Code error: The server committed a protocol breach. Section=Responsestatusline

Question

When I run this line of code to access a URL I get the message. The server committed a protocol violation. Section=Responsestatusline. Does anyone have any idea what it might be?

using (WebClient wc = new WebClient()) { var result = wc.DownloadString("http://192.168.0.100/H"); }

Answer 1

This error occurs because the server is delivering a poorly formed HTTP header.

In the HTTP documentation 1.1 section 6.1 is written:

6.1 Status line

The first line of a reply message is the status line, which consists of the version of the protocol followed by a numeric status code and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed, except in the final sequence of the CRLF.

https://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html

Some servers deliver headers whose lines end or with CR or LF which ends up generating this validation error.

To get around this problem you will have to configure your requests to ignore the validation of HTTP headers.

To do this you must edit your file .config. Remembering that it is web.config if the application is a server and app.config if the application is desktop.

<system.net>
    <settings>
        <httpWebRequest useUnsafeHeaderParsing="true" />
    </settings>
</system.net>

The estate HttpWebRequestElement.UseUnsafeHeaderParsing determines whether or not to ignore validation errors that occur during HTTP parsing.

While it is defined as false the following validations will be executed during http analysis:

• In end-of-line code, use CRLF; it is not allowed to use CR or LF alone.

• Header names should not have spaces.

• If there are multiple status lines, all additional status lines will be treated as malformed name/value pairs.

• The status line must have a status description in addition to a status code.

This setting does not affect error issuance if header names containing non-ASCII characters in them.