feat(lease): allow leases to be passively released (fixes #69)

src/lease.ts

@@ -151,6 +151,15 @@ export class Lease extends EventEmitter {
     });
   }
 
+  /**
+   * releasePassively stops making heartbeats for the lease, and allows it
+   * to expire automatically when its TTL rolls around. Use `revoke()` to
+   * actively tell etcd to terminate the lease.
+   */
+  public release() {
+    this.close();
+  }
+
   /**
    * Put returns a put builder that operates within the current lease.
    */

test/lease.test.ts

@@ -30,7 +30,7 @@ describe('lease()', () => {
 
   it('throws if trying to use too short of a ttl, or an undefined ttl', () => {
     expect(() => client.lease(0)).to.throw(/must be at least 1 second/);
-    expect(() => (<any> client.lease)()).to.throw(/must be at least 1 second/);
+    expect(() => (<any>client.lease)()).to.throw(/must be at least 1 second/);
   });
 
   it('reports a loss and errors if the client is invalid', async () => {
@@ -152,6 +152,13 @@ describe('lease()', () => {
       expect(res.TTL).to.equal('60');
     });
 
+    it('stops touching the lease if released passively', async () => {
+      const kaFired = watchEmission('keepaliveFired');
+      lease.release();
+      clock.tick(20000);
+      expect(kaFired.fired).to.be.false;
+    });
+
     it('tears down if the lease gets revoked', async () => {
       await client.leaseClient.leaseRevoke({ ID: await lease.grant() });
       clock.tick(20000);