feat: only read from master (ali-sdk#623)

set options.masterOnly = true to enable the feature

pick from ali-sdk#622

Author: fengmk2

lib/cluster.js

@@ -31,6 +31,8 @@ module.exports = function (OssClient) {
     }
 
     this.schedule = options.schedule || RR;
+    // only read from master, default is false
+    this.masterOnly = !!options.masterOnly;
     this.index = 0;
 
     const heartbeatInterval = options.heartbeatInterval || 10000;
@@ -180,6 +182,10 @@ module.exports = function (OssClient) {
 
   proto.chooseAvailable = function chooseAvailable() {
     if (this.schedule === MS) {
+      // only read from master
+      if (this.masterOnly) {
+        return this.clients[0];
+      }
       for (let i = 0; i < this.clients.length; i++) {
         if (this.availables[i]) {
           return this.clients[i];

test/node/cluster.test.js

@@ -230,6 +230,23 @@ describe('test/cluster.test.js', () => {
       this.store.removeListener('error', onerror);
     });
 
+    it('should MS always get from clients[0] when masterOnly === true', async function () {
+      mm(this.store, 'schedule', 'masterSlave');
+      mm(this.store, 'masterOnly', true);
+      mm(this.store.clients[1], 'get', 'mock error');
+      function onerror() {
+        throw new Error('should not emit error event');
+      }
+      this.store.on('error', onerror);
+
+      let res = await this.store.get(this.name);
+      res.res.status.should.equal(200);
+      res = await this.store.get(this.name);
+      res.res.status.should.equal(200);
+
+      this.store.removeListener('error', onerror);
+    });
+
     it('should get from clients[0] when clients[0] response 4xx ok', async function () {
       mm(this.store, 'schedule', 'masterSlave');
       mm.error(this.store.clients[0], 'get', 'mock error', { status: 403 });