Add appveyor support

[MoOx]

http://www.appveyor.com/
Their badge is weird (eg: https://github.com/gruntjs/grunt#readme )

[seanlinsley]

For posterity:

[espadrine]

The only API they seem to provide is about team management.

They also provide a webhook for project owners to specify. It wouldn't really be practical to use for us, since we need to store the information for them instead of requesting that data from their servers. We have no way to check that the information we have is up-to-date.

They block direct HEAD requests by returning a 405 Method Not Allowed. On the other hand, the image they produce can be directly accessed. There is no evidence of rate limiting in their HTTP headers:

HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 1749
Content-Type: image/png
Expires: -1
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Wed, 18 Jun 2014 17:28:21 GMT

So, I can see two ways to sneak in compatibility:

• Rely on the content length (as a PNG, we can be hopeful that the red badge will have a different size than the green badge). Pros: easy to implement. Cons: any change they make to the image can break it.
• Compare the bytes to those produced by the document example. Pros: probably won't break upon image change. Cons: requires to download the example badge regularly.
• Rely on the main color of the badge. Extract it from the raw data. Pros: harder for them to break. Cons: harder to implement, although there are libraries for it.

[espadrine]

I'd love to have an example of a failing badge for testing. Any pointers?

[traversaro]

Failing badge example: https://github.com/robotology/ycm

[espadrine]

@traversaro Thanks a lot!

[sebmck]

There's an API available from https://ci.appveyor.com/api/projects/gruntjs/grunt where the status of the latest build is available at "ProjectBuildResults Build Status".

[sebmck]

That's an XML API although if you pass "Accept:application/json" you get JSON API and the status is available from "project.build.status".

[espadrine]

@sebmck Good find! Plenty of thanks in your direction!

[espadrine]

@sebmck Oh, well… I read your comment a bit late…