aws/ec2metadata: Fix EC2 Metadata client panic with debug logging (#290)

Fixes a panic that could occur witihin the EC2 Metadata client when both
AWS_EC2_METADATA_DISABLED env var is set and log level is
LogDebugWithHTTPBody. The SDK's client response body debug functionality
would panic because the Request.HTTPResponse value was not specified.

Updates the client debug loggers to check if the response is set before
attempting to log.

V2 SDK port of: aws/aws-sdk-go#2461

aws/client_logger.go

@@ -71,6 +71,12 @@ const logRespErrMsg = `DEBUG ERROR: Response %s/%s:
 
 func logResponse(r *Request) {
 	lw := &logWriter{r.Config.Logger, bytes.NewBuffer(nil)}
+	if r.HTTPResponse.Body == nil {
+		lw.Logger.Log(fmt.Sprintf(logRespErrMsg,
+			r.Metadata.ServiceName, r.Operation.Name, "request's HTTPResponse is nil"))
+		return
+	}
+
 	r.HTTPResponse.Body = &teeReaderCloser{
 		Reader: io.TeeReader(r.HTTPResponse.Body, lw),
 		Source: r.HTTPResponse.Body,

aws/ec2metadata/service.go

@@ -58,6 +58,9 @@ func New(config aws.Config) *EC2Metadata {
 		svc.Handlers.Send.SwapNamed(aws.NamedHandler{
 			Name: defaults.SendHandler.Name,
 			Fn: func(r *aws.Request) {
+				r.HTTPResponse = &http.Response{
+					Header: http.Header{},
+				}
 				r.Error = awserr.New(
 					aws.ErrCodeRequestCanceled,
 					"EC2 IMDS access disabled via "+disableServiceEnvVar+" env var",

aws/ec2metadata/service_test.go

@@ -18,7 +18,10 @@ func TestClientDisableIMDS(t *testing.T) {
 
 	os.Setenv("AWS_EC2_METADATA_DISABLED", "true")
 
-	svc := ec2metadata.New(unit.Config())
+	cfg := unit.Config()
+	cfg.LogLevel = aws.LogDebugWithHTTPBody
+
+	svc := ec2metadata.New(cfg)
 	resp, err := svc.Region()
 	if err == nil {
 		t.Fatalf("expect error, got none")