feat(logger): add WithFields/FieldsFromContext methods for context (#1869)

Co-authored-by: Aleksey Myasnikov <asmyasnikov@ydb.tech>

Author: ulya-sidorina

CHANGELOG.md

@@ -1,5 +1,8 @@
+* Added helper methods `log.WithFields` and `log.FieldsFromContext` for working with structured logging fields via context.
+  These methods allow adding custom fields to the context, which are later extracted by the logger.
+
 ## v3.116.4
-* Fixed error handling in internaltopicreader.addOnTransactionCompletedHandler
+* Fixed error handling in `internaltopicreader.addOnTransactionCompletedHandler`
 
 ## v3.116.3
 * Default grpc message size adjusted to the server's defaults

log/context.go

@@ -5,8 +5,9 @@ import (
 )
 
 type (
-	ctxLevelKey struct{}
-	ctxNamesKey struct{}
+	ctxLevelKey  struct{}
+	ctxNamesKey  struct{}
+	ctxFieldsKey struct{}
 )
 
 func WithLevel(ctx context.Context, lvl Level) context.Context {
@@ -36,6 +37,21 @@ func NamesFromContext(ctx context.Context) []string {
 	return v[:len(v):len(v)] // prevent re
 }
 
+func WithFields(ctx context.Context, fields ...Field) context.Context {
+	return context.WithValue(ctx, ctxFieldsKey{}, append(
+		FieldsFromContext(ctx),
+		fields...,
+	))
+}
+
+func FieldsFromContext(ctx context.Context) []Field {
+	if fields, has := ctx.Value(ctxFieldsKey{}).([]Field); has && len(fields) > 0 {
+		return fields
+	}
+
+	return nil
+}
+
 func with(ctx context.Context, lvl Level, names ...string) context.Context {
 	return WithLevel(WithNames(ctx, names...), lvl)
 }

log/context_test.go

@@ -90,3 +90,37 @@ func TestWithNamesRaceRegression(t *testing.T) {
 		}
 	})
 }
+
+func TestFieldsFromContext(t *testing.T) {
+	for _, tt := range []struct {
+		ctx    context.Context //nolint:containedctx
+		fields []Field
+	}{
+		{
+			ctx:    context.Background(),
+			fields: nil,
+		},
+		{
+			ctx:    WithFields(context.Background(), String("a", "1"), String("b", "1")),
+			fields: []Field{String("a", "1"), String("b", "1")},
+		},
+		{
+			ctx: WithFields(
+				WithFields(context.Background(), String("a", "1"), String("b", "1")),
+				String("a", "1"), String("b", "1"),
+			),
+			fields: []Field{String("a", "1"), String("b", "1"), String("a", "1"), String("b", "1")},
+		},
+		{
+			ctx: WithFields(
+				WithFields(context.Background(), String("a", "1"), String("b", "1")),
+				String("a", "3"),
+			),
+			fields: []Field{String("a", "1"), String("b", "1"), String("a", "3")},
+		},
+	} {
+		t.Run("", func(t *testing.T) {
+			require.Equal(t, tt.fields, FieldsFromContext(tt.ctx))
+		})
+	}
+}

log/logger.go

@@ -92,7 +92,7 @@ func (l *defaultLogger) Log(ctx context.Context, msg string, fields ...Field) {
 
 	_, _ = io.WriteString(l.w, l.format(
 		NamesFromContext(ctx),
-		l.appendFields(msg, fields...),
+		appendFieldsToMsg(msg, append(FieldsFromContext(ctx), fields...)...),
 		lvl,
 	)+"\n")
 }
@@ -115,7 +115,7 @@ func wrapLogger(l Logger, opts ...Option) *wrapper {
 	return ll
 }
 
-func (l *defaultLogger) appendFields(msg string, fields ...Field) string {
+func appendFieldsToMsg(msg string, fields ...Field) string {
 	if len(fields) == 0 {
 		return msg
 	}