nmap/nselib/json.lua

---
-- Library methods for handling JSON data. It handles JSON encoding and
-- decoding according to RFC 4627.
--
-- There is a test section at the bottom which shows some example
-- parsing. If you want to parse JSON, you can test it by pasting sample JSON
-- into the <code>TESTS</code> table and run the <code>test</code> method
--
-- There is a straightforward mapping between JSON and Lua data types. One
-- exception is JSON <code>NULL</code>, which is not the same as Lua
-- <code>nil</code>. (A better match for Lua <code>nil</code> is JavaScript
-- <code>undefined</code>.) <code>NULL</code> values in JSON are represented by
-- the special value <code>json.NULL</code>.
--
-- @author Martin Holst Swende
-- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html

-- TODO: Unescape/escape unicode
-- Version 0.4
-- Created 01/25/2010 - v0.1 - created by Martin Holst Swende <martin@swende.se>
-- Heavily modified 02/22/2010 - v0.3. Rewrote the parser into an OO-form, to not have to handle
-- all kinds of state with parameters and return values.
-- Modified 02/27/2010 - v0.4 Added unicode handling (written by David Fifield). Renamed toJson
-- and fromJson into generate() and parse(), implemented more proper numeric parsing and added some more error checking.

local bit = require "bit"
local nmap = require "nmap"
local stdnse = require "stdnse"
local string = require "string"
local table = require "table"
local unicode = require "unicode"
_ENV = stdnse.module("json", stdnse.seeall)

--Some local shortcuts
local function dbg(str,...)
  stdnse.print_debug("Json:"..str, ...)
end
local function d4(str,...)
  if nmap.debugging() > 3 then dbg(str, ...) end
end
local function d3(str,...)
  if nmap.debugging() > 2 then dbg(str, ...) end
end

--local dbg =stdnse.print_debug
local function dbg_err(str,...)
  stdnse.print_debug("json-ERR:"..str, ...)
end

-- Javascript null representation, see explanation above
NULL = {}

-- See section 2.5 for escapes.
-- For convenience, ESCAPE_TABLE maps to escape sequences complete with
-- backslash, and REVERSE_ESCAPE_TABLE maps from single escape characters
-- (no backslash).
local ESCAPE_TABLE = {}
local REVERSE_ESCAPE_TABLE = {}
do
  local escapes = {
    [string.char(0x22)] = "\"",
    [string.char(0x5C)] = "\\",
    [string.char(0x2F)] = "/",
    [string.char(0x08)] = "b",
    [string.char(0x0C)] = "f",
    [string.char(0x0A)] = "n",
    [string.char(0x0D)] = "r",
    [string.char(0x09)] = "t",
  }
  for k, v in pairs(escapes) do
    ESCAPE_TABLE[k] = "\\" .. v
    REVERSE_ESCAPE_TABLE[v] = k
  end
end

-- Escapes a string
--@param str the string
--@return a string where the special chars have been escaped
local function escape(str)
  return "\"" .. string.gsub(str, ".", ESCAPE_TABLE) .. "\""
end

--- Makes a table be treated as a JSON Array when generating JSON
--
-- A table treated as an Array has all non-number indices ignored.
-- @param t a table to be treated as an array
function make_array(t)
  local mt = getmetatable(t) or {}
  mt["json"] = "array"
  setmetatable(t, mt)
end

--- Makes a table be treated as a JSON Object when generating JSON
--
-- A table treated as an Object has all non-number indices ignored.
-- @param t a table to be treated as an object
function make_object(t)
  local mt = getmetatable(t) or {}
  mt["json"] = "object"
  setmetatable(t, mt)
end

--- Checks what JSON type a variable will be treated as when generating JSON
-- @param var a variable to inspect
-- @return a string containing the JSON type. Valid values are "array",
--        "object", "number", "string", "boolean", and "null"
function typeof(var)
  local t = type(var)
  if var == NULL then
    return "null"
  elseif t == "table" then
    local mtval = rawget(getmetatable(var) or {}, "json")
    if mtval == "array" or (mtval ~= "object" and #var > 0) then
      return "array"
    else
      return "object"
    end
  else
    return t
  end
  error("Unknown data type in typeof")
end

--- Creates json data from an object
--@param obj a table containing data
--@return a string containing valid json
function generate(obj)

  -- NULL-check must be performed before
  -- checking type == table, since the NULL-object
  -- is a table
  if obj == NULL then
    return "null"
  elseif obj == false then
    return "false"
  elseif obj == true then
    return "true"
  elseif type(obj) == "number" then
    return string.format("%g", obj)
  elseif type(obj) == "string" then
    return escape(obj)
  elseif type(obj) == "table" then
    local k, v, elems, jtype
    elems = {}
    jtype = typeof(obj)
    if jtype == "array" then
      for _, v in ipairs(obj) do
        elems[#elems + 1] = generate(v)
      end
      return "[" .. table.concat(elems, ", ") .. "]"
    elseif jtype == "object" then
      for k, v in pairs(obj) do
        elems[#elems + 1] = escape(k) .. ": " .. generate(v)
      end
      return "{" .. table.concat(elems, ", ") .. "}"
    end
  end
  error("Unknown data type in generate")
end

