purge: fail to purge with query string

[Integralist]

A customer discovered purging URLs, that contained a query param, would fail to purge.

In the following example, the first URL would purge while the other two would not purge.

purgeURLs := []string{
  "https://example.com/john", 
  "https://example.com/john?payment=success", 
  "https://example.com/john?payment=cancelled",
}

for _, url := range purgeURLs {
  clearCache(url)
}

func (cp *cachePurger) clearCache(purgeURL string) {
  cp.client.Purge(&fastly.PurgeInput{URL: purgeURL})
}

Following a quick review of the API client code I discovered that the .Post() method internally calls .Request(), and that internally calls .RawRequest(). It's in that last method we see this:

go-fastly/fastly/request.go

Lines 44 to 48 in f56c86d

	var params = make(url.Values)
	for k, v := range ro.Params {
	params.Add(k, v)
	}
	request.URL.RawQuery = params.Encode()

Because the top-level Purge() method isn't setting ro.Params (which are passed all the way through to RawRequest()), it means the inner most method will replace any query string values with params.Encode(), which is going to be an empty string as there is no ro.Param content to iterate over and subsequently we never call params.Add to populate the params type, and thus params.Encode() returns an empty string.

The fix is to ensure thePurge() method parses the given URL and extracts its query string (if any) and assigns it to ro.Params so it's passed down to RawRequest() so the internal method can re-apply it as necessary.