feat(onretry): Add options.onRetry (#48)

Fixes: #21

README.md

@@ -27,6 +27,7 @@ pooling, proxies, retries, [and more](#features)!
     * [`opts.ca, opts.cert, opts.key`](#https-opts)
     * [`opts.maxSockets`](#opts-max-sockets)
     * [`opts.retry`](#opts-retry)
+    * [`opts.onRetry`](#opts-onretry)
     * [`opts.integrity`](#opts-integrity)
 * [Message From Our Sponsors](#wow)
 
@@ -143,6 +144,7 @@ make-fetch-happen augments the `node-fetch` API with additional features availab
 * [`opts.localAddress`](#opts-local-address)
 * [`opts.maxSockets`](#opts-max-sockets)
 * [`opts.retry`](#opts-retry) - Request retry settings
+* [`opts.onRetry`](#opts-onretry) - a function called whenever a retry is attempted
 * [`opts.integrity`](#opts-integrity) - [Subresource Integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity) metadata.
 
 #### <a name="opts-cache-manager"></a> `> opts.cacheManager`
@@ -363,6 +365,20 @@ fetch('http://one-more.site.com', {
 })
 ```
 
+#### <a name="opts-onretry"></a> `> opts.onRetry`
+
+A function called whenever a retry is attempted.
+
+##### Example
+
+```javascript
+fetch('https://flaky.site.com', {
+  onRetry() {
+    console.log('we will retry!')
+  }
+})
+```
+
 #### <a name="opts-integrity"></a> `> opts.integrity`
 
 Matches the response body against the given [Subresource Integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity) metadata. If verification fails, the request will fail with an `EINTEGRITY` error.
@@ -376,7 +392,7 @@ fetch('https://registry.npmjs.org/make-fetch-happen/-/make-fetch-happen-1.0.0.tg
   integrity: 'sha1-o47j7zAYnedYFn1dF/fR9OV3z8Q='
 }) // -> ok
 
-fetch('https://malicious-registry.org/make-fetch-happen/-/make-fetch-happen-1.0.0.tgz'. {
+fetch('https://malicious-registry.org/make-fetch-happen/-/make-fetch-happen-1.0.0.tgz', {
   integrity: 'sha1-o47j7zAYnedYFn1dF/fR9OV3z8Q='
 }) // Error: EINTEGRITY
 ```

index.js

@@ -355,6 +355,10 @@ function remoteFetch (uri, opts) {
             if (!isMethodGetHead) {
               return opts.cacheManager.delete(req).then(() => {
                 if (res.status >= 500 && req.method !== 'POST' && !isStream) {
+                  if (typeof opts.onRetry === 'function') {
+                    opts.onRetry(res)
+                  }
+
                   return retryHandler(res)
                 }
 
@@ -372,6 +376,10 @@ function remoteFetch (uri, opts) {
             )
 
           if (isRetriable) {
+            if (typeof opts.onRetry === 'function') {
+              opts.onRetry(res)
+            }
+
             return retryHandler(res)
           }
 
@@ -439,6 +447,10 @@ function remoteFetch (uri, opts) {
             throw err
           }
 
+          if (typeof opts.onRetry === 'function') {
+            opts.onRetry(err)
+          }
+
           return retryHandler(err)
         })
     },

test/fetch.js

@@ -442,4 +442,30 @@ test('accepts opts.retry shorthands', t => {
   })
 })
 
+test('calls opts.onRetry', t => {
+  const srv = tnock(t, HOST)
+  let retryNotification = 0
+  let attempt = 0
+
+  srv.get('/test').delay(100).times(2).reply(200, () => {
+    attempt++
+    if (attempt >= 2) {
+      srv.get('/test').reply(200, CONTENT)
+    }
+    return null
+  })
+  return fetch(`${HOST}/test`, {
+    timeout: 50,
+    retry: {
+      retries: 2,
+      minTimeout: 5
+    },
+    onRetry: () => {
+      retryNotification++
+    }
+  }).then(() => {
+    t.equal(retryNotification, 2, 'onRetry was called correct number of times')
+  })
+})
+
 test('retries non-POST requests on ECONNRESET')