/*	$NetBSD: base64.c,v 1.8 2022/09/23 12:15:33 christos Exp $	*/

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, you can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/*! \file */

#include <stdbool.h>

#include <isc/base64.h>
#include <isc/buffer.h>
#include <isc/lex.h>
#include <isc/string.h>
#include <isc/util.h>

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

/*@{*/
/*!
 * These static functions are also present in lib/dns/rdata.c.  I'm not
 * sure where they should go. -- bwelling
 */
static isc_result_t
str_totext(const char *source, isc_buffer_t *target);

static isc_result_t
mem_tobuffer(isc_buffer_t *target, void *base, unsigned int length);

static const char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvw"
			     "xyz0123456789+/=";
/*@}*/

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(str_totext(buf, target));
		isc_region_consume(source, 3);

		loops++;
		if (source->length != 0 && (int)((loops + 1) * 4) >= wordlength)
		{
			loops = 0;
			RETERR(str_totext(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(str_totext(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(str_totext(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 */
	bool seen_end;	      /*%< True if "=" end marker seen */
	int val[4];
} base64_decode_ctx_t;

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

static 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 = true;
			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(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 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_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length) {
	unsigned int before, after;
	base64_decode_ctx_t ctx;
	isc_textregion_t *tr;
	isc_token_t token;
	bool eol;

	REQUIRE(length >= -2);

	base64_decode_init(&ctx, length, target);

	before = isc_buffer_usedlength(target);
	while (!ctx.seen_end && (ctx.length != 0)) {
		unsigned int i;

		if (length > 0) {
			eol = false;
		} else {
			eol = true;
		}
		RETERR(isc_lex_getmastertoken(lexer, &token,
					      isc_tokentype_string, eol));
		if (token.type != isc_tokentype_string) {
			break;
		}
		tr = &token.value.as_textregion;
		for (i = 0; i < tr->length; i++) {
			RETERR(base64_decode_char(&ctx, tr->base[i]));
		}
	}
	after = isc_buffer_usedlength(target);
	if (ctx.length < 0 && !ctx.seen_end) {
		isc_lex_ungettoken(lexer, &token);
	}
	RETERR(base64_decode_finish(&ctx));
	if (length == -2 && before == after) {
		return (ISC_R_UNEXPECTEDEND);
	}
	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);
}

static isc_result_t
str_totext(const char *source, isc_buffer_t *target) {
	unsigned int l;
	isc_region_t region;

	isc_buffer_availableregion(target, &region);
	l = strlen(source);

	if (l > region.length) {
		return (ISC_R_NOSPACE);
	}

	memmove(region.base, source, l);
	isc_buffer_add(target, l);
	return (ISC_R_SUCCESS);
}

static isc_result_t
mem_tobuffer(isc_buffer_t *target, void *base, unsigned int length) {
	isc_region_t tr;

	isc_buffer_availableregion(target, &tr);
	if (length > tr.length) {
		return (ISC_R_NOSPACE);
	}
	memmove(tr.base, base, length);
	isc_buffer_add(target, length);
	return (ISC_R_SUCCESS);
}