request: in the event of failure, try other IPs (#6761) (#6813)

* request: in the event of failure, try other IPs (#6761)

In the case where a name has multiple A/AAAA records, we should
try subsequent records instead of immediately failing when we have a
failure on the first IP address.

This significantly improves delivery success when there are network
connectivity problems affecting only IPv4 or IPv6.

* fix method call style

* request_spec: adjust test case to use Addrinfo

* request: Request/open: move private addr check to within begin/rescue

* request_spec: add case to test failover, fix exception check

* Double Addrinfo.foreach so that it correctly yields instances

app/lib/request.rb

@@ -94,9 +94,16 @@ class Request
   class Socket < TCPSocket
     class << self
       def open(host, *args)
-        address = IPSocket.getaddress(host)
-        raise Mastodon::HostValidationError if PrivateAddressCheck.private_address? IPAddr.new(address)
-        super address, *args
+        outer_e = nil
+        Addrinfo.foreach(host, nil, nil, :SOCK_STREAM) do |address|
+          begin
+            raise Mastodon::HostValidationError if PrivateAddressCheck.private_address? IPAddr.new(address.ip_address)
+            return super address.ip_address, *args
+          rescue => e
+            outer_e = e
+          end
+        end
+        raise outer_e if outer_e
       end
 
       alias new open