[encoding/zipkinencodingextension] add default case (#28689)

**Description:** Fix bug when err is nil if an invalid version value is
supplied.

**Link to tracking Issue:** #28686

---------

Co-authored-by: Dmitrii Anoshin <anoshindx@gmail.com>

.chloggen/bugfix-zipkin-encoding.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: extension/zipkinencodingextension
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix bug when err is nil if invalid protocol value is supplied.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [28686]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: 
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

extension/encoding/zipkinencodingextension/extension.go

@@ -51,7 +51,7 @@ func newExtension(config *Config) (*zipkinExtension, error) {
 				unmarshaler: zipkinv2.NewProtobufTracesUnmarshaler(false, false),
 			}
 		default:
-			err = fmt.Errorf("unsupported version: %q and protocol: %q", version, protocol)
+			err = fmt.Errorf("protocol: %q, unsupported version: %q", protocol, version)
 		}
 	case zipkinJSONEncoding:
 		switch version {
@@ -77,8 +77,10 @@ func newExtension(config *Config) (*zipkinExtension, error) {
 				unmarshaler: zipkinv1.NewThriftTracesUnmarshaler(),
 			}
 		default:
-			err = fmt.Errorf("unsupported version: %q and protocol: %q", version, protocol)
+			err = fmt.Errorf("protocol: %q, unsupported version: %q", protocol, version)
 		}
+	default:
+		err = fmt.Errorf("unsupported protocol: %q", protocol)
 	}
 
 	return ex, err

extension/encoding/zipkinencodingextension/extension_test.go

@@ -0,0 +1,30 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package zipkinencodingextension // import "github.com/open-telemetry/opentelemetry-collector-contrib/extension/encoding/zipkinencodingextension"
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/component/componenttest"
+	"go.opentelemetry.io/collector/extension/extensiontest"
+)
+
+func TestExtension_Start(t *testing.T) {
+	j := &zipkinExtension{
+		config: createDefaultConfig().(*Config),
+	}
+	err := j.Start(context.Background(), componenttest.NewNopHost())
+	require.NoError(t, err)
+}
+
+func TestExtension_Err(t *testing.T) {
+	factory := NewFactory()
+	cfg := createDefaultConfig().(*Config)
+	cfg.Protocol = "v3"
+	_, err := factory.CreateExtension(context.Background(), extensiontest.NewNopCreateSettings(), cfg)
+	require.NotNil(t, err)
+	require.ErrorContains(t, err, "unsupported protocol: \"v3\"")
+}

extension/encoding/zipkinencodingextension/go.mod

@@ -5,13 +5,15 @@ go 1.20
 require (
 	github.com/open-telemetry/opentelemetry-collector-contrib/extension/encoding v0.0.0-00010101000000-000000000000
 	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/translator/zipkin v0.88.0
+	github.com/stretchr/testify v1.8.4
 	go.opentelemetry.io/collector/component v0.88.1-0.20231026220224-6405e152a2d9
 	go.opentelemetry.io/collector/extension v0.88.1-0.20231026220224-6405e152a2d9
 	go.opentelemetry.io/collector/pdata v1.0.0-rcv0017.0.20231026220224-6405e152a2d9
 )
 
 require (
 	github.com/apache/thrift v0.19.0 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/jaegertracing/jaeger v1.48.0 // indirect
@@ -27,6 +29,7 @@ require (
 	github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal v0.88.0 // indirect
 	github.com/opentracing/opentracing-go v1.2.0 // indirect
 	github.com/openzipkin/zipkin-go v0.4.2 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/uber/jaeger-client-go v2.30.0+incompatible // indirect
 	github.com/uber/jaeger-lib v2.4.1+incompatible // indirect
 	go.opentelemetry.io/collector/config/configtelemetry v0.88.1-0.20231026220224-6405e152a2d9 // indirect
@@ -45,6 +48,7 @@ require (
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20230822172742-b8732ec3820d // indirect
 	google.golang.org/grpc v1.59.0 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
 
 replace github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal => ../../../internal/coreinternal