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HTTP HEAD Requests get 405 HTTP error when access SOAP Web Services

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Most people are familiar with HTTP GET and POST requests. But actually HEAD is another useful verb.

HEAD Request and 405 Problem

Below is the response from an IIS 6 server using WFetch.

1.jpg

Note that the response only contains header information, so it is really a neat way to check site availability.

Here comes the question. Why such requests fail to query information about ASMX files on one of my IIS 6 server?

2.jpg 

Analysis Progress

For 405 status code, you may think that HEAD verb is disabled in IIS settings. But actually I have everything set up correctly. Take a look of my IIS Manager,

3.jpg

As I don’t have any third party ISAPI filter or other IIS extension installed, it is really hard to understand the reason, isn’t it?

Some people will suggest I test on IIS 7. Actually the result is the same. Even failed request tracing does not provide much information. The status code seems to be returned from within .NET Framework. So there must be a reason.

The Answer

Well, finally I decided to go back to ABC and started to digest the SOAP protocol itself, and BLAH, the answer is there!

 

Problem with Message

HTTP Status Code

HTTP Reason Phrase (informative)

Malformed Request Message

400

Bad request

HTTP Method is neither POST nor GET

405

Method Not Allowed

Unsupported message encapsulation method

415

Unsupported Media

 

Because any SOAP implementation honors the protocol itself and conforms to its requirements, ASP.NET web service as an SOAP implementation for .NET platform also follows the rules and returns 405 for HEAD requests.

Regards,

Lex Li