module/apmmongo: mongo.CommandError ErrorDetailer

Register an ErrorDetailer for mongo.CommandError,
extract the error code and labels.

error.go

@@ -557,7 +557,8 @@ var (
 )
 
 // ErrorDetails holds details of an error, which can be altered or
-// extended by registering an ErrorDetailer with RegisterErrorDetailer.
+// extended by registering an ErrorDetailer with RegisterErrorDetailer
+// or RegisterTypeErrorDetailer.
 type ErrorDetails struct {
 	attrs map[string]interface{}
 
@@ -604,6 +605,9 @@ func (d *ErrorDetails) SetAttr(k string, v interface{}) {
 }
 
 // ErrorDetailer defines an interface for altering or extending the ErrorDetails for an error.
+//
+// ErrorDetailers can be registered using the package-level functions RegisterErrorDetailer and
+// RegisterTypeErrorDetailer.
 type ErrorDetailer interface {
 	// ErrorDetails is called to update or alter details for err.
 	ErrorDetails(err error, details *ErrorDetails)

module/apmmongo/monitor.go

@@ -19,13 +19,15 @@ package apmmongo
 
 import (
 	"context"
+	"reflect"
 	"sync"
 	"time"
 
 	"go.mongodb.org/mongo-driver/bson"
 	"go.mongodb.org/mongo-driver/bson/bsoncodec"
 	"go.mongodb.org/mongo-driver/bson/bsonrw"
 	"go.mongodb.org/mongo-driver/event"
+	"go.mongodb.org/mongo-driver/mongo"
 
 	"go.elastic.co/apm"
 )
@@ -39,6 +41,17 @@ var (
 	}
 )
 
+func init() {
+	apm.RegisterTypeErrorDetailer(
+		reflect.TypeOf(mongo.CommandError{}),
+		apm.ErrorDetailerFunc(func(err error, details *apm.ErrorDetails) {
+			commandErr := err.(mongo.CommandError)
+			details.Code.String = commandErr.Name
+			details.SetAttr("labels", commandErr.Labels)
+		}),
+	)
+}
+
 // CommandMonitor returns a new event.CommandMonitor which will report a span
 // for each command executed within a context containing a sampled transaction.
 func CommandMonitor(opts ...Option) *event.CommandMonitor {

module/apmmongo/monitor_integration_test.go

@@ -110,5 +110,5 @@ func (suite *IntegrationSuite) TestCommandMonitor() {
 	suite.Require().Len(errs, 1)
 	suite.Equal(tx.ID, errs[0].ParentID)
 	suite.Equal("(UserNotFound) User 'bob@test_db' not found", errs[0].Exception.Message)
-	suite.Equal(model.ExceptionCode{}, errs[0].Exception.Code) // BUG(axw) https://github.com/elastic/apm-agent-go/issues/447
+	suite.Equal(model.ExceptionCode{String: "UserNotFound"}, errs[0].Exception.Code)
 }