[library/cpp/logger] Support meta flags with TLogElement

Support opportunity to use TMetaFlags with TLogElement.

**Use example:**
`Log().With("Property", "Value").With("Code", "Code") << LogMessage`

Such interface allows to not parse required by TLogBackend  properties from raw string.

1 files changed, 21 insertions, 0 deletions

diff --git a/library/cpp/logger/stream.cpp b/library/cpp/logger/stream.cpp
index 96787ad94ba..73cd5030ace 100644
--- a/library/cpp/logger/stream.cpp
+++ b/library/cpp/logger/stream.cpp
@@ -3,6 +3,7 @@
 
 #include <util/stream/output.h>
 
+
 TStreamLogBackend::TStreamLogBackend(IOutputStream* slave)
     : Slave_(slave)
 {
@@ -17,3 +18,23 @@ void TStreamLogBackend::WriteData(const TLogRecord& rec) {
 
 void TStreamLogBackend::ReopenLog() {
 }
+
+TStreamWithContextLogBackend::TStreamWithContextLogBackend(IOutputStream* slave)
+    : Slave_(slave)
+{
+}
+
+TStreamWithContextLogBackend::~TStreamWithContextLogBackend() {
+}
+
+void TStreamWithContextLogBackend::WriteData(const TLogRecord& rec) {
+    Slave_->Write(rec.Data, rec.Len);
+    Slave_->Write(DELIMITER);
+    for (const auto& [key, value] : rec.MetaFlags) {
+        Slave_->Write(TString::Join(key, "=", value));
+        Slave_->Write(DELIMITER);
+    }
+}
+
+void TStreamWithContextLogBackend::ReopenLog() {
+}