Adding IP filtering WIKI page

IP-filtering.md

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+# IP filtering
+
+## Introduction
+
+## Make a new ip table
+
+    ip_tables.insert_table = <table_name>
+
+Create a new empty table with the name `table_name`, with the default
+value returned being `0`.
+
+There is currently no use of the generic ip tables commands.
+
+## Add a new address block
+
+    ip_tables.add_address = <table_name>, 10.0.0.0/8, <value>
+
+Set `<value>` for all addresses in the address block, overwriting prior
+values.
+
+## Add a new address block
+
+    ip_tables.load = <table_name>, ~/foo.txt, <value>
+
+Set `<value>` for all addresses in the file `foo.txt` separated by
+newline, similar to `add_address`.
+
+## Get value for address
+
+    ip_tables.get = <table_name>, 10.10.10.10
+
+Returns the value set for an address, or the address block it belongs
+to. The default is `0`.
+
+## Size of data structures
+
+    ip_tables.size_data = <table_name>
+
+Returns the size in bytes of all data structures for this table,
+excluding the root class object itself. Note that the in-memory table is
+dynamically consolidated, as such memory use will always be based on
+actual fragmentation.
+
+The table is a b-tree with 1024 nodes per branch.
+
+## IPv4 filtering table
+
+    ipv4_filter.add_address = 10.0.0.0/8, unwanted
+    ipv4_filter.add_address = 11.0.0.0/8, preferred
+    ipv4_filter.load = ~/filters.txt, unwanted
+    ipv4_filter.get = 10.10.10.10
+    ipv4_filter.size_data =
+
+The main ip filter, currently supporting `unwanted` (do not allow
+connections) and `preferred` (currently used only in private code).
+
+## Constants
+
+    strings.ip_filter =
+    =>
+    { "unwanted",  PeerInfo::flag_unwanted },
+    { "preferred", PeerInfo::flag_preferred },
+
+Constants used by `ipv4_filter` values.