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1# Class: RetryHandler
2
3Extends: `undici.DispatcherHandlers`
4
5A handler class that implements the retry logic for a request.
6
7## `new RetryHandler(dispatchOptions, retryHandlers, [retryOptions])`
8
9Arguments:
10
11- **options** `Dispatch.DispatchOptions & RetryOptions` (required) - It is an intersection of `Dispatcher.DispatchOptions` and `RetryOptions`.
12- **retryHandlers** `RetryHandlers` (required) - Object containing the `dispatch` to be used on every retry, and `handler` for handling the `dispatch` lifecycle.
13
14Returns: `retryHandler`
15
16### Parameter: `Dispatch.DispatchOptions & RetryOptions`
17
18Extends: [`Dispatch.DispatchOptions`](Dispatcher.md#parameter-dispatchoptions).
19
20#### `RetryOptions`
21
22- **retry** `(err: Error, context: RetryContext, callback: (err?: Error | null) => void) => void` (optional) - Function to be called after every retry. It should pass error if no more retries should be performed.
23- **maxRetries** `number` (optional) - Maximum number of retries. Default: `5`
24- **maxTimeout** `number` (optional) - Maximum number of milliseconds to wait before retrying. Default: `30000` (30 seconds)
25- **minTimeout** `number` (optional) - Minimum number of milliseconds to wait before retrying. Default: `500` (half a second)
26- **timeoutFactor** `number` (optional) - Factor to multiply the timeout by for each retry attempt. Default: `2`
27- **retryAfter** `boolean` (optional) - It enables automatic retry after the `Retry-After` header is received. Default: `true`
28-
29- **methods** `string[]` (optional) - Array of HTTP methods to retry. Default: `['GET', 'PUT', 'HEAD', 'OPTIONS', 'DELETE']`
30- **statusCodes** `number[]` (optional) - Array of HTTP status codes to retry. Default: `[429, 500, 502, 503, 504]`
31- **errorCodes** `string[]` (optional) - Array of Error codes to retry. Default: `['ECONNRESET', 'ECONNREFUSED', 'ENOTFOUND', 'ENETDOWN','ENETUNREACH', 'EHOSTDOWN',
32
33**`RetryContext`**
34
35- `state`: `RetryState` - Current retry state. It can be mutated.
36- `opts`: `Dispatch.DispatchOptions & RetryOptions` - Options passed to the retry handler.
37
38### Parameter `RetryHandlers`
39
40- **dispatch** `(options: Dispatch.DispatchOptions, handlers: Dispatch.DispatchHandlers) => Promise<Dispatch.DispatchResponse>` (required) - Dispatch function to be called after every retry.
41- **handler** Extends [`Dispatch.DispatchHandlers`](Dispatcher.md#dispatcherdispatchoptions-handler) (required) - Handler function to be called after the request is successful or the retries are exhausted.
42
43Examples:
44
45```js
46const client = new Client(`http://localhost:${server.address().port}`);
47const chunks = [];
48const handler = new RetryHandler(
49  {
50    ...dispatchOptions,
51    retryOptions: {
52      // custom retry function
53      retry: function (err, state, callback) {
54        counter++;
55
56        if (err.code && err.code === "UND_ERR_DESTROYED") {
57          callback(err);
58          return;
59        }
60
61        if (err.statusCode === 206) {
62          callback(err);
63          return;
64        }
65
66        setTimeout(() => callback(null), 1000);
67      },
68    },
69  },
70  {
71    dispatch: (...args) => {
72      return client.dispatch(...args);
73    },
74    handler: {
75      onConnect() {},
76      onBodySent() {},
77      onHeaders(status, _rawHeaders, resume, _statusMessage) {
78        // do something with headers
79      },
80      onData(chunk) {
81        chunks.push(chunk);
82        return true;
83      },
84      onComplete() {},
85      onError() {
86        // handle error properly
87      },
88    },
89  }
90);
91```
92
93#### Example - Basic RetryHandler with defaults
94
95```js
96const client = new Client(`http://localhost:${server.address().port}`);
97const handler = new RetryHandler(dispatchOptions, {
98  dispatch: client.dispatch.bind(client),
99  handler: {
100    onConnect() {},
101    onBodySent() {},
102    onHeaders(status, _rawHeaders, resume, _statusMessage) {},
103    onData(chunk) {},
104    onComplete() {},
105    onError(err) {},
106  },
107});
108```
109