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+--- A relatively small implementation of the Service Location Protocol.
+-- It was initially designed to support requests for discovering Novell NCP
+-- servers, but should work for any other service as well.
+--
+-- The implementation is based on the following classes:
+-- * Request.Service
+--    - Contains necessary code to produce a service request
+--
+-- * Request.Attributes
+--    - Contains necessary code to produce a attribute request
+--
+-- * Reply.Service
+--    - Contains necessary code to process and parse the response to the
+--      service request
+--
+-- * Reply.Attributes
+--    - Contains necessary code to process and parse the response to the
+--      attribute request
+--
+-- The following code illustrates intended use of the library:
+--
+--  <code>
+--    local helper = srvloc.Helper:new()
+--    local status, tree = helper:ServiceRequest("ndap.novell", "DEFAULT")
+--    if ( status ) then tree = tree:match("%/%/%/(.*)%.$") end
+--  </code>
+
+--@author Patrik Karlsson <patrik@cqure.net>
+--@copyright Same as Nmap--See https://nmap.org/book/man-legal.html
+
+-- Version 0.1
+-- Created 24/04/2011 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>
+
+local nmap = require "nmap"
+local stdnse = require "stdnse"
+local string = require "string"
+local table = require "table"
+_ENV = stdnse.module("srvloc", stdnse.seeall)
+
+PacketFunction = {
+  SERVICE_REQUEST = 1,
+  SERVICE_REPLY = 2,
+  ATTRIB_REQUEST = 6,
+}
+
+Reply = {
+
+  Service = {
+
+    --- Creates a new instance of the Reply.Service class
+    -- @param data string containing the raw reply as read from the socket
+    -- @return o instance of Reply.Service
+    new = function(self, data)
+      local o = { data = data }
+      setmetatable(o, self)
+      self.__index = self
+      o:parse(data)
+      return o
+    end,
+
+    --- Parses the service reply raw packet data
+    -- @param data string containing the raw reply as read from the socket
+    parse = function(self, data)
+      local pos
+
+      self.version, self.func, self.len, self.flags, pos = string.unpack(">BBI3I2", data)
+
+      self.next_extension_offset, self.xid, self.lang_tag, pos = string.unpack(">I3I2s2", data, pos)
+
+      local no_urls, reserved, url_len
+      self.error_code, no_urls, pos = string.unpack(">I2I2", data, pos)
+
+      if ( no_urls > 0 ) then
+        local num_auths
+        self.url_lifetime, self.url, num_auths, pos = string.unpack(">xI2s2C", data, pos)
+      end
+    end,
+
+    --- Attempts to create an instance by reading data off the socket
+    -- @param socket socket connected to the SRVLOC service
+    -- @return new instance of the Reply.Service class
+    fromSocket = function(socket)
+      local status, data = socket:receive()
+      if ( not(status) ) then return end
+      return Reply.Service:new(data)
+    end,
+
+    --- Gets the url value from the reply
+    -- @return uri string containing the reply url
+    getUrl = function(self) return self.url end,
+  },
+
+  Attribute = {
+
+    --- Creates a new instance of Reply.Attribute
+    -- @param data string containing the raw reply as read from the socket
+    -- @return o instance of Reply.Attribute
+    new = function(self, data)
+      local o = { data = data }
+      setmetatable(o, self)
+      self.__index = self
+      o:parse(data)
+      return o
+    end,
+
+    --- Parses the service reply raw packet data
+    -- @param data string containing the raw reply as read from the socket
+    parse = function(self, data)
+      local pos
+
+      self.version, self.func, self.len, pos = string.unpack(">BBI3", data)
+      self.next_extension_offset, self.xid, self.lang_tag, pos = string.unpack(">I3I2s2", data, pos)
+
+      local num_auths
+      self.error_code, self.attrib_list, num_auths, pos = string.unpack(">I2s2B", data, pos)
