storage: don't drop port in endpoint

If the user creates a client with a custom endpoint, we should
retain the port for readhost.

Fixes #1737

Change-Id: Ic0cf928ae99fe115e1eebce46c3965044d682db4
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/50891
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>

storage/storage.go

@@ -128,7 +128,7 @@ func NewClient(ctx context.Context, opts ...option.ClientOption) (*Client, error
 		if err != nil {
 			return nil, fmt.Errorf("supplied endpoint %v is not valid: %v", ep, err)
 		}
-		readHost = u.Hostname()
+		readHost = u.Host
 	}
 
 	return &Client{

storage/storage_test.go

@@ -1148,7 +1148,7 @@ func TestAttrToFieldMapCoverage(t *testing.T) {
 // for writes) and readHost (used for reads) are both set correctly.
 func TestWithEndpoint(t *testing.T) {
 	ctx := context.Background()
-	endpoint := "https://fake.gcs.com/storage/v1"
+	endpoint := "https://fake.gcs.com:8080/storage/v1"
 	c, err := NewClient(ctx, option.WithEndpoint(endpoint))
 	if err != nil {
 		t.Fatalf("error creating client: %v", err)
@@ -1158,7 +1158,7 @@ func TestWithEndpoint(t *testing.T) {
 		t.Errorf("raw.BasePath not set correctly: got %v, want %v", c.raw.BasePath, endpoint)
 	}
 
-	want := "fake.gcs.com"
+	want := "fake.gcs.com:8080"
 	if c.readHost != want {
 		t.Errorf("readHost not set correctly: got %v, want %v", c.readHost, want)
 	}