cURL cannot connect to localhost but browser can

Question

I'm running a Rails app locally (Thin server), and I can connect locally from the browser (localhost:3000), but when I try to use curl, I get:

curl -H 'id:1' -i 'http://localhost:3000/api/data' -v  * Hostname was NOT found in DNS cache *   Trying ::1... * Adding handle: conn: 0x7fd121808200 * Adding handle: send: 0 * Adding handle: recv: 0 * Curl_addHandleToPipeline: length: 1 * - Conn 0 (0x7fd121808200) send_pipe: 1, recv_pipe: 0 * Connection failed * connect to ::1 port 3000 failed: Connection refused *   Trying fe80::1... * Connection failed * connect to fe80::1 port 3000 failed: Connection refused * Failed to connect to localhost port 3000: Connection refused * Closing connection 0 curl: (7) Failed to connect to localhost port 3000: Connection refused 

This used to work just fine, but I recently updated to Mavericks, which I suspect may have broken something. I can also curl successfully from the web.

Answer 1

This is a curl bug (a strange one), where curl fails to fall back to IPv4 if there's an IPv6 entry in /etc/hosts that doesn't respond.

You can force it to use IPv4 via the -4 option.

Answer 2

Instead of

curl localhost:3000 

try

curl 0.0.0.0:3000 

It works.
If it doesn't, check the output when you start your rails server:

=> Booting WEBrick => Rails 3.2.13 application starting in development on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server [2014-10-28 15:30:08] INFO  WEBrick 1.3.1 [2014-10-28 15:30:08] INFO  ruby 2.0.0 (2014-02-24) [x86_64-darwin12.5.0] [2014-10-28 15:30:08] INFO  WEBrick::HTTPServer#start: pid=4004 port=3000 

Use the url at the end of line 2 instead of ENV['HOST']