Fix #1338 - OVH provider should work when domain is not registered (#1340)

* Fix #1338 do not error if domain is not registered

OVH now allows to create zone without registering a domain. The ovh provider
was getting the NS from the registrar and not the zone, which doesn't work
in a scenario where only the zone exists at ovh.
This changeset makes the ovh provider fetch the NS from the registrar and if
there's none from the zone.

* OVH now supports all dual providers scenario

This change updates the OVH provider documentation accordingly.

docs/_providers/ovh.md

@@ -119,14 +119,13 @@ control panel manually.
 
 ## Dual providers scenario
 
-Since OVH doesn't allow to host DNS for a domain that is not registered in their registrar, some dual providers
-scenario are not possible:
+OVH now allows to host DNS zone for a domain that is not registered in their registrar (see: https://www.ovh.com/manager/web/#/zone). The following dual providers scenario are supported:
 
 | registrar | zone        | working? |
 |:---------:|:-----------:|:--------:|
 |  OVH      | other       |    √     |
 |  OVH      | OVH + other |    √     |
-|  other    | OVH         |    X     |
+|  other    | OVH         |    √     |
 
 ## Caveat
 

providers/ovh/ovhProvider.go

@@ -68,7 +68,7 @@ func (c *ovhProvider) GetNameservers(domain string) ([]*models.Nameserver, error
 		return nil, fmt.Errorf("'%s' not a zone in ovh account", domain)
 	}
 
-	ns, err := c.fetchRegistrarNS(domain)
+	ns, err := c.fetchNS(domain)
 	if err != nil {
 		return nil, err
 	}

providers/ovh/protocol.go

@@ -1,10 +1,13 @@
 package ovh
 
 import (
+	"errors"
 	"fmt"
+	"strings"
+
 	"github.com/StackExchange/dnscontrol/v3/models"
 	"github.com/miekg/dns/dnsutil"
-	"strings"
+	"github.com/ovh/go-ovh/ovh"
 )
 
 // Void an empty structure.
@@ -164,7 +167,7 @@ func (c *ovhProvider) refreshZone(fqdn string) error {
 
 // fetch the NS OVH attributed to this zone (which is distinct from fetchRealNS which
 // get the exact NS stored at the registrar
-func (c *ovhProvider) fetchNS(fqdn string) ([]string, error) {
+func (c *ovhProvider) fetchZoneNS(fqdn string) ([]string, error) {
 	zone, err := c.fetchZone(fqdn)
 	if err != nil {
 		return nil, err
@@ -173,6 +176,22 @@ func (c *ovhProvider) fetchNS(fqdn string) ([]string, error) {
 	return zone.NameServers, nil
 }
 
+// Fetch first the registrar NS, if none found, return the zone defined NS
+func (c *ovhProvider) fetchNS(fqdn string) ([]string, error) {
+	ns, err := c.fetchRegistrarNS(fqdn)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(ns) == 0 {
+		ns, err = c.fetchZoneNS(fqdn)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return ns, nil
+}
+
 // CurrentNameServer stores information about nameservers.
 type CurrentNameServer struct {
 	ToDelete bool   `json:"toDelete,omitempty"`
@@ -187,6 +206,10 @@ func (c *ovhProvider) fetchRegistrarNS(fqdn string) ([]string, error) {
 	var nameServersID []int
 	err := c.client.CallAPI("GET", "/domain/"+fqdn+"/nameServer", nil, &nameServersID, true)
 	if err != nil {
+		var apiError *ovh.APIError
+		if errors.As(err, &apiError) && apiError.Code == 404 {
+			return []string{}, nil
+		}
 		return nil, err
 	}