<httpListener> Element (Network Settings)

Article
02/04/2013

Customizes parameters used by the HttpListener class.

<configuration> Element
  <system.net> Element (Network Settings)
    <settings> Element (Network Settings)
      <httpListener> Element (Network Settings)

<httpListener
  unescapeRequestUrl ="true|false"
/>

Attributes and Elements

The following sections describe attributes, child elements, and parent elements.

Attributes

Attribute	Description
unescapeRequestUrl	A Boolean value that indicates if a HttpListener instance uses the raw unescaped URI instead of the converted URI.

Child Elements

None.

Parent Elements

Element	Description
<settings>	Configures basic network options for the System.Net namespace.

Remarks

The unescapeRequestUrl attribute indicates if HttpListener uses the raw unescaped URI instead of the converted URI where any percent-encoded values are converted and other normalization steps are taken.

When a HttpListener instance receives a request through the http.sys service, it creates an instance of the URI string provided by http.sys, and exposes it as the HttpListenerRequest.Url property.

The http.sys service exposes two request URI strings:

Raw URI
Converted URI

The raw URI is the System.Uri provided in the request line of a HTTP request:

GET /path/

Host: www.contoso.com

The raw URI provided by http.sys for the request mentioned above, is "/path/". This represents the string following the HTTP verb as it was sent over the network.

The http.sys service creates a converted URI from the information provided in the request by using the URI provided in the HTTP request line and the Host header to determine the origin server the request should be forwarded to. This is done by comparing the information from the request with a set of registered URI prefixes. The HTTP Server SDK documentation refers to this converted URI as the HTTP_COOKED_URL structure.

In order to be able to compare the request with registered URI prefixes, some normalization to the request needs to be done. For the sample above the converted URI would be as follows:

https://www.contoso.com/path/

The http.sys service combines the Uri.Host property value and the string in the request line to create a converted URI. In addition, http.sys and the System.Uri class also does the following:

Un-escapes all percent encoded values.
Converts percent-encoded non-ASCII characters into a UTF-16 character representation. Note that UTF-8 and ANSI/DBCS characters are supported as well as Unicode characters (Unicode encoding using the %uXXXX format).
Executes other normalization steps, like path compression.

Since the request doesn't contain any information about the encoding used for percent-encoded values, it may not be possible to determine the correct encoding just by parsing the percent-encoded values.

Therefore http.sys provides two registry keys for modifying the process:

Registry Key	Default Value	Description
EnableNonUTF8	1	If zero, http.sys accepts only UTF-8-encoded URLs. If non-zero, http.sys also accepts ANSI-encoded or DBCS-encoded URLs in requests.
FavorUTF8	1	If non-zero, http.sys always tries to decode a URL as UTF-8 first; if that conversion fails and EnableNonUTF8 is non-zero, Http.sys then tries to decode it as ANSI or DBCS. If zero (and EnableNonUTF8 is non-zero), http.sys tries to decode it as ANSI or DBCS; if that is not successful, it tries a UTF-8 conversion.

EnableNonUTF8

If zero, http.sys accepts only UTF-8-encoded URLs.

If non-zero, http.sys also accepts ANSI-encoded or DBCS-encoded URLs in requests.

FavorUTF8

If non-zero, http.sys always tries to decode a URL as UTF-8 first; if that conversion fails and EnableNonUTF8 is non-zero, Http.sys then tries to decode it as ANSI or DBCS.

If zero (and EnableNonUTF8 is non-zero), http.sys tries to decode it as ANSI or DBCS; if that is not successful, it tries a UTF-8 conversion.

When HttpListener receives a request, it uses the converted URI from http.sys as input to the Url property.

There is a need for supporting characters besides characters and numbers in URIs. An example is the following URI, which is used to retrieve customer information for customer number "1/3812":

https://www.contoso.com/Customer('1%2F3812')/

Note the percent-encoded slash in the Uri (%2F). This is necessary, since in this case the slash character represents data and not a path delimiter.

Passing the string to Uri constructor will lead to the following URI:

https://www.contoso.com/Customer('1/3812')/

Splitting the path into its segments would result in the following elements:

Customer('1

3812')

This is not the intent of the sender of the request.

If the unescapeRequestUrl attribute is set to false, then when the HttpListener receives a request, it uses the raw URI instead of the converted URI from http.sys as input to the Url property.

The default value for the unescapeRequestUrl attribute is true.

The UnescapeRequestUrl property can be used to get the current value of the unescapeRequestUrl attribute from applicable configuration files.

Example

The following code example shows how to configure the HttpListener class when it receives a request to use the raw URI instead of the converted URI from http.sys as input to the Url property.

<configuration>
  <system.net>
    <settings>
      <httpListener
        unescapeRequestUrl="false"
      />
    </settings>
  </system.net>
</configuration>

Element Information

Namespace	System.Net
Schema Name
Validation File
Can be Empty

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