+    end,
+
+    --- Attempts to create an instance by reading data off the socket
+    -- @param socket socket connected to the SRVLOC service
+    -- @return new instance of the Reply.Attribute class
+    fromSocket = function(socket)
+      local status, data = socket:receive()
+      if ( not(status) ) then return end
+      return Reply.Attribute:new(data)
+    end,
+
+    --- Gets the attribute list
+    -- @return attrib_list
+    getAttribList = function(self) return self.attrib_list end,
+  }
+}
+
+
+Request = {
+
+  -- The attribute request
+  Attribute = {
+
+    --- Creates a new instance of the Attribue request
+    -- @return o instance of Attribute
+    new = function(self)
+      local o = {
+        lang_tag = "en", version = 2, service_type = "",
+        scope = "", next_extension_offset = 0,
+        prev_resp_list_len = 0, slp_spi_len = 0 }
+      setmetatable(o, self)
+      self.__index = self
+      return o
+    end,
+
+    --- Sets the request scope
+    -- @param scope string containing the request scope
+    setScope = function(self, scope) self.scope = scope end,
+
+    --- Sets the language tag
+    -- @param lang string containing the language
+    setLangTag = function(self, lang) self.lang_tag = lang end,
+
+    --- Sets the request flags
+    -- @param flags number containing the numeric flag representation
+    setFlags = function(self, flags) self.flags = flags end,
+
+    --- Sets the request XID
+    -- @param xid number containing the request XID
+    setXID = function(self, xid) self.xid = xid end,
+
+    --- Sets the request function
+    -- @param func number containing the request function number
+    setFunction = function(self, func) self.func = func end,
+
+    --- Sets the request taglist
+    -- @param tl string containing the taglist
+    setTagList = function(self, tl) self.tag_list = tl end,
+
+    --- Sets the request url
+    -- @param u string containing the url
+    setUrl = function(self, u) self.url = u end,
+
+    --- "Serializes" the request to a string
+    -- @return data string containing a string representation of the request
+    __tostring = function(self)
+      assert(self.func, "Packet function was not specified")
+      assert(self.scope, "Packet scope was not specified")
+
+      local BASE_LEN = 24
+      local len = BASE_LEN + #self.lang_tag + self.prev_resp_list_len +
+      self.slp_spi_len + #self.service_type + #self.url +
+      #self.tag_list + #self.scope
+
+      local data = string.pack(">BBI3I2I3I2s2I2s2s2s2I2", self.version, self.func,
+        len, self.flags, self.next_extension_offset, self.xid, self.lang_tag,
+        self.prev_resp_list_len, self.url, self.scope,
+        self.tag_list, self.slp_spi_len)
+
+      return data
+    end
+  },
+
+  -- The Service request
+  Service = {
+
+    --- Creates a new instance of the Service request
+    -- @return o instance of Service
+    new = function(self)
+      local o = {
+        lang_tag = "en", version = 2, service_type = "",
+        scope = "", next_extension_offset = 0,
+        prev_resp_list_len = 0, predicate_len = 0, slp_spi_len = 0 }
+      setmetatable(o, self)
+      self.__index = self
+      return o
+    end,
+
+    --- Sets the service type of the request
+    -- @param t string containing the type of the request
+    setServiceType = function(self, t) self.service_type = t end,
+
+    --- Sets the request scope
+    -- @param scope string containing the request scope
+    setScope = function(self, scope) self.scope = scope end,
+
+    --- Sets the language tag
+    -- @param lang string containing the language
+    setLangTag = function(self, lang) self.lang_tag = lang end,
+
+    --- Sets the request flags
+    -- @param flags number containing the numeric flag representation
+    setFlags = function(self, flags) self.flags = flags end,
