util/tracing: move extractMsgFromRecord to the tracking pkg

This function was used in sql, but I want to start using it elsewhere
when dealing with traces.

Release note: None
Release justification: Minor code move, in support of the next commit.

pkg/sql/exec_util.go

@@ -1499,21 +1499,6 @@ func (st *SessionTracing) TraceExecEnd(ctx context.Context, err error, count int
 	}
 }
 
-// extractMsgFromRecord extracts the message of the event, which is either in an
-// "event" or "error" field.
-func extractMsgFromRecord(rec tracing.LogRecord) string {
-	for _, f := range rec.Fields {
-		key := f.Key
-		if key == "event" {
-			return f.Value
-		}
-		if key == "error" {
-			return fmt.Sprint("error:", f.Value)
-		}
-	}
-	return "<event missing in trace message>"
-}
-
 const (
 	// span_idx    INT NOT NULL,        -- The span's index.
 	traceSpanIdxCol = iota
@@ -1765,7 +1750,7 @@ func getMessagesForSubtrace(
 			allLogs = append(allLogs,
 				logRecordRow{
 					timestamp: logTime,
-					msg:       extractMsgFromRecord(span.Logs[i]),
+					msg:       span.Logs[i].Msg(),
 					span:      span,
 					// Add 1 to the index to account for the first dummy message in a
 					// span.

pkg/util/log/trace.go

@@ -125,7 +125,7 @@ func eventInternal(ctx context.Context, isErr, withTags bool, format string, arg
 		if sp != nil {
 			// TODO(radu): pass tags directly to sp.LogKV when LightStep supports
 			// that.
-			sp.LogFields(otlog.String("event", msg))
+			sp.LogFields(otlog.String(tracing.LogMessageField, msg))
 			// if isErr {
 			// 	// TODO(radu): figure out a way to signal that this is an error. We
 			// 	// could use a different "error" key (provided it shows up in

pkg/util/tracing/recorded_span.go

@@ -10,7 +10,14 @@
 
 package tracing
 
-import "strings"
+import (
+	"fmt"
+	"strings"
+)
+
+// LogMessageField is the field name used for the opentracing.Span.LogFields()
+// for a log message.
+const LogMessageField = "event"
 
 func (s *RecordedSpan) String() string {
 	sb := strings.Builder{}
@@ -20,3 +27,18 @@ func (s *RecordedSpan) String() string {
 	}
 	return sb.String()
 }
+
+// Msg extracts the message of the LogRecord, which is either in an "event" or
+// "error" field.
+func (l LogRecord) Msg() string {
+	for _, f := range l.Fields {
+		key := f.Key
+		if key == LogMessageField {
+			return f.Value
+		}
+		if key == "error" {
+			return fmt.Sprint("error:", f.Value)
+		}
+	}
+	return ""
+}

pkg/util/tracing/tracer_span.go

@@ -490,7 +490,7 @@ func (s *span) LogFields(fields ...otlog.Field) {
 		// TODO(radu): when LightStep supports arbitrary fields, we should make
 		// the formatting of the message consistent with that. Until then we treat
 		// legacy events that just have an "event" key specially.
-		if len(fields) == 1 && fields[0].Key() == "event" {
+		if len(fields) == 1 && fields[0].Key() == LogMessageField {
 			s.netTr.LazyPrintf("%s", fields[0].Value())
 		} else {
 			var buf bytes.Buffer
@@ -565,12 +565,12 @@ func (s *span) Tracer() opentracing.Tracer {
 
 // LogEvent is part of the opentracing.Span interface. Deprecated.
 func (s *span) LogEvent(event string) {
-	s.LogFields(otlog.String("event", event))
+	s.LogFields(otlog.String(LogMessageField, event))
 }
 
 // LogEventWithPayload is part of the opentracing.Span interface. Deprecated.
 func (s *span) LogEventWithPayload(event string, payload interface{}) {
-	s.LogFields(otlog.String("event", event), otlog.Object("payload", payload))
+	s.LogFields(otlog.String(LogMessageField, event), otlog.Object("payload", payload))
 }
 
 // Log is part of the opentracing.Span interface. Deprecated.