Fix tunnel parsing exception handling.

Rather than using STFATAL and exiting, bubble up tunnel parsing
exception to main and display the responsible option arg and print help
menu so the user need not dig into /tmp/etclient-* to determine why et
aborted.

Fixes #491

src/terminal/TerminalClient.cpp

@@ -51,8 +51,8 @@ vector<PortForwardSourceRequest> parseRangesToRequests(const string& input) {
         pfsrs.push_back(pfsr);
       }
     } catch (const std::logic_error& lr) {
-      STFATAL << "Logic error: " << lr.what();
-      exit(1);
+      string msg = "Invalid tunnel argument: " + input;
+      throw TunnelParseException(msg.c_str());
     }
   }
   return pfsrs;

src/terminal/TerminalClient.hpp

@@ -41,5 +41,16 @@ class TerminalClient {
   int keepaliveDuration;
 };
 
+class TunnelParseException : public std::exception {
+ public:
+  TunnelParseException(const char* msg) : message(msg) {}
+  const char* what() const noexcept override
+  {
+      return message.c_str();
+  }
+ private:
+  std::string message = " ";
+};
+
 }  // namespace et
 #endif  // __ET_TERMINAL_CLIENT__

src/terminal/TerminalClientMain.cpp

@@ -22,6 +22,12 @@ bool ping(SocketEndpoint socketEndpoint,
   return true;
 }
 
+void handleParseException(std::exception& e, cxxopts::Options& options) {
+  CLOG(INFO, "stdout") << "Exception: " << e.what() << "\n" << endl;
+  CLOG(INFO, "stdout") << options.help({}) << endl;
+  exit(1);
+}
+
 int main(int argc, char** argv) {
   WinsockContext context;
   string tmpDir = GetTempDirectory();
@@ -43,7 +49,7 @@ int main(int argc, char** argv) {
     options.custom_help("[OPTION...] [user@]host[:port]\n\n"
         "  Note that 'host' can be a hostname or ipv4 address with or without a port\n"
         "  or an ipv6 address. If the ipv6 address is abbreviated with :: then it must\n"
-        "  be specfied without a port (use -p,--port)."
+        "  be specified without a port (use -p,--port)."
     );
 
     options.add_options()
@@ -334,17 +340,20 @@ int main(int argc, char** argv) {
     }
     TelemetryService::get()->logToDatadog("Session Started", el::Level::Info,
                                           __FILE__, __LINE__);
+    string tunnel_arg =
+        result.count("tunnel") ? result["tunnel"].as<string>() : "";
+    string r_tunnel_arg =
+        result.count("reversetunnel") ? result["reversetunnel"].as<string>() : "";
     TerminalClient terminalClient(
         clientSocket, clientPipeSocket, socketEndpoint, id, passkey, console,
-        is_jumphost, result.count("t") ? result["t"].as<string>() : "",
-        result.count("r") ? result["r"].as<string>() : "", forwardAgent,
-        sshSocket, keepaliveDuration);
-    terminalClient.run(result.count("command") ? result["command"].as<string>()
-                                               : "");
+        is_jumphost, tunnel_arg, r_tunnel_arg,
+        forwardAgent, sshSocket, keepaliveDuration);
+    terminalClient.run(
+        result.count("command") ? result["command"].as<string>() : "");
+  } catch (TunnelParseException& tpe) {
+    handleParseException(tpe, options);
   } catch (cxxopts::OptionException& oe) {
-    CLOG(INFO, "stdout") << "Exception: " << oe.what() << "\n" << endl;
-    CLOG(INFO, "stdout") << options.help({}) << endl;
-    exit(1);
+    handleParseException(oe, options);
   }
 
 #ifdef WIN32