Avoid copying the result of a successful outcome (#100)

Adding rvalue ref-qualifiers to the 'outcome' class getters enables
moving out the result instead of copying it. In this case, we can avoid
copying the request payload.

* Remove static modifier from inline header functions

static inline makes no sense in a header file.

include/aws/lambda-runtime/outcome.h

@@ -23,48 +23,72 @@ namespace lambda_runtime {
 template <typename TResult, typename TFailure>
 class outcome {
 public:
-    outcome(TResult const& s) : s(s), m_success(true) {}
+    outcome(TResult const& s) : m_s(s), m_success(true) {}
+    outcome(TResult&& s) : m_s(std::move(s)), m_success(true) {}
 
-    outcome(TFailure const& f) : f(f), m_success(false) {}
+    outcome(TFailure const& f) : m_f(f), m_success(false) {}
+    outcome(TFailure&& f) : m_f(std::move(f)), m_success(false) {}
+
+    outcome(outcome const& other) : m_success(other.m_success)
+    {
+        if (m_success) {
+            new (&m_s) TResult(other.m_s);
+        }
+        else {
+            new (&m_f) TFailure(other.m_f);
+        }
+    }
 
     outcome(outcome&& other) noexcept : m_success(other.m_success)
     {
         if (m_success) {
-            s = std::move(other.s);
+            new (&m_s) TResult(std::move(other.m_s));
         }
         else {
-            f = std::move(other.f);
+            new (&m_f) TFailure(std::move(other.m_f));
         }
     }
 
     ~outcome()
     {
         if (m_success) {
-            s.~TResult();
+            m_s.~TResult();
         }
         else {
-            f.~TFailure();
+            m_f.~TFailure();
         }
     }
 
-    TResult const& get_result() const
+    TResult const& get_result() const&
     {
         assert(m_success);
-        return s;
+        return m_s;
+    }
+
+    TResult&& get_result() &&
+    {
+        assert(m_success);
+        return std::move(m_s);
+    }
+
+    TFailure const& get_failure() const&
+    {
+        assert(!m_success);
+        return m_f;
     }
 
-    TFailure const& get_failure() const
+    TFailure&& get_failure() &&
     {
         assert(!m_success);
-        return f;
+        return std::move(m_f);
     }
 
     bool is_success() const { return m_success; }
 
 private:
     union {
-        TResult s;
-        TFailure f;
+        TResult m_s;
+        TFailure m_f;
     };
     bool m_success;
 };

include/aws/logging/logging.h

@@ -27,7 +27,7 @@ enum class verbosity {
 
 void log(verbosity v, char const* tag, char const* msg, va_list args);
 
-[[gnu::format(printf, 2, 3)]] static inline void log_error(char const* tag, char const* msg, ...)
+[[gnu::format(printf, 2, 3)]] inline void log_error(char const* tag, char const* msg, ...)
 {
     va_list args;
     va_start(args, msg);
@@ -37,7 +37,7 @@ void log(verbosity v, char const* tag, char const* msg, va_list args);
     (void)msg;
 }
 
-[[gnu::format(printf, 2, 3)]] static inline void log_info(char const* tag, char const* msg, ...)
+[[gnu::format(printf, 2, 3)]] inline void log_info(char const* tag, char const* msg, ...)
 {
 #if AWS_LAMBDA_LOG >= 1
     va_list args;
@@ -50,7 +50,7 @@ void log(verbosity v, char const* tag, char const* msg, va_list args);
 #endif
 }
 
-[[gnu::format(printf, 2, 3)]] static inline void log_debug(char const* tag, char const* msg, ...)
+[[gnu::format(printf, 2, 3)]] inline void log_debug(char const* tag, char const* msg, ...)
 {
 #if AWS_LAMBDA_LOG >= 2
     va_list args;

src/runtime.cpp

@@ -412,7 +412,7 @@ void run_handler(std::function<invocation_response(invocation_request const&)> c
     size_t const max_retries = 3;
 
     while (retries < max_retries) {
-        const auto next_outcome = rt.get_next();
+        auto next_outcome = rt.get_next();
         if (!next_outcome.is_success()) {
             if (next_outcome.get_failure() == aws::http::response_code::REQUEST_NOT_MADE) {
                 ++retries;
@@ -429,7 +429,7 @@ void run_handler(std::function<invocation_response(invocation_request const&)> c
 
         retries = 0;
 
-        auto const& req = next_outcome.get_result();
+        auto const req = std::move(next_outcome).get_result();
         logging::log_info(LOG_TAG, "Invoking user handler");
         invocation_response res = handler(req);
         logging::log_info(LOG_TAG, "Invoking user handler completed.");