+
+    --- Sets the request XID
+    -- @param xid number containing the request XID
+    setXID = function(self, xid) self.xid = xid end,
+
+    --- Sets the request function
+    -- @param func number containing the request function number
+    setFunction = function(self, func) self.func = func end,
+
+    --- "Serializes" the request to a string
+    -- @return data string containing a string representation of the request
+    __tostring = function(self)
+      assert(self.func, "Packet function was not specified")
+      assert(self.scope, "Packet scope was not specified")
+
+      local BASE_LEN = 24
+      local len = BASE_LEN + #self.lang_tag + self.prev_resp_list_len +
+        self.predicate_len + self.slp_spi_len + #self.service_type +
+        #self.scope
+      local len_hi = ((len >> 16) & 0x00FF)
+      local len_lo = (len & 0xFFFF)
+      local neo_hi = ((self.next_extension_offset >> 16) & 0x00FF)
+      local neo_lo = (self.next_extension_offset & 0xFFFF)
+
+      local data = string.pack(">BBI3I2I3I2s2I2s2s2I2I2", self.version, self.func,
+        len, self.flags, self.next_extension_offset, self.xid, self.lang_tag,
+        self.prev_resp_list_len, self.service_type,
+        self.scope, self.predicate_len, self.slp_spi_len)
+
+      return data
+    end
+  }
+
+}
+
+
+-- The Helper class serves as primary interface for scripts using the library
+Helper = {
+
+  new = function(self, host, port)
+    local o = { xid = 1, socket = nmap.new_socket("udp") }
+    setmetatable(o, self)
+    self.__index = self
+    local family = nmap.address_family()
+    o.host = host or (family=="inet6" and "FF02::116" or "239.255.255.253")
+    o.port = port or { number=427, proto="udp" }
+    return o
+  end,
+
+  --- Sends a service request and waits for the response
+  -- @param srvtype string containing the service type to query
+  -- @param scope string containing the scope of the request
+  -- @return true on success, false on failure
+  -- @return url string (on success) containing the url of the ServiceReply
+  -- @return err string (on failure) containing the error message
+  ServiceRequest = function(self, srvtype, scope)
+    local srvtype = srvtype or ""
+    local scope = scope or ""
+    local sr = Request.Service:new()
+    sr:setXID(self.xid)
+    sr:setServiceType(srvtype)
+    sr:setScope(scope)
+    sr:setFunction(PacketFunction.SERVICE_REQUEST)
+    sr:setFlags(0x2000)
+
+    self.socket:set_timeout(5000)
+    self.socket:sendto( self.host, self.port, tostring(sr) )
+
+    local result = {}
+    repeat
+      local r = Reply.Service.fromSocket(self.socket)
+      if ( r ) then
+        table.insert(result, r:getUrl())
+      end
+      self.xid = self.xid + 1
+    until(not(r))
+
+    if ( #result == 0 ) then
+      return false, "ERROR: Helper.Locate no response received"
+    end
+    return true, result
+  end,
+
+  --- Requests an attribute from the server
+  -- @param url as retrieved by the Service request
+  -- @param scope string containing the request scope
+  -- @param taglist string containing the request tag list
+  AttributeRequest = function(self, url, scope, taglist)
+    local url = url or ""
+    local scope = scope or ""
+    local taglist = taglist or ""
+    local ar = Request.Attribute:new()
+    ar:setXID(self.xid)
+    ar:setScope(scope)
+    ar:setUrl(url)
+    ar:setTagList(taglist)
+    ar:setFunction(PacketFunction.ATTRIB_REQUEST)
+    ar:setFlags(0x2000)
+
+    self.socket:set_timeout(5000)
+    self.socket:sendto( self.host, self.port, tostring(ar) )
+
+    local r = Reply.Attribute.fromSocket(self.socket)
+
+    self.xid = self.xid + 1
+    if ( not(r) ) then
+      return false, "ERROR: Helper.Locate no response received"
+    end
+    return true, r:getAttribList()
+  end,
+
+  close = function(self)
+    return self.socket:close()
+  end,
+}
+
+return _ENV;