如何通过Ajax将下载的文件保留在内存中

Question

I am making a html5 web app based on an existing ios app. It targets most recent two versions of ios Safari browser. For this web app to work, I need to use an api that handles communication between current ios app and php backend.

The very first hurdle is that api config files (gzipped) needs to be downloaded from server on a regular basis (for example each time app starts) to keep itself updated. Then I need to unzip to get config files, which basically contains key-value pairs of command name and http address. When I need certain command, eg display a user's profile pic, I lookup the config files by command number to find the corresponding request address so that I could make request to server.

To summerize the steps:

1. Download (gziped) configuration files by ajax
   
   I don't think html anchor tag (with or without download attribute) is an option. Because in that way Safari will prompt user to open the downloaded file using file handling apps (eg FilesApp). The download must happen in the dark.

2. Unzip the downloaded file
   
   I know a few js library promise to do this work. I haven't tested them yet for step one is not solved. Any recommandatio is welcomed.

3. Lookup http address in those files whenever making a api call
   
   It should be no problem though.

For ios app, I can simply download the config files into app sandbox and do whatever I want with it. But for web app, even newest ios Safari don't suppor HTML5 file system api. What can I do?

Answer 1

Step 1.

Safari should support HTTP compression. Your best best is to leverage this, as opposed to figuring out a way to unzip a file using JavaScript. It looks like there are a few options with PHP:

• http://php.net/manual/en/zlib.configuration.php
• http://php.net/manual/en/function.ob-gzhandler.php

Or even at the server level:

• http://httpd.apache.org/docs/2.2/mod/mod_deflate.html

Step 2.

Use sessionStorage to cache the configuration settings. The data will be cleared out each time a user closes their browser.

Step 3.

The PHP handler that is called by the AJAX request should take care of parsing the config files and send JavaScript-friendly JSON to the browser. Use JSON.parse() and JSON.stringify() to serialize/de-serialize data as you read/save to sessionStorage .