/sys/doc/ Documentation archive

The browser runs under the wm(1) window manager, or directly on the draw(3) and cons(3) devices. When charon starts, it checks to see if wm is running; if it is then charon creates a new wm window for its display, otherwise it uses the whole area of the display device.

Charon implements an image cache to help reduce the overhead of revisiting pages. The image cache resides in memory for the duration of a session. The cache is managed by discarding least recently used images once the cache bounds have been reached. Currently, charon does not provide a general purpose web cache; all other resources have to be reloaded when needed.

Navigation

Charon provides navigation controls familiar to any web-surfer: back, forward, reload, home, stop and URL entry. Navigation of web-based information is by means of following HTML links, this is done by clicking on them using mouse button-1, or the touch-screen. Clicking mouse button-2 on a link causes its address to be displayed in the status line of charon's display. Navigation to other information is achieved by clicking on the URL entry field and typing the address of the resource, followed by the Enter key.

The retrieval and processing of the current page is immediately terminated by clicking the Stop button.

As resources are browsed, a history of their web addresses (URLs) is built up. At any time you can navigate forwards and backwards through this list using the Forward and Back buttons. Additionally, clicking the History button, displays the entire history list as a set of links enabling the user to quickly jump to any position in the list.

Sometimes, it is not possible to retrieve all of the components of a web document at the time that it is requested. Often this is because the remote server is very busy or not available. This can result in the presentation of the document being incomplete or even corrupted. Clicking the Reload button causes charon to attempt to retrieve the current document and all of its components again.

Charon displays a progress panel to indicate the download status of each of the components of the current document. The progress panel is displayed at the bottom of the charon window. Each component of the current document is represented by a rectangular block in the progress panel. As the download of a component progresses, its corresponding block is gradually filled in. If an error occurs while downloading or processing the component, its block is coloured red. The component address and amount downloaded, or reason for failure, can be obtained by clicking mouse button-1 on its progress block.

Web Standards

Standards are the life-blood of the World-Wide-Web; without them, the web could not exist. Web standards are under constant review with revised editions and complete new standards being published all of the time. This section lists the standards supported by charon at the time of writing this manual entry. The version of the standard is given, if appropriate, alongside any comments on its implementation.

Protocols

HTTP versions 1.0 and 1.1

HTTPS: SSL Protocol versions 2.0 and 3.0. X.509.v3 server certificates.

FTP: charon supports retrieval of plain text files only, directory listings are not generated.

FILE: Charon attempts to determine the file type by a combination of the filename extension and examination of the first few bytes of the file. Directory listings are not generated.

HTML

It is intended that charon supports HTML version 3.2, but in reality there is no single standard! Charon attempts to be as close as possible to Netscape Navigator Version 3 in terms of its markup support. Obvious bugs in Navigator 3 and the Netscape security model have not been adopted.

JavaScript

Charon implements ECMAscript-262 2nd Edition, which is roughly equivalent to JavaScript1.1. The ECMA-262 standard does not define the host objects and classes that should implemented by the browser. Charon implements the set of host objects and classes of Netscape Navigator version 3.

Encodings

US_Ascii, ISO_8859_1, UTF_8, Unicode (big-endian)

Images

GIF87a and GIF89a - animated GIFs always loop.
JPEG, XBitmap, Inferno BIT image(6) format.

Configuration

While using charon, a sub-set of the configuration options can be modified. Clicking the Configuration button displays a config popup window, enabling the user to modify the current values of the available options.

The full set of configuration options can be modified on the command line or in a configuration file. Comand line options are processed after the configuration file. The configuration file is loaded from /usr/user/charon/config where user is obtained by reading the file /dev/user. If this file does not exist, the file /services/config/charon.cfg is read instead. Options are processed in order; some options override settings affected by others and so the order in which they are used is important.

Options are specified using a key, value pair. On the command line this takes the form:

-key value

Where -key and value are individual items in the argument list to charon.

In the config file options take the form:

key=value

Where value is the remainder of the input line after the `=' character. Any text lines in the config file that start with a `#' character are ignored as comment lines.

userdir

The directory where charon expects to find its configuration files such as, bookmark and cookie files. The default value is /usr/user/charon/ where user is obtained by reading the file /dev/user.

starturl

Specifies the URL of the first document to be displayed by charon at startup. The default value is file://localhost/services/webget/start.html

homeurl

Specifies the URL of the document to retrieve when the Home button is clicked. The homeurl can only be changed if the change_homeurl option is enabled. Setting homeurl also set the value of the starturl option. The default value is file://localhost/services/webget/start.html

change_homeurl

Enables editing of the Home URL in the configuration popup window. A non-zero integer value enables this option, all other values disable it This option also enables the homeurl option. The default value is 1.

