The new type [KeepAliveConfig] permits fine-tuning the keep-alive
options for TCP connections, via a new [TCPConn.SetKeepAliveConfig]

pkg syscall (darwin-arm64), const TCP_KEEPINTVL = 257
pkg syscall (darwin-arm64), const TCP_KEEPINTVL ideal-int
pkg syscall (darwin-arm64), const TCP_MAXHLEN = 60
pkg syscall (darwin-arm64), const TCP_MAXHLEN ideal-int
pkg syscall (darwin-arm64), const TCP_MAXOLEN = 40
pkg syscall (darwin-arm64), const TCP_MAXOLEN ideal-int
pkg syscall (darwin-arm64), const TCP_MAXSEG = 2
pkg syscall (darwin-arm64), const TCP_MAXSEG ideal-int

pkg syscall (freebsd-arm64), const TCP_KEEPIDLE = 256
pkg syscall (freebsd-arm64), const TCP_KEEPIDLE ideal-int
pkg syscall (freebsd-arm64), const TCP_KEEPINIT = 128
pkg syscall (freebsd-arm64), const TCP_KEEPINIT ideal-int
pkg syscall (freebsd-arm64), const TCP_KEEPINTVL = 512
pkg syscall (freebsd-arm64), const TCP_KEEPINTVL ideal-int
pkg syscall (freebsd-arm64), const TCP_MAX_SACK = 4
pkg syscall (freebsd-arm64), const TCP_MAX_SACK ideal-int

pkg syscall (freebsd-riscv64), const TCP_MD5SIG ideal-int #53466
pkg syscall (freebsd-riscv64), const TCP_MINMSS = 216 #53466
pkg syscall (freebsd-riscv64), const TCP_MINMSS ideal-int #53466
pkg syscall (freebsd-riscv64), const TCP_MSS = 536 #53466
pkg syscall (freebsd-riscv64), const TCP_MSS ideal-int #53466
pkg syscall (freebsd-riscv64), const TCP_NOOPT = 8 #53466

pkg syscall (freebsd-386-cgo), const TCP_MAXHLEN = 60
pkg syscall (freebsd-386-cgo), const TCP_MAXOLEN = 40
pkg syscall (freebsd-386-cgo), const TCP_MAXSEG = 2
pkg syscall (freebsd-386-cgo), const TCP_MAXWIN = 65535
pkg syscall (freebsd-386-cgo), const TCP_MAX_SACK = 4
pkg syscall (freebsd-386-cgo), const TCP_MAX_WINSHIFT = 14
pkg syscall (freebsd-386-cgo), const TCP_MD5SIG = 16

forms, controlled by the
[`multipartmaxheaders` and `multipartmaxparts` settings](/pkg/mime/multipart#hdr-Limits)
respectively.
This behavior was backported to Go 1.19.8+ and Go 1.20.3+.

Go 1.21 adds the support of Multipath TCP but it is only used if the application
explicitly asked for it. This behavior can be controlled by the
[`multipathtcp` setting](/pkg/net#Dialer.SetMultipathTCP).

There is no plan to remove any of these settings.

	closer := func() {
		cmd.Process.Kill()
		<-errChan
	}
	// Dial localhost:3222 to ensure the proxy is ready.
	delay := time.Second / 4
	for attempt := 0; attempt < 5; attempt++ {
		conn, err := net.DialTimeout("tcp", "localhost:3222", 5*time.Second)
		if err == nil {
			conn.Close()
			return closer, nil
		}
		select {
		case <-time.After(delay):
			delay *= 2
		case err := <-errChan:
			return nil, err
		}