Maybe me maybe not -


I have upgraded to 4.0.56 from 4.0.54 and just noticed that DTO Validation errors (400 - Bad Requests) are coming back from SS with a content-type of text/html rather than application/json even though the Accept request header is correct.

I have made a bunch of changes alongside the upgrade, but having looked through them I can’t see anything that would cause this behaviour. I have also tried setting HostConfig.DefaultContentType = MimeTypes.Json but no effect.

I have been changing some header-based code (e.g. removing X-Powered-By etc) but can’t see anything that should/would cause this behaviour. Any ideas on why this could be happening or how to troubleshoot? I can’t debugInfo as all are POSTS.


The description alone without a repro won’t be enough to identify the issue, can you post the raw HTTP Request and Response Headers? You can get them with Fiddler, Chrome WebInspector or WireShark, etc.

Ok - found the problem here in case anyone else sees it:

I was setting the X-Powered-By header to something custom within the HostConfig intialiser, rather than:

Instance.Config.GlobalResponseHeaders["X-Powered-By"] = "Me";

This was causing “Key already present” exception and this then the symptoms I was seeing. G

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After further investigation, previous diagnosis was wrong - hopefully this will avoid someone else wasting time on this.

This is caused by the parent application in IIS having an system.webServer/httpErrors element with a existingResponse=“Replace” attribute in web.config. Even if the httpError element doesn’t contain any child elements relating to the affected HTTP status code (I only want a custom 404), helpfully adjusts all HTTP responses content type to text/html.

Resolution is to set existingResponse=“Auto”

Well that’s a day of my life gone.

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