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8.8 KiB
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228 lines
8.8 KiB
Markdown
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[](http://travis-ci.org/tim-kos/node-retry "Check this project's build status on TravisCI")
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[](https://codecov.io/gh/tim-kos/node-retry)
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# retry
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Abstraction for exponential and custom retry strategies for failed operations.
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## Installation
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npm install retry
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## Current Status
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This module has been tested and is ready to be used.
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## Tutorial
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The example below will retry a potentially failing `dns.resolve` operation
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`10` times using an exponential backoff strategy. With the default settings, this
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means the last attempt is made after `17 minutes and 3 seconds`.
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``` javascript
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var dns = require('dns');
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var retry = require('retry');
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function faultTolerantResolve(address, cb) {
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var operation = retry.operation();
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operation.attempt(function(currentAttempt) {
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dns.resolve(address, function(err, addresses) {
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if (operation.retry(err)) {
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return;
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}
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cb(err ? operation.mainError() : null, addresses);
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});
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});
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}
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faultTolerantResolve('nodejs.org', function(err, addresses) {
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console.log(err, addresses);
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});
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```
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Of course you can also configure the factors that go into the exponential
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backoff. See the API documentation below for all available settings.
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currentAttempt is an int representing the number of attempts so far.
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``` javascript
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var operation = retry.operation({
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retries: 5,
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factor: 3,
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minTimeout: 1 * 1000,
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maxTimeout: 60 * 1000,
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randomize: true,
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});
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```
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## API
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### retry.operation([options])
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Creates a new `RetryOperation` object. `options` is the same as `retry.timeouts()`'s `options`, with two additions:
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* `forever`: Whether to retry forever, defaults to `false`.
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* `unref`: Whether to [unref](https://nodejs.org/api/timers.html#timers_unref) the setTimeout's, defaults to `false`.
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* `maxRetryTime`: The maximum time (in milliseconds) that the retried operation is allowed to run. Default is `Infinity`.
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### retry.timeouts([options])
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Returns an array of timeouts. All time `options` and return values are in
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milliseconds. If `options` is an array, a copy of that array is returned.
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`options` is a JS object that can contain any of the following keys:
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* `retries`: The maximum amount of times to retry the operation. Default is `10`. Seting this to `1` means `do it once, then retry it once`.
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* `factor`: The exponential factor to use. Default is `2`.
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* `minTimeout`: The number of milliseconds before starting the first retry. Default is `1000`.
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* `maxTimeout`: The maximum number of milliseconds between two retries. Default is `Infinity`.
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* `randomize`: Randomizes the timeouts by multiplying with a factor between `1` to `2`. Default is `false`.
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The formula used to calculate the individual timeouts is:
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```
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Math.min(random * minTimeout * Math.pow(factor, attempt), maxTimeout)
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```
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Have a look at [this article][article] for a better explanation of approach.
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If you want to tune your `factor` / `times` settings to attempt the last retry
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after a certain amount of time, you can use wolfram alpha. For example in order
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to tune for `10` attempts in `5 minutes`, you can use this equation:
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Explaining the various values from left to right:
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* `k = 0 ... 9`: The `retries` value (10)
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* `1000`: The `minTimeout` value in ms (1000)
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* `x^k`: No need to change this, `x` will be your resulting factor
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* `5 * 60 * 1000`: The desired total amount of time for retrying in ms (5 minutes)
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To make this a little easier for you, use wolfram alpha to do the calculations:
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<http://www.wolframalpha.com/input/?i=Sum%5B1000*x^k%2C+{k%2C+0%2C+9}%5D+%3D+5+*+60+*+1000>
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[article]: http://dthain.blogspot.com/2009/02/exponential-backoff-in-distributed.html
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### retry.createTimeout(attempt, opts)
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Returns a new `timeout` (integer in milliseconds) based on the given parameters.
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`attempt` is an integer representing for which retry the timeout should be calculated. If your retry operation was executed 4 times you had one attempt and 3 retries. If you then want to calculate a new timeout, you should set `attempt` to 4 (attempts are zero-indexed).
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`opts` can include `factor`, `minTimeout`, `randomize` (boolean) and `maxTimeout`. They are documented above.