helpurl

Specifies the URL of the document to retrieve when the Help button is clicked. The default value is file://localhost/services/webget/help.html

httpproxy

Specifies the host name and port of a web proxy server. The address is given in the form of a URL, where the optional port number can be specified after the server name by separating them by a colon `:'. The default value is the empty string, specifying that no web proxy server should be used.

noproxy or noproxydoms

Specifies a list of network domains for which a web proxy should not be used. The domains in the list can be separated by semicolon, comma, space or tab characters. The default value is the empty list.

usessl

Extends SSL support. Accepted values are ``v2'' and ``v3''. Initially SSL support is configured off. Enabling version 1 or version 2 support restricts SSL support to that specific version. Specifying the option twice, once with each of the options, enables dual version SSL support whereby the remote server is probed to determine which version it supports. Some servers only support one of the versions and may not tolerate the special version2/3 probe.

buttons

Specifies the set of buttons that appear on the window manager title-bar. The buttons are given as a list of button names separated by comma, space or tab characters. Valid button names are help, resize and hide. The default value is for all buttons to be displayed.

defaultwidth or width

Set the initial window width. This option is only meaningful when running under the window manager. If the specified width exceeds the screen width then the screen width is used. The default value is 630.

defaultheight or height

Set the initial height of the main display panel, this does not include the height of the control and progress panels. This option is only meaningful when running under the window manager. If the total height of the charon window exceeds the screen height, the main display panel height will be reduced to fit. The default value is 450.

x and/or y

Set the initial window position. These options are only meaningful when running under the window manager. The default value for both options is 0.

imagelvl

Specify how to handle image components of a document. This option takes a numeric argument. A value of 0 prevents images from being downloaded or displayed. A value of 1 will download and display images but not animate GIFS - only the first frame of an animated GIF will be displayed. A value of 2 or more enables full image processing. The default value enables full image processing.

imagecachenum

Specify the maximum number of images that can remain resident in the image cache. The default value is 60.

imagecachemem

Specify the maximum amount of image memory available to the image cache in bytes. The cache is managed such that neither the imagecachenum nor imagecachemem limits are exceeded. The image cache tries to ensure that no more than 80% of available system image memory is taken by the cache, irrespective of the value of this option. The default value is 80% of the system image memory that was available when charon was started.

docookies

Enable cookie handling. A non-zero numeric value enables cookie handling, all other values disable it. The cookie cache is maintained in the cookies file in the userdir directory. The default value is 0, cookie handling disabled.

doscripts

Enable JavaScript support. A non-zero numeric value enables JavaScript, all other values disable it. The default value is 0, JavaScript processing disabled.

showprogress

A non-zero numeric value results in the progress panel being displayed. All other values hide the progress panel, leaving more vertical space for the main display area. The default value is 1, causing the progress panel to be displayed

http

Set the version of HTTP to use when communicating with web servers. Supported versions are 1.0 and 1.1. Any value other than 1.1 results in HTTP1.0 being used. The default value is 1.0.

nthreads

Specifies the maximum number of concurrent downloads of document components. Generally, if this number is higher, pages will complete faster as charon will not have to wait for the download of one component to complete before another can be started. The downside is that a higher number of concurrent downloads will use more memory during the download process. The default value is 4.

/services/config/charon.cfg

The default configuration file.

userdir/config

The user specific configuration file. userdir is given by the value of the userdir option.

userdir/cookies

The cookie cache. userdir is given by the value of the userdir option.

/services/webget/start.html

The default start page.

/services/webget/help.html

The default help page.

/appl/charon/

The main charon source files.

/appl/lib/ecmascript/

Javascript (ECMA-262) implementation.

Charon implements its table layout as per the algorithm described in rfc1942. This sometimes results in table-based documents being laid out differently to other browsers.

JavaScript is a source of many problems. Many scripts do not specify the language version they employ. Additionally different language versions and browsers imply a different set of host objects and classes. Such differences often give rise to syntax or null reference errors. This whole situation places a great burden on the script author to write safe and compliant scripts; unfortunately authors are rarely aware of this burden!

The following elements of JavaScript1.1 are not fully implemented:

Document.applets, Document.embeds and Document.plugins: Java Applets are not supported, the arrays are always empty.

Document.onunload: The property exists and can be assigned to, but the event is never raised.

Window.open(): A new window is never opened. If a URL is specified for the new window, the current document will be replaced with that of the new URL.

Other annoyances include:

Window resize forces a complete document reload.

Frames in a frameset are processed one at a time, not concurrently.

It is not possible to save downloaded data to file. This is particularly annoying for MIME types that charon does not support.

The history list can get confused, especially when following links in framesets before the complete frameset has been downloaded.