fix(Sentinel): unreachable errors when sentinals are healthy

lib/connectors/SentinelConnector/SentinelIterator.ts

@@ -0,0 +1,43 @@
+import {ISentinelAddress} from './types'
+
+function isSentinelEql (a: ISentinelAddress, b: ISentinelAddress): boolean {
+  return ((a.host || '127.0.0.1') === (b.host || '127.0.0.1')) &&
+    ((a.port || 26379) === (b.port || 26379))
+}
+
+export default class SentinelIterator {
+  private cursor: number = 0
+
+  constructor (private sentinels: ISentinelAddress[]) {}
+
+  hasNext (): boolean {
+    return this.cursor < this.sentinels.length
+  }
+
+  next (): ISentinelAddress | null {
+    return this.hasNext() ? this.sentinels[this.cursor++] : null
+  }
+
+  reset (success: boolean): void {
+    if (success && this.sentinels.length > 1 && this.cursor !== 1) {
+      const remains = this.sentinels.slice(this.cursor - 1)
+      this.sentinels = remains.concat(this.sentinels.slice(0, this.cursor - 1))
+    }
+    this.cursor = 0
+  }
+
+  add (sentinel: ISentinelAddress): boolean {
+    for (let i = 0; i < this.sentinels.length; i++) {
+      if (isSentinelEql(sentinel, this.sentinels[i])) {
+        return false
+      }
+    }
+
+    this.sentinels.push(sentinel)
+    return true
+  }
+
+  toString (): string {
+    return JSON.stringify(this.sentinels)
+  }
+}