net: Invalid CIDR in net.ParseCIDR causes panic

[radeksimko]

I wanted to check if a given CIDR from user is valid, so I tried using the following approach:

_, ipnet, err := net.ParseCIDR("10.256.0.0/16")
if err != nil {
    fmt.Printf("%#v, %#v", ipnet.String(), err)
}

but that caused panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x57850]

goroutine 1 [running]:
net.networkNumberAndMask(0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
    /usr/local/Cellar/go/1.4.2/libexec/src/net/ip.go:436 +0x200
net.(*IPNet).String(0x0, 0x0, 0x0)
    /usr/local/Cellar/go/1.4.2/libexec/src/net/ip.go:486 +0x4b
main.main()
    /var/workspace/terraform-test/test.go:11 +0x68

goroutine 2 [runnable]:
runtime.forcegchelper()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/proc.go:90
runtime.goexit()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/asm_amd64.s:2232 +0x1

goroutine 3 [runnable]:
runtime.bgsweep()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/mgc0.go:82
runtime.goexit()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/asm_amd64.s:2232 +0x1

goroutine 4 [runnable]:
runtime.runfinq()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/malloc.go:712
runtime.goexit()
    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/asm_amd64.s:2232 +0x1
exit status 2

I'm using go 1.4.2 as it's obvious from the log above.
See on playground: http://play.golang.org/p/CqmfdTgQLm

The cleanest workaround I was able to come up with:

func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Invalid CIDR")
            return
        }
    }()
    _, ipnet, err := net.ParseCIDR("10.256.0.0/16")
    if err != nil {
        fmt.Printf("%#v, %#v", ipnet.String(), err)
    }
}

[mikioh]

When ParseCIDR fails, the returned values are:

ip = net.IP(nil)
ipnet = (*net.IPNet)(nil)
err = &net.ParseError{Type:"CIDR address", Text:"10.256.0.0/16"}

[radeksimko]

True, it's actually me causing the panic by calling .String()! Sorry!