add android tcp ping test

Signed-off-by: Jakub Sokołowski <jakub@status.im>

.gitignore

@@ -1,5 +1,6 @@
 cloudflare/CloudFlare
 nix/nix-*.sh
+tcp-ping/tcp-ping-*
 .terraform
 terraform.tfvars
 terraform.tfstate*

tcp-ping/Makefile

@@ -0,0 +1,6 @@
+amd64:
+	GOARCH=$@ go build -o tcp-ping-$@ main.go 
+
+arm64:
+	GOARCH=$@ go build -o tcp-ping-$@ main.go
+

tcp-ping/main.go

@@ -0,0 +1,112 @@
+package main
+
+import (
+	"errors"
+	"log"
+	"net"
+	"os"
+	"syscall"
+	"time"
+)
+
+var addresses = []string{
+	"8.8.8.8:53", // will succeed
+	//"8.8.8.8:88", // will fail
+}
+
+const timeout time.Duration = 2000 * time.Millisecond
+
+const epollET = 1 << 31
+
+func parseSockAddr(addr string) (syscall.Sockaddr, error) {
+	tAddr, err := net.ResolveTCPAddr("tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+	var addr4 [4]byte
+	if tAddr.IP != nil {
+		copy(addr4[:], tAddr.IP.To4()) // copy last 4 bytes of slice to array
+	}
+	return &syscall.SockaddrInet4{Port: tAddr.Port, Addr: addr4}, nil
+}
+
+func Ping(address string, timeout time.Duration) error {
+	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		return os.NewSyscallError("socket", err)
+	}
+	syscall.CloseOnExec(fd)
+	log.Println("Socket FD:", fd)
+
+	err = syscall.SetsockoptInt(fd, syscall.SOL_TCP, syscall.TCP_QUICKACK, 0)
+	if err != nil {
+		return os.NewSyscallError("setsockopt", err)
+	}
+
+	var zeroLinger = syscall.Linger{Onoff: 1, Linger: 0}
+	err = syscall.SetsockoptLinger(fd, syscall.SOL_SOCKET, syscall.SO_LINGER, &zeroLinger)
+	if err != nil {
+		return os.NewSyscallError("setsockoptlinger", err)
+	}
+
+	rAddr, err := parseSockAddr(address)
+	if err != nil {
+		return errors.New("failed to parse address")
+	}
+
+	err = syscall.Connect(fd, rAddr)
+	if err != nil {
+		return os.NewSyscallError("connect", err)
+	}
+
+	epfd, err := syscall.EpollCreate1(syscall.EPOLL_CLOEXEC)
+	if err != nil {
+		return os.NewSyscallError("epoll_create1", err)
+	}
+	log.Println("Epoll FD:", epfd)
+
+	var event syscall.EpollEvent
+	event.Events = (syscall.EPOLLOUT | syscall.EPOLLIN | epollET)
+	event.Fd = int32(fd)
+
+	err = syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, fd, &event)
+	if err != nil {
+		return os.NewSyscallError("epoll_ctl", err)
+	}
+
+	var epollEvents [1]syscall.EpollEvent
+	var nEvents int
+	nEvents, err = syscall.EpollWait(epfd, epollEvents[:], int(timeout.Milliseconds()))
+
+	log.Println("EpollWait #:", nEvents)
+	if nEvents == 0 {
+		return errors.New("no events found")
+	}
+
+	errCode, err := syscall.GetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_ERROR)
+	if err != nil {
+		return os.NewSyscallError("getsockoptint", err)
+	}
+	log.Println("SO_ERROR:", errCode)
+
+	log.Println("EpollEvent:", epollEvents[0])
+	if epollEvents[0].Events&syscall.EPOLLOUT != 0 {
+		return nil
+	}
+
+	return errors.New("UNKNOWN ")
+}
+
+func main() {
+	log.SetPrefix("TCP_PING:")
+
+	for i := 0; i < len(addresses); i++ {
+		log.Println("PINGING:", addresses[i])
+		err := Ping(addresses[i], timeout)
+		if err != nil {
+			log.Println("FAILURE:", err)
+		} else {
+			log.Println("SUCCESS")
+		}
+	}
+}