PollNetMapHandler: refactor with chan lifetimes in mind

* Resolves an issue where sometimes attempted sends on a closed channel
  happened by ensuring the channels remain open for the entire goroutine.
* May be of help with regards to issue #203

Makefile

@@ -18,7 +18,7 @@ test:
 	@go test -coverprofile=coverage.out ./...
 
 test_integration:
-	go test -tags integration -timeout 30m ./...
+	go test -tags integration -timeout 30m -count=1 ./...
 
 test_integration_cli:
 	go test -tags integration -v integration_cli_test.go integration_common_test.go

poll.go

@@ -1,8 +1,10 @@
 package headscale
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"time"
@@ -152,14 +154,33 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 		Str("id", ctx.Param("id")).
 		Str("machine", machine.Name).
 		Msg("Loading or creating update channel")
-	updateChan := make(chan struct{})
 
-	pollDataChan := make(chan []byte)
+	// TODO: could probably remove all that duplication once generics land.
+	closeChanWithLog := func(channel interface{}, name string) {
+		log.Trace().
+			Str("handler", "PollNetMap").
+			Str("machine", machine.Name).
+			Str("channel", "Done").
+			Msg(fmt.Sprintf("Closing %s channel", name))
+
+		switch c := channel.(type) {
+		case (chan struct{}):
+			close(c)
+
+		case (chan []byte):
+			close(c)
+		}
+	}
+
+	const chanSize = 8
+	updateChan := make(chan struct{}, chanSize)
+	defer closeChanWithLog(updateChan, "updateChan")
+
+	pollDataChan := make(chan []byte, chanSize)
+	defer closeChanWithLog(pollDataChan, "pollDataChan")
 
 	keepAliveChan := make(chan []byte)
-
-	cancelKeepAlive := make(chan struct{})
-	defer close(cancelKeepAlive)
+	defer closeChanWithLog(keepAliveChan, "keepAliveChan")
 
 	if req.OmitPeers && !req.Stream {
 		log.Info().
@@ -172,7 +193,7 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 		// even tho the comments in the tailscale code dont explicitly say so.
 		updateRequestsFromNode.WithLabelValues(machine.Name, machine.Namespace.Name, "endpoint-update").
 			Inc()
-		go func() { updateChan <- struct{}{} }()
+		updateChan <- struct{}{}
 
 		return
 	} else if req.OmitPeers && req.Stream {
@@ -193,7 +214,7 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 		Str("handler", "PollNetMap").
 		Str("machine", machine.Name).
 		Msg("Sending initial map")
-	go func() { pollDataChan <- data }()
+	pollDataChan <- data
 
 	log.Info().
 		Str("handler", "PollNetMap").
@@ -201,7 +222,7 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 		Msg("Notifying peers")
 	updateRequestsFromNode.WithLabelValues(machine.Name, machine.Namespace.Name, "full-update").
 		Inc()
-	go func() { updateChan <- struct{}{} }()
+	updateChan <- struct{}{}
 
 	h.PollNetMapStream(
 		ctx,
@@ -211,7 +232,6 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 		pollDataChan,
 		keepAliveChan,
 		updateChan,
-		cancelKeepAlive,
 	)
 	log.Trace().
 		Str("handler", "PollNetMap").
@@ -231,16 +251,20 @@ func (h *Headscale) PollNetMapStream(
 	pollDataChan chan []byte,
 	keepAliveChan chan []byte,
 	updateChan chan struct{},
-	cancelKeepAlive chan struct{},
 ) {
-	go h.scheduledPollWorker(
-		cancelKeepAlive,
-		updateChan,
-		keepAliveChan,
-		machineKey,
-		mapRequest,
-		machine,
-	)
+	{
+		ctx, cancel := context.WithCancel(ctx.Request.Context())
+		defer cancel()
+
+		go h.scheduledPollWorker(
+			ctx,
+			updateChan,
+			keepAliveChan,
+			machineKey,
+			mapRequest,
+			machine,
+		)
+	}
 
 	ctx.Stream(func(writer io.Writer) bool {
 		log.Trace().
@@ -455,42 +479,13 @@ func (h *Headscale) PollNetMapStream(
 			machine.LastSeen = &now
 			h.db.Save(&machine)
 
-			log.Trace().
-				Str("handler", "PollNetMapStream").
-				Str("machine", machine.Name).
-				Str("channel", "Done").
-				Msg("Cancelling keepAlive channel")
-			cancelKeepAlive <- struct{}{}
-
-			log.Trace().
-				Str("handler", "PollNetMapStream").
-				Str("machine", machine.Name).
-				Str("channel", "Done").
-				Msg("Closing update channel")
-			// h.closeUpdateChannel(m)
-			close(updateChan)
-
-			log.Trace().
-				Str("handler", "PollNetMapStream").
-				Str("machine", machine.Name).
-				Str("channel", "Done").
-				Msg("Closing pollData channel")
-			close(pollDataChan)
-
-			log.Trace().
-				Str("handler", "PollNetMapStream").
-				Str("machine", machine.Name).
-				Str("channel", "Done").
-				Msg("Closing keepAliveChan channel")
-			close(keepAliveChan)
-
 			return false
 		}
 	})
 }
 
 func (h *Headscale) scheduledPollWorker(
-	cancelChan <-chan struct{},
+	ctx context.Context,
 	updateChan chan<- struct{},
 	keepAliveChan chan<- []byte,
 	machineKey key.MachinePublic,
@@ -502,7 +497,7 @@ func (h *Headscale) scheduledPollWorker(
 
 	for {
 		select {
-		case <-cancelChan:
+		case <-ctx.Done():
 			return
 
 		case <-keepAliveTicker.C: