rewind Body on retry

this is really not ideal, and there are libraries for this kind of
thing, but I'd have to figure out how to make the libraries work with
everywhere we're already creating stdlib http clients.

http/client.go

@@ -1745,13 +1745,33 @@ func giveRawResponse(b bool) executeRequestOption {
 	}
 }
 
+type nopCloser struct {
+	*bytes.Reader
+}
+
+func (n nopCloser) Close() error {
+	return nil
+}
+
 func (c *InternalClient) doWithRetry(req *http.Request) (*http.Response, error) {
 	sleepDuration := time.Second
+	newBody := nopCloser{}
+	if req.Body != nil {
+		bod, err := ioutil.ReadAll(req.Body)
+		if err != nil {
+			return nil, errors.Wrap(err, "reading body")
+		}
+		newBody.Reader = bytes.NewReader(bod)
+		req.Body = newBody
+	}
 	resp, err := c.httpClient.Do(req)
 	// start timer after first request, so if retryPeriod > 0 we
 	// pretty much always do at least one retry
 	start := time.Now()
 	for ; err != nil || resp.StatusCode < 200 || resp.StatusCode >= 300; resp, err = c.httpClient.Do(req) {
+		if newBody.Reader != nil {
+			newBody.Seek(0, io.SeekStart)
+		}
 		if time.Since(start) > c.retryPeriod {
 			break
 		}