Go Build Example with Net package

Go Build with Net package

The package net defines many types, functions and methods of use in Go network programming. The type IP is defined as an array of bytes

type IP []byte

There are several functions to manipulate a variable of type IP, but you are likely to use only some of them in practice. For example, the function ParseIP(String) will take a dotted IPv4 address or a colon IPv6 address, while the IP method String will return a string.

pradeep:~$cat ip.go 
/* IP
 */

package main

import (
    "net"
    "os"
    "fmt"
)

func main() {
    if len(os.Args) != 2 {
        fmt.Fprintf(os.Stderr, "Usage: %s ip-addr\n", os.Args[0])
        os.Exit(1)
    }
    name := os.Args[1]

    addr := net.ParseIP(name)
    if addr == nil {
        fmt.Println("Invalid address")
    } else {
        fmt.Println("The address is ", addr.String())
    }
    os.Exit(0)
}

So far we have been using go run to compile and run our Go code.

pradeep:~$go run ip.go 
Usage: /var/folders/cf/vzmh318x285f0c1sbsnm14m40000gn/T/go-build3102043780/b001/exe/ip ip-addr
exit status 1

pradeep:~$go run ip.go ip 127.0.0.1
Usage: /var/folders/cf/vzmh318x285f0c1sbsnm14m40000gn/T/go-build1045950479/b001/exe/ip ip-addr
exit status 1

Lets build this time.

pradeep:~$go build ip.go           

As a result of the go build command, we can see a new file with the name of the package.

pradeep:~$ls -la | grep ip
-rwxr-xr-x   1 pradeep  staff  1997584 Apr 30 16:59 ip
-rw-r--r--   1 pradeep  staff      402 Apr 30 16:58 ip.go
pradeep:~$

Let us call this code ip

pradeep:~$ip 127.0.0.1
zsh: command not found: ip

Indicate that we are referring to the ip in the current directory by using ./

pradeep:~$./ip 127.0.0.1
The address is  127.0.0.1

pradeep:~$./ip 192.168.1.567
Invalid address

pradeep:~$./ip 192.168.1.5  
The address is  192.168.1.5

An example IPv6 address

pradeep:~$./ip 2003:abcd:ef::12
The address is  2003:abcd:ef::12

pradeep:~$cat mask.go 
package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    if len(os.Args) != 2 {
        fmt.Fprintf(os.Stderr, "Usage: %s dotted-ip-addr\n", os.Args[0])
        os.Exit(1)
    }
    dotAddr := os.Args[1]

    addr := net.ParseIP(dotAddr)
    if addr == nil {
        fmt.Println("Invalid address")
        os.Exit(1)
    }
    mask := addr.DefaultMask()
    network := addr.Mask(mask)
    ones, bits := mask.Size()
    fmt.Println("Address is ", addr.String(),
        " Default mask length is ", bits,
        "Leading ones count is ", ones,
        "Mask is (hex) ", mask.String(),
        " Network is ", network.String())
    os.Exit(0)
}

pradeep:~$go build mask.go 

pradeep:~$./mask 192.168.1.5
Address is  192.168.1.5  Default mask length is  32 Leading ones count is  24 Mask is (hex)  ffffff00  Network is  192.168.1.0

pradeep:~$./mask 10.20.30.5    
Address is  10.20.30.5  Default mask length is  32 Leading ones count is  8 Mask is (hex)  ff000000  Network is  10.0.0.0

pradeep:~$./mask 172.16.1.5
Address is  172.16.1.5  Default mask length is  32 Leading ones count is  16 Mask is (hex)  ffff0000  Network is  172.16.0.0