File IO: Difference between revisions

From MozillaZine Knowledge Base
Jump to navigationJump to search
m (native initializers note)
mNo edit summary
Line 1: Line 1:
==Introduction==
=Introduction=
This article describes local file input/output in Javascript.
This article describes local file input/output in Javascript.


Line 8: Line 8:
MonkeeSage's module is much smaller and very easy to use (simple examples are included in the module).
MonkeeSage's module is much smaller and very easy to use (simple examples are included in the module).


==Snippets using XPCOM directly==
=Snippets using XPCOM directly=


===Creating a file object (opening files)===
==Creating a file object (opening files)==
<pre>var file = Components.classes["@mozilla.org/file/local;1"].
<pre>var file = Components.classes["@mozilla.org/file/local;1"].
createInstance(Components.interfaces.nsILocalFile);
createInstance(Components.interfaces.nsILocalFile);
Line 17: Line 17:
Note: the path passed to ''initWithPath()'' should be in 'native' form (eg. <tt>"C:\\Windows"</tt>). If you need to use ''file://'' URIs as initializers, see below.
Note: the path passed to ''initWithPath()'' should be in 'native' form (eg. <tt>"C:\\Windows"</tt>). If you need to use ''file://'' URIs as initializers, see below.


===Opening special files===
==Opening special files==
<pre>// get profile directory
<pre>// get profile directory
var file = Components.classes["@mozilla.org/file/directory_service;1"].
var file = Components.classes["@mozilla.org/file/directory_service;1"].
Line 57: Line 57:




===nsIFile and path strings===
==nsIFile and path strings==
You can use nsIFile::path to get platform-specific path string, eg. <tt>C:\Windows\System32</tt> or <tt>/usr/share</tt>. If you want to get a ''file://'' URL of a file or an nsIFile from ''file://'' URL, you need to use [http://xulplanet.com/references/xpcomref/ifaces/nsIFileProtocolHandler.html nsIFileProtocolHandler]:
You can use nsIFile::path to get platform-specific path string, eg. <tt>C:\Windows\System32</tt> or <tt>/usr/share</tt>. If you want to get a ''file://'' URL of a file or an nsIFile from ''file://'' URL, you need to use [http://xulplanet.com/references/xpcomref/ifaces/nsIFileProtocolHandler.html nsIFileProtocolHandler]:
<pre>// file is nsIFile
<pre>// file is nsIFile
Line 69: Line 69:
Also note that generally you don't need to use nsIFile::path. Use nsIFile directly wherever possible. An example below shows how you should save a path in user prefs.
Also note that generally you don't need to use nsIFile::path. Use nsIFile directly wherever possible. An example below shows how you should save a path in user prefs.


====Saving path in a userpref====
==Saving path in a userpref==
This snippet shows the right way to save a file path in user preferences:
This snippet shows the right way to save a file path in user preferences:
<pre>// |file| is nsILocalFile
<pre>// |file| is nsILocalFile
Line 83: Line 83:




===Navigating with nsIFile===
==Navigating with nsIFile==
====Get a file in given directory====
===Get a file in given directory===
Assume, ''file'' is an nsIFile pointing to some directory (f.e. a user profile directory). You can use this code: <tt>file.append("myfile.txt");</tt> - to make ''file'' point to myfile.txt inside that directory.
Assume, ''file'' is an nsIFile pointing to some directory (f.e. a user profile directory). You can use this code: <tt>file.append("myfile.txt");</tt> - to make ''file'' point to myfile.txt inside that directory.


Line 92: Line 92:
is possible, but the nsIFile::append() is much easier to read and is guaranteed to work on all platforms Mozilla itself works.
is possible, but the nsIFile::append() is much easier to read and is guaranteed to work on all platforms Mozilla itself works.


