fix crash when log backtrace is used

Author: odygrd

include/quill/backend/BackendWorker.h

@@ -528,6 +528,8 @@ class BackendWorker
     // Allocate a new TransitEvent or use an existing one to store the message from the queue
     TransitEvent* transit_event = thread_context->_transit_event_buffer->back();
 
+    assert(transit_event->formatted_msg);
+
     std::memcpy(&transit_event->timestamp, read_pos, sizeof(transit_event->timestamp));
     read_pos += sizeof(transit_event->timestamp);
 
@@ -828,9 +830,14 @@ class BackendWorker
       {
         if (transit_event.logger_base->backtrace_storage)
         {
-          // this is a backtrace log and we will store it
+          // this is a backtrace log and we will store the transit event
+          // we need to pass a copy of transit_event here and not move the existing
+          // the transit events are reused
+          TransitEvent transit_event_copy;
+          transit_event.copy_to(transit_event_copy);
+
           transit_event.logger_base->backtrace_storage->store(
-            std::move(transit_event), thread_context.thread_id(), thread_context.thread_name());
+            std::move(transit_event_copy), thread_context.thread_id(), thread_context.thread_name());
         }
         else
         {

include/quill/backend/TransitEvent.h

@@ -39,7 +39,10 @@ struct TransitEvent
   /***/
   ~TransitEvent() = default;
 
-  /***/
+  /**
+   * Copy constructor and assignment operator are deleted to prevent accidental copying.
+   * Use the `clone` function for explicit and controlled duplication.
+   */
   TransitEvent(TransitEvent const& other) = delete;
   TransitEvent& operator=(TransitEvent const& other) = delete;
 
@@ -72,6 +75,23 @@ struct TransitEvent
     return *this;
   }
 
+  /***/
+  void copy_to(TransitEvent& other) const {
+    other.timestamp = timestamp;
+    other.macro_metadata = macro_metadata;
+    other.logger_base = logger_base;
+    other.flush_flag = flush_flag;
+    other.dynamic_log_level = dynamic_log_level;
+
+    // manually copy the fmt::buffer
+    other.formatted_msg->reserve(formatted_msg->size());
+    other.formatted_msg->append(*formatted_msg);
+
+    if (this->named_args) {
+      other.named_args = std::make_unique<std::vector<std::pair<std::string, std::string>>>(*this->named_args);
+    }
+  }
+
   /***/
   QUILL_NODISCARD QUILL_ATTRIBUTE_HOT LogLevel log_level() const noexcept
   {

test/integration_tests/BacktraceFlushOnErrorTest.cpp

@@ -6,6 +6,7 @@
 #include "quill/LogMacros.h"
 #include "quill/sinks/FileSink.h"
 
+#include <chrono>
 #include <cstdio>
 #include <string>
 #include <vector>
@@ -52,6 +53,19 @@ TEST_CASE("backtrace_flush_on_error")
   }
   LOG_ERROR(logger, "After error");
 
+  // flush here and resume test
+  logger->flush_log();
+
+  // Enable backtrace for 2 messages for error
+  logger->init_backtrace(4, LogLevel::Error);
+
+  for (size_t i = 0; i < 512; ++i)
+  {
+    LOG_BACKTRACE(logger, "More backtrace log {}", i);
+    std::this_thread::sleep_for(std::chrono::milliseconds(1));
+  }
+  LOG_ERROR(logger, "After another error");
+
   logger->flush_log();
   Frontend::remove_logger(logger);
 
@@ -61,7 +75,7 @@ TEST_CASE("backtrace_flush_on_error")
   // Read file and check
   std::vector<std::string> const file_contents = quill::testing::file_contents(filename);
 
-  REQUIRE_EQ(file_contents.size(), 4);
+  REQUIRE_EQ(file_contents.size(), 9);
 
   std::string expected_string_1 = "LOG_INFO      " + logger_name + "       Before backtrace log";
   REQUIRE(quill::testing::file_contains(file_contents, expected_string_1));
@@ -75,5 +89,20 @@ TEST_CASE("backtrace_flush_on_error")
   std::string expected_string_4 = "LOG_BACKTRACE " + logger_name + "       Backtrace log 11";
   REQUIRE(quill::testing::file_contains(file_contents, expected_string_4));
 
+  std::string expected_string_5 = "LOG_BACKTRACE " + logger_name + "       More backtrace log 508";
+  REQUIRE(quill::testing::file_contains(file_contents, expected_string_5));
+
+  std::string expected_string_6 = "LOG_BACKTRACE " + logger_name + "       More backtrace log 509";
+  REQUIRE(quill::testing::file_contains(file_contents, expected_string_6));
+
+  std::string expected_string_7 = "LOG_BACKTRACE " + logger_name + "       More backtrace log 510";
+  REQUIRE(quill::testing::file_contains(file_contents, expected_string_7));
+
+  std::string expected_string_8 = "LOG_BACKTRACE " + logger_name + "       More backtrace log 511";
+  REQUIRE(quill::testing::file_contains(file_contents, expected_string_8));
+
+  std::string expected_string_9 = "LOG_ERROR     " + logger_name + "       After another error";
+  REQUIRE(quill::testing::file_contains(file_contents, expected_string_9));
+
   testing::remove_file(filename);
 }