---
-- A smallish implementation of the Couchbase Membase TAP protocol
-- Based on the scarce documentation from the Couchbase Wiki:
-- x http://www.couchbase.org/wiki/display/membase/SASL+Authentication+Example
--
-- @author "Patrik Karlsson <patrik@cqure.net>"
--


local bin = require "bin"
local match = require "match"
local nmap = require "nmap"
local sasl = require "sasl"
local stdnse = require "stdnse"
local table = require "table"
_ENV = stdnse.module("membase", stdnse.seeall)

-- A minimalistic implementation of the Couchbase Membase TAP protocol
TAP = {
	
	-- Operations
	Op = {
		LIST_SASL_MECHS = 0x20,
		AUTHENTICATE	= 0x21,
	},
	
	-- Requests
	Request = {
		
		-- Header breakdown
		-- Field        (offset) (value)
		-- Magic            (0): 0x80 (PROTOCOL_BINARY_REQ)
		-- Opcode           (1): 0x00
		-- Key length     (2-3): 0x0000 (0)
		-- Extra length     (4): 0x00
		-- Data type        (5): 0x00
		-- vbucket        (6-7): 0x0000 (0)
		-- Total body    (8-11): 0x00000000 (0)
		-- Opaque       (12-15): 0x00000000 (0)
		-- CAS          (16-23): 0x0000000000000000 (0)
		Header = {	
		
			-- Creates a new instance of Header
			-- @param opcode number containing the operation
			-- @return o new instance of Header
			new = function(self, opcode)
				local o = {
					magic		= 0x80,
					opcode		= tonumber(opcode),
					keylen 		= 0x0000,
					extlen 		= 0x00,
					data_type	= 0x00,
					vbucket		= 0x0000,
					total_body 	= 0x00000000,
					opaque 		= 0x00000000,
					CAS			= 0x0000000000000000,
				}
				setmetatable(o, self)
				self.__index = self
				return o
			end,
	
			-- Converts the header to string
			-- @return string containing the Header as string
			__tostring = function(self)
				return bin.pack(">CCSCCSIIL", self.magic, self.opcode, self.keylen,
					self.extlen, self.data_type, self.vbucket, self.total_body,
					self.opaque, self.CAS)
			end,
		},
	
		-- List SASL authentication mechanism
		SASLList = {

			-- Creates a new instance of the request
			-- @return o instance of request
			new = function(self)
				local o = {
					-- 0x20 SASL List Mechs
					header = TAP.Request.Header:new(TAP.Op.LIST_SASL_MECHS)
				}
				setmetatable(o, self)
				self.__index = self
				return o
			end,

			-- Converts the request to string
			-- @return string containing the request as string
			__tostring = function(self)
				return tostring(self.header)
			end,
		},
	
		-- Authenticates using SASL
		Authenticate = {

			-- Creates a new instance of the request
			-- @param username string containing the username
			-- @param password string containing the password
			-- @param mech string containing the SASL mechanism, currently suppored:
			--        PLAIN - plain-text authentication
			-- @return o instance of request
			new = function(self, username, password, mech)
				local o = {
					-- 0x20 SASL List Mechs
					header = TAP.Request.Header:new(TAP.Op.AUTHENTICATE),
					username = username,
					password = password,
					mech = mech,
				}
				setmetatable(o, self)
				self.__index = self
				return o
			end,

			-- Converts the request to string
			-- @return string containing the request as string
			__tostring = function(self)
				if ( self.mech == "PLAIN" ) then
					local mech_params = { self.username, self.password }
					local auth_data = sasl.Helper:new(self.mech):encode(table.unpack(mech_params))
					
					self.header.keylen = #self.mech
					self.header.total_body = #auth_data + #self.mech
					return tostring(self.header) .. self.mech .. auth_data
				end
			end,

		}
	
	},
	
	-- Responses
	Response = {
	
		-- The response header
		-- Header breakdown
		-- Field        (offset) (value)
		-- Magic            (0): 0x81 (PROTOCOL_BINARY_RES)
		-- Opcode           (1): 0x00
		-- Key length     (2-3): 0x0000 (0)
		-- Extra length     (4): 0x00
		-- Data type        (5): 0x00
		-- Status         (6-7): 0x0000 (SUCCESS)
		-- Total body    (8-11): 0x00000005 (5)
		-- Opaque       (12-15): 0x00000000 (0)
		-- CAS          (16-23): 0x0000000000000000 (0)
		Header = {
		
			-- Creates a new instance of Header
			-- @param data string containing the raw data
			-- @return o new instance of Header
			new = function(self, data)
				local o = {
					data = data
				}
				setmetatable(o, self)
				self.__index = self
				if ( o:parse() ) then
					return o
				end
			end,
		
