private fun decodeIpv6(input: String): ByteArray? = decodeIpv6(input, 0, input.length)

  @Test
  fun testToCanonicalHost() {
    // IPv4
    assertThat("127.0.0.1".toCanonicalHost()).isEqualTo("127.0.0.1")
    assertThat("1.2.3.4".toCanonicalHost()).isEqualTo("1.2.3.4")

    // IPv6
    assertThat("::1".toCanonicalHost()).isEqualTo("::1")
    assertThat("2001:db8::1".toCanonicalHost()).isEqualTo("2001:db8::1")

 * [system DNS service][SYSTEM], which is the default. Some applications may provide their own
 * implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4 addresses,
 * or to force a specific known IP address.
 *
 * Implementations of this interface must be safe for concurrent use.
 */
fun interface Dns {
  /**

 * Prefer to alternate IP addresses from different address families, (IPv6 / IPv4), starting with IPv6.
 * Don't start a new attempt until 250 ms after the most recent attempt was started.
 * Keep whichever TCP connection succeeds first and cancel all the others.

        
        if (rssCapable) score += 1000;   // Prefer RSS-capable
        if (rdmaCapable) score += 2000;  // Prefer RDMA-capable
        if (!ipv6) score += 100;         // Slight preference for IPv4
        
        return score;
    }
    
    private boolean checkRSSCapability() {
        // Platform-specific RSS detection
        // Simplified implementation
        try {

_2022-02-01_

**This release introduces fast fallback to better support mixed IPv4+IPv6 networks.** Fast fallback
is what we're calling our implementation of Happy Eyeballs, [RFC 8305][rfc_8305]. With this
feature OkHttp will attempt both IPv6 and IPv4 connections concurrently, keeping whichever connects
first. Fast fallback gives IPv6 connections a 250 ms head start so IPv6 is preferred on networks
where it's available.

        private final int flags;
        
        public static final int IPV4 = 0x01;
        public static final int IPV6 = 0x02;
        
        public WitnessIPAddress(InetAddress address) {
            this.address = address;
            this.flags = address.getAddress().length == 4 ? IPV4 : IPV6;
        }
        
        public InetAddress getAddress() { return address; }

OkHttp perseveres when the network is troublesome: it will silently recover from common connection
problems. If your service has multiple IP addresses, OkHttp will attempt alternate addresses if the
first connect fails. This is necessary for IPv4+IPv6 and services hosted in redundant data
centers. OkHttp supports modern TLS features (TLS 1.3, ALPN, certificate pinning). It can be
configured to fall back for broad connectivity.

          sudo sysctl net.ipv6.conf.all.disable_ipv6=0
          sudo sysctl net.ipv6.conf.default.disable_ipv6=0
          make test-pbac

      - name: Test Config File
        run: |
          sudo sysctl net.ipv6.conf.all.disable_ipv6=0
          sudo sysctl net.ipv6.conf.default.disable_ipv6=0
          make test-configfile

      - name: Test Replication
        run: |
          sudo sysctl net.ipv6.conf.all.disable_ipv6=0

		"",
	)

	ErrInvalidAddressFlag = newErrFn(
		"--address input is invalid",
		"Please check --address parameter",
		`--address binds to a specific ADDRESS:PORT, ADDRESS can be an IPv4/IPv6 address or hostname (default port is ':9000')
	Examples: --address ':443'
		  --address '172.16.34.31:9000'
		  --address '[fe80::da00:a6c8:e3ae:ddd7]:9000'`,
	)

	ErrInvalidEndpoint = newErrFn(

	return atomic.LoadInt64(&s.end) - s.pos
}

// read byte at current position (without advancing)
func (s *scanner) cur() byte { return s.buf[s.ipos] }

// read next byte
func (s *scanner) next() byte {
	if s.pos >= atomic.LoadInt64(&s.end) {
		return nullByte
	}
	s.ipos++

	if s.ipos > s.ifill { // internal buffer is exhausted
		s.ifill = <-s.fillReady