fix(compute/metadata): remove leading slash for Get suffix (#2760)

Updates #2750

compute/metadata/metadata.go

@@ -296,6 +296,7 @@ func (c *Client) getETag(suffix string) (value, etag string, err error) {
 		// being stable anyway.
 		host = metadataIP
 	}
+	suffix = strings.TrimLeft(suffix, "/")
 	u := "http://" + host + "/computeMetadata/v1/" + suffix
 	req, err := http.NewRequest("GET", u, nil)
 	if err != nil {

compute/metadata/metadata_test.go

@@ -73,6 +73,42 @@ func TestGetFailsOnBadURL(t *testing.T) {
 	}
 }
 
+func TestGet_LeadingSlash(t *testing.T) {
+	want := "http://169.254.169.254/computeMetadata/v1/instance/service-accounts/default/identity?audience=http://example.com"
+	tests := []struct {
+		name   string
+		suffix string
+	}{
+		{
+			name:   "without leading slash",
+			suffix: "instance/service-accounts/default/identity?audience=http://example.com",
+		},
+		{
+			name:   "with leading slash",
+			suffix: "/instance/service-accounts/default/identity?audience=http://example.com",
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			ct := &captureTransport{}
+			c := NewClient(&http.Client{Transport: ct})
+			c.Get(tc.suffix)
+			if ct.url != want {
+				t.Fatalf("got %v, want %v", ct.url, want)
+			}
+		})
+	}
+}
+
+type captureTransport struct {
+	url string
+}
+
+func (ct *captureTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	ct.url = req.URL.String()
+	return &http.Response{Body: ioutil.NopCloser(bytes.NewReader(nil))}, nil
+}
+
 type userAgentTransport struct {
 	userAgent string
 	base      http.RoundTripper