From 3ca03fd4a935a0e333f6f06b3c223c325e27fb5d Mon Sep 17 00:00:00 2001
From: Kyle Carberry <kyle@carberry.com>
Date: Fri, 2 Sep 2022 18:25:34 -0500
Subject: [PATCH] fix: Allow disabling built-in DERP server

---
 cli/server.go      |  8 ++++++--
 tailnet/derpmap.go | 42 +++++++++++++++++++++++-------------------
 2 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/cli/server.go b/cli/server.go
index 40e738bad4107..f1c654f9ac629 100644
--- a/cli/server.go
+++ b/cli/server.go
@@ -329,7 +329,7 @@ func Server(newAPI func(*coderd.Options) *coderd.API) *cobra.Command {
 				validatedAutoImportTemplates[i] = v
 			}
 
-			derpMap, err := tailnet.NewDERPMap(ctx, &tailcfg.DERPRegion{
+			defaultRegion := &tailcfg.DERPRegion{
 				RegionID:   derpServerRegionID,
 				RegionCode: derpServerRegionCode,
 				RegionName: derpServerRegionName,
@@ -341,7 +341,11 @@ func Server(newAPI func(*coderd.Options) *coderd.API) *cobra.Command {
 					STUNPort:  -1,
 					ForceHTTP: accessURLParsed.Scheme == "http",
 				}},
-			}, derpServerSTUNAddrs, derpConfigURL)
+			}
+			if !derpServerEnabled {
+				defaultRegion = nil
+			}
+			derpMap, err := tailnet.NewDERPMap(ctx, defaultRegion, derpServerSTUNAddrs, derpConfigURL)
 			if err != nil {
 				return xerrors.Errorf("create derp map: %w", err)
 			}
diff --git a/tailnet/derpmap.go b/tailnet/derpmap.go
index 9c8122238cec7..cbc03cec4140b 100644
--- a/tailnet/derpmap.go
+++ b/tailnet/derpmap.go
@@ -15,22 +15,24 @@ import (
 // NewDERPMap constructs a DERPMap from a set of STUN addresses and optionally a remote
 // URL to fetch a mapping from e.g. https://controlplane.tailscale.com/derpmap/default.
 func NewDERPMap(ctx context.Context, region *tailcfg.DERPRegion, stunAddrs []string, remoteURL string) (*tailcfg.DERPMap, error) {
-	for index, stunAddr := range stunAddrs {
-		host, rawPort, err := net.SplitHostPort(stunAddr)
-		if err != nil {
-			return nil, xerrors.Errorf("split host port for %q: %w", stunAddr, err)
-		}
-		port, err := strconv.Atoi(rawPort)
-		if err != nil {
-			return nil, xerrors.Errorf("parse port for %q: %w", stunAddr, err)
+	if region != nil {
+		for index, stunAddr := range stunAddrs {
+			host, rawPort, err := net.SplitHostPort(stunAddr)
+			if err != nil {
+				return nil, xerrors.Errorf("split host port for %q: %w", stunAddr, err)
+			}
+			port, err := strconv.Atoi(rawPort)
+			if err != nil {
+				return nil, xerrors.Errorf("parse port for %q: %w", stunAddr, err)
+			}
+			region.Nodes = append([]*tailcfg.DERPNode{{
+				Name:     fmt.Sprintf("%dstun%d", region.RegionID, index),
+				RegionID: region.RegionID,
+				HostName: host,
+				STUNOnly: true,
+				STUNPort: port,
+			}}, region.Nodes...)
 		}
-		region.Nodes = append([]*tailcfg.DERPNode{{
-			Name:     fmt.Sprintf("%dstun%d", region.RegionID, index),
-			RegionID: region.RegionID,
-			HostName: host,
-			STUNOnly: true,
-			STUNPort: port,
-		}}, region.Nodes...)
 	}
 
 	derpMap := &tailcfg.DERPMap{
@@ -51,10 +53,12 @@ func NewDERPMap(ctx context.Context, region *tailcfg.DERPRegion, stunAddrs []str
 			return nil, xerrors.Errorf("fetch derpmap: %w", err)
 		}
 	}
-	_, conflicts := derpMap.Regions[region.RegionID]
-	if conflicts {
-		return nil, xerrors.Errorf("the default region ID conflicts with a remote region from %q", remoteURL)
+	if region != nil {
+		_, conflicts := derpMap.Regions[region.RegionID]
+		if conflicts {
+			return nil, xerrors.Errorf("the default region ID conflicts with a remote region from %q", remoteURL)
+		}
+		derpMap.Regions[region.RegionID] = region
 	}
-	derpMap.Regions[region.RegionID] = region
 	return derpMap, nil
 }