dhcp4d: add HostnameOverride field

This can be used to permanently override a hostname, regardless of whether the
lease is static or not. We use a separate field because we want devices to be
able to change their hostname themselves, until we override it.

cmd/dhcp4d/dhcp4d.go

@@ -106,7 +106,7 @@ th {
   padding-top: 1em;
   text-align: left;
 }
-span.active, span.expired, span.static {
+span.active, span.expired, span.static, span.hostname-override {
   min-width: 5em;
   display: inline-block;
   text-align: center;
@@ -119,6 +119,10 @@ span.active {
 span.expired {
   background-color: #f00000;
 }
+span.hostname-override {
+  min-width: 1em;
+  background-color: orange;
+}
 .ipaddr, .hwaddr {
   font-family: monospace;
 }
@@ -139,7 +143,12 @@ tr:nth-child(even) {
 {{ range $idx, $l := . }}
 <tr>
 <td class="ipaddr">{{$l.Addr}}</td>
-<td>{{$l.Hostname}}</td>
+<td>
+{{$l.Hostname}}
+{{ if (ne $l.HostnameOverride "") }}
+<span class="hostname-override">!</span>
+{{ end }}
+</td>
 <td class="hwaddr">{{$l.HardwareAddr}}</td>
 <td>{{$l.Vendor}}</td>
 <td title="{{ timefmt $l.Expiry }}">

internal/dhcp4d/dhcp4d.go

@@ -35,6 +35,7 @@ type Lease struct {
 	Addr             net.IP    `json:"addr"`
 	HardwareAddr     string    `json:"hardware_addr"`
 	Hostname         string    `json:"hostname"`
+	HostnameOverride string    `json:"hostname_override"`
 	Expiry           time.Time `json:"expiry"`
 }
 
@@ -277,6 +278,10 @@ func (h *Handler) serveDHCP(p dhcp4.Packet, msgType dhcp4.MessageType, options d
 				lease.Expiry = time.Time{}
 				lease.Hostname = l.Hostname
 			}
+			if l.HostnameOverride != "" {
+				lease.Hostname = l.HostnameOverride
+				lease.HostnameOverride = l.HostnameOverride
+			}
 
 			// Release any old leases for this client
 			delete(h.leasesIP, l.Num)