Allow custom retry interval

lib/retry.js

@@ -64,16 +64,20 @@ export default function retry(times, task, callback) {
     var DEFAULT_TIMES = 5;
     var DEFAULT_INTERVAL = 0;
 
-
     var opts = {
         times: DEFAULT_TIMES,
-        interval: DEFAULT_INTERVAL
+        intervalFunc: constantIntervalFunc(DEFAULT_INTERVAL)
     };
 
     function parseTimes(acc, t) {
         if (typeof t === 'object') {
             acc.times = +t.times || DEFAULT_TIMES;
-            acc.interval = +t.interval || DEFAULT_INTERVAL;
+
+            if (typeof t.interval === 'function') {
+                acc.intervalFunc = t.interval;
+            } else {
+                acc.intervalFunc = constantIntervalFunc(+t.interval || DEFAULT_INTERVAL);
+            }
         } else if (typeof t === 'number' || typeof t === 'string') {
             acc.times = +t || DEFAULT_TIMES;
         } else {
@@ -95,13 +99,13 @@ export default function retry(times, task, callback) {
         throw new Error("Invalid arguments for async.retry");
     }
 
-
     var attempts = [];
-    while (opts.times) {
-        var isFinalAttempt = !(opts.times -= 1);
+    for (var i = 1; i < opts.times + 1; i++) {
+        var isFinalAttempt = (i == opts.times);
         attempts.push(retryAttempt(isFinalAttempt));
-        if (!isFinalAttempt && opts.interval > 0) {
-            attempts.push(retryInterval(opts.interval));
+        var interval = opts.intervalFunc(i);
+        if (!isFinalAttempt && interval > 0) {
+            attempts.push(retryInterval(interval));
         }
     }
 
@@ -129,4 +133,10 @@ export default function retry(times, task, callback) {
             }, interval);
         };
     }
+
+    function constantIntervalFunc(interval) {
+        return function() {
+            return interval;
+        };
+    }
 }

mocha_test/retry.js

@@ -23,7 +23,7 @@ describe("retry", function () {
         });
     });
 
-    it('retry when all attempts succeeds',function(done) {
+    it('retry when all attempts fail',function(done) {
         var times = 3;
         var callCount = 0;
         var error = 'ERROR';
@@ -53,7 +53,7 @@ describe("retry", function () {
         done();
     });
 
-    it('retry with interval when all attempts succeeds',function(done) {
+    it('retry with interval when all attempts fail',function(done) {
         var times = 3;
         var interval = 50;
         var callCount = 0;
@@ -75,6 +75,28 @@ describe("retry", function () {
         });
     });
 
+    it('retry with custom interval when all attempts fail',function(done) {
+        var times = 3;
+        var intervalFunc = function(retryCount) { return retryCount * 100; };
+        var callCount = 0;
+        var error = 'ERROR';
+        var erroredResult = 'RESULT';
+        function fn(callback) {
+            callCount++;
+            callback(error + callCount, erroredResult + callCount); // respond with indexed values
+        }
+        var start = new Date().getTime();
+        async.retry({ times: times, interval: intervalFunc}, fn, function(err, result){
+            var now = new Date().getTime();
+            var duration = now - start;
+            assert(duration >= 300,  'did not include custom interval');
+            assert.equal(callCount, 3, "did not retry the correct number of times");
+            assert.equal(err, error + times, "Incorrect error was returned");
+            assert.equal(result, erroredResult + times, "Incorrect result was returned");
+            done();
+        });
+    });
+
     it("should not require a callback", function (done) {
         var called = false;
         async.retry(3, function(cb) {