linkchecker/FAQ

Q1: LinkChecker produced an error, but my web page is ok with
   Netscape/IE/Opera/...
   Is this a bug in LinkChecker?
A1: Please check your web pages first. Are they really ok? Use
   a syntax highlighting editor! Use HTML Tidy from www.w3c.org!
   Check if the web server is accepting HEAD requests as well.
   Check if you are using a Proxy which produces the error.


Q2.1: I still get an error, but the page is definitely ok.
Q2.2: I get an error "too much redirections", but the URL displays ok in my
   browser.
A2: The difference between LinkChecker and web browsers is the type of HTTP
   request. LinkChecker does a HEAD request, browsers do a GET request of
   the same URL. Now, a lot of servers are broken when it comes to HEAD
   support. LinkChecker tries to detect some of them, but can not catch all.
   Nevertheless, this is an error. If the URL is on your own web server,
   make sure that your server is handling HEAD requests!


Q3: How can I tell LinkChecker which proxy to use?
A3: LinkChecker works transparently with proxies. In a Unix or Windows
   environment, set the http_proxy, https_proxy, ftp_proxy or gopher_proxy
   environment variables to a URL that identifies the proxy server before
   starting LinkChecker. For example
   # http_proxy="http://www.someproxy.com:3128"
   # export http_proxy

   In a Macintosh environment, LinkChecker will retrieve proxy information
   from Internet Config.


Q4: The link "mailto:john@company.com?subject=Hello John" is reported
   as an error.
A4: You have to quote special characters (e.g. spaces) in the subject field.
   The correct link should be "mailto:...?subject=Hello%20John"
   Unfortunately browsers like IE and Netscape do not enforce this.


Q5: Has LinkChecker JavaScript support?
A5: No, it never will. JavaScript sucks. If your page is not
   working without JS then your web design is broken.
   Learn PHP or Zope or ASP, and use JavaScript just as an addon for your
   web pages.


Q6: I have a pretty large site to check. How can I restrict link checking
   to check only my own pages?
A6: Look at the options --intern, --extern, --strict, --denyallow  and
   --recursion-level.


Q7: I dont get this --extern/--intern stuff.
A7: When it comes to checking there are three types of URLs:
   1) strict extern URLs:
      We do only syntax checking. Intern URLs are never strict.
   2) extern URLs:
      Like 1), but we additionally check if they are valid by connect()ing
      to them
   3) intern URLs:
      Like 2), but we additionally check if they are HTML pages and if so,
      we descend recursively into this link and check all the links in the
      HTML content.
      The --recursion-level option restricts the number of such recursive
      descends.

   LinkChecker provides four options which affect URLs to fall in one
   of those three categories: --intern, --extern, --strict and
   --denyallow.
   By default all URLs are intern. With --extern you specify what URLs
   are extern. With --intern you specify what URLs are intern.
   Now imagine you have both --extern and --intern. What happens
   when an URL matches both patterns? Or when it matches none? In this
   situation the --denyallow option specifies the order in which we match
   the URL. By default it is intern/extern, with --denyallow the order is
   extern/intern. Either way, the first match counts, and if none matches,
   the last checked category is the category for the URL.
   Finally, with --strict all extern URLs are strict.
   
   Oh, and just to boggle your mind: you can have more than one extern
   regular expression in a config file and for each of those expressions
   you can specify if those matched extern URLs should be strict or not.

   An example. Assume we want to check only urls of our domains named
   'mydomain.com' and 'myotherdomain.com'. Then we specify
   -i'^http://my(other)?domain\.com' as intern regular expression, all other
   urls are treated extern. Easy.

   Another example. We dont want to check mailto urls. Then its
   -i'!^mailto:'. The '!' negates an expression. With --strict, we dont
   even connect to any mail hosts.
   
   Yet another example. We check our site www.mycompany.com, dont recurse
   into extern links point outside from our site and want to ignore links to
   hollowood.com and hullabulla.com completely.
   This can only be done with a configuration entry like
   [filtering]
   extern1=hollowood.com 1
   extern2=hullabulla.com 1
   # the 1 means strict extern ie dont even connect
   and the command
   linkchecker --intern=www.mycompany.com www.mycompany.com


Q8: Are Cookies insecure?
A8: Cookies can not store more information as is in the HTTP request itself,
   so you are not giving away any more system information.
   After storing however, the cookies are sent out to the server on request.
   Not to every server, but only to the one who the cookie originated from!
   This could be used to "track" subsequent requests to this server,
   and this is what some people annoys (including me).
   Cookies are only stored in memory. After LinkChecker finishes, they
   are lost. So the tracking is restricted to the checking time.


Q9: I want to have my own logging class. How can I use it in LinkChecker?
A9: Currently, only a Python API lets you define new logging classes.
   Define your own logging class as a subclass of StandardLogger or any other
   logging class in the log module.
   Then call the addLogger function in Config.Configuration to register
   your new Logger.
   After this append a new Logging instance to the fileoutput.

   import linkcheck, MyLogger
   log_format = 'mylog'
   log_args = {'fileoutput': log_format, 'filename': 'foo.txt'}
   cfg = linkcheck.Config.Configuration()
   cfg.addLogger(log_format, MyLogger.MyLogger)
   cfg['fileoutput'].append(cfg.newLogger(log_format, log_args)) 

Q10.1: LinkChecker does not ignore anchor references on caching.
Q10.2: Some links with anchors are getting checked twice.
A10: This is not a bug.
   Its common practice to believe that if an URL ABC#anchor1 works then
   ABC#anchor2 works too. Thats not specified anywhere and I have seen
   server-side scripts that fail on some anchors and not on others.
   This is the reason for always checking URLs with different anchors.
   If you really want to disable this, use --no-anchor-caching.