New rate_limit plugin

config/rate_limit.ini

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+; Example configuration file for the rate_limit plugin
+
+; redis_server = 1.2.3.4
+; tarpit_delay = 30
+
+[concurrency]
+; NOTE: this limit is per server child and does not use Redis
+; Limit an IP or host to a maximum number of connections
+
+; Don't limit connections from localhost
+127 = 0
+
+; Freemail
+; hotmail.com = 20
+; yahoo.com = 20
+; google.com = 20
+
+; default = 5
+
+[rate_conn]
+; Maximum number of connections from an IP or host over an interval
+
+127 = 0
+; default = 5  ; no interval defaults to 60s
+
+[rate_rcpt_host]
+; Maximum number of recipients from an IP or host over an interval
+
+127 = 0
+; default = 50/5m  ; 50 RCPT To: maximum in 5 minutes
+
+[rate_rcpt_sender]
+; Maximum number of recipients from a sender over an interval
+
+127 = 0
+; default = 50/5m
+
+[rate_rcpt]
+; Limit the rate of message attempts over a interval to a recipient
+
+127 = 0
+; default = 50/5m
+
+[rate_rcpt_null]
+; Limit the number of DSN/MDN messages by recipient
+
+; default = 1

docs/plugins/rate_limit.md

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+rate_limit
+==========
+
+This pluign enforces limits on connection concurrency, connection rate and 
+recipient rate.
+
+By default DENYSOFT will be returned when the limits are exceeded, but for 
+concurrency, connection rate and recipient rate by host you can optionally 
+tarpit the connection by adding a delay before every response sent back to the 
+client instead of sending a DENYSOFT.  To do this requires the 'tarpit' plugin 
+to run immediately after this plugin.
+
+To use this plugin you will need a Redis server and will need the redis, 
+hiredis and ipaddr.js packages installed via:
+
+    cd /path/to/haraka/home
+    npm install redis hiredis ipaddr.js
+
+Configuration
+-------------
+
+This plugin uses the configuration file rate_limit.ini which is checked for 
+updates before each hook, so changes to this file will never require a restart 
+and will take effect immediately after the changes are saved.
+
+The configuration options for each heading are detailed below:
+
+### [main]
+
+- redis_server = \<ip | host\>[:port] *(optional)*
+
+    If port is missing then it defaults to 6379.  
+    If this setting is missing entirely then it defaults to 127.0.0.1:6379.
+
+    Note that Redis does not currently support IPv6.
+
+- tarpit_delay = seconds *(optional)*
+
+    Set this to the length in seconds that you want to delay every SMTP 
+    response to a remote client that has exceeded the rate limits.  For this 
+    to work the 'tarpit' plugin must be loaded **after** this plugin in 
+    config/plugins. 
+
+    If 'tarpit' is not loaded or is loaded before this plugin, then no
+    rate throttling will occur.
+
+* * *
+
+All of the following sections are optional.  Any missing section disables 
+that particular test.
+
+They all use a common configuration format:
+
+- \<lookup\> = \<limit\>[/time[unit]]  *(optional)*
+
+   'lookup' is based upon the limit being enforced and is either an IP 
+   address, rDNS name, sender address or recipient address either in full 
+   or part.  
+   The lookup order is as follows and the first match in this order is 
+   returned and is used as the record key in Redis (except for 'default' 
+   which always uses the full lookup for that test as the record key):
+
+   **IPv4/IPv6 address or rDNS hostname:**
+
+   <pre>
+   fe80:0:0:0:202:b3ff:fe1e:8329
+   fe80:0:0:0:202:b3ff:fe1e
+   fe80:0:0:0:202:b3ff
+   fe80:0:0:0:202
+   fe80:0:0:0
+   fe80:0:0
+   fe80:0
+   fe80
+   1.2.3.4
+   1.2.3
+   1.2
+   1
+   host.part.domain.com
+   part.domain.com
+   domain.com
+   com
+   default
+   </pre>
+
+   **Sender or Recipient address:**
+
+   <pre>
+   [email protected]
+   host.sub.part.domain.com
+   sub.part.domain.com
+   part.domain.com
+   domain.com
+   com
+   default
+   </pre>
+
+   In all tests 'default' is used to specify a default limit if nothing else has 
+   matched.
+
+   'limit' specifies the limit for this lookup.  Specify 0 (zero) to disable 
+   limits on a matching lookup.
+
+   'time' is optional and if missing defaults to 60 seconds.  You can optionally 
+   specify the following time units (case-insensitive):
+
+   - s (seconds)
+   - m (minutes)
+   - h (hours)
+   - d (days)
+
+### [concurrency]
+
+**IMPORTANT NOTE:** connection concurrency is recorded in-memory (in 
+connection.server.notes) and not in Redis, so the limits are per-server and 
+per-child if you use the cluster module.
+
+IP and rDNS names are looked up by this test.  This section does *not* accept an 
+interval.  It's a hard limit on the number of connections and not based on time.
+
+### [rate_conn]
+
+This section limits the number of connections per interval from a given host 
+or set of hosts.
+
+IP and rDNS names are looked up by this test.
+
+### [rate_rcpt_host]
+
+This section limits the number of recipients per interval from a given host or 
+set of hosts. 
+
+IP and rDNS names are looked up by this test.
+
+### [rate_rcpt_sender]
+
+This section limits the number of recipients per interval from a sender or 
+sender domain.
+
+The sender is looked up by this test.
+
+### [rate_rcpt]
+
+This section limits the rate which a recipient or recipient domain can 
+receive messages over an interval.
+
+Each recipient is looked up by this test.
+
+### [rate_rcpt_null]
+
+This section limits the rate at which a recipient can receive messages from 
+a null sender (e.g. DSN, MDN etc.) over an interval.
+
+Each recipient is looked up by this test.