			-- Parse the raw header and populates the class members
			-- @return status true on success, false on failure
			parse = function(self)
				if ( 24 > #self.data ) then
					stdnse.print_debug("membase: Header packet too short (%d bytes)", #self.data)
					return false, "Packet to short"
				end
				local pos
				pos, self.magic, self.opcode, self.keylen, self.extlen, 
					self.data_type,	self.status, self.total_body, self.opaque,
					self.CAS = bin.unpack(">CCSCCSIIL", self.data)
				return true
			end
			
		},
		
		-- Decoders
		Decoder = {
			
			-- TAP.Op.LIST_SASL_MECHS
			[0x20] = {
				-- Creates a new instance of the decoder
				-- @param data string containing the raw response
				-- @return o instance if successfully parsed, nil on failure
				--         the member variable <code>mechs</code> contains the
				--         supported authentication mechanisms.
				new = function(self, data)
					local o = { data = data }
					setmetatable(o, self)
					self.__index = self
					if ( o:parse() ) then
						return o
					end
				end,

				-- Parses the raw response
				-- @return true on success
				parse = function(self)
					self.mechs = self.data
					return true
				end
			},
			
			-- Login response
			[0x21] = {
				-- Creates a new instance of the decoder
				-- @param data string containing the raw response
				-- @return o instance if successfully parsed, nil on failure
				--         the member variable <code>status</code> contains the
				--         servers authentication response.
				new = function(self, data)
					local o = { data = data }
					setmetatable(o, self)
					self.__index = self
					if ( o:parse() ) then
						return o
					end
				end,

				-- Parses the raw response
				-- @return true on success
				parse = function(self)
					self.status = self.data
					return true
				end
			}
			
		}
	
	},
	
}

-- The Helper class is the main script interface
Helper = {
	
	-- Creates a new instance of the helper
	-- @param host table as received by the action method
	-- @param port table as received by the action method
	-- @param options table including options to the helper, currently:
	--        <code>timeout</code> - socket timeout in milliseconds
	new = function(self, host, port, options)
		local o = { 
			host = host,
			port = port,
			mech = stdnse.get_script_args("membase.authmech"),
			options = options or {}
		}
		setmetatable(o, self)
		self.__index = self
		return o
	end,
	
	-- Connects the socket to the server
	-- @return true on success, false on failure
	connect = function(self)
		self.socket = nmap.new_socket()
		self.socket:set_timeout(self.options.timeout or 10000)
		return self.socket:connect(self.host, self.port)
	end,
	
	-- Closes the socket
	close = function(self)
		return self.socket:close()
	end,
	
	-- Sends a request to the server, receives and parses the response
	-- @param req a Request instance
	-- @return status true on success, false on failure
	-- @return response instance of Response
	exch = function(self, req)
		local status, err = self.socket:send(tostring(req))
		if ( not(status) ) then
			return false, "Failed to send data"
		end
		
		local data
		status, data = self.socket:receive_buf(match.numbytes(24), true)
		if ( not(status) ) then
			return false, "Failed to receive data"
		end

		local header = TAP.Response.Header:new(data)
		
		if ( header.opcode ~= req.header.opcode ) then
			stdnse.print_debug("WARNING: Received invalid op code, request contained (%d), response contained (%d)", req.header.opcode, header.opcode)
		end
		
		if ( not(TAP.Response.Decoder[tonumber(header.opcode)]) ) then
			return false, ("No response handler for opcode: %d"):format(header.opcode)
		end
		
		local status, data = self.socket:receive_buf(match.numbytes(header.total_body), true)
		if ( not(status) ) then
			return false, "Failed to receive data"
		end
		
		local response = TAP.Response.Decoder[tonumber(header.opcode)]:new(data)
		if ( not(response) ) then
			return false, "Failed to parse response from server"
		end
		return true, response
	end,
	
	-- Gets list of supported SASL authentication mechanisms
	getSASLMechList = function(self)
		return self:exch(TAP.Request.SASLList:new())
	end,
	
	-- Logins to the server
	-- @param username string containing the username
	-- @param password string containing the password
	-- @param mech string containing the SASL mechanism to use
	-- @return status true on success, false on failure
	-- @return respons string containing "Auth failure" on failure
	login = function(self, username, password, mech)
		mech = mech or self.mech or "PLAIN"
		local status, response = self:exch(TAP.Request.Authenticate:new(username, password, mech))
		if ( not(status) ) then
			return false, "Auth failure"
		end
		if ( response.status == "Auth failure" ) then
			return false, response.status
		end
		return true, response.status
	end,
}



return _ENV;
