Programming Assignment 2a - URL Rewriting

See the assignment turn-in page (last modified on 3 September 2003) for instructions on turning in your assignment.

The port portion of the address is optional and defaults to :80 if omitted. (The protocol portion is not optional; get() assumes it's http: and adds it to the URL if omitted.)

The directory part of the URL is similar to the Unix directory structure: a sequence of names delimited by slash characters. The final, right-most name is name of the resource to retrieve, while all proceeding names are directory names. For example, the URL

http://www.monmouth.edu/path/visitors.asp

refers to the visitors.asp resource in the path directory. The left-most slash in a directory is known as the root of the server's resource directory.

A directory that ends in a slash refers to the default resource stored in the associated directory. The actual document returned depends on the Web server used and how its configured; the default is to return the resource index.html if it exists or an error otherwise. This is also what happens when the directory is omitted from the URL; the server returns the default resource in its root directory (or an error if otherwise configured).

A resource name may contain an hash character # possibly followed by more text, such as in

http://www.w3.org/Consortium/Legal/ipr-notice#Copyright

This is called a name reference and is used to refer to a particular location within the resource given to the left of the hash. Stripping the hash and everything to the right produces a URL to the resource.

A relative URL is a URL consisting of only a directory. For example, the resource with URL http://www.w3.org/Overview.html contains the HREF URL /Help/siteindex. The context for a relative URL comes from the resource containing the URL. In the previous example, the protocol and host for /Help/siteindex comes from the protocol and host for its containing document Overview.html; that is, the protocol is http: and the host is www.w3.org.

Similar to Unix directories, a URL directory need not start with a slash. If the URL directory doesn't start with a slash, it is interpreted relative to the location of its containing resource. For example, the resource

http://www.w3.org/Style/CSS/Overview.html

contains the images/Ark-CSS HREF URL. Because it doesn't start with a slash, its location interpreted relative to the containing resource; that is, the absolute URL is

http://www.w3.org/Style/CSS/images/Ark-CSS

On the other hand

http://www.w3.org/Style/CSS/Overview.html

also contains the /TR/WD-positioning HREF URL. Because it does start with a slash, its location interpreted relative to the server's root; that is, the absolute URL is

http://www.w3.org/TR/WD-positioning

Also similar to Unix, directories may contain references to the .. directory, which moves one directory up towards the root. To continue the example, the resource

http://www.w3.org/Style/CSS/Overview.html

contains the HREF URL

../../Graphics/SVG/Test/BE-ImpStatus-20011026.html

Because it doesn't start with a slash, the HREF URL's location is interpreted relative to its containing resources' location, or

http://www.w3.org/Style/CSS

The first two directories are .., which moves the location two directories closer to the server's root, skipping the directories CSS and Style; the practical effect of this is to move directly under the server's root. From there, the resource BE-ImpStatus-20011026.html can be found by following the Graphics, SVG and Test directories

http://www.w3.org/Graphics/SVG/Test/BE-ImpStatus-20011026.html

Any URL that attempts to move above the server's root is invalid and should be ignored.

The command line to your revised program remains the same: a single URL. The output of your revised program also remains the same: href URLs in the associated resource should be written to std-out one per line, only now the URLs will be absolute urls. Remember that the resource associated with the command-line URL need not be a HTML document.

Your program still doesn't have to check the URLs for validity, or figure out what kind of URLs they are, or retrieve the resources associated with the URLs; all that will come next.

A data structure and procedure have been provided to help you parse URLs; for more details, see get.h and get.cc, which can be found in the assignment directory

/export/home/class/cs-305/pa2a

Be careful if you copy these files to a more convenient location; you are responsible for making sure you are using the most recent version of these files. If you do copy the files, you shouldn't change them; get.h and get.cc are deleted if you turn them in.

You can find os-print-urls, my solution to this assignment, in the assignment directory; os is one of linux or solaris. Remember, the objective of this assignment is to correctly print links in HTML documents; it is not to faithfully reproduce the behavior of my solution. If my solution's wrong and you copy the error, you're going to lose points.