reverseproxy: Accept EOF when buffering

Before this change, a read of size (let's say) < 10, into a buffer of size 10, will return EOF because we're using CopyN to limit to the size of the buffer. That resulted in the body being read from later, which should only happen if it couldn't fit in the buffer.

With this change, the body is properly NOT set when it can all fit in the buffer.

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -444,6 +444,13 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyht
 		if done {
 			break
 		}
+		if h.VerboseLogs {
+			var lbWait time.Duration
+			if h.LoadBalancing != nil {
+				lbWait = time.Duration(h.LoadBalancing.TryInterval)
+			}
+			h.logger.Debug("retrying", zap.Error(proxyErr), zap.Duration("after", lbWait))
+		}
 		retries++
 	}
 
@@ -1131,7 +1138,7 @@ func (h Handler) bufferedBody(originalBody io.ReadCloser, limit int64) (io.ReadC
 	buf.Reset()
 	if limit > 0 {
 		n, err := io.CopyN(buf, originalBody, limit)
-		if err != nil || n == limit {
+		if (err != nil && err != io.EOF) || n == limit {
 			return bodyReadCloser{
 				Reader: io.MultiReader(buf, originalBody),
 				buf:    buf,