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/*
* Authored by Alex Hultman, 2018-2021.
* Intellectual property of third-party.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef UWS_WEBSOCKETEXTENSIONS_H
#define UWS_WEBSOCKETEXTENSIONS_H
/* There is a new, huge bug scenario that needs to be fixed:
* pub/sub does not support being in DEDICATED_COMPRESSOR-mode while having
* some clients downgraded to SHARED_COMPRESSOR - we cannot allow the client to
* demand a downgrade to SHARED_COMPRESSOR (yet) until we fix that scenario in pub/sub */
// #define UWS_ALLOW_SHARED_AND_DEDICATED_COMPRESSOR_MIX
/* We forbid negotiating 8 windowBits since Zlib has a bug with this */
// #define UWS_ALLOW_8_WINDOW_BITS
#include <climits>
#include <cctype>
#include <string>
#include <string_view>
#include <tuple>
namespace uWS {
enum ExtensionTokens {
/* Standard permessage-deflate tokens */
TOK_PERMESSAGE_DEFLATE = 1838,
TOK_SERVER_NO_CONTEXT_TAKEOVER = 2807,
TOK_CLIENT_NO_CONTEXT_TAKEOVER = 2783,
TOK_SERVER_MAX_WINDOW_BITS = 2372,
TOK_CLIENT_MAX_WINDOW_BITS = 2348,
/* Non-standard alias for Safari */
TOK_X_WEBKIT_DEFLATE_FRAME = 2149,
TOK_NO_CONTEXT_TAKEOVER = 2049,
TOK_MAX_WINDOW_BITS = 1614
};
struct ExtensionsParser {
private:
int *lastInteger = nullptr;
public:
/* Standard */
bool perMessageDeflate = false;
bool serverNoContextTakeover = false;
bool clientNoContextTakeover = false;
int serverMaxWindowBits = 0;
int clientMaxWindowBits = 0;
/* Non-standard Safari */
bool xWebKitDeflateFrame = false;
bool noContextTakeover = false;
int maxWindowBits = 0;
int getToken(const char *&in, const char *stop) {
while (in != stop && !isalnum(*in)) {
in++;
}
/* Don't care more than this for now */
static_assert(SHRT_MIN > INT_MIN, "Integer overflow fix is invalid for this platform, report this as a bug!");
int hashedToken = 0;
while (in != stop && (isalnum(*in) || *in == '-' || *in == '_')) {
if (isdigit(*in)) {
/* This check is a quick and incorrect fix for integer overflow
* in oss-fuzz but we don't care as it doesn't matter either way */
if (hashedToken > SHRT_MIN && hashedToken < SHRT_MAX) {
hashedToken = hashedToken * 10 - (*in - '0');
}
} else {
hashedToken += *in;
}
in++;
}
return hashedToken;
}
ExtensionsParser(const char *data, size_t length) {
const char *stop = data + length;
int token = 1;
/* Ignore anything before permessage-deflate or x-webkit-deflate-frame */
for (; token && token != TOK_PERMESSAGE_DEFLATE && token != TOK_X_WEBKIT_DEFLATE_FRAME; token = getToken(data, stop));
/* What protocol are we going to use? */
perMessageDeflate = (token == TOK_PERMESSAGE_DEFLATE);
xWebKitDeflateFrame = (token == TOK_X_WEBKIT_DEFLATE_FRAME);
while ((token = getToken(data, stop))) {
switch (token) {
case TOK_X_WEBKIT_DEFLATE_FRAME:
/* Duplicates not allowed/supported */
return;
case TOK_NO_CONTEXT_TAKEOVER:
noContextTakeover = true;
break;
case TOK_MAX_WINDOW_BITS:
maxWindowBits = 1;
lastInteger = &maxWindowBits;
break;
case TOK_PERMESSAGE_DEFLATE:
/* Duplicates not allowed/supported */
return;
case TOK_SERVER_NO_CONTEXT_TAKEOVER:
serverNoContextTakeover = true;
break;
case TOK_CLIENT_NO_CONTEXT_TAKEOVER:
clientNoContextTakeover = true;
break;
case TOK_SERVER_MAX_WINDOW_BITS:
serverMaxWindowBits = 1;
lastInteger = &serverMaxWindowBits;
break;
case TOK_CLIENT_MAX_WINDOW_BITS:
clientMaxWindowBits = 1;
lastInteger = &clientMaxWindowBits;
break;
default:
if (token < 0 && lastInteger) {
*lastInteger = -token;
}
break;
}
}
}
};
/* Takes what we (the server) wants, returns what we got */
