From 177f1eca06ff3f046ac75c921f01ccf1b0eb80ab Mon Sep 17 00:00:00 2001
From: Kristoffer Dalby <kradalby@kradalby.no>
Date: Fri, 22 Oct 2021 16:55:35 +0000
Subject: [PATCH] Add helper functions for building derp maps from urls and
 file

---
 derp.go | 152 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 derp.go

diff --git a/derp.go b/derp.go
new file mode 100644
index 00000000..39e63210
--- /dev/null
+++ b/derp.go
@@ -0,0 +1,152 @@
+package headscale
+
+import (
+	"encoding/json"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"os"
+	"time"
+
+	"github.com/rs/zerolog/log"
+
+	"gopkg.in/yaml.v2"
+
+	"tailscale.com/tailcfg"
+)
+
+func loadDERPMapFromPath(path string) (*tailcfg.DERPMap, error) {
+	derpFile, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer derpFile.Close()
+	var derpMap tailcfg.DERPMap
+	b, err := io.ReadAll(derpFile)
+	if err != nil {
+		return nil, err
+	}
+	err = yaml.Unmarshal(b, &derpMap)
+	return &derpMap, err
+}
+
+func loadDERPMapFromURL(addr url.URL) (*tailcfg.DERPMap, error) {
+	client := http.Client{
+		Timeout: 10 * time.Second,
+	}
+	resp, err := client.Get(addr.String())
+	if err != nil {
+		return nil, err
+	}
+
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var derpMap tailcfg.DERPMap
+	err = json.Unmarshal(body, &derpMap)
+	return &derpMap, err
+}
+
+// mergeDERPMaps naively merges a list of DERPMaps into a single
+// DERPMap, it will _only_ look at the Regions, an integer.
+// If a region exists in two of the given DERPMaps, the region
+// form the _last_ DERPMap will be preserved.
+// An empty DERPMap list will result in a DERPMap with no regions
+func mergeDERPMaps(derpMaps []*tailcfg.DERPMap) *tailcfg.DERPMap {
+	result := tailcfg.DERPMap{
+		OmitDefaultRegions: false,
+		Regions:            map[int]*tailcfg.DERPRegion{},
+	}
+
+	for _, derpMap := range derpMaps {
+		for id, region := range derpMap.Regions {
+			result.Regions[id] = region
+		}
+	}
+
+	return &result
+}
+
+func GetDERPMap(cfg DERPConfig) *tailcfg.DERPMap {
+	derpMaps := make([]*tailcfg.DERPMap, 0)
+
+	for _, path := range cfg.Paths {
+		log.Debug().
+			Str("func", "GetDERPMap").
+			Str("path", path).
+			Msg("Loading DERPMap from path")
+		derpMap, err := loadDERPMapFromPath(path)
+		if err != nil {
+			log.Error().
+				Str("func", "GetDERPMap").
+				Str("path", path).
+				Err(err).
+				Msg("Could not load DERP map from path")
+			break
+		}
+
+		derpMaps = append(derpMaps, derpMap)
+	}
+
+	for _, addr := range cfg.URLs {
+		derpMap, err := loadDERPMapFromURL(addr)
+		log.Debug().
+			Str("func", "GetDERPMap").
+			Str("url", addr.String()).
+			Msg("Loading DERPMap from path")
+		if err != nil {
+			log.Error().
+				Str("func", "GetDERPMap").
+				Str("url", addr.String()).
+				Err(err).
+				Msg("Could not load DERP map from path")
+			break
+		}
+
+		derpMaps = append(derpMaps, derpMap)
+	}
+
+	derpMap := mergeDERPMaps(derpMaps)
+
+	log.Trace().Interface("derpMap", derpMap).Msg("DERPMap loaded")
+
+	if len(derpMap.Regions) == 0 {
+		log.Warn().
+			Msg("DERP map is empty, not a single DERP map datasource was loaded correctly or contained a region")
+	}
+
+	return derpMap
+}
+
+func (h *Headscale) scheduledDERPMapUpdateWorker(cancelChan <-chan struct{}) {
+	log.Info().
+		Dur("frequency", h.cfg.DERP.UpdateFrequency).
+		Msg("Setting up a DERPMap update worker")
+	ticker := time.NewTicker(h.cfg.DERP.UpdateFrequency)
+
+	for {
+		select {
+		case <-cancelChan:
+			return
+
+		case <-ticker.C:
+			log.Info().Msg("Fetching DERPMap updates")
+			h.DERPMap = GetDERPMap(h.cfg.DERP)
+
+			namespaces, err := h.ListNamespaces()
+			if err != nil {
+				log.Error().
+					Err(err).
+					Msg("Failed to fetch namespaces")
+			}
+
+			for _, namespace := range *namespaces {
+				h.setLastStateChangeToNow(namespace.Name)
+			}
+		}
+	}
+}