Replace database locks with transactions (#1701)

This commits removes the locks used to guard data integrity for the
database and replaces them with Transactions, turns out that SQL had
a way to deal with this all along.

This reduces the complexity we had with multiple locks that might stack
or recurse (database, nofitifer, mapper). All notifications and state
updates are now triggered _after_ a database change.


Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/types/common.go

@@ -1,15 +1,19 @@
 package types
 
 import (
+	"context"
 	"database/sql/driver"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"net/netip"
+	"time"
 
 	"tailscale.com/tailcfg"
 )
 
+const SelfUpdateIdentifier = "self-update"
+
 var ErrCannotParsePrefix = errors.New("cannot parse prefix")
 
 type IPPrefix netip.Prefix
@@ -160,3 +164,37 @@ func (su *StateUpdate) Valid() bool {
 
 	return true
 }
+
+// Empty reports if there are any updates in the StateUpdate.
+func (su *StateUpdate) Empty() bool {
+	switch su.Type {
+	case StatePeerChanged:
+		return len(su.ChangeNodes) == 0
+	case StatePeerChangedPatch:
+		return len(su.ChangePatches) == 0
+	case StatePeerRemoved:
+		return len(su.Removed) == 0
+	}
+
+	return false
+}
+
+func StateUpdateExpire(nodeID uint64, expiry time.Time) StateUpdate {
+	return StateUpdate{
+		Type: StatePeerChangedPatch,
+		ChangePatches: []*tailcfg.PeerChange{
+			{
+				NodeID:    tailcfg.NodeID(nodeID),
+				KeyExpiry: &expiry,
+			},
+		},
+	}
+}
+
+func NotifyCtx(ctx context.Context, origin, hostname string) context.Context {
+	ctx2, _ := context.WithTimeout(
+		context.WithValue(context.WithValue(ctx, "hostname", hostname), "origin", origin),
+		3*time.Second,
+	)
+	return ctx2
+}