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-
-Volta
-=====
-
-What is volta?
---------------
-
-Volta is a high performance, low resource URI rewriter for use with the
-Squid caching proxy server (http://www.squid-cache.org/.) With it, you
-can dynamically alter URI requests that pass through Squid based on
-various criteria.
-
-It uses a state machine to parse URIs and rules, and a constant database
-to store and access those rules. It can then either perform conditional
-rewrites internally, or by evaluating Lua scripts.
-
-
-Why is it called "volta"?
--------------------------
-
-It's a type of old Italian music written in triple-time. Quick!
-
-
-How fast is it?
----------------
-
-On a 2Ghz Xeon 5130, it can process a million squid requests against
-10000 rules in less than 8 seconds, using about 800k of ram. On an
-1.8Ghz Intel E4300, it can do it in 3 seconds.
-
-Your mileage may vary, but for most all intents and purposes the answer
-is "definitely fast enough."
-
-
-Configuring squid
------------------
-
-You must enable url rewriting from within the squid.conf file.
-
- url_rewrite_program /usr/local/bin/volta
-
-... and that's it. You may need some additional customization, like where
-the volta database is stored on disk:
-
- url_rewrite_program /usr/local/bin/volta -f /var/db/squid/volta.db
-
-Busy servers:
-
-While Volta is lightweight enough to simply increase the amount of
-rewriter children, it also supports Squid's rewrite_concurrency format
-if you find that to be more efficient for your environment. Adjust to
-taste.
-
- url_rewrite_children 5 startup=1 idle=2 concurrency=50
-
-
-Using volta
------------
-
-See the INSTALL file for instructions on how to compile volta.
-
-Volta reads its rewrite rules from a local database. You can create the
-rules in a text editor, then convert it to the database like so:
-
- % volta -c rules.txt
-
-You'll be left with a "volta.db" file in the current directory. Put it
-wherever you please, and use the -f flag to point to it.
-
-
-Rule file syntax
-----------------
-
-Volta's rule syntax is designed to be easy to parse by humans and
-machines. Blank lines are skipped, as is any line that starts with the
-'#' character, so you can keep the ascii version of your rules well
-documented and in version control. There is no practical limit on the
-number of rules in this database.
-
-When compiling the ruleset into the database format, volta detects
-malformed rules and stops if there are any problems, leaving your
-original database intact. You can change the ruleset at any time while
-volta is running, and the new rules will take affect within about 10
-seconds. No need to restart squid!
-
-There are two types of rules -- positive matches, and negative matches.
-Positive matches cause the rewrite, negative matches intentionally allow
-the original request to pass. Rule order is consistent, top-down, first
-match wins. Fields are separated by any amount of whitespace (spaces or
-tabs.)
-
-
-### Positive matches:
-
- First field: the hostname to match.
-
- You can use an exact hostname (www.example.com), or the top level
- domain (tld) if you want to match everything under a specific host
- (example.com.) You can also use a single '*' to match every request,
- though this essentially bypasses a lot of what makes volta quick, it
- is included for completeness. You may have an unlimited amount of
- rules per hostname. Hostnames are compared without case sensitivity.
-
-
- Second field: the path to match.
-
- This can be an exact match ('/path/to/something.html'), a regular
- expression ('\.(jpg|gif|png)$'), or a single '*' to match for any
- path. Regular expressions are matched without case sensitivity. There
- is currently no internal support for captures, though you can use
- a Lua rule (see below) for more complex processing.
-
-
- Third field: The redirect code and url to rewrite to.
-
- Any pieces of a url that are omitted are automatically replaced
- with the original request's element -- the exception is a hostname,
- which is required. If you omit a redirect code, the URL rewrite is
- transparent to the client. You can attach a 301: or 302: prefix to
- cause a permanent or temporary code to be respectively sent, instead.
-
- If you require more complex processing than what volta provides
- internally, you can also specify a path to a Lua script (prefixed
- with 'lua:'.) See the 'Lua rules' section of this README for more
- information.
-
-
-### Negative matches:
-
- First field: the hostname to match.
-
- See above -- all the same rules apply.
-
-
- Second field: the path to match.
-
- See above -- all the same rules apply.
-
-
- Third field: the 'negative' marker.
-
- This is simply the '-' character, that signals to volta that this is
- a negative matching rule.
-
-
-You can easily test your rules by running volta on the command line, and
-pasting URLs into it. Boost the debug level (-d4) if you're having any issues.
-
-
-Examples
---------
-
-Rewrite all requests to Google to the SSL version:
-
- google.com * 302:https://www.google.com
-
- This will redirect the request "http://www.google.com/search?q=test" to
- "https://www.google.com/search?q=test".
-
-
-Transparently alter all uploaded images on imgur to be my face: :)
-
- i.imgur.com \.(gif|png|jpg)$ http://www.martini.nu/images/mahlon.jpg
-
-
-Expand a local, non qualified hostname to a FQDN (useful alongside the
-'dns_defnames' squid setting to enforce browser proxy behaviors):
-
- local-example * local-example.company.com
-
-
-Cause all blog content except for 2011 posts to permanently redirect to
-an archival page:
-
- martini.nu /blog/2011 -
- martini.nu /blog 301:martini.nu/content-archived.html
-
-
-Send all requests to reddit/r/WTF/* through a lua script for further processing.
-
- reddit.com /r/wtf lua:/path/to/a/lua-script.lua
-
-
-Turn off rewriting for specific network segment or IP address:
-
- Squid has this ability built in -- see the 'url_rewrite_access' setting.
- Alternatively, do the checks in lua.
-
-
-
-Lua Rules
----------
-
-Volta has an embedded Lua interpreter that you can use to perform all
-kinds of conditional rewrites. Read more about the syntax of the Lua
-language here: http://www.lua.org/manual/5.1/
-
-### Loading a script
-
-To use a Lua script, prefix the rewrite target of a volta rule with
-'lua:'. The rest of the target is then treated as a path to the script.
-(You can find an example in the Examples section of this README.)
-
-You can specify a path to either an ascii file, or Lua bytecode. (If
-speed is an absolute premium, I'm seeing around a 25% performance
-increase by using Lua bytecode files.)
-
-You can use different scripts for different rules, or use the same
-script across any number of separate rules.
-
-There is no need to restart squid when modifying Lua rules. Changes are
-seen immediately.
-
-
-### Environment
-
-* Global variable declarations are disabled, so scripts can't accidently stomp on each other. All variables must be declared with the 'local' keyword.
-* There is a global table called 'shared' you may use if you want to share data between separate scripts, or remember things in-between rule evaluations.
-* The details of the request can be found in a table, appropriately named 'request'. HTTP scheme, host, path, port, method, client_ip, and domain are all available by default from the request table.
-* Calling Lua's print() function emits debug information to stderr. Use a debug level of 2 or higher to see it.
-
-
-### Return value
-
-The return value of the script is sent unmodified to squid, which should
-be a URL the request is rewritten to, with an optional redirect code
-prefix (301 or 302.)
-
-Omitting a return value, or returning 'nil' has the same effect as a negative
-rule match -- the original request is allowed through without any rewrite.
-
-
-An extremely simple Lua rule script can be found in the 'examples'
-directory, distributed with volta.
-
-