Cmdline: use exceptions for control flow

This is generally frowned upon but it makes this code 10x cleaner.
We handle commandLine usage msg printing by using exceptions for
control flow. This allows us to centralize the logic for killing
the Mind threads in one place. At least with respect to printing
the usage msg.

smocore/include/opts.h

@@ -4,6 +4,8 @@
 #include <vector>
 #include <string>
 #include <getopt.h>
+#include <stdexcept>
+#include <exception>
 
 // Define a class to hold the options and parse arguments
 class OptionParser
@@ -23,6 +25,14 @@ public:
     }
 
 public:
+    class Exception : public std::exception
+    {
+    public:
+        Exception() = default;
+        ~Exception() override = default;
+        const char* what() const noexcept override = 0;
+    };
+
     std::string argv0;
     std::vector<std::string> senseApiLibPath;
     std::vector<std::string> senseApiLibs;
@@ -33,4 +43,25 @@ public:
     static struct option longOptions[];
 };
 
+class OptionsParserError
+: public std::invalid_argument, public OptionParser::Exception
+{
+public:
+    OptionsParserError(
+        const std::string& errorMessage, const OptionParser& parser);
+
+    const char* what() const noexcept override;
+};
+
+class JustPrintUsageNoError
+: public OptionParser::Exception
+{
+public:
+    explicit JustPrintUsageNoError(const OptionParser& parser);
+    const char* what() const noexcept override;
+
+private:
+    std::string message;
+};
+
 #endif // OPTS_H

smocore/marionette/marionette.cpp

@@ -8,6 +8,7 @@
 #include <marionette/marionette.h>
 #include <salmanoff.h>
 #include <boost/asio/signal_set.hpp>
+#include <typeinfo>
 
 namespace smo {
 
@@ -55,34 +56,15 @@ void ComponentThread::marionetteMain(ComponentThread& self)
 		std::cout << __func__ << ": " << PACKAGE_NAME << " " << PACKAGE_VERSION
 			<< std::endl;
 
-		try {
 		options.parseArguments(
 			crtCommandLineArgs.argc, crtCommandLineArgs.argv,
 			crtCommandLineArgs.envp);
 
 		std::cout << __func__ << ": " << options.stringifyOptions()
 			<< std::endl;
-		}
-		catch (const std::invalid_argument& e)
-		{
-			std::cerr << __func__ << ": Exception occurred: " << e.what()
-				<< '\n';
 
-			options.printUsage = true;
-			mrntt::exitCode = EXIT_FAILURE;
-		}
-
-		if (options.printUsage)
-		{
-			/* We could make RAII guard classes to always shutdown the mind
-			 * threads properly in these pre-event loop situations.
-			 */
-			mind.finalizeReq([]{
-				mrntt::mrntt->getIoService().stop();
-			});
-			self.getIoService().reset();
-			self.getIoService().run();
-			return;
+		if (options.printUsage) {
+			throw JustPrintUsageNoError(options);
 		}
 
 		self.getIoService().post([]()
@@ -130,6 +112,25 @@ void ComponentThread::marionetteMain(ComponentThread& self)
         std::cout << __func__ << ": Exited event loop" << "\n";
 		shutdownSalmanoff();
 	}
+	catch (const OptionParser::Exception& e)
+	{
+		std::ostream &out = std::cout;
+		std::string outUsageMsg;
+
+		if (typeid(e) == typeid(OptionsParserError))
+		{
+			mrntt::exitCode = EXIT_FAILURE;
+			outUsageMsg = std::string(__func__) + ": ";
+		}
+
+		out << outUsageMsg << e.what() << std::endl;
+		mind.finalizeReq([]{
+			mrntt::mrntt->getIoService().stop();
+		});
+		self.getIoService().reset();
+		self.getIoService().run();
+		return;
+	}
 	catch (const std::exception& e)
 	{
 		std::cerr << __func__ << ": Exception occurred: " << e.what()

smocore/opts.cpp

@@ -1,6 +1,7 @@
 #include <opts.h>
 #include <iostream>
 #include <stdexcept>
+#include <exception>
 #include <getopt.h>
 #include <string>
 #include <vector>
@@ -8,6 +9,28 @@
 #include <sstream>
 
 
+OptionsParserError::OptionsParserError(
+    const std::string& errorMessage, const OptionParser& parser
+)
+: std::invalid_argument(errorMessage + "\n" + parser.getUsage())
+{
+}
+
+const char* OptionsParserError::what() const noexcept
+{
+    return std::invalid_argument::what();
+}
+
+JustPrintUsageNoError::JustPrintUsageNoError(const OptionParser& parser)
+: message(parser.getUsage())
+{
+}
+
+const char* JustPrintUsageNoError::what() const noexcept
+{
+    return message.c_str();
+}
+
 struct option OptionParser::longOptions[] = {
     {"devicespec", required_argument, 0, 's'},
     {"spec", required_argument, 0, 's'},
@@ -59,9 +82,9 @@ void OptionParser::parseArguments(int argc, char *argv[], char **envp)
 
             if (stat(optarg, &info) != 0 || !(info.st_mode & S_IFDIR))
             {
-                throw std::invalid_argument(
+                throw OptionsParserError(
                     std::string(__func__) + " - The specified path is not a "
-                    "directory: " + optarg);
+                    "directory: " + optarg, *this);
             }
 
             senseApiLibPath.push_back(optarg);
@@ -71,12 +94,11 @@ void OptionParser::parseArguments(int argc, char *argv[], char **envp)
             verbose = true;
             break;
         case 'h':
-            printUsage = true;
-            return;
+            throw JustPrintUsageNoError(*this);
         case '?':
-            throw std::invalid_argument(
+            throw OptionsParserError(
                 std::string(__func__) + " - Invalid argument encountered: "
-                + std::string(argv[optind - 1]));
+                + std::string(argv[optind - 1]), *this);
         }
     }
 }