Added mdc from pull #2907

src/pattern_formatter.cpp

@@ -7,7 +7,6 @@
 #include <array>
 #include <cctype>
 #include <chrono>
-#include <cstring>
 #include <ctime>
 #include <string>
 #include <thread>
@@ -17,6 +16,7 @@
 #include "spdlog/details/fmt_helper.h"
 #include "spdlog/details/log_msg.h"
 #include "spdlog/details/os.h"
+#include <spdlog/mdc.h>
 #include "spdlog/fmt/fmt.h"
 #include "spdlog/formatter.h"
 
@@ -811,7 +811,6 @@ public:
             dest.push_back(']');
             dest.push_back(' ');
         }
-        // fmt_helper::append_string_view(msg.msg(), dest);
         fmt_helper::append_string_view(msg.payload, dest);
     }
 
@@ -820,6 +819,44 @@ private:
     memory_buf_t cached_datetime_;
 };
 
+// Class for formatting Mapped Diagnostic Context (MDC) in log messages.
+// Example: [logger-name] [info] [mdc_key_1:mdc_value_1 mdc_key_2:mdc_value_2] some message
+template <typename ScopedPadder>
+class mdc_formatter : public flag_formatter {
+public:
+    explicit mdc_formatter(padding_info padinfo)
+            : flag_formatter(padinfo) {}
+
+    void format(const details::log_msg &, const std::tm &, memory_buf_t &dest) override {
+        auto mdc_map = mdc::get_context();
+        if (mdc_map.empty()) {
+            ScopedPadder p(0, padinfo_, dest);
+            return;
+        } else {
+            auto last_element = --mdc_map.end();
+            for (auto it = mdc_map.begin(); it != mdc_map.end(); ++it) {
+                auto &pair = *it;
+                const auto &key = pair.first;
+                const auto &value = pair.second;
+                size_t content_size = key.size() + value.size() + 1;  // 1 for ':'
+
+                if (it != last_element) {
+                    content_size++;  // 1 for ' '
+                }
+
+                ScopedPadder p(content_size, padinfo_, dest);
+                fmt_helper::append_string_view(key, dest);
+                fmt_helper::append_string_view(":", dest);
+                fmt_helper::append_string_view(value, dest);
+                if (it != last_element) {
+                    fmt_helper::append_string_view(" ", dest);
+                }
+            }
+        }
+    }
+};
+
+
 }  // namespace details
 
 pattern_formatter::pattern_formatter(std::string pattern,
@@ -1096,6 +1133,10 @@ void pattern_formatter::handle_flag_(char flag, details::padding_info padding) {
             formatters_.push_back(std::make_unique<details::elapsed_formatter<Padder, std::chrono::seconds>>(padding));
             break;
 
+        case ('&'):
+            formatters_.push_back(std::make_unique<details::mdc_formatter<Padder>>(padding));
+            break;
+
         default:  // Unknown flag appears as is
             auto unknown_flag = std::make_unique<details::aggregate_formatter>();