_t *ctx, int c) {
        const char *s;

        if (ctx->seen_end)
                return (ISC_R_BADBASE64);
        if ((s = strchr(base64, c)) == NULL)
                return (ISC_R_BADBASE64);
        ctx->val[ctx->digits++] = (int)(s - base64);
        if (ctx->digits == 4) {
                int n;
                unsigned char buf[3];
                if (ctx->val[0] == 64 || ctx->val[1] == 64)
                        return (ISC_R_BADBASE64);
                if (ctx->val[2] == 64 && ctx->val[3] != 64)
                        return (ISC_R_BADBASE64);
                /*
                 * Check that bits that should be zero are.
                 */
                if (ctx->val[2] == 64 && (ctx->val[1] & 0xf) != 0)
                        return (ISC_R_BADBASE64);
                /*
                 * We don't need to test for ctx->val[2] != 64 as
                 * the bottom two bits of 64 are zero.
                 */
                if (ctx->val[3] == 64 && (ctx->val[2] & 0x3) != 0)
                        return (ISC_R_BADBASE64);
                n = (ctx->val[2] == 64) ? 1 :
                        (ctx->val[3] == 64) ? 2 : 3;
                if (n != 3) {
                        ctx->seen_end = 1;
                        if (ctx->val[2] == 64)
                                ctx->val[2] = 0;
                        if (ctx->val[3] == 64)
                                ctx->val[3] = 0;
                }
                buf[0] = (ctx->val[0]<<2)|(ctx->val[1]>>4);
                buf[1] = (ctx->val[1]<<4)|(ctx->val[2]>>2);
                buf[2] = (ctx->val[2]<<6)|(ctx->val[3]);
                RETERR(isc_mem_tobuffer(ctx->target, buf, n));
                if (ctx->length >= 0) {
                        if (n > ctx->length)
                                return (ISC_R_BADBASE64);
                        else
                                ctx->length -= n;
                }
                ctx->digits = 0;
        }
        return (ISC_R_SUCCESS);
}

static inline isc_result_t
base64_decode_finish(base64_decode_ctx_t *ctx) {
        if (ctx->length > 0)
                return (ISC_R_UNEXPECTEDEND);
        if (ctx->digits != 0)
                return (ISC_R_BADBASE64);
        return (ISC_R_SUCCESS);
}

isc_result_t
isc_base64_decodestring(const char *cstr, isc_buffer_t *target) {
        base64_decode_ctx_t ctx;

        base64_decode_init(&ctx, -1, target);
        for (;;) {
                int c = *cstr++;
                if (c == '\0')
                        break;
                if (c == ' ' || c == '\t' || c == '\n' || c== '\r')
                        continue;
                RETERR(base64_decode_char(&ctx, c));
        }
        RETERR(base64_decode_finish(&ctx));
        return (ISC_R_SUCCESS);
}