Parsing Exceptions

HTTP Server API provides registry keys to support parsing exceptions to the HTTP/1.1 specification for backward compatibility. These exceptions are not enabled by default and should be enabled only on a case-by-case basis, when the server experiences compatibility issues with HTTP clients. These values are created under the following registry location:


The following table lists registry keys provided to support the exceptions listed. To enable an exception set the corresponding key value to 1 and restart the HTTP service.

Key nameDescription
AllowWeakHeaderNameSyntax (DWORD)Allows the HTTP parser to accept header names with separator characters such as '?'.
AllowWeakHeaderValueSyntax (DWORD)Allows the HTTP parser to accept header values with raw (unescaped) control characters in it.
AllowCaseInsensitiveVerbs (DWORD)Allows the HTTP parser to accept lowercase HTTP methods/verbs such as "get".
AllowUnEscapedRestrictedChars (DWORD)Allows the HTTP parser to accept control characters in abspath and query strings of the URL. In case of an absolute URL, control characters will not be allowed in the hostname. All flavors of URLs, namely UTF8, DBCS and ANSI, will allow control characters. All ASCII control characters except NUL (0x00), LF (0x0a), CR (0x0d) and Horizontal Tab(0x09) will be allowed.