BIND: Simplify serial number generation (#652)

* The old algorithm was very complex for no good reason.
* The new algorithm is simply: Use yymmdd00 or (previous serial number +1) whichever is bigger.

providers/bind/serial.go

@@ -3,7 +3,6 @@ package bind
 import (
 	"log"
 	"strconv"
-	"strings"
 	"time"
 )
 
@@ -20,36 +19,20 @@ func generateSerial(oldSerial uint32) uint32 {
 	// At no time will a serial number == 0 be returned.
 
 	original := oldSerial
-	oldSerialStr := strconv.FormatUint(uint64(oldSerial), 10)
 	var newSerial uint32
 
 	// Make draft new serial number:
 	today := nowFunc().UTC()
 	todayStr := today.Format("20060102")
-	version := uint32(1)
 	todayNum, err := strconv.ParseUint(todayStr, 10, 32)
 	if err != nil {
 		log.Fatalf("new serial won't fit in 32 bits: %v", err)
 	}
-	draft := uint32(todayNum)*100 + version
+	draft := uint32(todayNum * 100)
 
 	method := "none" // Used only in debugging.
-	if oldSerial > draft {
-		// If old_serial was really slow, upgrade to new yyyymmddvv standard:
-		method = "o>d"
-		newSerial = oldSerial + 1
-		newSerial = oldSerial + 1
-	} else if oldSerial == draft {
-		// Edge case: increment old serial:
-		method = "o=d"
-		newSerial = draft + 1
-	} else if len(oldSerialStr) != 10 {
-		// If old_serial is wrong number of digits, upgrade to yyyymmddvv standard:
-		method = "len!=10"
-		newSerial = draft
-	} else if strings.HasPrefix(oldSerialStr, todayStr) {
-		// If old_serial just needs to be incremented:
-		method = "prefix"
+	if oldSerial >= draft {
+		method = "o>=d"
 		newSerial = oldSerial + 1
 	} else {
 		// First serial number to be requested today: