Fix support for HTTP proxies (mastodon#11245)

* Disable incorrect check for hidden services in Socket

Hidden services can only be accessed with an HTTP proxy, in which
case the host seen by the Socket class will be the proxy, not the
target host.

Hidden services are already filtered in `Request#initialize`.

* Use our Socket class to connect to HTTP proxies

Avoid the timeout logic being bypassed

* Add support for IP addresses in Request::Socket

* Refactor a bit, no need to keep the DNS resolver around

app/lib/request.rb

@@ -30,7 +30,8 @@ def initialize(verb, url, **options)
     @verb        = verb
     @url         = Addressable::URI.parse(url).normalize
     @http_client = options.delete(:http_client)
-    @options     = options.merge(use_proxy? ? Rails.configuration.x.http_client_proxy : { socket_class: Socket })
+    @options     = options.merge(socket_class: use_proxy? ? ProxySocket : Socket)
+    @options     = @options.merge(Rails.configuration.x.http_client_proxy) if use_proxy?
     @headers     = {}
 
     raise Mastodon::HostValidationError, 'Instance does not support hidden service connections' if block_hidden_service?
@@ -177,47 +178,49 @@ def body_with_limit(limit = 1.megabyte)
   class Socket < TCPSocket
     class << self
       def open(host, *args)
-        return super(host, *args) if thru_hidden_service?(host)
-
         outer_e = nil
         port    = args.first
 
-        Resolv::DNS.open do |dns|
-          dns.timeouts = 5
+        addresses = []
+        begin
+          addresses = [IPAddr.new(host)]
+        rescue IPAddr::InvalidAddressError
+          Resolv::DNS.open do |dns|
+            dns.timeouts = 5
+            addresses = dns.getaddresses(host).take(2)
+          end
+        end
 
-          addresses = dns.getaddresses(host).take(2)
+        addresses.each do |address|
+          begin
+            check_private_address(address)
+
+            sock     = ::Socket.new(address.is_a?(Resolv::IPv6) ? ::Socket::AF_INET6 : ::Socket::AF_INET, ::Socket::SOCK_STREAM, 0)
+            sockaddr = ::Socket.pack_sockaddr_in(port, address.to_s)
+
+            sock.setsockopt(::Socket::IPPROTO_TCP, ::Socket::TCP_NODELAY, 1)
 
-          addresses.each do |address|
             begin
-              raise Mastodon::HostValidationError if PrivateAddressCheck.private_address?(IPAddr.new(address.to_s))
-
-              sock     = ::Socket.new(address.is_a?(Resolv::IPv6) ? ::Socket::AF_INET6 : ::Socket::AF_INET, ::Socket::SOCK_STREAM, 0)
-              sockaddr = ::Socket.pack_sockaddr_in(port, address.to_s)
-
-              sock.setsockopt(::Socket::IPPROTO_TCP, ::Socket::TCP_NODELAY, 1)
-
-              begin
-                sock.connect_nonblock(sockaddr)
-              rescue IO::WaitWritable
-                if IO.select(nil, [sock], nil, Request::TIMEOUT[:connect])
-                  begin
-                    sock.connect_nonblock(sockaddr)
-                  rescue Errno::EISCONN
-                    # Yippee!
-                  rescue
-                    sock.close
-                    raise
-                  end
-                else
+              sock.connect_nonblock(sockaddr)
+            rescue IO::WaitWritable
+              if IO.select(nil, [sock], nil, Request::TIMEOUT[:connect])
+                begin
+                  sock.connect_nonblock(sockaddr)
+                rescue Errno::EISCONN
+                  # Yippee!
+                rescue
                   sock.close
-                  raise HTTP::TimeoutError, "Connect timed out after #{Request::TIMEOUT[:connect]} seconds"
+                  raise
                 end
+              else
+                sock.close
+                raise HTTP::TimeoutError, "Connect timed out after #{Request::TIMEOUT[:connect]} seconds"
               end
-
-              return sock
-            rescue => e
-              outer_e = e
             end
+
+            return sock
+          rescue => e
+            outer_e = e
           end
         end
 
@@ -230,11 +233,21 @@ def open(host, *args)
 
       alias new open
 
-      def thru_hidden_service?(host)
-        Rails.configuration.x.access_to_hidden_service && /\.(onion|i2p)$/.match(host)
+      def check_private_address(address)
+        raise Mastodon::HostValidationError if PrivateAddressCheck.private_address?(IPAddr.new(address.to_s))
+      end
+    end
+  end
+
+  class ProxySocket < Socket
+    class << self
+      def check_private_address(_address)
+        # Accept connections to private addresses as HTTP proxies will usually
+        # be on local addresses
+        nil
       end
     end
   end
 
-  private_constant :ClientLimit, :Socket
+  private_constant :ClientLimit, :Socket, :ProxySocket
 end