+=head2 Plugin C<curl>
+
+The curl plugin uses the B<libcurl> (L<http://curl.haxx.se/>) to read web pages
+and the match infrastructure (the same code used by the tail plugin) to use
+regular expressions with the received data.
+
+The following example will read the current value of AMD stock from google's
+finance page and dispatch the value to collectd.
+
+ <Plugin curl>
+ <Page "stock_quotes">
+ URL "http://finance.google.com/finance?q=NYSE%3AAMD"
+ User "foo"
+ Password "bar"
+ <Match>
+ Regex "<span +class=\"pr\"[^>]*> *([0-9]*\\.[0-9]+) *</span>"
+ DSType "GaugeAverage"
+ # Note: `stock_value' is not a standard type.
+ Type "stock_value"
+ Instance "AMD"
+ </Match>
+ </Page>
+ </Plugin>
+
+In the B<Plugin> block, there may be one or more B<Page> blocks, each defining
+a web page and one or more "matches" to be performed on the returned data. The
+string argument to the B<Page> block is used as plugin instance.
+
+The following options are valid within B<Page> blocks:
+
+=over 4
+
+=item B<URL> I<URL>
+
+URL of the web site to retrieve. Since a regular expression will be used to
+extract information from this data, non-binary data is a big plus here ;)
+
+=item B<User> I<Name>
+
+Username to use if authorization is required to read the page.
+
+=item B<Password> I<Password>
+
+Password to use if authorization is required to read the page.
+
+=item B<VerifyPeer> B<true>|B<false>
+
+Enable or disable peer SSL certificate verification. See
+L<http://curl.haxx.se/docs/sslcerts.html> for details. Enabled by default.
+
+=item B<VerifyHost> B<true>|B<false>
+
+Enable or disable peer host name verification. If enabled, the plugin checks if
+the C<Common Name> or a C<Subject Alternate Name> field of the SSL certificate
+matches the host name provided by the B<URL> option. If this identity check
+fails, the connection is aborted. Obviously, only works when connecting to a
+SSL enabled server. Enabled by default.
+
+=item B<CACert> I<file>
+
+File that holds one or more SSL certificates. If you want to use HTTPS you will
+possibly need this option. What CA certificates come bundled with C<libcurl>
+and are checked by default depends on the distribution you use.
+
+=item B<MeasureResponseTime> B<true>|B<false>
+
+Measure response time for the request. Disabled by default.
+
+=item B<E<lt>MatchE<gt>>
+
+One or more B<Match> blocks that define how to match information in the data
+returned by C<libcurl>. The C<curl> plugin uses the same infrastructure that's
+used by the C<tail> plugin, so please see the documentation of the C<tail>
+plugin below on how matches are defined.
+
+=back
+
+=head2 Plugin C<curl_json>
+
+The B<curl_json plugin> uses B<libcurl> (L<http://curl.haxx.se/>) and
+B<libyajl> (L<http://www.lloydforge.org/projects/yajl/>) to retrieve JSON data
+via cURL. This can be used to collect values from CouchDB documents (which are
+stored JSON notation), for example.
+
+The following example will collect several values from the built-in `_stats'
+runtime statistics module of CouchDB
+(L<http://wiki.apache.org/couchdb/Runtime_Statistics>).
+
+ <Plugin curl_json>
+ <URL "http://localhost:5984/_stats">
+ Instance "httpd"
+ <Key "httpd/requests/count">
+ Type "http_requests"
+ </Key>
+
+ <Key "httpd_request_methods/*/count">
+ Type "http_request_methods"
+ </Key>
+
+ <Key "httpd_status_codes/*/count">
+ Type "http_response_codes"
+ </Key>
+ </URL>
+ </Plugin>
+
+Another CouchDB example:
+The following example will collect the status values from each database:
+
+ <URL "http://localhost:5984/_all_dbs">
+ Instance "dbs"
+ <Key "*/doc_count">
+ Type "gauge"
+ </Key>
+ <Key "*/doc_del_count">
+ Type "counter"
+ </Key>
+ <Key "*/disk_size">
+ Type "bytes"
+ </Key>
+ </URL>
+
+In the B<Plugin> block, there may be one or more B<URL> blocks, each defining
+a URL to be fetched via HTTP (using libcurl) and one or more B<Key> blocks.
+The B<Key> string argument must be in a path format, of which is used to collect
+a value from a JSON map object. If a B<Key> path element is that of a I<*> wildcard,
+the values for all keys will be collectd.
+
+The following options are valid within B<URL> blocks:
+
+=over 4
+
+=item B<Instance> I<Instance>
+
+Sets the plugin instance to I<Instance>.
+
+=item B<User> I<Name>
+
+Username to use if authorization is required to read the page.
+
+=item B<Password> I<Password>
+
+Password to use if authorization is required to read the page.
+
+=item B<VerifyPeer> B<true>|B<false>
+
+Enable or disable peer SSL certificate verification. See
+L<http://curl.haxx.se/docs/sslcerts.html> for details. Enabled by default.
