Follow the `Location`

[sadovnik]

Here is what if found recently in Heroku logs:

2017-05-04T10:50:29.341525+00:00 app[web.1]: I, [2017-05-04T10:50:29.341441 #4]  INFO -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951] Started POST "/subscriptions" for 77.236.239.35 at 2017-05-04 10:50:29 +0000
2017-05-04T10:50:29.342347+00:00 app[web.1]: I, [2017-05-04T10:50:29.342291 #4]  INFO -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951] Processing by SubscriptionsController#create as JS
2017-05-04T10:50:29.342451+00:00 app[web.1]: I, [2017-05-04T10:50:29.342384 #4]  INFO -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   Parameters: {"utf8"=>"✓", "subscription_form"=>{"url"=>"http://blog.byndyu.ru"}, "commit"=>"Subscribe"}
2017-05-04T10:50:29.348380+00:00 app[web.1]: D, [2017-05-04T10:50:29.348302 #4] DEBUG -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   �[1m�[36mUser Load (2.6ms)�[0m  �[1m�[34mSELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2�[0m  [["id", 1], ["LIMIT", 1]]
2017-05-04T10:50:29.739074+00:00 heroku[router]: at=info method=POST path="/subscriptions" host=reader-app.herokuapp.com request_id=5535e134-3a8d-4aab-a74a-f7d4ce900951 fwd="77.236.239.35" dyno=web.1 connect=3ms service=407ms status=500 bytes=1669 protocol=https
2017-05-04T10:50:29.703327+00:00 app[web.1]: D, [2017-05-04T10:50:29.703218 #4] DEBUG -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   �[1m�[36mSource Load (2.6ms)�[0m  �[1m�[34mSELECT  "sources".* FROM "sources" WHERE (url = 'http://blog.byndyu.ru' OR site_url = 'http://blog.byndyu.ru') ORDER BY "sources"."id" ASC LIMIT $1�[0m  [["LIMIT", 1]]
2017-05-04T10:50:29.706263+00:00 app[web.1]: D, [2017-05-04T10:50:29.706186 #4] DEBUG -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   �[1m�[36mSource Load (2.4ms)�[0m  �[1m�[34mSELECT  "sources".* FROM "sources" WHERE "sources"."url" = $1 LIMIT $2�[0m  [["url", "http://blog.byndyu.ru"], ["LIMIT", 1]]
2017-05-04T10:50:29.733477+00:00 app[web.1]: I, [2017-05-04T10:50:29.733374 #4]  INFO -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951] Completed 500 Internal Server Error in 391ms (ActiveRecord: 7.5ms)
2017-05-04T10:50:29.734210+00:00 app[web.1]: F, [2017-05-04T10:50:29.734145 #4] FATAL -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   
2017-05-04T10:50:29.734277+00:00 app[web.1]: F, [2017-05-04T10:50:29.734217 #4] FATAL -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951] Feedjira::NoParserAvailable (No valid parser for XML.):
2017-05-04T10:50:29.734332+00:00 app[web.1]: F, [2017-05-04T10:50:29.734279 #4] FATAL -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951]   
2017-05-04T10:50:29.734422+00:00 app[web.1]: F, [2017-05-04T10:50:29.734346 #4] FATAL -- : [5535e134-3a8d-4aab-a74a-f7d4ce900951] app/services/feed_fetcher.rb:26:in `fetch'
2017-05-04T10:50:29.734423+00:00 app[web.1]: [5535e134-3a8d-4aab-a74a-f7d4ce900951] app/services/source_fetcher.rb:12:in `fetch'
2017-05-04T10:50:29.734423+00:00 app[web.1]: [5535e134-3a8d-4aab-a74a-f7d4ce900951] app/controllers/subscriptions_controller.rb:31:in `create'

The source that results in such failure is http://blog.byndyu.ru. I inspected it and found out that the feed endpoint found on the page responds with 302:

[I] cyril@macbook ~/p/reader> http http://blog.byndyu.ru/feeds/posts/default
HTTP/1.1 302 Found
Cache-Control: public, must-revalidate, proxy-revalidate, max-age=1
Content-Length: 0
Content-Type: text/html; charset=UTF-8
Date: Thu, 04 May 2017 11:01:22 GMT
ETag: W/"f8505c0c-c0df-4ff3-968c-b3a38fdd6d66"
Expires: Thu, 04 May 2017 11:01:23 GMT
Location: http://feeds.feedburner.com/byndyu
Server: blogger-renderd
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block

Such case wouldn't happen if the http client will follow the Location.