-- This is the parser, implemented in OO-form to deal with state better
Json = {}
-- Constructor
function Json:new(input)
  local o = {}
  setmetatable(o, self)
  self.__index = self
  o.input = input
  o.pos = 1 -- Pos is where the NEXT letter will be read
  return o
end

-- Gets next character and ups the position
--@return next character
function Json:next()
  self.pos = self.pos+1
  return self.input:sub(self.pos-1, self.pos-1)
end
-- Updates the position to next non whitespace position
function Json:eatWhiteSpace()
  --Find next non-white char
  local a,b = self.input:find("%S",self.pos)
  if not a then
    self:syntaxerror("Empty data")
    return
  end
  self.pos = a
end

-- Jumps to a specified position
--@param position where to go
function Json:jumpTo(position)
  self.pos = position
end

-- Returns next character, but without upping position
--@return next character
function Json:peek()
  return self.input:sub(self.pos, self.pos)
end

--@return true if more input is in store
function Json:hasMore()
  return self.input:len() >= self.pos
end

-- Checks that the following input is equal to a string
-- and updates position so next char will be after that string
-- If false, triggers a syntax error
--@param str the string to test
function Json:assertStr(str)
  local content = self.input:sub(self.pos,self.pos+str:len()-1)
  if(content == str) then-- All ok
    -- Jump forward
    self:jumpTo(self.pos+str:len())
    return
  end
  self:syntaxerror(("Expected '%s' but got '%s'"):format( str, content))
end

-- Trigger a syntax error
function Json:syntaxerror(reason)
  self.error = ("Syntax error near pos %d: %s input: %s"):format( self.pos, reason, self.input)
  dbg(self.error)
end
-- Check if any errors has occurred
function Json:errors()
  return self.error ~= nil
end
-- Parses a top-level JSON structure (object or array).
--@return the parsed object or puts error messages in self.error
function Json:parseStart()
  -- The top level of JSON only allows an object or an array. Only inside
  -- of the outermost container can other types appear.
  self:eatWhiteSpace()
  local c = self:peek()
  if c == '{' then
    return self:parseObject()
  elseif c == '[' then
    return self:parseArray()
  else
    self:syntaxerror(("JSON must start with object or array (started with %s)"):format(c))
    return
  end
end

-- Parses a value
--@return the parsed value
function Json:parseValue()
  self:eatWhiteSpace()
  local c = self:peek()

  local value
  if c == '{' then
    value = self:parseObject()
  elseif c == '[' then
    value = self:parseArray()
  elseif c == '"' then
    value = self:parseString()
  elseif c == 'n' then
    self:assertStr("null")
    value = NULL
  elseif c == 't' then
    self:assertStr("true")
    value = true
  elseif c == 'f' then
    self:assertStr("false")
    value = false
  else -- numeric
    -- number = [ minus ] int [ frac ] [ exp ]
    local a,b =self.input:find("-?%d+%.?%d*[eE]?[+-]?%d*", self.pos)
    if not a or not b then
      self:syntaxerror("Error 1 parsing numeric value")
      return
    end
    value = tonumber(self.input:sub(a,b))
    if(value == nil) then
      self:syntaxerror("Error 2 parsing numeric value")
      return
    end
    self:jumpTo(b+1)
  end
  return value
end
-- Parses a json object {}
--@return the object (or triggers a syntax error)
function Json:parseObject()
  local object  = {}
  make_object(object)
  local _= self:next() -- Eat {

  while(self:hasMore() and not self:errors()) do
    self:eatWhiteSpace()
    local c = self:peek()
    if(c == '}') then -- Empty object, probably
      self:next() -- Eat it
      return object
    end

    if(c ~= '"') then
      self:syntaxerror(("Expected '\"', got '%s'"):format(c))
      return
    end

    local key = self:parseString()
    if self:errors() then
      return
    end
    self:eatWhiteSpace()
    c = self:next()
    if(c ~= ':') then
      self:syntaxerror("Expected ':' got "..c)
      return
    end
    local value = self:parseValue()

    if self:errors() then
      return
    end

    object[key] = value

    self:eatWhiteSpace()
    c = self:next()
    -- Valid now is , or }
    if(c == '}') then
      return object
    end
    if(c ~= ',') then
      self:syntaxerror("Expected ',' or '}', got "..c)
      return
    end
  end
end
-- Parses a json array [] or triggers a syntax error
--@return the array object
function Json:parseArray()
  local array  = {}
  make_array(array)
  self:next()
  while(self:hasMore() and not self:errors()) do
    self:eatWhiteSpace()
    if(self:peek() == ']') then -- Empty array, probably
      self:next()
      break
    end
    local value = self:parseValue()
    if self:errors() then
      return
    end
    table.insert(array, value)
    self:eatWhiteSpace()
    local c = self:next()
    -- Valid now is , or ]
    if(c == ']') then return array end
    if(c ~= ',') then
      self:syntaxerror(("Expected ',' but got '%s'"):format(c))
      return
    end
  end
  return array
end

