Always load machine object from DB before save/modify

We are currently holding Machine objects in memory for a long time,
while waiting for stream/longpoll, this might make us end up with stale
objects, that we just call save on, potentially overwriting stuff in
the database.

A typical scenario would be someone changing something from the CLI,
e.g. enabling routes, which in turn is overwritten again by the stale
object in the longpolling function.

The code has been left with TODO's and a discussion is available in juanfont#93.

poll.go

@@ -79,6 +79,18 @@ func (h *Headscale) PollNetMapHandler(c *gin.Context) {
 	//
 	// The intended use is for clients to discover the DERP map at start-up
 	// before their first real endpoint update.
+
+	// TODO: Abstract away all the database calls, this can cause race conditions
+	// when an outdated machine object is kept alive, e.g. db is update from
+	// command line, but then overwritten.
+	err = h.UpdateMachine(&m)
+	if err != nil {
+		log.Error().
+			Str("handler", "PollNetMap").
+			Str("machine", m.Name).
+			Err(err).
+			Msg("Cannot update machine from database")
+	}
 	if !req.ReadOnly {
 		endpoints, _ := json.Marshal(req.Endpoints)
 		m.Endpoints = datatypes.JSON(endpoints)
@@ -234,6 +246,18 @@ func (h *Headscale) PollNetMapStream(
 				Str("channel", "pollData").
 				Int("bytes", len(data)).
 				Msg("Data from pollData channel written successfully")
+				// TODO: Abstract away all the database calls, this can cause race conditions
+				// when an outdated machine object is kept alive, e.g. db is update from
+				// command line, but then overwritten.
+			err = h.UpdateMachine(&m)
+			if err != nil {
+				log.Error().
+					Str("handler", "PollNetMapStream").
+					Str("machine", m.Name).
+					Str("channel", "pollData").
+					Err(err).
+					Msg("Cannot update machine from database")
+			}
 			now := time.Now().UTC()
 			m.LastSeen = &now
 			m.LastSuccessfulUpdate = &now
@@ -268,6 +292,18 @@ func (h *Headscale) PollNetMapStream(
 				Str("channel", "keepAlive").
 				Int("bytes", len(data)).
 				Msg("Keep alive sent successfully")
+				// TODO: Abstract away all the database calls, this can cause race conditions
+				// when an outdated machine object is kept alive, e.g. db is update from
+				// command line, but then overwritten.
+			err = h.UpdateMachine(&m)
+			if err != nil {
+				log.Error().
+					Str("handler", "PollNetMapStream").
+					Str("machine", m.Name).
+					Str("channel", "keepAlive").
+					Err(err).
+					Msg("Cannot update machine from database")
+			}
 			now := time.Now().UTC()
 			m.LastSeen = &now
 			h.db.Save(&m)
@@ -316,10 +352,22 @@ func (h *Headscale) PollNetMapStream(
 					Str("channel", "update").
 					Msg("Updated Map has been sent")
 
-				// Keep track of the last successful update,
-				// we sometimes end in a state were the update
-				// is not picked up by a client and we use this
-				// to determine if we should "force" an update.
+					// Keep track of the last successful update,
+					// we sometimes end in a state were the update
+					// is not picked up by a client and we use this
+					// to determine if we should "force" an update.
+					// TODO: Abstract away all the database calls, this can cause race conditions
+					// when an outdated machine object is kept alive, e.g. db is update from
+					// command line, but then overwritten.
+				err = h.UpdateMachine(&m)
+				if err != nil {
+					log.Error().
+						Str("handler", "PollNetMapStream").
+						Str("machine", m.Name).
+						Str("channel", "update").
+						Err(err).
+						Msg("Cannot update machine from database")
+				}
 				now := time.Now().UTC()
 				m.LastSuccessfulUpdate = &now
 				h.db.Save(&m)
@@ -338,6 +386,18 @@ func (h *Headscale) PollNetMapStream(
 				Str("handler", "PollNetMapStream").
 				Str("machine", m.Name).
 				Msg("The client has closed the connection")
+				// TODO: Abstract away all the database calls, this can cause race conditions
+				// when an outdated machine object is kept alive, e.g. db is update from
+				// command line, but then overwritten.
+			err := h.UpdateMachine(&m)
+			if err != nil {
+				log.Error().
+					Str("handler", "PollNetMapStream").
+					Str("machine", m.Name).
+					Str("channel", "Done").
+					Err(err).
+					Msg("Cannot update machine from database")
+			}
 			now := time.Now().UTC()
 			m.LastSeen = &now
 			h.db.Save(&m)