doc/userguide: add lua packetlib docs

doc/userguide/lua/libs/index.rst

@@ -9,3 +9,4 @@ environment without access to additional modules.
 .. toctree::
 
    hashlib
+   packetlib

doc/userguide/lua/libs/packetlib.rst

@@ -0,0 +1,177 @@
+Packet
+------
+
+Packets are exposed to Lua scripts with ``suricata.packet``
+library. For example::
+
+    local packet = require("suricata.packet")
+
+Initialization
+~~~~~~~~~~~~~~
+
+``get``
+^^^^^^^
+
+Init the packet for use in the script. The packet is the current packet the engine is processing.
+
+::
+
+    p = packet.get()
+
+
+Time
+~~~~
+
+``timestamp``
+^^^^^^^^^^^^^
+
+Get packet timestamp as 2 numbers: seconds & microseconds elapsed since
+1970-01-01 00:00:00 UTC.
+
+::
+
+    p = packet.get()
+    local sec, usec = p:timestamp()
+
+
+``timestring_legacy``
+^^^^^^^^^^^^^^^^^^^^^
+
+Get packet timestamp as a string in the format: `11/24/2009-18:57:25.179869`.
+This is the format used by `fast.log`, `http.log` and other legacy outputs.
+
+::
+
+    p = packet.get()
+    print p:timestring_legacy()
+
+
+``timestring_iso8601``
+^^^^^^^^^^^^^^^^^^^^^^
+
+Get packet timestamp as a string in the format: `2015-10-06T15:16:43.137833+0000`.
+This is the format used by `eve`.
+
+::
+
+    p = packet.get()
+    print p:timestring_iso8601()
+
+
+Ports and Addresses
+~~~~~~~~~~~~~~~~~~~
+
+``tuple``
+^^^^^^^^^
+
+Using the `tuple` method the IP version (4 or 6), src IP and dest IP (as string), IP protocol (int) and ports (ints) are retrieved.
+
+The protocol value comes from the IP header, see further https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml
+
+::
+
+    p = packet.get()
+    ipver, srcip, dstip, proto, sp, dp = p:tuple()
+
+
+If the protocol is ICMPv4 or ICMPv6, so when `proto == 1` or `proto == 58`, then the final two results are `icmp type` and `icmp code`.
+
+::
+
+    p = packet.get()
+    ipver, srcip, dstip, proto, itype, icode = p:tuple()
+    if ipver == 6 and proto == 1 then
+        -- weird, ICMPv4 on IPv6
+        return 1
+    end
+
+
+``sp``
+^^^^^^
+
+Get the packets TCP, UDP or SCTP source port as an int. Returns `nil` for other protocols.
+
+::
+
+    p = packet.get()
+    source_port = p:sp()
+    if source_port == 31337 then
+        return 1
+    end
+
+
+``dp``
+^^^^^^
+
+Get the packets TCP, UDP or SCTP destination port as an int. Returns `nil` for other protocols.
+
+::
+
+    p = packet.get()
+    dest_port = p:dp()
+    -- not port 443
+    if dest_port ~= 443 then
+        return 1
+    end
+
+
+Data
+~~~~
+
+``payload``
+^^^^^^^^^^^
+
+Packet payload.
+
+::
+
+    payload = p:payload()
+
+
+``packet``
+^^^^^^^^^^
+
+Entire packet, including headers for protocols like TCP, Ethernet, VLAN, etc.
+
+::
+
+    raw_packet = p:packet()
+
+
+Misc
+~~~~
+
+``pcap_cnt``
+^^^^^^^^^^^^
+
+The packet number when reading from a pcap file.
+
+::
+
+    p = packet.get()
+    print p:pcap_cnt()
+
+
+Example
+~~~~~~~
+
+Example `match` function that takes a packet, inspect the payload line by line and checks if it finds the HTTP request line.
+If it is found, issue a notice log with packet details.
+
+::
+
+    function match (args)
+        p = packet.get()
+        payload = p:payload()
+        ts = p:timestring()
+
+        for line in payload:gmatch("([^\r\n]*)[\r\n]+") do
+            if line == "GET /index.html HTTP/1.0" then
+                ipver, srcip, dstip, proto, sp, dp = p:tuple()
+                SCLogNotice(string.format("%s %s->%s %d->%d (pcap_cnt:%d) match! %s", ts, srcip, dstip, sp, dp, p:pcap_cnt(), line));
+                return 1
+            end
+        end
+
+        return 0
+    end