static inline std::tuple<bool, int, int, std::string_view> negotiateCompression(bool wantCompression, int wantedCompressionWindow, int wantedInflationWindow, std::string_view offer) {
/* If we don't want compression then we are done here */
if (!wantCompression) {
return {false, 0, 0, ""};
}
ExtensionsParser ep(offer.data(), offer.length());
static thread_local std::string response;
response = "";
int compressionWindow = wantedCompressionWindow;
int inflationWindow = wantedInflationWindow;
bool compression = false;
if (ep.xWebKitDeflateFrame) {
/* We now have compression */
compression = true;
response = "x-webkit-deflate-frame";
/* If the other peer has DEMANDED us no sliding window,
* we cannot compress with anything other than shared compressor */
if (ep.noContextTakeover) {
/* We must fail here right now (fix pub/sub) */
#ifndef UWS_ALLOW_SHARED_AND_DEDICATED_COMPRESSOR_MIX
if (wantedCompressionWindow != 0) {
return {false, 0, 0, ""};
}
#endif
compressionWindow = 0;
}
/* If the other peer has DEMANDED us to use a limited sliding window,
* we have to limit out compression sliding window */
if (ep.maxWindowBits && ep.maxWindowBits < compressionWindow) {
compressionWindow = ep.maxWindowBits;
#ifndef UWS_ALLOW_8_WINDOW_BITS
/* We cannot really deny this, so we have to disable compression in this case */
if (compressionWindow == 8) {
return {false, 0, 0, ""};
}
#endif
}
/* We decide our own inflation sliding window (and their compression sliding window) */
if (wantedInflationWindow < 15) {
if (!wantedInflationWindow) {
response += "; no_context_takeover";
} else {
response += "; max_window_bits=" + std::to_string(wantedInflationWindow);
}
}
} else if (ep.perMessageDeflate) {
/* We now have compression */
compression = true;
response = "permessage-deflate";
if (ep.clientNoContextTakeover) {
inflationWindow = 0;
} else if (ep.clientMaxWindowBits && ep.clientMaxWindowBits != 1) {
inflationWindow = std::min<int>(ep.clientMaxWindowBits, inflationWindow);
}
/* Whatever we have now, write */
if (inflationWindow < 15) {
if (!inflationWindow || !ep.clientMaxWindowBits) {
response += "; client_no_context_takeover";
inflationWindow = 0;
} else {
response += "; client_max_window_bits=" + std::to_string(inflationWindow);
}
}
/* This block basically lets the client lower it */
if (ep.serverNoContextTakeover) {
/* This is an important (temporary) fix since we haven't allowed
* these two modes to mix, and pub/sub will not handle this case (yet) */
#ifdef UWS_ALLOW_SHARED_AND_DEDICATED_COMPRESSOR_MIX
compressionWindow = 0;
#endif
} else if (ep.serverMaxWindowBits) {
compressionWindow = std::min<int>(ep.serverMaxWindowBits, compressionWindow);
#ifndef UWS_ALLOW_8_WINDOW_BITS
/* Zlib cannot do windowBits=8, memLevel=1 so we raise it up to 9 minimum */
if (compressionWindow == 8) {
compressionWindow = 9;
}
#endif
}
/* Whatever we have now, write */
if (compressionWindow < 15) {
if (!compressionWindow) {
response += "; server_no_context_takeover";
} else {
response += "; server_max_window_bits=" + std::to_string(compressionWindow);
}
}
}
/* A final sanity check (this check does not actually catch too high values!) */
if ((compressionWindow && compressionWindow < 8) || compressionWindow > 15 || (inflationWindow && inflationWindow < 8) || inflationWindow > 15) {
return {false, 0, 0, ""};
}
return {compression, compressionWindow, inflationWindow, response};
}
}
#endif // UWS_WEBSOCKETEXTENSIONS_H
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