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113 lines
3.7 KiB
Markdown
113 lines
3.7 KiB
Markdown
---
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title: appcache
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description: Documentation of Meteor's `appcache` package.
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---
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The `appcache` package stores the static parts of a Meteor application
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(the client side Javascript, HTML, CSS, and images) in the browser's
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[application cache](https://en.wikipedia.org/wiki/AppCache). To enable
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caching simply add the `appcache` package to your project.
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* Once a user has visited a Meteor application for the first time and
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the application has been cached, on subsequent visits the web page
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loads faster because the browser can load the application out of the
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cache without contacting the server first.
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* Hot code pushes are loaded by the browser in the background while the
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app continues to run. Once the new code has been fully loaded the
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browser is able to switch over to the new code quickly.
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* The application cache allows the application to be loaded even when
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the browser doesn't have an Internet connection, and so enables using
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the app offline.
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(Note however that the `appcache` package by itself doesn't make
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*data* available offline: in an application loaded offline, a Meteor
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Collection will appear to be empty in the client until the Internet
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becomes available and the browser is able to establish a DDP
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connection).
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To turn AppCache off for specific browsers use:
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```js
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Meteor.AppCache.config({
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chrome: false,
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firefox: false
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});
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```
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The supported browsers that can be enabled or disabled include, but are
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not limited to, `android`, `chrome`, `chromium`, `chromeMobileIOS`,
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`firefox`, `ie`, `mobileSafari` and `safari`.
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Browsers limit the amount of data they will put in the application
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cache, which can vary due to factors such as how much disk space is
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free. Unfortunately if your application goes over the limit rather
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than disabling the application cache altogether and running the
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application online, the browser will instead fail that particular
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*update* of the cache, leaving your users running old code.
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Thus it's best to keep the size of the cache below 5MB. The
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`appcache` package will print a warning on the Meteor server console
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if the total size of the resources being cached is over 5MB.
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Starting from `appcache@1.2.5`, if you need more advanced logic
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to enable/disable the cache, you can use the `enableCallback` option
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that is evaluated on a per-request basis. For example:
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```js
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// Enable offline mode using a value from database and certificate validation
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Meteor.AppCache.config({
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// This option is available starting from appcache@1.2.4
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enableCallback: () => {
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if (!getSettingsFromDb("public.appcache_enabled")) {
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return false;
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}
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const validation = validateClientCert({
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clientCertPayload: req.headers["x-client-cert"],
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url: req.url.href,
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});
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return validation.passed;
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},
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});
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```
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If you have files too large to fit in the cache you can disable
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caching by URL prefix. For example,
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```js
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Meteor.AppCache.config({ onlineOnly: ['/online/'] });
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```
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causes files in your `public/online` directory to not be cached, and
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so they will only be available online. You can then move your large
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files into that directory and refer to them at the new URL:
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```html
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<img src="/online/bigimage.jpg">
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```
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If you'd prefer not to move your files, you can use the file names
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themselves as the URL prefix:
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```js
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Meteor.AppCache.config({
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onlineOnly: [
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'/bigimage.jpg',
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'/largedata.json'
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]
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});
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```
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though keep in mind that since the exclusion is by prefix (this is a
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limitation of the application cache manifest), excluding
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`/largedata.json` will also exclude such URLs as
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`/largedata.json.orig` and `/largedata.json/file1`.
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For more information about how Meteor interacts with the application
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cache, see the
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[AppCache page](https://github.com/meteor/meteor/wiki/AppCache)
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in the Meteor wiki.
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