Logging: Pass LogData struct to logging callback

The previous logging callback signature is deprecated and support will be
removed in a future release.

Also adds a <functional> include to calculator example to make IWYU happy.

Author: theuni

example/calculator.cpp

@@ -9,6 +9,7 @@
 #include <charconv>
 #include <cstring>
 #include <fstream>
+#include <functional>
 #include <iostream>
 #include <kj/async.h>
 #include <kj/common.h>
@@ -37,6 +38,7 @@ class InitImpl : public Init
     }
 };
 
+// Exercises deprecated log callback signature
 static void LogPrint(bool raise, const std::string& message)
 {
     if (raise) throw std::runtime_error(message);

example/example.cpp

@@ -35,10 +35,10 @@ static auto Spawn(mp::EventLoop& loop, const std::string& process_argv0, const s
     return std::make_tuple(mp::ConnectStream<InitInterface>(loop, fd), pid);
 }
 
-static void LogPrint(bool raise, const std::string& message)
+static void LogPrint(mp::LogMessage log_data)
 {
-    if (raise) throw std::runtime_error(message);
-    std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
+    if (log_data.level == mp::Log::Raise) throw std::runtime_error(log_data.message);
+    std::ofstream("debug.log", std::ios_base::app) << log_data.message << std::endl;
 }
 
 int main(int argc, char** argv)

example/printer.cpp

@@ -32,10 +32,10 @@ class InitImpl : public Init
     std::unique_ptr<Printer> makePrinter() override { return std::make_unique<PrinterImpl>(); }
 };
 
-static void LogPrint(bool raise, const std::string& message)
+static void LogPrint(mp::LogMessage log_data)
 {
-    if (raise) throw std::runtime_error(message);
-    std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
+    if (log_data.level == mp::Log::Raise) throw std::runtime_error(log_data.message);
+    std::ofstream("debug.log", std::ios_base::app) << log_data.message << std::endl;
 }
 
 int main(int argc, char** argv)

include/mp/proxy-io.h

@@ -107,7 +107,16 @@ enum class Log {
     Raise,
 };
 
-using LogFn = std::function<void(bool raise, std::string message)>;
+struct LogMessage {
+
+    //! Message to be logged
+    std::string message;
+
+    //! The severity level of this message
+    Log level;
+};
+
+using LogFn = std::function<void(LogMessage)>;
 
 struct LogOptions {
 
@@ -135,7 +144,7 @@ class Logger
 
     ~Logger() noexcept(false)
     {
-        if (enabled()) m_options.log_fn(m_log_level == Log::Raise, m_buffer.str());
+        if (enabled()) m_options.log_fn({std::move(m_buffer).str(), m_log_level});
     }
 
     template <typename T>
@@ -208,6 +217,12 @@ class EventLoop
     //! Construct event loop object with specified logging options.
     EventLoop(const char* exe_name, LogOptions log_opts, void* context = nullptr);
 
+    //! Backwards-compatible constructor for previous (deprecated) logging callback signature
+    EventLoop(const char* exe_name, std::function<void(bool, std::string)> old_callback, void* context = nullptr)
+        : EventLoop(exe_name,
+                LogFn{[&](LogMessage log_data) {old_callback(log_data.level == Log::Raise, std::move(log_data.message));}},
+                context){}
+
     ~EventLoop();
 
     //! Run event loop. Does not return until shutdown. This should only be

test/mp/test/test.cpp

@@ -60,9 +60,9 @@ class TestSetup
 
     TestSetup(bool client_owns_connection = true)
         : thread{[&] {
-              EventLoop loop("mptest", [](bool raise, const std::string& log) {
-                  std::cout << "LOG" << raise << ": " << log << "\n";
-                  if (raise) throw std::runtime_error(log);
+              EventLoop loop("mptest", [](mp::LogMessage log_data) {
+                  std::cout << "LOG" << (int)log_data.level << ": " << log_data.message << "\n";
+                  if (log_data.level == mp::Log::Raise) throw std::runtime_error(log_data.message);
               });
               auto pipe = loop.m_io_context.provider->newTwoWayPipe();