ASP.NET 4 introduces new options for expanding the size of application URLs. Previous versions of ASP.NET constrained URL path lengths to 260 characters, based on the NTFS file-path limit. In ASP.NET 4, you have the option to increase (or decrease) this limit as appropriate for your applications, using two new httpRuntime configuration attributes. The following example shows these new attributes.
<httpRuntime maxRequestPathLength="260" maxQueryStringLength="2048" />
To allow longer or shorter paths (the portion of the URL that does not include protocol, server name, and query string), modify the maxRequestPathLength attribute. To allow longer or shorter query strings, modify the value of the maxQueryStringLength attribute.
ASP.NET 4 also enables you to configure the characters that are used by the URL character check. When ASP.NET finds an invalid character in the path portion of a URL, it rejects the request and issues an HTTP 400 error. In previous versions of ASP.NET, the URL character checks were limited to a fixed set of characters. In ASP.NET 4, you can customize the set of valid characters using the new requestPathInvalidChars attribute of the httpRuntime configuration element, as shown in the following example:
<httpRuntime requestPathInvalidChars="<,>,*,%,&,:,\,?" />
By default, the requestPathInvalidChars attribute defines eight characters as invalid. (In the string that is assigned to requestPathInvalidChars by default, the less than (<), greater than (>), and ampersand (&) characters are encoded, because the Web.config file is an XML file.) You can customize the set of invalid characters as needed.
