feat: use structured logging for exceptions

google/cloud/functions/integration_tests/basic_integration_test.cc

@@ -19,6 +19,7 @@
 #include <boost/filesystem.hpp>
 #include <boost/process.hpp>
 #include <gmock/gmock.h>
+#include <nlohmann/json.hpp>
 #include <chrono>
 #include <string>
 
@@ -138,8 +139,12 @@ TEST(RunIntegrationTest, ExceptionLogsToStderr) {
 
   std::string line;
   std::getline(child_stderr, line);
-  EXPECT_THAT(line, HasSubstr("standard C++ exception"));
-  EXPECT_THAT(line, HasSubstr("/exception/test-string"));
+  auto log = nlohmann::json::parse(line, /*cb=*/nullptr,
+                                   /*allow_exceptions=*/false);
+  ASSERT_TRUE(log.is_object());
+  EXPECT_EQ(log.value("severity", ""), "error");
+  EXPECT_THAT(log.value("message", ""), HasSubstr("standard C++ exception"));
+  EXPECT_THAT(log.value("message", ""), HasSubstr("/exception/test-string"));
 
   try {
     (void)HttpGet("localhost", "8010", "/quit/program/0");

google/cloud/functions/integration_tests/cloud_event_integration_test.cc

@@ -249,8 +249,12 @@ TEST(RunIntegrationTest, ExceptionLogsToStderr) {
 
   std::string line;
   std::getline(child_stderr, line);
-  EXPECT_THAT(line, HasSubstr("standard C++ exception"));
-  EXPECT_THAT(line, HasSubstr("/exception/test-string"));
+  auto log = nlohmann::json::parse(line, /*cb=*/nullptr,
+                                   /*allow_exceptions=*/false);
+  ASSERT_TRUE(log.is_object());
+  EXPECT_EQ(log.value("severity", ""), "error");
+  EXPECT_THAT(log.value("message", ""), HasSubstr("standard C++ exception"));
+  EXPECT_THAT(log.value("message", ""), HasSubstr("/exception/test-string"));
 
   try {
     (void)HttpPost("localhost", "8020", "/quit/program/0");

google/cloud/functions/internal/call_user_function.cc

@@ -16,6 +16,7 @@
 #include "google/cloud/functions/internal/parse_cloud_event_http.h"
 #include "google/cloud/functions/internal/wrap_request.h"
 #include "google/cloud/functions/internal/wrap_response.h"
+#include <nlohmann/json.hpp>
 #include <iostream>
 #include <stdexcept>
 
@@ -32,6 +33,36 @@ struct UnwrapResponse {
   }
 };
 
+namespace {
+BeastResponse ApplicationError(nlohmann::json const& error) {
+  auto msg = error.dump();
+  // Log the message to stderr. If the message is properly formatted, as it is
+  // done here, they are sent picked up and parsed by Cloud Logging:
+  //     https://cloud.google.com/functions/docs/monitoring/logging#writing_structured_logs
+  std::cerr << msg << std::endl;
+  BeastResponse response;
+  response.result(be::http::status::internal_server_error);
+  response.insert("content-type", "application/json");
+  response.body() = std::move(msg);
+  return response;
+}
+
+BeastResponse ReportExceptionInFunction(std::exception const& ex) {
+  return ApplicationError(
+      {{"severity", "error"},
+       {"message",
+        std::string("standard C++ exception thrown by the function: ") +
+            ex.what()}});
+}
+
+BeastResponse ReportUnknownExceptionInFunction() {
+  return ApplicationError({
+      {"severity", "error"},
+      {"message", std::string("unknown C++ exception thrown by the function")},
+  });
+}
+}  // namespace
+
 BeastResponse CallUserFunction(functions::UserHttpFunction const& function,
                                BeastRequest request) try {
   if (request.target() == "/favicon.ico" || request.target() == "/robots.txt") {
@@ -42,15 +73,9 @@ BeastResponse CallUserFunction(functions::UserHttpFunction const& function,
   auto response = function(MakeHttpRequest(std::move(request)));
   return UnwrapResponse::unwrap(std::move(response));
 } catch (std::exception const& ex) {
-  std::cerr << "standard C++ exception thrown: " << ex.what() << std::endl;
-  BeastResponse response;
-  response.result(be::http::status::internal_server_error);
-  return response;
+  return ReportExceptionInFunction(ex);
 } catch (...) {
-  std::cerr << "unknown c++ exception thrown" << std::endl;
-  BeastResponse response;
-  response.result(be::http::status::internal_server_error);
-  return response;
+  return ReportUnknownExceptionInFunction();
 }
 
 BeastResponse CallUserFunction(
@@ -67,15 +92,9 @@ BeastResponse CallUserFunction(
   }
   return BeastResponse{};
 } catch (std::exception const& ex) {
-  std::cerr << "standard C++ exception thrown: " << ex.what() << std::endl;
-  BeastResponse response;
-  response.result(be::http::status::internal_server_error);
-  return response;
+  return ReportExceptionInFunction(ex);
 } catch (...) {
-  std::cerr << "unknown c++ exception thrown" << std::endl;
-  BeastResponse response;
-  response.result(be::http::status::internal_server_error);
-  return response;
+  return ReportUnknownExceptionInFunction();
 }
 
 }  // namespace FUNCTIONS_FRAMEWORK_CPP_NS