Format log message before logging with logr (#4143)

* Format log message before logging with logr

Fixes #4141

The logr calling convention does not support fmt semantics for message
formatting. Format the message before it is sent to logr for logging.

* Add change to changelog

* Fix lint

Don't shadow the log pkg.

* Replace buflogr with funcr

* Run make

* Update exporters/zipkin/zipkin_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

CHANGELOG.md

@@ -22,6 +22,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `NewPeriodicReader` in `go.opentelemetry.io/otel/sdk/metric` returns `*PeriodicReader` instead of `Reader`. (#4244)
 - Count the Collect time in the PeriodicReader timeout. (#4221)
 
+### Fixed
+
+- Correctly format log messages from the `go.opentelemetry.io/otel/exporters/zipkin` exporter. (#4143)
+
 ## [1.16.0/0.39.0] 2023-05-18
 
 This release contains the first stable release of the OpenTelemetry Go [metric API].

exporters/zipkin/zipkin.go

@@ -181,7 +181,7 @@ func (e *Exporter) Shutdown(ctx context.Context) error {
 
 func (e *Exporter) logf(format string, args ...interface{}) {
 	if e.logger != emptyLogger {
-		e.logger.Info(format, args)
+		e.logger.Info(fmt.Sprintf(format, args...))
 	}
 }
 

exporters/zipkin/zipkin_test.go

@@ -15,6 +15,7 @@
 package zipkin
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -28,6 +29,7 @@ import (
 
 	ottest "go.opentelemetry.io/otel/internal/internaltest"
 
+	"github.com/go-logr/logr/funcr"
 	zkmodel "github.com/openzipkin/zipkin-go/model"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -364,3 +366,21 @@ func TestErrorOnExportShutdownExporter(t *testing.T) {
 	assert.NoError(t, exp.Shutdown(context.Background()))
 	assert.NoError(t, exp.ExportSpans(context.Background(), nil))
 }
+
+func TestLogrFormatting(t *testing.T) {
+	format := "string %q, int %d"
+	args := []interface{}{"s", 1}
+
+	var buf bytes.Buffer
+	l := funcr.New(func(prefix, args string) {
+		_, _ = buf.WriteString(fmt.Sprint(prefix, args))
+	}, funcr.Options{})
+	exp, err := New("", WithLogr(l))
+	require.NoError(t, err)
+
+	exp.logf(format, args...)
+
+	want := "\"level\"=0 \"msg\"=\"string \\\"s\\\", int 1\""
+	got := buf.String()
+	assert.Equal(t, want, got)
+}