webfile: make Size() work before Read

webfile.go

@@ -26,23 +26,30 @@ func NewWebFile(url *url.URL) *WebFile {
 	}
 }
 
-// Read reads the File from it's web location. On the first
-// call to Read, a GET request will be performed against the
-// WebFile's URL, using Go's default HTTP client. Any further
-// reads will keep reading from the HTTP Request body.
-func (wf *WebFile) Read(b []byte) (int, error) {
+func (wf *WebFile) start() error {
 	if wf.body == nil {
 		s := wf.url.String()
 		resp, err := http.Get(s)
 		if err != nil {
-			return 0, err
+			return err
 		}
 		if resp.StatusCode < 200 || resp.StatusCode > 299 {
-			return 0, fmt.Errorf("got non-2XX status code %d: %s", resp.StatusCode, s)
+			return fmt.Errorf("got non-2XX status code %d: %s", resp.StatusCode, s)
 		}
 		wf.body = resp.Body
 		wf.contentLength = resp.ContentLength
 	}
+	return nil
+}
+
+// Read reads the File from it's web location. On the first
+// call to Read, a GET request will be performed against the
+// WebFile's URL, using Go's default HTTP client. Any further
+// reads will keep reading from the HTTP Request body.
+func (wf *WebFile) Read(b []byte) (int, error) {
+	if err := wf.start(); err != nil {
+		return 0, err
+	}
 	return wf.body.Read(b)
 }
 
@@ -60,6 +67,9 @@ func (wf *WebFile) Seek(offset int64, whence int) (int64, error) {
 }
 
 func (wf *WebFile) Size() (int64, error) {
+	if err := wf.start(); err != nil {
+		return 0, err
+	}
 	if wf.contentLength < 0 {
 		return -1, errors.New("Content-Length hearer was not set")
 	}

webfile_test.go

@@ -46,3 +46,52 @@ func TestWebFile_notFound(t *testing.T) {
 		t.Fatal("expected error")
 	}
 }
+
+func TestWebFileSize(t *testing.T) {
+	body := "Hello world!"
+	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, body)
+	}))
+	defer s.Close()
+
+	u, err := url.Parse(s.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Read size before reading file.
+
+	wf1 := NewWebFile(u)
+	if size, err := wf1.Size(); err != nil {
+		t.Error(err)
+	} else if int(size) != len(body) {
+		t.Errorf("expected size to be %d, got %d", len(body), size)
+	}
+
+	actual, err := ioutil.ReadAll(wf1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(actual) != body {
+		t.Fatal("should have read the web file")
+	}
+
+	wf1.Close()
+
+	// Read size after reading file.
+
+	wf2 := NewWebFile(u)
+	actual, err = ioutil.ReadAll(wf2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(actual) != body {
+		t.Fatal("should have read the web file")
+	}
+
+	if size, err := wf2.Size(); err != nil {
+		t.Error(err)
+	} else if int(size) != len(body) {
+		t.Errorf("expected size to be %d, got %d", len(body), size)
+	}
+}