+
+=item B<VerifyHost> B<true>|B<false>
+
+Enable or disable peer host name verification. If enabled, the plugin checks if
+the C<Common Name> or a C<Subject Alternate Name> field of the SSL certificate
+matches the host name provided by the B<URL> option. If this identity check
+fails, the connection is aborted. Obviously, only works when connecting to a
+SSL enabled server. Enabled by default.
+
+=item B<CACert> I<file>
+
+File that holds one or more SSL certificates. If you want to use HTTPS you will
+possibly need this option. What CA certificates come bundled with C<libcurl>
+and are checked by default depends on the distribution you use.
+
+=back
+
+The following options are valid within B<Key> blocks:
+
+=over 4
+
+=item B<Type> I<Type>
+
+Sets the type used to dispatch the values to the daemon. Detailed information
+about types and their configuration can be found in L<types.db(5)>. This
+option is mandatory.
+
+=item B<Instance> I<Instance>
+
+Type-instance to use. Defaults to the current map key or current string array element value.
+
+=back
+
+=head2 Plugin C<dbi>
+
+This plugin uses the B<dbi> library (L<http://libdbi.sourceforge.net/>) to
+connect to various databases, execute I<SQL> statements and read back the
+results. I<dbi> is an acronym for "database interface" in case you were
+wondering about the name. You can configure how each column is to be
+interpreted and the plugin will generate one or more data sets from each row
+returned according to these rules.
+
+Because the plugin is very generic, the configuration is a little more complex
+than those of other plugins. It usually looks something like this:
+
+ <Plugin dbi>
+ <Query "out_of_stock">
+ Statement "SELECT category, COUNT(*) AS value FROM products WHERE in_stock = 0 GROUP BY category"
+ # Use with MySQL 5.0.0 or later
+ MinVersion 50000
+ <Result>
+ Type "gauge"
+ InstancePrefix "out_of_stock"
+ InstancesFrom "category"
+ ValuesFrom "value"
+ </Result>
+ </Query>
+ <Database "product_information">
+ Driver "mysql"
+ DriverOption "host" "localhost"
+ DriverOption "username" "collectd"
+ DriverOption "password" "aZo6daiw"
+ DriverOption "dbname" "prod_info"
+ SelectDB "prod_info"
+ Query "out_of_stock"
+ </Database>
+ </Plugin>
+
+The configuration above defines one query with one result and one database. The
+query is then linked to the database with the B<Query> option I<within> the
+B<E<lt>DatabaseE<gt>> block. You can have any number of queries and databases
+and you can also use the B<Include> statement to split up the configuration
+file in multiple, smaller files. However, the B<E<lt>QueryE<gt>> block I<must>
+precede the B<E<lt>DatabaseE<gt>> blocks, because the file is interpreted from
+top to bottom!
+
+The following is a complete list of options:
+
+=head3 B<Query> blocks
+
+Query blocks define I<SQL> statements and how the returned data should be
+interpreted. They are identified by the name that is given in the opening line
+of the block. Thus the name needs to be unique. Other than that, the name is
+not used in collectd.
+
+In each B<Query> block, there is one or more B<Result> blocks. B<Result> blocks
+define which column holds which value or instance information. You can use
+multiple B<Result> blocks to create multiple values from one returned row. This
+is especially useful, when queries take a long time and sending almost the same
+query again and again is not desirable.
+
+Example:
+
+ <Query "environment">
+ Statement "select station, temperature, humidity from environment"
+ <Result>
+ Type "temperature"
+ # InstancePrefix "foo"
+ InstancesFrom "station"
+ ValuesFrom "temperature"
+ </Result>
+ <Result>
+ Type "humidity"
+ InstancesFrom "station"
+ ValuesFrom "humidity"
+ </Result>
+ </Query>
+
+The following options are accepted:
+
+=over 4
+
+=item B<Statement> I<SQL>
+
+Sets the statement that should be executed on the server. This is B<not>
+interpreted by collectd, but simply passed to the database server. Therefore,
+the SQL dialect that's used depends on the server collectd is connected to.
+
+The query has to return at least two columns, one for the instance and one
+value. You cannot omit the instance, even if the statement is guaranteed to
+always return exactly one line. In that case, you can usually specify something
+like this:
+
+ Statement "SELECT \"instance\", COUNT(*) AS value FROM table"
+
+(That works with MySQL but may not be valid SQL according to the spec. If you
+use a more strict database server, you may have to select from a dummy table or
+something.)
+
+Please note that some databases, for example B<Oracle>, will fail if you
+include a semicolon at the end of the statement.
+
+=item B<MinVersion> I<Version>
+
+=item B<MaxVersion> I<Value>
+
+Only use this query for the specified database version. You can use these
+options to provide multiple queries with the same name but with a slightly
+different syntax. The plugin will use only those queries, where the specified
+minimum and maximum versions fit the version of the database in use.
+
+The database version is determined by C<dbi_conn_get_engine_version>, see the
+L<libdbi documentation|http://libdbi.sourceforge.net/docs/programmers-guide/reference-conn.html#DBI-CONN-GET-ENGINE-VERSION>
+for details. Basically, each part of the version is assumed to be in the range
+from B<00> to B<99> and all dots are removed. So version "4.1.2" becomes
+"40102", version "5.0.42" becomes "50042".
