Homework 5: Web browser, part 2

Processing HTML

HTML (HyperText Markup Language) is the language used to define the appearance of a web page. The primary task of a browser is to render a document that corresponds to the downloaded HTML instructions. An HTML document contains tags that are interspersed with regular text. To process an HTML document, we can proceed as follows:

Separate the text into tag and non-tag elements.
Determine the properties of each tag.
Render the doucment by iterating through the processed text from start to finish:
- Some tags have a one-time effect and may be subsequently ignored.
- Other tags change how all subsequent text is rendered, until a matching closing tag is encountered or a different tag cancels the effect.
- Tags that the browser does not recognize may be ignored.

Tag Structure

A tag starts with a name. It is alphanumeric text, delimited with a space or a closing symbol.
Arbitrary spaces may seperate elements of a tag, including the opening and closing characters.
A tag may contain properties. Each property is either a single word or an assignment.
An assignment has a word on the left-hand side, an equals sign, and either a word or a quoted string on the right-hand side.
If it is a quoted string, anything can appear in the quotes, even the closing symbol.

The following tags should be supported:

Headers: <h1>, <h2>, <h3>
- You need not change the font size; it suffices to put each header on a line by itself, with a blank line preceding it and another blank line following it.
Hyperlinks: <a>
Newlines: <br>
Lists: <ul>, <ol>, <li>
Comment tags (i.e. ignore all text inside them)

Additional Text Processing

Paragraphs: <p> tags will start a new paragraph. A new paragraph is defined to be an end-of-line followed by a blank line in the rendered output.
Formatted Text: Wrap text so that it does not exceed the horizontal bounds of the browser window. Replace newline characters from the source document with spaces; also collapse all tabs and all sequences of spaces more than one character long into a single space character.
- Important Exception: Two or more consecutive newline characters should start a new paragraph.
Special characters: Convert the escape sequences using the ampersand to the implied characters. This will allow rendering of <, >, &, and ". View the source for this page to see the escape codes.

Buttons

Your browser should implement the proper behavior for the Forward, Back, Home, Stop, and Reload buttons. Store pages visited in the current session in an appropriate data structure. The Forward and Back buttons will then access this data structure in order to perform their work.

Augument the user interface to enable the user to set the home page. At your option, you may also allow the user to tell the browser to always load this page when it starts up. Also augment the user interface to enable the user to view the HTML source for a given page.

Hyperlinks

All hyperlinks should be visually differentiated from the surrounding text. Clicking on a hyperlink with the mouse should load the hyperlinked page. Relative hyperlinks should be handled properly. Also, clicking on a hyperlink in the link window for the page should also work.

URL Bar

The user should be able to enter a URL in the URL bar. When the user performs an appropriate action, the URL in the URL bar should be loaded into the browser.

Threading

Create a thread that will be responsible for the network communication. At your discretion, the thread can also handle parsing and rendering.

Deadlines

For Friday, 10/23:

Develop and implement the data structure for storing a processed HTML document.
Be prepared to discuss control flow and rendering strategy in class.

For Monday, 10/26:

Demonstrate your program during class.
It may still have a few bugs.

EXTENDED DEADLINE For Friday, 10/30:

Program due at noon.
Submit via Sauron.
Code reviews in class:
- Check for contracts and unit tests (whether jUnit or main() methods)
- Check for design issues
- Check for code duplication

For Monday, 11/2:

Code review due at 8:10 am.
Code review must cover the entire browser, including the parts implemented in the first part of the assignment.
Submit via Sauron.