Fix: Subscriptions with empty subscribed_fields results in 500

[lluft]

Facebooks Api can't handle an empty array in the query params resulting in a 500:

19:53:50 web.1  | <- "POST /v3.2/me/subscribed_apps?access_token=XXX&subscribed_fields[]= HTTP/1.1\r\nAccept-Encoding: gzip;q=1.0,deflate;q=0.6,identity;q=0.3\r\nAccept: */*\r\nUser-Agent: Ruby\r\nConnection: close\r\nHost: grap
h.facebook.com\r\nContent-Length: 0\r\nContent-Type: application/x-www-form-urlencoded\r\n\r\n"
19:53:50 web.1  | <- ""
19:53:50 web.1  | -> "HTTP/1.1 500 Internal Server Error\r\n"
19:53:50 web.1  | -> "x-page-usage: {\"call_count\":2,\"total_cputime\":1,\"total_time\":1}\r\n"
19:53:50 web.1  | -> "x-app-usage: {\"call_count\":0,\"total_cputime\":0,\"total_time\":0}\r\n"
19:53:50 web.1  | -> "WWW-Authenticate: OAuth \"Facebook Platform\" \"unknown_error\" \"An unknown error has occurred.\"\r\n"
19:53:50 web.1  | -> "Content-Type: application/json; charset=UTF-8\r\n"
19:53:50 web.1  | -> "facebook-api-version: v3.2\r\n"
19:53:50 web.1  | -> "Strict-Transport-Security: max-age=15552000; preload\r\n"
19:53:50 web.1  | -> "Pragma: no-cache\r\n"
19:53:50 web.1  | -> "x-fb-rev: 1000627010\r\n"
19:53:50 web.1  | -> "Access-Control-Allow-Origin: *\r\n"
19:53:50 web.1  | -> "Cache-Control: no-store\r\n"
19:53:50 web.1  | -> "x-fb-trace-id: XXX\r\n"
19:53:50 web.1  | -> "x-fb-request-id: XXX\r\n"
19:53:50 web.1  | -> "Expires: Sat, 01 Jan 2000 00:00:00 GMT\r\n"
19:53:50 web.1  | -> "X-FB-Debug: XXX==\r\n"
19:53:50 web.1  | -> "Date: Sat, 20 Apr 2019 17:53:50 GMT\r\n"
19:53:50 web.1  | -> "Connection: close\r\n"
19:53:50 web.1  | -> "Content-Length: 114\r\n"
19:53:50 web.1  | -> "\r\n"
19:53:50 web.1  | reading 114 bytes...
19:53:50 web.1  | -> "{\"error\":{\"message\":\"An unknown error has occurred.\",\"type\":\"OAuthException\",\"code\":1,\"fbtrace_id\":\"XXX\"}}"
19:53:50 web.1  | read 114 bytes
19:53:50 web.1  | Conn close

Changing to sending the payload in the body fixes this and returns the correct error message:

20:01:56 web.1  | -> "HTTP/1.1 400 Bad Request\r\n"
20:01:56 web.1  | -> "x-page-usage: {\"call_count\":2,\"total_cputime\":1,\"total_time\":1}\r\n"
20:01:56 web.1  | -> "x-app-usage: {\"call_count\":0,\"total_cputime\":0,\"total_time\":0}\r\n"
20:01:56 web.1  | -> "WWW-Authenticate: OAuth \"Facebook Platform\" \"invalid_request\" \"(#100) The parameter subscribed_fields is required.\"\r\n"
20:01:56 web.1  | -> "Content-Type: text/javascript; charset=UTF-8\r\n"
20:01:56 web.1  | -> "facebook-api-version: v3.2\r\n"
20:01:56 web.1  | -> "Strict-Transport-Security: max-age=15552000; preload\r\n"
20:01:56 web.1  | -> "Pragma: no-cache\r\n"
20:01:56 web.1  | -> "x-fb-rev: 1000627010\r\n"
20:01:56 web.1  | -> "Access-Control-Allow-Origin: *\r\n"
20:01:56 web.1  | -> "Cache-Control: no-store\r\n"
20:01:56 web.1  | -> "x-fb-trace-id: XXX\r\n"
20:01:56 web.1  | -> "x-fb-request-id: XXX\r\n"
20:01:56 web.1  | -> "Expires: Sat, 01 Jan 2000 00:00:00 GMT\r\n"
20:01:56 web.1  | -> "X-FB-Debug:XXX==\r\n"
20:01:56 web.1  | -> "Date: Sat, 20 Apr 2019 18:01:56 GMT\r\n"
20:01:56 web.1  | -> "Connection: close\r\n"
20:01:56 web.1  | -> "Content-Length: 137\r\n"
20:01:56 web.1  | -> "\r\n"
20:01:56 web.1  | reading 137 bytes...
20:01:56 web.1  | -> "{\"error\":{\"message\":\"(#100) The parameter subscribed_fields is required.\",\"type\":\"OAuthException\",\"code\":100,\"fbtrace_id\":\"XXX\"}}"
20:01:56 web.1  | read 137 bytes
20:01:56 web.1  | Conn close

[jgorset]

Thanks @lluft! I have just two questions about Facebook's behaviour for the tests, but otherwise this looks good to merge.

[lluft]

@jgorset addressed your comments. Should be ready to merge, right?

[jgorset]

Thanks @lluft! This is a good change, and I've merged it.

I double checked against Facebook's API just to make sure that our testing stubs reflect what the API actually returns, and it looks like Facebook actually returns HTTP 200 either way, so I updated them accordingly.