Support new secret types for path-ed WEB proxies.

Telegram/SourceFiles/boxes/connection_box.cpp

@@ -134,7 +134,9 @@ using ProxyData = MTP::ProxyData;
 			? "&pass=" + qthelp::url_encode(proxy.password) : "")
 		+ (((proxy.type == Type::Mtproto || proxy.type == Type::Web)
 				&& !proxy.password.isEmpty())
-			? "&secret=" + proxy.password : "");
+			? "&secret=" + ((proxy.type == Type::Web)
+				? MTP::EncodeWebProxyLinkSecret(proxy)
+				: proxy.password) : "");
 }
 
 [[nodiscard]] QString ProxyDataToLocalLink(const ProxyData &proxy) {
@@ -347,6 +349,11 @@ void ShareProxy(
 	} else if (type == ProxyData::Type::Mtproto || web) {
 		proxy.password = fields.value(u"secret"_q);
 		proxy.password.replace('+', '-').replace('/', '_');
+		if (web) {
+			proxy.password = MTP::DecodeWebProxyLinkSecret(
+				proxy.password,
+				!proxy.webBasePath().isEmpty());
+		}
 	}
 	return proxy;
 };

Telegram/SourceFiles/mtproto/mtproto_proxy_data.cpp

@@ -193,6 +193,15 @@ namespace {
 		QByteArray::Base64UrlEncoding | QByteArray::OmitTrailingEquals));
 }
 
+// A base path needs a client that understands one, so a link that carries a
+// path encodes its secret as base64url of this marker byte followed by the real
+// secret. A client without path support decodes 17 bytes whose first byte is not
+// the 0xDD of a padded secret, so it reports the link as an unsupported proxy
+// type and asks the user to update, instead of accepting a pathless entry.
+// 0xDD is the one byte that must never be used here: the older parser reads a
+// 17-byte secret starting with it as an ordinary valid one.
+constexpr auto kWebProxyLinkSecretMarker = uchar(0x70);
+
 // The address field accepts a pasted URL, so the scheme is removed before the
 // address is parsed and only the canonical form is stored. `http://` is left in
 // place, and therefore rejected: HTTPS and port 443 are fixed for a WEB proxy.
@@ -333,6 +342,12 @@ QString WebProxyBridgeCapability(const ProxyData &proxy) {
 			== u"Proxy.Example.COM/App/"_q);
 		Assert(StripWebProxyScheme(u"http://proxy.example.com"_q)
 			== u"http://proxy.example.com"_q);
+		const auto plainSecret = u"8561944064fc730cbfa4473562d8ec59"_q;
+		const auto markedSecret = u"cIVhlEBk_HMMv6RHNWLY7Fk"_q;
+		Assert(DecodeWebProxyLinkSecret(markedSecret, true) == plainSecret);
+		Assert(DecodeWebProxyLinkSecret(markedSecret, false) == plainSecret);
+		Assert(DecodeWebProxyLinkSecret(plainSecret, false) == plainSecret);
+		Assert(DecodeWebProxyLinkSecret(plainSecret, true).isEmpty());
 		Assert(NormalizeWebProxyBasePath(u"per%20cent"_q).isEmpty());
 		Assert(NormalizeWebProxyBasePath(u"dot.ted"_q).isEmpty());
 		Assert(NormalizeWebProxyBasePath(u".."_q).isEmpty());
@@ -377,6 +392,43 @@ QString WebProxyBridgeCapability(const ProxyData &proxy) {
 		key);
 }
 
+QString EncodeWebProxyLinkSecret(const ProxyData &proxy) {
+	Expects(proxy.type == ProxyData::Type::Web);
+
+	const auto secret = proxy.secretFromMtprotoPassword();
+	if (proxy.webBasePath().isEmpty() || secret.empty()) {
+		return proxy.password;
+	}
+	auto marked = QByteArray(1, char(kWebProxyLinkSecretMarker));
+	marked.append(
+		reinterpret_cast<const char*>(secret.data()),
+		int(secret.size()));
+	return QString::fromLatin1(marked.toBase64(
+		QByteArray::Base64UrlEncoding | QByteArray::OmitTrailingEquals));
+}
+
+QString DecodeWebProxyLinkSecret(const QString &value, bool hasBasePath) {
+	const auto decoded = QByteArray::fromBase64(
+		value.toLatin1(),
+		QByteArray::Base64UrlEncoding
+			| QByteArray::AbortOnBase64DecodingErrors);
+
+	// A canonical secret is 16 bytes, 17 starting with 0xDD, or 21+ starting
+	// with 0xEE, so a longer value behind this marker is never ambiguous.
+	const auto marked = (decoded.size() >= 17)
+		&& (uchar(decoded[0]) == kWebProxyLinkSecretMarker);
+	if (marked) {
+		return QString::fromLatin1(decoded.mid(1).toHex());
+	}
+
+	// An unmarked secret on a link that carries a base path is rejected rather
+	// than accepted: that is exactly the link a client without path support
+	// would take for a pathless proxy on an empty host, so the marked form is
+	// required once a path is present. A root link keeps the plain secret and
+	// still works in those clients.
+	return hasBasePath ? QString() : value;
+}
+
 QString WebProxyBridgePath(const ProxyData &proxy) {
 	Expects(proxy.type == ProxyData::Type::Web);
 

Telegram/SourceFiles/mtproto/mtproto_proxy_data.h

@@ -66,6 +66,10 @@ struct ProxyData {
 
 [[nodiscard]] QString NormalizeWebProxyHost(const QString &value);
 [[nodiscard]] QString WebProxyBridgeCapability(const ProxyData &proxy);
+[[nodiscard]] QString EncodeWebProxyLinkSecret(const ProxyData &proxy);
+[[nodiscard]] QString DecodeWebProxyLinkSecret(
+	const QString &value,
+	bool hasBasePath);
 [[nodiscard]] QString WebProxyBridgePath(const ProxyData &proxy);
 [[nodiscard]] QString WebProxyBridgeUrl(const ProxyData &proxy);
 [[nodiscard]] ProxyData ToDirectIpProxy(

docs/web-proxy-plan.md

@@ -552,10 +552,14 @@ tg://webproxy?server=<address>&secret=<secret>
 
 `<address>` is the percent-encoded `host` or `host/path`, so a base path travels in
 the same parameter as `proxy.example.com%2Fdobry-cola-super-app`. There is no
-separate path parameter. Following either link shows the address and secret with
-one connect action. It does not check status or enable the proxy until that action
-is invoked. Saved WEB entries can be shared as a public link or a direct-scheme QR
-link.
+separate path parameter. A link that carries a path also encodes its secret as
+unpadded base64url of `0x70` plus the real secret, so a client without path
+support reports an unsupported proxy type and asks the user to update, instead of
+normalizing the address to an empty host and offering to connect to it. A
+root link keeps the plain secret and still works in those clients. Following
+either link shows the address and secret with one connect action. It does not
+check status or enable the proxy until that action is invoked. Saved WEB entries
+can be shared as a public link or a direct-scheme QR link.
 
 Application proxy changes configure/deconfigure the web transport before MTP
 sessions restart. WEB follows the MTProxy path in `Session`, `SessionPrivate`, and