Migrate to go.elastic.co/fastjson

- Remove internal/fastjson
- Use go.elastic.co/fastjson

gofuzz.go

@@ -18,9 +18,9 @@ import (
 	"github.com/santhosh-tekuri/jsonschema"
 
 	"go.elastic.co/apm/internal/apmschema"
-	"go.elastic.co/apm/internal/fastjson"
 	"go.elastic.co/apm/model"
 	"go.elastic.co/apm/stacktrace"
+	"go.elastic.co/fastjson"
 )
 
 func Fuzz(data []byte) int {
@@ -224,21 +224,27 @@ type gofuzzTransport struct {
 
 func (t *gofuzzTransport) SendErrors(ctx context.Context, payload *model.ErrorsPayload) error {
 	t.writer.Reset()
-	payload.MarshalFastJSON(&t.writer)
+	if err := payload.MarshalFastJSON(&t.writer); err != nil {
+		return err
+	}
 	t.validate(apmschema.Errors)
 	return nil
 }
 
 func (t *gofuzzTransport) SendMetrics(ctx context.Context, payload *model.MetricsPayload) error {
 	t.writer.Reset()
-	payload.MarshalFastJSON(&t.writer)
+	if err := payload.MarshalFastJSON(&t.writer); err != nil {
+		return err
+	}
 	t.validate(apmschema.Metrics)
 	return nil
 }
 
 func (t *gofuzzTransport) SendTransactions(ctx context.Context, payload *model.TransactionsPayload) error {
 	t.writer.Reset()
-	payload.MarshalFastJSON(&t.writer)
+	if err := payload.MarshalFastJSON(&t.writer); err != nil {
+		return err
+	}
 	t.validate(apmschema.Transactions)
 	return nil
 }

internal/apmhttputil/url_test.go

@@ -9,8 +9,8 @@ import (
 	"github.com/stretchr/testify/assert"
 
 	"go.elastic.co/apm/internal/apmhttputil"
-	"go.elastic.co/apm/internal/fastjson"
 	"go.elastic.co/apm/model"
+	"go.elastic.co/fastjson"
 )
 
 func TestRequestURLClient(t *testing.T) {
@@ -97,12 +97,13 @@ func TestRequestURLHeaders(t *testing.T) {
 
 			// Marshal the URL to gets its "full" representation.
 			var w fastjson.Writer
-			out.MarshalFastJSON(&w)
+			err := out.MarshalFastJSON(&w)
+			assert.NoError(t, err)
 
 			var decoded struct {
 				Full string
 			}
-			err := json.Unmarshal(w.Bytes(), &decoded)
+			err = json.Unmarshal(w.Bytes(), &decoded)
 			assert.NoError(t, err)
 			assert.Equal(t, test.full, decoded.Full)
 		})