encoding: fix duplicate compressor names

encoding/encoding.go

@@ -75,7 +75,9 @@ var registeredCompressor = make(map[string]Compressor)
 // registered with the same name, the one registered last will take effect.
 func RegisterCompressor(c Compressor) {
 	registeredCompressor[c.Name()] = c
-	grpcutil.RegisteredCompressorNames = append(grpcutil.RegisteredCompressorNames, c.Name())
+	if !grpcutil.IsCompressorNameRegistered(c.Name()) {
+		grpcutil.RegisteredCompressorNames = append(grpcutil.RegisteredCompressorNames, c.Name())
+	}
 }
 
 // GetCompressor returns Compressor for the given compressor name.

encoding/encoding_test.go

@@ -0,0 +1,37 @@
+package encoding
+
+import (
+	"reflect"
+	"testing"
+
+	"google.golang.org/grpc/internal/grpcutil"
+)
+
+type mockNamedCompressor struct {
+	Compressor
+}
+
+func (mockNamedCompressor) Name() string {
+	return "mock-compressor"
+}
+
+func TestDuplicateCompressorRegister(t *testing.T) {
+	defer func(m map[string]Compressor) { registeredCompressor = m }(registeredCompressor)
+	defer func(c []string) { grpcutil.RegisteredCompressorNames = c }(grpcutil.RegisteredCompressorNames)
+	registeredCompressor = map[string]Compressor{}
+	grpcutil.RegisteredCompressorNames = []string{}
+
+	RegisterCompressor(&mockNamedCompressor{})
+
+	// Register another instance of the same compressor.
+	mc := &mockNamedCompressor{}
+	RegisterCompressor(mc)
+	if got := registeredCompressor["mock-compressor"]; got != mc {
+		t.Fatalf("Unexpected compressor, got: %+v, want:%+v", got, mc)
+	}
+
+	wantNames := []string{"mock-compressor"}
+	if !reflect.DeepEqual(wantNames, grpcutil.RegisteredCompressorNames) {
+		t.Fatalf("Unexpected compressor names, got: %+v, want:%+v", grpcutil.RegisteredCompressorNames, wantNames)
+	}
+}