mirror of https://github.com/OISF/suricata
transform: adds url_decode keyword
Fixes https://redmine.openinfosecfoundation.org/issues/2689 Adds a new source file to handle this keyword. And modifies documentation, Makefile, and registration accordingly. url_decode decodes url-encoded data, ie replacing '+' with space and '%HH' with its value.pull/5257/head
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/* Copyright (C) 2020 Open Information Security Foundation
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*
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* You can copy, redistribute or modify this Program under the terms of
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* the GNU General Public License version 2 as published by the Free
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* Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* version 2 along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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/**
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* \file
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*
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* \author Philippe Antoine <p.antoine@catenacyber.fr>
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*
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* Implements the url_decode transform keyword
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*/
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#include "suricata-common.h"
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#include "detect.h"
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#include "detect-engine.h"
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#include "detect-engine-prefilter.h"
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#include "detect-parse.h"
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#include "detect-transform-urldecode.h"
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#include "util-unittest.h"
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#include "util-print.h"
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static int DetectTransformUrlDecodeSetup (DetectEngineCtx *, Signature *, const char *);
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#ifdef UNITTESTS
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static void DetectTransformUrlDecodeRegisterTests(void);
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#endif
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static void TransformUrlDecode(InspectionBuffer *buffer, void *options);
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void DetectTransformUrlDecodeRegister(void)
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{
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].name = "url_decode";
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].desc =
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"modify buffer to decode urlencoded data before inspection";
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].url = "/rules/transforms.html#url-decode";
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].Transform =
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TransformUrlDecode;
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].Setup =
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DetectTransformUrlDecodeSetup;
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#ifdef UNITTESTS
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].RegisterTests =
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DetectTransformUrlDecodeRegisterTests;
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#endif
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sigmatch_table[DETECT_TRANSFORM_URL_DECODE].flags |= SIGMATCH_NOOPT;
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}
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/**
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* \internal
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* \brief Apply the transform keyword to the last pattern match
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* \param det_ctx detection engine ctx
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* \param s signature
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* \param nullstr should be null
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* \retval 0 ok
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* \retval -1 failure
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*/
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static int DetectTransformUrlDecodeSetup (DetectEngineCtx *de_ctx, Signature *s, const char *nullstr)
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{
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SCEnter();
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int r = DetectSignatureAddTransform(s, DETECT_TRANSFORM_URL_DECODE, NULL);
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SCReturnInt(r);
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}
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// util function so as to ease reuse sometimes
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static bool BufferUrlDecode(const uint8_t *input, const uint32_t input_len, uint8_t *output, uint32_t *output_size)
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{
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bool changed = false;
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uint8_t *oi = output;
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//PrintRawDataFp(stdout, input, input_len);
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for (uint32_t i = 0; i < input_len; i++) {
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if (input[i] == '%') {
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if (i + 2 < input_len) {
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if ((isxdigit(input[i+1])) && (isxdigit(input[i+2]))) {
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// Decode %HH encoding.
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*oi = (input[i+1] >= 'A' ? ((input[i+1] & 0xdf) - 'A') + 10 : (input[i+1] - '0')) << 4;
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*oi |= (input[i+2] >= 'A' ? ((input[i+2] & 0xdf) - 'A') + 10 : (input[i+2] - '0'));
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oi++;
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// one more increment before looping
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i += 2;
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changed = true;
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} else {
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// leaves incorrect percent
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// does not handle unicode %u encoding
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*oi++ = input[i];
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}
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} else {
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// leaves trailing incomplete percent
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*oi++ = input[i];
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}
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} else if (input[i] == '+') {
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*oi++ = ' ';
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changed = true;
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} else {
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*oi++ = input[i];
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}
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}
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*output_size = oi - output;
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return changed;
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}
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static void TransformUrlDecode(InspectionBuffer *buffer, void *options)
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{
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uint32_t output_size;
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bool changed;
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const uint8_t *input = buffer->inspect;
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const uint32_t input_len = buffer->inspect_len;
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uint8_t output[input_len]; // we can only shrink
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changed = BufferUrlDecode(input, input_len, output, &output_size);
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if (changed) {
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InspectionBufferCopy(buffer, output, output_size);
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}
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}
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#ifdef UNITTESTS
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static int DetectTransformUrlDecodeTest01(void)
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{
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const uint8_t *input = (const uint8_t *)"Suricata%20is+%27%61wesome%21%27%25%30%30%ZZ%4";
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uint32_t input_len = strlen((char *)input);
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InspectionBuffer buffer;
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InspectionBufferInit(&buffer, 8);
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InspectionBufferSetup(&buffer, input, input_len);
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PrintRawDataFp(stdout, buffer.inspect, buffer.inspect_len);
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TransformUrlDecode(&buffer, NULL);
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PrintRawDataFp(stdout, buffer.inspect, buffer.inspect_len);
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FAIL_IF (buffer.inspect_len != strlen("Suricata is 'awesome!'%00%ZZ%4"));
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FAIL_IF (memcmp(buffer.inspect, "Suricata is 'awesome!'%00%ZZ%4", buffer.inspect_len) != 0);
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InspectionBufferFree(&buffer);
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PASS;
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}
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static int DetectTransformUrlDecodeTest02(void)
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{
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const char rule[] = "alert http any any -> any any (http.request_body; url_decode; content:\"mail=test@oisf.net\"; sid:1;)";
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ThreadVars th_v;
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DetectEngineThreadCtx *det_ctx = NULL;
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memset(&th_v, 0, sizeof(th_v));
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DetectEngineCtx *de_ctx = DetectEngineCtxInit();
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FAIL_IF_NULL(de_ctx);
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Signature *s = DetectEngineAppendSig(de_ctx, rule);
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FAIL_IF_NULL(s);
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SigGroupBuild(de_ctx);
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DetectEngineThreadCtxInit(&th_v, (void *)de_ctx, (void *)&det_ctx);
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DetectEngineThreadCtxDeinit(&th_v, (void *)det_ctx);
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DetectEngineCtxFree(de_ctx);
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PASS;
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}
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static void DetectTransformUrlDecodeRegisterTests(void)
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{
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UtRegisterTest("DetectTransformUrlDecodeTest01",
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DetectTransformUrlDecodeTest01);
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UtRegisterTest("DetectTransformUrlDecodeTest02",
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DetectTransformUrlDecodeTest02);
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}
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#endif
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@ -0,0 +1,30 @@
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/* Copyright (C) 2020 Open Information Security Foundation
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*
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* You can copy, redistribute or modify this Program under the terms of
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* the GNU General Public License version 2 as published by the Free
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* Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* version 2 along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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/**
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* \file
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*
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* \author Philippe Antoine <p.antoine@catenacyber.fr>
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*/
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#ifndef __DETECT_TRANSFORM_URLDECODE_H__
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#define __DETECT_TRANSFORM_URLDECODE_H__
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/* prototypes */
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void DetectTransformUrlDecodeRegister (void);
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#endif /* __DETECT_TRANSFORM_URLDECODE_H__ */
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