Method: Socket.tcp_fast_fallback=

Defined in:

socket.c

.tcp_fast_fallback= ⇒ Boolean

Enable or disable Happy Eyeballs Version 2 (RFC 8305) globally, which is provided starting from Ruby 3.4 when using TCPSocket.new and Socket.tcp.

When set to true, the feature is enabled for both ‘TCPSocket.new` and `Socket.tcp`. (Note: This feature is not available when using TCPSocket.new on Windows.)

When set to false, the behavior reverts to that of Ruby 3.3 or earlier.

The default value is true if no value is explicitly set by calling this method. However, when the environment variable RUBY_TCP_NO_FAST_FALLBACK=1 is set, the default is false.

To control the setting on a per-method basis, use the fast_fallback keyword argument for each method.

Happy Eyeballs Version 2

Happy Eyeballs Version 2 (RFC 8305) is an algorithm designed to improve client socket connectivity.
It aims for more reliable and efficient connections by performing hostname resolution and connection attempts in parallel, instead of serially.

Starting from Ruby 3.4, this method operates as follows with this algorithm:

1. Start resolving both IPv6 and IPv4 addresses concurrently.

2. Start connecting to the one of the addresses that are obtained first.
   If IPv4 addresses are obtained first, the method waits 50 ms for IPv6 name resolution to prioritize IPv6 connections.

3. After starting a connection attempt, wait 250 ms for the connection to be established.
   If no connection is established within this time, a new connection is started every 250 ms
   until a connection is established or there are no more candidate addresses.
   (Although RFC 8305 strictly specifies sorting addresses,
   this method only alternates between IPv6 / IPv4 addresses due to the performance concerns)

4. Once a connection is established, all remaining connection attempts are canceled.

Returns:

• (Boolean)

# File 'socket.c', line 1915

VALUE socket_s_tcp_fast_fallback_set(VALUE self, VALUE value) {
    rb_ivar_set(rb_cSocket, tcp_fast_fallback, value);
    return value;
}