AbstractMockHttpServletRequestBuilder#buildRequest is not idempotent

[reda-alaoui]

I have testing components making use of MockHttpServletRequestBuilder. These components should be able to mutate the builder but also to check the builder state (e.g. "what is the http method currently stored by the builder?").

By design, the only way to access MockHttpServletRequestBuilder state is to invoke buildRequest to retrieve a MockHttpServletRequest that will allow to check the state via its getters.
I am fine with that.

But I discovered that invoking buildRequest mutates the value of MockHttpServletRequestBuilder#pathInfo:

spring-framework/spring-test/src/main/java/org/springframework/test/web/servlet/request/AbstractMockHttpServletRequestBuilder.java

Lines 901 to 909 in 88812ed

	if ("".equals(this.pathInfo)) {
	if (!requestUri.startsWith(this.contextPath + this.servletPath)) {
	throw new IllegalArgumentException(
	"Invalid servlet path [" + this.servletPath + "] for request URI [" + requestUri + "]");
	}
	String extraPath = requestUri.substring(this.contextPath.length() + this.servletPath.length());
	this.pathInfo = (StringUtils.hasText(extraPath) ?
	UrlPathHelper.defaultInstance.decodeRequestString(request, extraPath) : null);
	}

This mutation can break the builder once you try to pass it to MockMvc#perform.
An example of scenario:

1. Make sure MockMvc has a non null defaultRequestBuilder that will be merged in the consumer's provided MockHttpServletRequestBuilder
2. Create MockHttpServletRequestBuilder instance foo
3. Invoke MockHttpServletRequestBuilder#buildRequest on foo (with the injectable ServletContext)
4. Now invoke MockMvc#perform with foo as argument
5. You may end up with a 404 not found

TLDR: calling buildRequest twice on the MockHttpServletRequestBuilder is not safe. This pull request fixes this.