+
+B<Warning:> The plugin will use B<all> matching queries, so if you specify
+multiple queries with the same name and B<overlapping> ranges, weird stuff will
+happen. Don't to it! A valid example would be something along these lines:
+
+ MinVersion 40000
+ MaxVersion 49999
+ ...
+ MinVersion 50000
+ MaxVersion 50099
+ ...
+ MinVersion 50100
+ # No maximum
+
+In the above example, there are three ranges that don't overlap. The last one
+goes from version "5.1.0" to infinity, meaning "all later versions". Versions
+before "4.0.0" are not specified.
+
+=item B<Type> I<Type>
+
+The B<type> that's used for each line returned. See L<types.db(5)> for more
+details on how types are defined. In short: A type is a predefined layout of
+data and the number of values and type of values has to match the type
+definition.
+
+If you specify "temperature" here, you need exactly one gauge column. If you
+specify "if_octets", you will need two counter columns. See the B<ValuesFrom>
+setting below.
+
+There must be exactly one B<Type> option inside each B<Result> block.
+
+=item B<InstancePrefix> I<prefix>
+
+Prepends I<prefix> to the type instance. If B<InstancesFrom> (see below) is not
+given, the string is simply copied. If B<InstancesFrom> is given, I<prefix> and
+all strings returned in the appropriate columns are concatenated together,
+separated by dashes I<("-")>.
+
+=item B<InstancesFrom> I<column0> [I<column1> ...]
+
+Specifies the columns whose values will be used to create the "type-instance"
+for each row. If you specify more than one column, the value of all columns
+will be joined together with dashes I<("-")> as separation characters.
+
+The plugin itself does not check whether or not all built instances are
+different. It's your responsibility to assure that each is unique. This is
+especially true, if you do not specify B<InstancesFrom>: B<You> have to make
+sure that only one row is returned in this case.
+
+If neither B<InstancePrefix> nor B<InstancesFrom> is given, the type-instance
+will be empty.
+
+=item B<ValuesFrom> I<column0> [I<column1> ...]
+
+Names the columns whose content is used as the actual data for the data sets
+that are dispatched to the daemon. How many such columns you need is determined
+by the B<Type> setting above. If you specify too many or not enough columns,
+the plugin will complain about that and no data will be submitted to the
+daemon.
+
+The actual data type in the columns is not that important. The plugin will
+automatically cast the values to the right type if it know how to do that. So
+it should be able to handle integer an floating point types, as well as strings
+(if they include a number at the beginning).
+
+There must be at least one B<ValuesFrom> option inside each B<Result> block.
+
+=back
+
+=head3 B<Database> blocks
+
+Database blocks define a connection to a database and which queries should be
+sent to that database. Since the used "dbi" library can handle a wide variety
+of databases, the configuration is very generic. If in doubt, refer to libdbi's
+documentationE<nbsp>- we stick as close to the terminology used there.
+
+Each database needs a "name" as string argument in the starting tag of the
+block. This name will be used as "PluginInstance" in the values submitted to
+the daemon. Other than that, that name is not used.
+
+=over 4
+
+=item B<Driver> I<Driver>
+
+Specifies the driver to use to connect to the database. In many cases those
+drivers are named after the database they can connect to, but this is not a
+technical necessity. These drivers are sometimes referred to as "DBD",
+B<D>ataB<B>ase B<D>river, and some distributions ship them in separate
+packages. Drivers for the "dbi" library are developed by the B<libdbi-drivers>
+project at L<http://libdbi-drivers.sourceforge.net/>.
+
+You need to give the driver name as expected by the "dbi" library here. You
+should be able to find that in the documentation for each driver. If you
+mistype the driver name, the plugin will dump a list of all known driver names
+to the log.
+
+=item B<DriverOption> I<Key> I<Value>
+
+Sets driver-specific options. What option a driver supports can be found in the
+documentation for each driver, somewhere at
+L<http://libdbi-drivers.sourceforge.net/>. However, the options "host",
+"username", "password", and "dbname" seem to be deE<nbsp>facto standards.
+
+Unfortunately, drivers are not too keen to report errors when an unknown option
+is passed to them, so invalid settings here may go unnoticed. This is not the
+plugin's fault, it will report errors if it gets them from the libraryE<nbsp>/
+the driver. If a driver complains about an option, the plugin will dump a
+complete list of all options understood by that driver to the log.
+
+=item B<SelectDB> I<Database>
+
+In some cases, the database name you connect with is not the database name you
+want to use for querying data. If this option is set, the plugin will "select"
+(switch to) that database after the connection is established.
+
+=item B<Query> I<QueryName>
+
+Associates the query named I<QueryName> with this database connection. The
+query needs to be defined I<before> this statement, i.E<nbsp>e. all query
+blocks you want to refer to must be placed above the database block you want to
+refer to them from.
+
+=back
+