Add support for debug logging (#29)

client.go

@@ -19,6 +19,8 @@ const (
 	APIVersion = "v1"
 )
 
+type Logger = resty.Logger
+
 // Client represents an instance of a Linode Metadata Service client.
 type Client struct {
 	managedTokenExpiry time.Time
@@ -91,6 +93,11 @@ func NewClient(ctx context.Context, opts ...ClientOption) (*Client, error) {
 		result.UseToken(clientOpts.StartingToken)
 	}
 
+	result.resty.SetDebug(clientOpts.Debug)
+	if clientOpts.DebugLogger != nil {
+		result.resty.SetLogger(clientOpts.DebugLogger)
+	}
+
 	result.resty.OnBeforeRequest(result.middlewareTokenRefresh)
 
 	return &result, nil
@@ -184,6 +191,9 @@ type clientCreateConfig struct {
 	ManagedTokenOpts []TokenOption
 
 	StartingToken string
+
+	Debug       bool
+	DebugLogger Logger
 }
 
 // ClientOption is an option that can be used
@@ -252,3 +262,24 @@ func ClientWithToken(token string) ClientOption {
 		options.StartingToken = token
 	}
 }
+
+// ClientWithDebug enables debug mode for the metadata client.
+// If this option is specified, all metadata service API requests
+// and responses will be written to the client logger (default: stderr).
+//
+// To override the client logger, refer to ClientWithLogger.
+func ClientWithDebug() ClientOption {
+	return func(options *clientCreateConfig) {
+		options.Debug = true
+	}
+}
+
+// ClientWithLogger specifies the logger that should be used
+// when outputting debug logs. The logger argument should implement
+// the Logger interface.
+// Default: stderr
+func ClientWithLogger(logger Logger) ClientOption {
+	return func(options *clientCreateConfig) {
+		options.DebugLogger = logger
+	}
+}

examples/instancewatcher/main.go

@@ -2,9 +2,10 @@ package main
 
 import (
 	"context"
-	metadata "github.com/linode/go-metadata"
 	"log"
 	"time"
+
+	metadata "github.com/linode/go-metadata"
 )
 
 func main() {

examples/networkwatcher/main.go

@@ -2,9 +2,10 @@ package main
 
 import (
 	"context"
-	metadata "github.com/linode/go-metadata"
 	"log"
 	"time"
+
+	metadata "github.com/linode/go-metadata"
 )
 
 func main() {

test/integration/client_test.go

@@ -2,10 +2,11 @@ package integration
 
 import (
 	"context"
-	"github.com/linode/go-metadata"
-	"github.com/stretchr/testify/assert"
 	"testing"
 	"time"
+
+	"github.com/linode/go-metadata"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestClient_UnmanagedTokenExpired(t *testing.T) {
@@ -42,3 +43,24 @@ func TestClient_ManagedTokenRefresh(t *testing.T) {
 	_, err = mdClient.GetInstance(context.Background())
 	assert.NoError(t, err)
 }
+
+func TestClient_DebugLogs(t *testing.T) {
+	var logger testLogger
+
+	mdClient, err := metadata.NewClient(
+		context.Background(),
+		metadata.ClientWithDebug(),
+		metadata.ClientWithLogger(&logger),
+	)
+	assert.NoError(t, err)
+
+	_, err = mdClient.GetInstance(context.Background())
+	assert.NoError(t, err)
+
+	debugOutput := logger.Data.String()
+
+	// Validate a few arbitrary bits of the debug output
+	assert.Contains(t, debugOutput, "User-Agent: go-metadata")
+	assert.Contains(t, debugOutput, "/v1/token")
+	assert.Contains(t, debugOutput, "/v1/instance")
+}

test/integration/helper_test.go

@@ -9,9 +9,11 @@ import (
 	"github.com/linode/linodego"
 )
 
-var testToken = os.Getenv("LINODE_TOKEN")
-var metadataClient *metadata.Client
-var linodeClient *linodego.Client
+var (
+	testToken      = os.Getenv("LINODE_TOKEN")
+	metadataClient *metadata.Client
+	linodeClient   *linodego.Client
+)
 
 func init() {
 	if testToken == "" {

test/integration/instance_test.go

@@ -2,8 +2,9 @@ package integration
 
 import (
 	"context"
-	"github.com/stretchr/testify/assert"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestGetInstance(t *testing.T) {

test/integration/userdata_test.go

@@ -2,8 +2,9 @@ package integration
 
 import (
 	"context"
-	"github.com/stretchr/testify/assert"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestGetUserData(t *testing.T) {

test/integration/util_test.go

@@ -0,0 +1,22 @@
+package integration
+
+import (
+	"bytes"
+	"fmt"
+)
+
+type testLogger struct {
+	Data bytes.Buffer
+}
+
+func (l *testLogger) Errorf(format string, v ...interface{}) {
+	l.Data.WriteString("[ERROR] " + fmt.Sprintf(format, v...))
+}
+
+func (l *testLogger) Warnf(format string, v ...interface{}) {
+	l.Data.WriteString("[WARN] " + fmt.Sprintf(format, v...))
+}
+
+func (l *testLogger) Debugf(format string, v ...interface{}) {
+	l.Data.WriteString("[DEBUG] " + fmt.Sprintf(format, v...))
+}