Cache manifest validator Proxy Error on manifest-validator.com - html

Question

I am trying to use http://manifest-validator.com/ to check my cache manifest file by URI. It has been failing with the message:
Proxy Error
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /validate.
Reason: Error reading from remote server
I have tried removing my robots.txt file in case Disallow: / was causing problems.
Has anyone else experienced this Proxy Error?
Is this something that I can fix or is it an error with manifest-validator.com ?

Answer 1

In short
The reason for your error in this validator is a missing content-type attribute in your http response headers. Add one like text/cache-manifest and it will work.
Explaining the details
First of all, here are the response headers sent by your server. Note the missing content-type:
robert#robert-ubuntu:~$ curl -I -X HEAD http://nucreativetesting.co.uk/cache-test/test003/manifest.appcache
HTTP/1.1 200 OK
Date: Tue, 07 Oct 2014 16:25:59 GMT
Server: Apache/2.4.9 (Unix)
Last-Modified: Mon, 11 Aug 2014 13:45:07 GMT
ETag: "46c-5005ac34a2331"
Accept-Ranges: bytes
Content-Length: 1132
Why the proxy error?
The validator you are using is a NodeJS project, proxied by an apache webserver. The reason you get an error is that the apache waits for NodeJS to generate a response but it's hanging. After some time it gets a timeout and returns your error.
So why is it hanging?
In the current implementation of this validator you find the following code [1]:
try {
contentType = res.headers['content-type'].split(';')[0];
if ( ['text/plain', 'text/cache-manifest'].indexOf( contentType ) === -1 ) {
callback('ERR_MANIFEST_MIMETYPE');
return;
}
} catch(e) {
// TODO: Debug statement in production, had some strange output in the error logs.
// Should be removed again
console.error('manifest.js: Content-Type');
return;
}
We see that res.headers['content-type'] should get split, but if there's no content type in your request header, this will raise an Exception because res.headers['content-type'] is undefined. The Exception itself is just logged to the servers output but isn't handled with their callback() function. Thats the reason the request is hanging till timeout.
Conclusion
It might be a bug or bad error handling on their side or just very unusual to not have a content type in your header. I don't know. But it should work with a content type ;).
References
[1]: https://github.com/fhemberger/manifest-validator/blob/6d82bc4660c4daaa131fee3c19a88ae6e462a44b/app/lib/manifest.js#L63 code producing your error