feat: Dynamic client Barrier/Synergy hello back response to server

src/lib/client/Client.cpp

@@ -674,22 +674,31 @@ bool Client::isCompatible(int major, int minor) const
 void Client::handleHello(const Event &, void *)
 {
   SInt16 major, minor;
-  if (!ProtocolUtil::readf(m_stream, kMsgHello, &major, &minor)) {
-    sendConnectionFailedEvent("Protocol error from server, check encryption settings");
+
+  // as luck would have it, both "Synergy" and "Barrier" are 7 chars,
+  // so we eat 7 chars and then test for either protocol name.
+  // we cannot re-use `readf` to check for various hello messages,
+  // as `readf` eats bytes (advances the stream position reference).
+  std::string protocolName;
+  ProtocolUtil::readf(m_stream, kMsgHello, &protocolName, &major, &minor);
+
+  if (protocolName != kSynergyProtocolName && protocolName != kBarrierProtocolName) {
+    sendConnectionFailedEvent("got invalid hello message from server");
     cleanupTimer();
     cleanupConnection();
     return;
   }
 
   // check versions
-  LOG((CLOG_DEBUG1 "got hello version %d.%d", major, minor));
+  LOG_DEBUG("got hello version %s, %d.%d", protocolName.c_str(), 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
+    // because 1.6 is compatable with 1.7 and 1.8 - downgrading protocol for
     // server
-    LOG((CLOG_NOTE "downgrading protocol version for server"));
+    LOG_NOTE("downgrading protocol version for server");
     helloBackMinor = minor;
   } else if (major < kProtocolMajorVersion || (major == kProtocolMajorVersion && minor < kProtocolMinorVersion)) {
     sendConnectionFailedEvent(XIncompatibleClient(major, minor).what());
@@ -699,8 +708,12 @@ void Client::handleHello(const Event &, void *)
   }
 
   // say hello back
-  LOG((CLOG_DEBUG1 "say hello version %d.%d", helloBackMajor, helloBackMinor));
-  ProtocolUtil::writef(m_stream, kMsgHelloBack, helloBackMajor, helloBackMinor, &m_name);
+  LOG_DEBUG("say hello version %s %d.%d", protocolName.c_str(), helloBackMajor, helloBackMinor);
+
+  // dynamically build write format for hello back since `writef` doesn't
+  // support fixed length strings yet.
+  std::string helloBackMessage = protocolName + "%2i%2i%s";
+  ProtocolUtil::writef(m_stream, helloBackMessage.c_str(), helloBackMajor, helloBackMinor, &m_name);
 
   // now connected but waiting to complete handshake
   setupScreen();

src/lib/deskflow/ProtocolUtil.cpp

@@ -502,11 +502,15 @@ void ProtocolUtil::readVector4BytesInt(deskflow::IStream *stream, std::vector<UI
 
 void ProtocolUtil::readBytes(deskflow::IStream *stream, UInt32 len, String *destination)
 {
-  assert(len == 0);
-
   // read the string length
   UInt8 buffer[128];
-  len = read4BytesInt(stream);
+
+  // when string length is 0, this implies that the size of the string is
+  // variable and embedded and will be found in the stream.
+  if (len == 0) {
+    len = read4BytesInt(stream);
+  }
+
   // use a fixed size buffer if its big enough
   const bool useFixed = (len <= sizeof(buffer));
 

src/lib/deskflow/protocol_types.cpp

@@ -18,9 +18,13 @@
 
 #include "deskflow/protocol_types.h"
 
-// Keep the "Synergy" name for hello to preserve compatibility with Synergy
-const char *const kMsgHello = "Synergy%2i%2i";
-const char *const kMsgHelloBack = "Synergy%2i%2i%s";
+const char *const kSynergyProtocolName = "Synergy";
+const char *const kBarrierProtocolName = "Barrier";
+
+// The protocol name string within the hello and hello back messages must be
+// 7 chars for backward compatibility (Synergy and Barrier are 7 chars).
+const char *const kMsgHello = "%7s%2i%2i";
+const char *const kMsgHelloBack = "%7s%2i%2i%s";
 const char *const kMsgCNoop = "CNOP";
 const char *const kMsgCClose = "CBYE";
 const char *const kMsgCEnter = "CINN%2i%2i%4i%2i";

src/lib/deskflow/protocol_types.h

@@ -106,6 +106,12 @@ enum EDataReceived
 // greeting handshake messages
 //
 
+// used to say hello back to the server as Synergy
+extern const char *const kSynergyProtocolName;
+
+// used to say hello back to the server as Barrier
+extern const char *const kBarrierProtocolName;
+
 // say hello to client;  primary -> secondary
 // $1 = protocol major version number supported by server.  $2 =
 // protocol minor version number supported by server. $3 = server

src/lib/server/ClientProxyUnknown.cpp

@@ -224,7 +224,9 @@ void ClientProxyUnknown::handleData(const Event &, void *)
 
     // parse the reply to hello
     SInt16 major, minor;
-    if (!ProtocolUtil::readf(m_stream, kMsgHelloBack, &major, &minor, &name)) {
+    std::string protocolName;
+    if (!ProtocolUtil::readf(
+            m_stream, kMsgHelloBack, &protocolName, &major, &minor, &name)) {
       throw XBadClient();
     }