fileio: Sandboxed Filesystem

File Sandbox

The filesystem used by Opera Unite is located deep in the /Documents and Settings/ folder, so there is no real way to load file with absolute path (i.e. get out of sandbox and do something nasty). For futher explanation - see fileio docs →.

In short - you can only access the storage folder (where your app creates files) or folder where your app resides (in read-only mode) or folder explicitly specified by user.

File reading/saving

A full example is file_wrap.js.

Here's an example of how to Load/Save a simple integer var:

1. Start with Basic HowTo, then:

Enabling fileio library

Change config.xml, add this:
(right above <feature name="http://xmlns.opera.com/webserver">):

<feature name="http://xmlns.opera.com/fileio">
</feature>

This enabled Opera Unite to use filesystem.

How to load from file

This line is common for both reading and writing:

var dir = opera.io.filesystem.mountSystemDirectory('storage');

Then:

try {
	stream = dir.open(dir.resolve('/storage/newfile'),    
        opera.io.filemode.READ);
	if (stream) {
		var counter = parseInt(stream.readLine());
		stream.close();
	};
} catch(err) { // message: FILE_NOT_FOUND_ERR
	var counter = 0;
};

Warning This reads only one line. To read whole file, see file_wrap.js

Opera says → there's a method .exists(), that could be used to check whether file exists, but I haven't found it. (Tried all combinations I can think of) dir.open raises FILE_NOT_FOUND_ERR Exception if it haven't found file.

These lines above are loading integer from a file /storage/newfile/. It's not an absolute path, the read path would be smth. like: /Documents and settings/..../Local settings/..../4393408934/storage/newfile (this is why it's Sandbox - you can't go to just any arbitrary file, unless you use shared folder)

How to save to file

var stream = dir.open('/storage/newfile', opera.io.filemode.WRITE);
stream.write(counter);
stream.close();

Sources

Example counter source →
This source is suboptimal, due to the fact that it saves each time a request is made, but I haven't found a way to save only when Opera/service closes.

There's no onunload, but there's '_close event' that does the same. The code for saving the state should go there.

JSON

Ideally we need to save JSON representation of object, but I haven't discovered a simple way to use JSON under Opera Unite.

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