WebVal is a system that will scan documents for
fully-qualified HTTP URLs, keeping its database
fresh with newly-seen URLs. It can then be
requested to validate the URLs, whereby it will
attempt to access each URL via an HTTP request and
record the response code; it maintains a list of
the most recent codes that have been retrieved.
Response codes are classified as "good" (URL is
correct and a valid page is there) and "bad" (URL
is invalid or outdated). By default any code
other than a 2xx code is considered bad, but this
can be changed (e.g. to ignore 3xx redirection
codes). WebVal can then be used in report mode
where it will scan documents for URLs as before,
but will report invalid URLs (that is, URLs in
the database which have a number of "bad" codes
exceeding a certain threshold). These are then
printed to stderr in a format that shows the file
and line number the URLs were seen in so that
they can be corrected.
