feat(ipconverter): add a tool to convert IPv4 to int and vice-versa

It's sometimes useful to store IPv4 addresses as an integer. This tool
helps with the conversion, and also does the reverse conversion.

```
% go run . int2ip 3232235521
3232235521      192.168.0.1
% go run . ip2int 192.168.0.1
192.168.0.1     3232235521
```

Change-Id: Ic1e44057bca3539b4c183d387c635f69f5bf3f36
Reviewed-on: https://cl.fcuny.net/c/world/+/441
Tested-by: CI
Reviewed-by: Franck Cuny <franck@fcuny.net>

1 files changed, 58 insertions, 0 deletions

diff --git a/tools/ipconverter/main.go b/tools/ipconverter/main.go
new file mode 100644
index 0000000..1211970
--- /dev/null
+++ b/tools/ipconverter/main.go
@@ -0,0 +1,58 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math/big"
+	"net"
+	"os"
+	"path"
+	"strconv"
+)
+
+func main() {
+	cmd := path.Base(os.Args[1])
+
+	switch cmd {
+	case "ip2int":
+		for _, ip := range os.Args[2:] {
+			r, err := IPtoInt(ip)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "failed to parse %s to an int: %s", ip, err)
+				continue
+			}
+			fmt.Printf("%s\t%d\n", ip, r)
+		}
+	case "int2ip":
+		for _, ip := range os.Args[2:] {
+			r, err := IPtoN(ip)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "failed to parse %s to an addresse IP: %s", ip, err)
+				continue
+			}
+			fmt.Printf("%s\t%s", ip, r)
+		}
+	default:
+		fmt.Printf("`%s' is not a supported command", cmd)
+		os.Exit(1)
+	}
+}
+
+func IPtoInt(ip string) (*big.Int, error) {
+	i := net.ParseIP(ip)
+	if len(i.To4()) == 4 {
+		return big.NewInt(0).SetBytes(i.To4()), nil
+	} else {
+		return nil, fmt.Errorf("%s is not an IPv4 address", ip)
+	}
+}
+
+func IPtoN(ip string) (string, error) {
+	r, err := strconv.Atoi(ip)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse %s to an int: %s", ip, err)
+	}
+	newIP := make(net.IP, 4)
+	binary.BigEndian.PutUint32(newIP, uint32(r))
+	return newIP.To4().String(), nil
+}