fix: avoid infinite loop in agent derp-map (#8848)

codersdk/agentsdk/agentsdk.go

@@ -211,18 +211,26 @@ func (c *Client) DERPMapUpdates(ctx context.Context) (<-chan DERPMapUpdate, io.C
 			if err != nil {
 				update.Err = err
 				update.DERPMap = nil
-				return
 			}
+			if update.DERPMap != nil {
 				err = c.rewriteDerpMap(update.DERPMap)
 				if err != nil {
 					update.Err = err
 					update.DERPMap = nil
-				return
+				}
 			}
 
 			select {
 			case updates <- update:
 			case <-ctx.Done():
+				// Unblock the caller if they're waiting for an update.
+				select {
+				case updates <- DERPMapUpdate{Err: ctx.Err()}:
+				default:
+				}
+				return
+			}
+			if update.Err != nil {
 				return
 			}
 		}
@@ -231,8 +239,8 @@ func (c *Client) DERPMapUpdates(ctx context.Context) (<-chan DERPMapUpdate, io.C
 	return updates, &closer{
 		closeFunc: func() error {
 			cancelFunc()
-			_ = wsNetConn.Close()
 			<-pingClosed
+			_ = conn.Close(websocket.StatusGoingAway, "Listen closed")
 			<-updatesClosed
 			return nil
 		},

enterprise/coderd/coderd.go

@@ -706,6 +706,10 @@ func derpMapper(logger slog.Logger, cfg *codersdk.DeploymentValues, proxyHealth
 			// existing ID in the DERP map.
 			regionID := int(startingRegionID) + int(status.Proxy.RegionID)
 			regionCode := fmt.Sprintf("coder_%s", strings.ToLower(status.Proxy.Name))
+			regionName := status.Proxy.DisplayName
+			if regionName == "" {
+				regionName = status.Proxy.Name
+			}
 			for _, r := range derpMap.Regions {
 				if r.RegionID == regionID || r.RegionCode == regionCode {
 					// Log a warning if we haven't logged one in the last
@@ -768,7 +772,7 @@ func derpMapper(logger slog.Logger, cfg *codersdk.DeploymentValues, proxyHealth
 				EmbeddedRelay: false,
 				RegionID:      regionID,
 				RegionCode:    regionCode,
-				RegionName:    status.Proxy.Name,
+				RegionName:    regionName,
 				Nodes:         nodes,
 			}
 		}