dns: swap Priority to *uint16

[jacobbednarz]

DNSRecord priority was initially an int. This worked most of the time
however in some cases, 0 was intended to be used as a zero value and in
others, a valid value. This causes confusion and in combination with
omitempty on the struct, makes it impossible to send 0 as a value.

type DNSRecord struct {
	Type     string  `json:"type,omitempty"`
	Priority int `json:"priority,omitempty"`
}

func main() {
	// using 0 as a value
	var p = int(0)
	d := DNSRecord{
		Type:     "MX",
		Priority: p,
	}
	b, _ := json.Marshal(d)
	fmt.Println(string(b))

	// => {"type":"MX"}
}

To rectify, I've swapped the struct to *uint16 which accomplishes two
things. The first, aligns with our internal representation of the data
struct. The second, allows us to use 0 in both contexts as a zero value
but also as a value reference where it is needed.

type DNSRecord struct {
	Type     string  `json:"type,omitempty"`
	Priority *uint16 `json:"priority,omitempty"`
}

func main() {
	var p1 = uint16(0)
	d1 := DNSRecord{
		Type:     "MX",
		Priority: &p1,
	}
	b1, _ := json.Marshal(d1)
	fmt.Println(string(b1))
	// => {"type":"MX","priority":0}

	var p2 = uint16(10)
	d2 := DNSRecord{
		Type:     "MX",
		Priority: &p2,
	}
	b2, _ := json.Marshal(d2)
	fmt.Println(string(b2))
	// => {"type":"MX","priority":10}

	d3 := DNSRecord{
		Type:       "MX",
		Priority: nil,
	}
	b3, _ := json.Marshal(d3)
	fmt.Println(string(b3))
	// => {"type":"MX"}
}

Fixes SDK-114 and lays the ground work for the Terraform provider fix.

[jacobbednarz]

To add some more context, upstream in Terraform, I'm thinking of the following to allow people to set the priority = 0 in their configuration.

@@ -291,9 +291,9 @@ func resourceCloudflareRecord() *schema.Resource {

 func resourceCloudflareRecordCreate(d *schema.ResourceData, meta interface{}) error {
        client := meta.(*cloudflare.API)
-
+       rrType := d.Get("type").(string)
        newRecord := cloudflare.DNSRecord{
-               Type:    d.Get("type").(string),
+               Type:    rrType,
                Name:    d.Get("name").(string),
                Proxied: d.Get("proxied").(bool),
                ZoneID:  d.Get("zone_id").(string),
@@ -329,8 +329,9 @@ func resourceCloudflareRecordCreate(d *schema.ResourceData, meta interface{}) er
                        valueOk, dataOk)
        }

-       if priority, ok := d.GetOk("priority"); ok {
-               newRecord.Priority = priority.(int)
+       if rrType == "MX" {
+               priority := d.Get("priority").(uint16)
+               newRecord.Priority = &priority
        }

Where rrType is any record type where we require priority to be send to the API regardless of the value.

[patryk]

Yeah, I agree with your reasoning. But we would need to release a breaking change release hre to indicate a backwards-incompatible change.

[jacobbednarz]

i've pushed a 0.14 branch up and this is now going to merge into that for testing instead of master.