214 lines
7.1 KiB
C
214 lines
7.1 KiB
C
/*
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* Text detection based on ascmagic.c from the file(1) utility.
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*
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* Portions Copyright (C) 2013-2022 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
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* Portions Copyright (C) 2008-2013 Sourcefire, Inc.
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*
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* Copyright (c) Ian F. Darwin 1986-1995.
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* Software written by Ian F. Darwin and others;
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* maintained 1995-present by Christos Zoulas and others.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice immediately at the beginning of the file, without modification,
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* this list of conditions, and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
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* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if HAVE_CONFIG_H
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#include "clamav-config.h"
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#endif
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#include <stdio.h>
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#include <string.h>
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#include <memory.h>
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#include <ctype.h>
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#include <stdlib.h>
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#ifdef HAVE_UNISTD_H
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#include <unistd.h>
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#endif
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#include "clamav.h"
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#include "filetypes.h"
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#include "textdet.h"
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#include "others.h"
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#define F 0 /* character never appears in text */
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#define T 1 /* character appears in plain ASCII text */
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#define I 2 /* character appears in ISO-8859 text */
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#define X 3 /* character appears in non-ISO extended ASCII (Mac, IBM PC) */
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// clang-format off
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static char text_chars[256] = {
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/* BEL BS HT LF FF CR */
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F, F, F, F, F, F, F, T, T, T, T, F, T, T, F, F, /* 0x0X */
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/* ESC */
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F, F, F, F, F, F, F, F, F, F, F, T, F, F, F, F, /* 0x1X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x2X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x3X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x4X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x5X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, /* 0x6X */
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T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, F, /* 0x7X */
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/* NEL */
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X, X, X, X, X, T, X, X, X, X, X, X, X, X, X, X, /* 0x8X */
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X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, /* 0x9X */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xaX */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xbX */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xcX */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xdX */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, /* 0xeX */
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I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I /* 0xfX */
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};
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// clang-format on
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static int td_isascii(const unsigned char *buf, unsigned int len)
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{
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unsigned int i;
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/* Validate that the data all falls within the bounds of
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* plain ASCII, ISO-8859 text, and non-ISO extended ASCII (Mac, IBM PC)
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*/
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for (i = 0; i < len; i++)
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if (text_chars[buf[i]] == F)
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return 0;
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return 1;
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}
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static int td_isutf8(const unsigned char *buf, unsigned int len)
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{
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unsigned int i, j, gotone = 0;
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for (i = 0; i < len; i++) {
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if ((buf[i] & 0x80) == 0) { /* 0xxxxxxx is plain ASCII */
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/*
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* Even if the whole file is valid UTF-8 sequences,
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* still reject it if it uses weird control characters.
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*/
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if (text_chars[buf[i]] != T)
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return 0;
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} else if ((buf[i] & 0x40) == 0) { /* 10xxxxxx never 1st byte */
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return 0;
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} else { /* 11xxxxxx begins UTF-8 */
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unsigned int following;
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if ((buf[i] & 0x20) == 0) { /* 110xxxxx */
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/* c = buf[i] & 0x1f; */
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following = 1;
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} else if ((buf[i] & 0x10) == 0) { /* 1110xxxx */
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/* c = buf[i] & 0x0f; */
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following = 2;
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} else if ((buf[i] & 0x08) == 0) { /* 11110xxx */
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/* c = buf[i] & 0x07; */
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following = 3;
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} else if ((buf[i] & 0x04) == 0) { /* 111110xx */
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/* c = buf[i] & 0x03; */
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following = 4;
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} else if ((buf[i] & 0x02) == 0) { /* 1111110x */
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/* c = buf[i] & 0x01; */
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following = 5;
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} else {
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return 0;
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}
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for (j = 0; j < following; j++) {
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if (++i >= len)
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return gotone;
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if ((buf[i] & 0x80) == 0 || (buf[i] & 0x40))
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return 0;
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/* c = (c << 6) + (buf[i] & 0x3f); */
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}
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gotone = 1;
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}
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}
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return gotone;
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}
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static int td_isutf16(const unsigned char *buf, unsigned int len)
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{
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unsigned int be = 1, nobom = 0, i, c, bad = 0, high = 0;
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if (len < 2)
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return 0;
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if (buf[0] == 0xff && buf[1] == 0xfe)
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be = 0;
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else if (buf[0] == 0xfe && buf[1] == 0xff)
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be = 1;
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else
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nobom = 1;
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for (i = 2; i + 1 < len; i += 2) {
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if (be)
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c = buf[i + 1] + 256 * buf[i];
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else
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c = buf[i] + 256 * buf[i + 1];
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if (c == 0xfffe)
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return 0;
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if (c < 128 && text_chars[c] != T) {
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if (nobom)
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return 0;
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else
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bad++;
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} else if (c >= 128) {
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high++;
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}
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}
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// if (nobom && high >= len / 4)
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// return 0;
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if (!nobom && bad >= len / 2)
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return 0;
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return 1 + be;
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}
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cli_file_t cli_texttype(const unsigned char *buf, unsigned int len)
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{
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int ret;
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/*
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* @TODO: Add UTF8/16/32 BOM Detection to improve text type accuracy.
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* Significant regression testing would be needed to ensure that re-typing
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* files does not impact efficacy.
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*/
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if (td_isascii(buf, len)) {
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cli_dbgmsg("Recognized ASCII text\n");
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return CL_TYPE_TEXT_ASCII;
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} else if (td_isutf8(buf, len)) {
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cli_dbgmsg("Recognized UTF-8 character data\n");
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return CL_TYPE_TEXT_UTF8;
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} else if ((ret = td_isutf16(buf, len))) {
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cli_dbgmsg("Recognized %s character data\n", (ret == 1) ? "UTF-16LE" : "UTF-16BE");
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return (ret == 1) ? CL_TYPE_TEXT_UTF16LE : CL_TYPE_TEXT_UTF16BE;
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} else {
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cli_dbgmsg("Recognized binary data\n");
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return CL_TYPE_BINARY_DATA;
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}
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}
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