auto discovery: support relative URLs

[derhuerst]

As of 3.0-RC, the GBFS spec merely defines the url field as "URL for the feed […]". It does not limit the field to absolute URLs, so my interpretation is that relative URLs (e.g. system_information.json, ./system_information.json or ../foo/system_information.json) should be valid.

I have also asked in the GBFS repo to clarify this: MobilityData/gbfs#189 (comment)

{
  "data": {
    "en": {
      "feeds": [
        {
          "name": "system_information",
          "url": "./system_information.json"
        },
        // …
      ]
    }
  },
  // …
}

---

With the example above, Lamassu currently seems to fail fetching the feed with the following log message:

{
	"serviceContext": {
		"service": "lamassu"
	},
	"message": "Failed to setup subscription, trying again in 5 seconds - systemId=deer\n",
	"reportLocation": {
		"filePath": "org.entur.lamassu.leader.FeedUpdater",
		"lineNumber": "130",
		"functionName": "createSubscription"
	},
	"severity": "WARNING"
}

[testower]

Thanks - I'll await the clarification on the spec. I have never expected it to work the way you suggest.

[futuretap]

We’ve interpreted the spec to require absolute URLs and don’t support relative URLs in our consumer code. We’re also not aware of any producer publishing relative URLs.

[testower]

It seems unlikely that this will be added in the spec, but in the event that it does, this issue may be reopened.