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`retry.createTimeout()` is used internally by `retry.timeouts()` and is public for you to be able to create your own timeouts for reinserting an item, see [issue #13](https://github.com/tim-kos/node-retry/issues/13).
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### retry.wrap(obj, [options], [methodNames])
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Wrap all functions of the `obj` with retry. Optionally you can pass operation options and
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an array of method names which need to be wrapped.
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```
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retry.wrap(obj)
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retry.wrap(obj, ['method1', 'method2'])
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retry.wrap(obj, {retries: 3})
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retry.wrap(obj, {retries: 3}, ['method1', 'method2'])
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```
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The `options` object can take any options that the usual call to `retry.operation` can take.
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### new RetryOperation(timeouts, [options])
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Creates a new `RetryOperation` where `timeouts` is an array where each value is
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a timeout given in milliseconds.
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Available options:
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* `forever`: Whether to retry forever, defaults to `false`.
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* `unref`: Wether to [unref](https://nodejs.org/api/timers.html#timers_unref) the setTimeout's, defaults to `false`.
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If `forever` is true, the following changes happen:
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* `RetryOperation.errors()` will only output an array of one item: the last error.
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* `RetryOperation` will repeatedly use the `timeouts` array. Once all of its timeouts have been used up, it restarts with the first timeout, then uses the second and so on.
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#### retryOperation.errors()
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Returns an array of all errors that have been passed to `retryOperation.retry()` so far. The
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returning array has the errors ordered chronologically based on when they were passed to
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`retryOperation.retry()`, which means the first passed error is at index zero and the last is
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at the last index.
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#### retryOperation.mainError()
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A reference to the error object that occured most frequently. Errors are
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compared using the `error.message` property.
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If multiple error messages occured the same amount of time, the last error
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object with that message is returned.
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If no errors occured so far, the value is `null`.
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#### retryOperation.attempt(fn, timeoutOps)
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Defines the function `fn` that is to be retried and executes it for the first
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time right away. The `fn` function can receive an optional `currentAttempt` callback that represents the number of attempts to execute `fn` so far.
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Optionally defines `timeoutOps` which is an object having a property `timeout` in miliseconds and a property `cb` callback function.
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Whenever your retry operation takes longer than `timeout` to execute, the timeout callback function `cb` is called.
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#### retryOperation.try(fn)
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This is an alias for `retryOperation.attempt(fn)`. This is deprecated. Please use `retryOperation.attempt(fn)` instead.
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#### retryOperation.start(fn)
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This is an alias for `retryOperation.attempt(fn)`. This is deprecated. Please use `retryOperation.attempt(fn)` instead.
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#### retryOperation.retry(error)
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Returns `false` when no `error` value is given, or the maximum amount of retries
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has been reached.
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Otherwise it returns `true`, and retries the operation after the timeout for
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the current attempt number.
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#### retryOperation.stop()
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Allows you to stop the operation being retried. Useful for aborting the operation on a fatal error etc.
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#### retryOperation.reset()
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Resets the internal state of the operation object, so that you can call `attempt()` again as if this was a new operation object.
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#### retryOperation.attempts()
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Returns an int representing the number of attempts it took to call `fn` before it was successful.
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## License
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retry is licensed under the MIT license.
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# Changelog
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0.10.0 Adding `stop` functionality, thanks to @maxnachlinger.
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0.9.0 Adding `unref` functionality, thanks to @satazor.
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0.8.0 Implementing retry.wrap.
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0.7.0 Some bug fixes and made retry.createTimeout() public. Fixed issues [#10](https://github.com/tim-kos/node-retry/issues/10), [#12](https://github.com/tim-kos/node-retry/issues/12), and [#13](https://github.com/tim-kos/node-retry/issues/13).
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0.6.0 Introduced optional timeOps parameter for the attempt() function which is an object having a property timeout in milliseconds and a property cb callback function. Whenever your retry operation takes longer than timeout to execute, the timeout callback function cb is called.
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0.5.0 Some minor refactoring.
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0.4.0 Changed retryOperation.try() to retryOperation.attempt(). Deprecated the aliases start() and try() for it.
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0.3.0 Added retryOperation.start() which is an alias for retryOperation.try().
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0.2.0 Added attempts() function and parameter to retryOperation.try() representing the number of attempts it took to call fn().
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