Make the ErrNothingRead to be exposed. (#827)

* Make the ErrNothingRead to be exposed.

* Update header.go

update annotation.

Co-authored-by: Erik Dubbelboer <erik@dubbelboer.com>

header.go

@@ -1351,7 +1351,7 @@ func (h *RequestHeader) tryRead(r *bufio.Reader, n int) error {
 		// n == 1 on the first read for the request.
 		if n == 1 {
 			// We didn't read a single byte.
-			return errNothingRead{err}
+			return ErrNothingRead{err}
 		}
 
 		return fmt.Errorf("error when reading request headers: %s", err)
@@ -2247,7 +2247,9 @@ var (
 	errSmallBuffer = errors.New("small read buffer. Increase ReadBufferSize")
 )
 
-type errNothingRead struct {
+// ErrNothingRead is returned when a keep-alive connection is closed,
+// either because the remote closed it or because of a read timeout.
+type ErrNothingRead struct {
 	error
 }
 

server.go

@@ -2018,7 +2018,7 @@ func (s *Server) serveConn(c net.Conn) (err error) {
 					// If reading from a keep-alive connection returns nothing it means
 					// the connection was closed (either timeout or from the other side).
 					if err != io.EOF {
-						err = errNothingRead{err}
+						err = ErrNothingRead{err}
 					}
 				}
 			}
@@ -2077,7 +2077,7 @@ func (s *Server) serveConn(c net.Conn) (err error) {
 		if err != nil {
 			if err == io.EOF {
 				err = nil
-			} else if nr, ok := err.(errNothingRead); ok {
+			} else if nr, ok := err.(ErrNothingRead); ok {
 				if connRequestNum > 1 {
 					// This is not the first request and we haven't read a single byte
 					// of a new request yet. This means it's just a keep-alive connection