wxWidgets: wxFileSystem Overview

| Version: 3.0.4

wxFileSystem Overview

The wxHTML library uses a virtual file system mechanism similar to the one used in Midnight Commander, Dos Navigator, FAR or almost any modern file manager.

It allows the user to access data stored in archives as if they were ordinary files. On-the-fly generated files that exist only in memory are also supported.

# Classes

Three classes are used in order to provide virtual file systems mechanism:

- The wxFSFile class provides information about opened file (name, input stream, mime type and anchor).
- The wxFileSystem class is the interface. Its main methods are ChangePathTo() and OpenFile(). This class is most often used by the end user.
- The wxFileSystemHandler is the core of virtual file systems mechanism. You can derive your own handler and pass it to the VFS mechanism. You can derive your own handler and pass it to wxFileSystem's AddHandler() method. In the new handler you only need to override the OpenFile() and CanOpen() methods.

# Locations

Locations (aka filenames aka addresses) are constructed from four parts:

- protocol - handler can recognize if it is able to open a file by checking its protocol. Examples are "http", "file" or "ftp".
- right location - is the name of file within the protocol. In "http://www.wxwidgets.org/index.html" the right location is "//www.wxwidgets.org/index.html".
- anchor - an anchor is optional and is usually not present. In "index.htm#chapter2" the anchor is "chapter2".
- left location - this is usually an empty string. It is used by 'local' protocols such as ZIP. See Combined Protocols paragraph for details.

# Combined Protocols

The left location precedes the protocol in the URL string.

It is not used by global protocols like HTTP but it becomes handy when nesting protocols - for example you may want to access files in a ZIP archive: file:archives/cpp_doc.zip#zip:reference/fopen.htm#syntax In this example, the protocol is "zip", right location is "reference/fopen.htm", anchor is "syntax" and left location is "file:archives/cpp_doc.zip".

There are two protocols used in this example: "zip" and "file".

# File Systems Included in wxHTML

The following virtual file system handlers are part of wxWidgets so far:

- wxArchiveFSHandler: A handler for archives such as zip and tar. Include file is wx/fs_arc.h. URLs examples: "archive.zip#zip:filename", "archive.tar.gz#gzip:#tar:filename".
- wxFilterFSHandler: A handler for compression schemes such as gzip. Header is wx/fs_filter.h. URLs are in the form, e.g.: "document.ps.gz#gzip:".
- wxInternetFSHandler: A handler for accessing documents via HTTP or FTP protocols. Include file is wx/fs_inet.h.
- wxMemoryFSHandler: This handler allows you to access data stored in memory (such as bitmaps) as if they were regular files. See wxMemoryFSHandler for details. Include file is wx/fs_mem.h. URL is prefixed with memory:, e.g. "memory:myfile.htm"

In addition, wxFileSystem itself can access local files.

# Initializing file system handlers

Use wxFileSystem::AddHandler to initialize a handler, for example:

#include <wx/fs_mem.h>
...
bool MyApp::OnInit()
{
wxFileSystem::AddHandler(new wxMemoryFSHandler);
...
}