[#549] Add tracing attributes

Signed-off-by: Roman Loginov <r.loginov@yadro.com>

cmd/s3-gw/app_settings.go

@@ -163,10 +163,11 @@ const ( // Settings.
 	cfgPProfAddress      = "pprof.address"
 
 	// Tracing.
-	cfgTracingEnabled   = "tracing.enabled"
-	cfgTracingExporter  = "tracing.exporter"
-	cfgTracingEndpoint  = "tracing.endpoint"
-	cfgTracingTrustedCa = "tracing.trusted_ca"
+	cfgTracingEnabled    = "tracing.enabled"
+	cfgTracingExporter   = "tracing.exporter"
+	cfgTracingEndpoint   = "tracing.endpoint"
+	cfgTracingTrustedCa  = "tracing.trusted_ca"
+	cfgTracingAttributes = "tracing.attributes"
 
 	cfgListenDomains = "listen_domains"
 
@@ -779,6 +780,30 @@ func fetchMultinetConfig(v *viper.Viper, logger *zap.Logger) (cfg internalnet.Co
 	return
 }
 
+func fetchTracingAttributes(v *viper.Viper) (map[string]string, error) {
+	attributes := make(map[string]string)
+	for i := 0; ; i++ {
+		key := cfgTracingAttributes + "." + strconv.Itoa(i) + "."
+		attrKey := v.GetString(key + "key")
+		attrValue := v.GetString(key + "value")
+		if attrKey == "" {
+			break
+		}
+
+		if _, ok := attributes[attrKey]; ok {
+			return nil, fmt.Errorf("tracing attribute key %s defined more than once", attrKey)
+		}
+
+		if attrValue == "" {
+			return nil, fmt.Errorf("empty tracing attribute value for key %s", attrKey)
+		}
+
+		attributes[attrKey] = attrValue
+	}
+
+	return attributes, nil
+}
+
 func newSettings() *viper.Viper {
 	v := viper.New()