Perfect 404 response filter

filter.swift

struct Filter404: HTTPResponseFilter {
	func filterBody(response: HTTPResponse, callback: (HTTPResponseFilterResult) -> ()) {
		callback(.continue)
	}
	
	func filterHeaders(response: HTTPResponse, callback: (HTTPResponseFilterResult) -> ()) {
		if case .notFound = response.status {
			response.bodyBytes.removeAll()
			response.appendBody(string: "The file \(response.request.path) was not found.")
			response.setHeader(.contentLength, value: "\(response.bodyBytes.count)")
			callback(.done)
		} else {
			callback(.continue)
		}
	}
}