I have software running on a machine that is getting intermittent 404 responses when calling a Rest API.
The IIS logs do not show the 404 being returned, however the HTTPERR log file does, so I understand this to be a problem with HTTP.SYS before it would pass the request on to IIS.
The HTTPERR log shows:
2023-07-27 09:38:49 XXX.XXX.XXX.XXX XXXXX XXX.XXX.XXX.XXX 80 - PROXY TCP4 - 400 - BadRequest -
Generating a trace file shows additional information about the problem.
Opcode: ParseRequestFailed
Reason: VersionInvalid
Message: Parsing of request (request ID 17293822575545184345) failed due to reason: VersionInvalid. Request may not be compliant with HTTP/1.1.
I'm now uncertain of how to proceed.
- I don't think attaching Fiddler to watch the client traffic is going to be helpful, there is a proxy involved and I'll see traffic coming out of the client to the proxy and not what the proxy is sending to the server. The client is used on a lot of systems without issue. Am I correct in this assumption?
- I think that I need to see the actual traffic going into the web server, but I'm not sure I want to attach something to intercept all the traffic as it's a production machine (and only a production machine) that has this issue. Is there another way to see the body of the message that is causing the problem?
- What is the HTTPERR log showing when it says "PROXY TCP4"? Is this a part of the body of the request that is coming in?