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Remove protocol downgrade restriction #161

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Merged
nbolton merged 5 commits into from
Mar 3, 2026
Merged

Remove protocol downgrade restriction #161

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371af24
Remove protocol downgrade restriction
nbolton Mar 3, 2026
4adb757
Conditionally downgrade
nbolton Mar 3, 2026
f86d529
Fix log message to clarify client protocol version downgrade
nbolton Mar 3, 2026
460c06e
Restrict client protocol version downgrade to minor versions only
nbolton Mar 3, 2026
032595a
Remove redundant assignment of helloBackMajor in protocol downgrade h…
nbolton Mar 3, 2026
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36 changes: 9 additions & 27 deletions src/lib/client/Client.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -651,26 +651,6 @@ void Client::handleClipboardGrabbed(const Event &event, void *)
}
}

bool Client::isCompatible(int major, int minor) const
{
const std::map<int, std::set<int>> compatibleTable{
{6, {7, 8}}, // 1.6 is compatible with 1.7 and 1.8
{7, {8}} // 1.7 is compatible with 1.8
};

bool isCompatible = false;

if (major == kProtocolMajorVersion) {
auto versions = compatibleTable.find(minor);
if (versions != compatibleTable.end()) {
auto compatibleVersions = versions->second;
isCompatible = compatibleVersions.find(kProtocolMinorVersion) != compatibleVersions.end();
}
}

return isCompatible;
}

void Client::handleHello(const Event &, void *)
{
SInt16 major, minor;
Expand All @@ -682,24 +662,26 @@ void Client::handleHello(const Event &, void *)
}

// check versions
LOG((CLOG_DEBUG1 "got hello version %d.%d", major, minor));
LOG((CLOG_DEBUG "got hello version %d.%d", major, minor));
SInt16 helloBackMajor = kProtocolMajorVersion;
SInt16 helloBackMinor = kProtocolMinorVersion;

if (isCompatible(major, minor)) {
// because 1.6 is comptable with 1.7 and 1.8 - downgrading protocol for
// server
LOG((CLOG_NOTE "downgrading protocol version for server"));
// only allow client minor version to downgrade, as major versions will likely not be compatible.
if (major == kProtocolMajorVersion && minor < kProtocolMinorVersion) {
helloBackMinor = minor;
} else if (major < kProtocolMajorVersion || (major == kProtocolMajorVersion && minor < kProtocolMinorVersion)) {
LOG_NOTE(
"downgrading client protocol version from %d.%d to %d.%d", //
kProtocolMajorVersion, kProtocolMinorVersion, helloBackMajor, helloBackMinor
);
} else if (major != kProtocolMajorVersion) {
sendConnectionFailedEvent(XIncompatibleClient(major, minor).what());
cleanupTimer();
cleanupConnection();
return;
}

// say hello back
LOG((CLOG_DEBUG1 "say hello version %d.%d", helloBackMajor, helloBackMinor));
LOG((CLOG_DEBUG "say hello version %d.%d", helloBackMajor, helloBackMinor));
ProtocolUtil::writef(m_stream, kMsgHelloBack, helloBackMajor, helloBackMinor, &m_name);

// now connected but waiting to complete handshake
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1 change: 0 additions & 1 deletion src/lib/client/Client.h
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Original file line number Diff line number Diff line change
Expand Up @@ -217,7 +217,6 @@ class Client : public IClient, public INode
void handleDisconnected(const Event &, void *);
void handleShapeChanged(const Event &, void *);
void handleClipboardGrabbed(const Event &, void *);
bool isCompatible(int major, int minor) const;
void handleHello(const Event &, void *);
void handleSuspend(const Event &event, void *);
void handleResume(const Event &event, void *);
Expand Down
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