chain: allow setting the client's birthday after creation

chain/bitcoind_client.go

@@ -108,6 +108,10 @@ type BitcoindClient struct {
 	wg   sync.WaitGroup
 }
 
+// A compile-time check to ensure that BitcoindClient satisfies the
+// chain.Interface interface.
+var _ Interface = (*BitcoindClient)(nil)
+
 // BackEnd returns the name of the driver.
 func (c *BitcoindClient) BackEnd() string {
 	return "bitcoind"
@@ -596,6 +600,14 @@ func (c *BitcoindClient) ntfnHandler() {
 	}
 }
 
+// SetBirthday sets the birthday of the bitcoind rescan client.
+//
+// NOTE: This should be done before the client has been started in order for it
+// to properly carry its duties.
+func (c *BitcoindClient) SetBirthday(t time.Time) {
+	c.birthday = t
+}
+
 // BlockStamp returns the latest block notified by the client, or an error
 // if the client has been shut down.
 func (c *BitcoindClient) BlockStamp() (*waddrmgr.BlockStamp, error) {

chain/bitcoind_conn.go

@@ -333,15 +333,13 @@ func (c *BitcoindConn) getCurrentNet() (wire.BitcoinNet, error) {
 
 // NewBitcoindClient returns a bitcoind client using the current bitcoind
 // connection. This allows us to share the same connection using multiple
-// clients. The birthday signifies the earliest time for which we should begin
-// scanning the chain.
-func (c *BitcoindConn) NewBitcoindClient(birthday time.Time) *BitcoindClient {
+// clients.
+func (c *BitcoindConn) NewBitcoindClient() *BitcoindClient {
 	return &BitcoindClient{
 		quit: make(chan struct{}),
 
 		id: atomic.AddUint64(&c.rescanClientCounter, 1),
 
-		birthday:    birthday,
 		chainParams: c.chainParams,
 		chainConn:   c,