// need again. (On the other hand it does make repeated go test slower.)
	// It also makes repeated go run slower, which is a win in itself:
	// we don't want people to treat go run like a scripting environment.
	if err := b.updateBuildID(a, a.Target, !a.Package.Internal.OmitDebug); err != nil {
		return err
	}

	a.built = a.Target
	return nil
}

				//      respond with 501 (Unimplemented).
				code := StatusNotImplemented

				// We purposefully aren't echoing back the transfer-encoding's value,
				// so as to mitigate the risk of cross side scripting by an attacker.
				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
				return

			case isCommonNetReadError(err):
				return // don't reply