====Traverse directories====
===Traverse directories===
''todo''
''todo''






===Reading from a file===
==Reading from a file==


====Simple ====
===Simple ===


====Line by line====
===Line by line===
<pre>
<pre>
// open an input stream from file
// open an input stream from file

Revision as of 21:03, 16 September 2004

Introduction

This article describes local file input/output in Javascript.

You access the filesystem using Mozilla XPCOM components. The list of components used for local IO is available at XulPlanet.com.

Available libraries

There are a few JavaScript wrappers for IO XPCOM components. See JSLib and MonkeeSage's IO module. MonkeeSage's module is much smaller and very easy to use (simple examples are included in the module).

Snippets using XPCOM directly

Creating a file object (opening files)

var file = Components.classes["@mozilla.org/file/local;1"].
	createInstance(Components.interfaces.nsILocalFile);
file.initWithPath("/home");

Note: the path passed to initWithPath() should be in 'native' form (eg. "C:\\Windows"). If you need to use file:// URIs as initializers, see below.

Opening special files

// get profile directory
var file = Components.classes["@mozilla.org/file/directory_service;1"].
	createInstance(Components.interfaces.nsIProperties).
	get("ProfD", Components.interfaces.nsIFile);

Here is the list of strings you can put in place of "ProfD" (stolen from MonkeeSage's IO module comments)

String Meaning
ProfD profile directory
DefProfRt user (e.g., /root/.mozilla)
UChrm %profile%/chrome
DefRt installation
PrfDef %installation%/defaults/pref
ProfDefNoLoc %installation%/defaults/profile
APlugns %installation%/plugins
AChrom %installation%/chrome
ComsD %installation%/components
CurProcD installation (usually)
Home OS root (e.g., /root)
TmpD OS tmp (e.g., /tmp)

Look in the Source for other strings available: [1] [2].


nsIFile and path strings

You can use nsIFile::path to get platform-specific path string, eg. C:\Windows\System32 or /usr/share. If you want to get a file:// URL of a file or an nsIFile from file:// URL, you need to use nsIFileProtocolHandler:

// file is nsIFile
var URL = Components.classes["@mozilla.org/network/protocol;1?name=file"]. 
	createInstance(Components.interfaces.nsIFileProtocolHandler). 
	getURLSpecFromFile(file);

Note: do not use nsILocalFile::persistentDescriptor to get the file path!

Also note that generally you don't need to use nsIFile::path. Use nsIFile directly wherever possible. An example below shows how you should save a path in user prefs.

Saving path in a userpref

This snippet shows the right way to save a file path in user preferences:

// |file| is nsILocalFile
var prefs = Components.classes["@mozilla.org/preferences-service;1"]. 
	getService(Components.interfaces.nsIPrefService). 
	getBranch("extensions.myext.");
prefs.setComplexValue("filename", Components.interfaces.nsILocalFile, file);

/* You can read it later with this statement:
var file = prefs.getComplexValue("filename", Components.interfaces.nsILocalFile);
*/


Navigating with nsIFile

Get a file in given directory

Assume, file is an nsIFile pointing to some directory (f.e. a user profile directory). You can use this code: file.append("myfile.txt"); - to make file point to myfile.txt inside that directory.

Notes: avoid using dir.path+"\\"+"myfile.txt", as it is not cross-platform code. Using something like ((path.search(/\\/) != -1) ? path + "\\" : path + "/") + "myfile.txt"; is possible, but the nsIFile::append() is much easier to read and is guaranteed to work on all platforms Mozilla itself works.

Traverse directories

todo


Reading from a file

Simple

Line by line

// open an input stream from file
var istream = Components.classes["@mozilla.org/network/file-input-stream;1"]
                .createInstance(Components.interfaces.nsIFileInputStream);
istream.init( file, 0x01, 00004, null );
istream.QueryInterface(Components.interfaces.nsILineInputStream);

// read lines into array
var line = {}, lines = {}, hasmore;
do {
  hasmore = istream.readLine(line);
  lines.push(line.value); 
} while(hasmore);

istream.close();

// do something with read data
alert(lines);