GetNameservers is inconsistent across providers (#655)

* Warn if GetNameservers returns FQDN+dot strings
* Simplify logic that covers for the inconsistency
* Fix azuredns, gcloud, bind, route53
* Clean up cloudflare, digitalocean, dnsimple, gandi_v5, namedotcom

models/dns.go

@@ -2,6 +2,7 @@ package models
 
 import (
 	"encoding/json"
+	"fmt"
 	"strings"
 )
 
@@ -49,6 +50,7 @@ type DNSProviderConfig struct {
 // Nameserver describes a nameserver.
 type Nameserver struct {
 	Name string `json:"name"` // Normalized to a FQDN with NO trailing "."
+	// NB(tlim): DomainConfig.Nameservers are stored WITH a trailing "." (Sorry!)
 }
 
 func (n *Nameserver) String() string {
@@ -56,6 +58,8 @@ func (n *Nameserver) String() string {
 }
 
 // StringsToNameservers constructs a list of *Nameserver structs using a list of FQDNs.
+// Deprecated. Please use ToNameservers, or maybe ToNameserversStripTD instead.
+// See https://github.com/StackExchange/dnscontrol/issues/491
 func StringsToNameservers(nss []string) []*Nameserver {
 	nservers := []*Nameserver{}
 	for _, ns := range nss {
@@ -64,7 +68,37 @@ func StringsToNameservers(nss []string) []*Nameserver {
 	return nservers
 }
 
-// NameserversToStrings constructs a list of lists from *Nameserver structs
+// ToNameservers turns a list of strings into a list of Nameservers.
+// It is an error if any string has a trailing dot. Either remove the
+// trailing dot before you call this or (much preferred) use ToNameserversStripTD.
+func ToNameservers(nss []string) ([]*Nameserver, error) {
+	nservers := []*Nameserver{}
+	for _, ns := range nss {
+		if strings.HasSuffix(ns, ".") {
+			return nil, fmt.Errorf("provider code leaves trailing dot on nameserver")
+			// If you see this error, maybe the provider should call
+			// ToNameserversStripTD instead.
+		}
+		nservers = append(nservers, &Nameserver{Name: ns})
+	}
+	return nservers, nil
+}
+
+// ToNameserversStripTD is like ToNameservers but strips the trailing
+// dot from each item. It is an error if there is no trailing dot.
+func ToNameserversStripTD(nss []string) ([]*Nameserver, error) {
+	nservers := []*Nameserver{}
+	for _, ns := range nss {
+		if !strings.HasSuffix(ns, ".") {
+			return nil, fmt.Errorf("provider code already removed nameserver trailing dot (%v)", ns)
+			// If you see this error, maybe the provider should call ToNameservers instead.
+		}
+		nservers = append(nservers, &Nameserver{Name: ns[0 : len(ns)-1]})
+	}
+	return nservers, nil
+}
+
+// NameserversToStrings constructs a list of strings from *Nameserver structs
 func NameserversToStrings(nss []*Nameserver) (s []string) {
 	for _, ns := range nss {
 		s = append(s, ns.Name)