2 files changed, 153 insertions, 0 deletions
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..3e2c40a
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module porter
+
+go 1.16
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..0218d9f
--- /dev/null
+++ b/main.go
@@ -0,0 +1,150 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"strconv"
+	"sync"
+	"syscall"
+	"time"
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr,
+		"Usage: porter action host min max\n\n"+
+			"-- action is any of dial, listen\n"+
+			"-- min, max is tcp port values\n",
+	)
+	os.Exit(2)
+}
+
+func parsePositive(s string) int {
+	n, err := strconv.Atoi(s)
+	if err != nil || n <= 0 {
+		return -1
+	}
+	return n
+}
+
+func setlimit(total int) {
+	nfds := uint64(total)
+	rlim := syscall.Rlimit{}
+
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil {
+		log.Fatal(err)
+	}
+
+	if nfds > rlim.Max {
+		log.Fatalf("too big port range %d, max %d", nfds, rlim.Max)
+	}
+
+	if nfds > rlim.Cur {
+		rlim.Cur = nfds
+		if err := syscall.Setrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func dial(host string, min, max int) {
+	var wg sync.WaitGroup
+
+	setlimit((max - min + 1) + 32)
+
+	tout := time.Second
+
+	for n := min; n <= max; n++ {
+		wg.Add(1)
+
+		go func(port int) {
+			defer wg.Done()
+
+			c, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", host, port), tout)
+			if err != nil {
+				fmt.Printf("fail %d dial: %s\n", port, err)
+				return
+			}
+
+			fmt.Printf("ok %d dial\n", port)
+			fmt.Fprint(c, "test")
+			c.Close()
+		}(n)
+	}
+
+	wg.Wait()
+}
+
+func listen(host string, min, max int) {
+	ready := make(chan struct{})
+
+	setlimit(2*(max-min+1) + 32)
+
+	for n := min; n <= max; n++ {
+		l, err := net.Listen("tcp", fmt.Sprintf("%s:%d", host, n))
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		go func(l net.Listener, port int) {
+			<-ready
+
+			for {
+				c, err := l.Accept()
+				if err != nil {
+					fmt.Printf("fail %d accept: %s\n", port, err)
+					continue
+				}
+				fmt.Printf("ok %d accept\n", port)
+
+				buf := make([]byte, 1024)
+				for {
+					n, err := c.Read(buf)
+					if err != nil {
+						if err == io.EOF {
+							fmt.Printf("ok %d close\n", port)
+						} else {
+							fmt.Printf("fail %d read: %s\n", port, err)
+						}
+						break
+					}
+					fmt.Printf("ok %d read %d bytes\n", port, n)
+				}
+				c.Close()
+			}
+		}(l, n)
+	}
+
+	close(ready)
+
+	syscall.Pause()
+}
+
+func main() {
+	log.SetFlags(0)
+
+	if len(os.Args) < 5 {
+		usage()
+	}
+
+	action := os.Args[1]
+	host := os.Args[2]
+
+	min := parsePositive(os.Args[3])
+	max := parsePositive(os.Args[4])
+
+	if min < 0 || max < 0 || min > max {
+		usage()
+	}
+
+	switch action {
+	case "dial":
+		dial(host, min, max)
+	case "listen":
+		listen(host, min, max)
+	default:
+		usage()
+	}
+}