sigv4: support nil body (#673)

Fixes #562
Fixes #465

Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>

sigv4/sigv4.go

@@ -110,11 +110,14 @@ func (rt *sigV4RoundTripper) RoundTrip(req *http.Request) (*http.Response, error
 		buf.Reset()
 		rt.pool.Put(buf)
 	}()
-	if _, err := io.Copy(buf, req.Body); err != nil {
-		return nil, err
+
+	if req.Body != nil {
+		if _, err := io.Copy(buf, req.Body); err != nil {
+			return nil, err
+		}
+		// Close the original body since we don't need it anymore.
+		_ = req.Body.Close()
 	}
-	// Close the original body since we don't need it anymore.
-	_ = req.Body.Close()
 
 	// Ensure our seeker is back at the start of the buffer once we return.
 	var seeker io.ReadSeeker = bytes.NewReader(buf.Bytes())

sigv4/sigv4_test.go

@@ -107,4 +107,11 @@ func TestSigV4RoundTripper(t *testing.T) {
 
 		require.Equal(t, "/test/test", gotReq.URL.Path)
 	})
+
+	t.Run("No body", func(t *testing.T) {
+		req, err := http.NewRequest(http.MethodGet, "https://example.com/test/test", nil)
+		require.NoError(t, err)
+		_, err = cli.Do(req)
+		require.NoError(t, err)
+	})
 }