public HttpPreClient decorate(HttpPreClient execution) {
        for (HttpPreprocessor preprocessor : preprocessors) {
            final HttpPreClient execution0 = execution;
            execution = (ctx, req) -> preprocessor.execute(execution0, ctx, req);
        }
        return execution;
    }
Decorates the specified {@link HttpPreClient} using preprocessors.

@param execution the {@link HttpPreClient} being decorated
core/src/main/java/com/linecorp/armeria/client/ClientPreprocessors.java