-- Decode a Unicode escape, assuming that self.pos starts just after the
-- initial \u. May consume an additional escape in the case of a UTF-16
-- surrogate pair. See RFC 2781 for UTF-16.
function Json:parseUnicodeEscape()
  local n, cp
  local hex, lowhex
  local s, e

  s, e, hex = self.input:find("^(....)", self.pos)
  if not hex then
    self:syntaxerror(("EOF in Unicode escape \\u%s"):format(self.input:sub(self.pos)))
    return
  end
  n = tonumber(hex, 16)
  if not n then
    self:syntaxerror(("Bad unicode escape \\u%s"):format(hex))
    return
  end
  cp = n
  self.pos = e + 1
  if n < 0xD800 or n > 0xDFFF then
    return cp
  end
  if n >= 0xDC00 and n <= 0xDFFF then
    self:syntaxerror(("Not a Unicode character: U+%04X"):format(cp))
    return
  end

  -- Beginning of a UTF-16 surrogate.
  s, e, lowhex = self.input:find("^\\u(....)", self.pos)
  if not lowhex then
    self:syntaxerror(("Bad unicode escape \\u%s (missing low surrogate)"):format(hex))
    return
  end
  n = tonumber(lowhex, 16)
  if not n or not (n >= 0xDC00 and n <= 0xDFFF) then
    self:syntaxerror(("Bad unicode escape \\u%s\\u%s (bad low surrogate)"):format(hex, lowhex))
    return
  end
  self.pos = e + 1
  cp = 0x10000 + bit.band(cp, 0x3FF) * 0x400 + bit.band(n, 0x3FF)
  -- also remove last "
  return cp
end

-- Parses a json string
-- @return the string or triggers syntax error
function Json:parseString()

  local val = ''
  local c = self:next()
  assert( c == '"')
  while(self:hasMore()) do
    local c  = self:next()

    if(c == '"') then -- end of string
    break
  elseif(c == '\\') then-- Escaped char
    local d = self:next()
    if REVERSE_ESCAPE_TABLE[d] ~= nil then
      val = val .. REVERSE_ESCAPE_TABLE[d]
    elseif d == 'u' then -- Unicode chars
      local codepoint = self:parseUnicodeEscape()
      if not codepoint then
        return
      end
      val = val .. unicode.utf8_enc(codepoint)
    else
      self:syntaxerror(("Undefined escape character '%s'"):format(d))
      return false
    end
  else -- Char
    val = val .. c
  end
end
return val
end
--- Parses json data into an object form
--
-- This is the method you probably want to use if you
-- use this library from a script.
--@param data a json string
--@return status true if ok, false if bad
--@return an object representing the json, or error message
function parse(data)
  local parser = Json:new(data)
  local result = parser:parseStart()
  if(parser.error) then
    return false, parser.error
  end
  return true, result
end

----------------------------------------------------------------------------------
-- Test-code for debugging purposes below
----------------------------------------------------------------------------------

local TESTS = {
  '{"a":1}',
  '{"a":true}',
  '{"a":     false}',
  '{"a":     null     \r\n, \t "b"  \f:"ehlo"}',
  '{"a\\"a":"a\\"b\\"c\\"d"}',
  '{"foo":"gaz\\"onk", "pi":3.14159,"hello":{ "wo":"rld"}}',
  '{"a":1, "b":2}',
  '{"foo":"gazonk", "pi":3.14159,"hello":{ "wo":"rl\\td"}}',
  '[1,2,3,4,5,null,false,true,"\195\164\195\165\195\182\195\177","bar"]',
  '[]',-- This will yield {} in toJson, since in lua there is only one basic datatype - and no difference when empty
  '{}',

  '', -- error
  'null', -- error
  '"abc"', -- error
  '{a":1}', -- error
  '{"a" bad :1}', -- error
  '["a\\\\t"]',  -- Should become Lua {"a\\t"}
  '[0.0.0]',  -- error
  '[-1]',
  '[-1.123e-2]',
  '[5e3]',
  '[5e+3]',
  '[5E-3]',
  '[5.5e3]',
  '["a\\\\"]',  -- Should become Lua {"a\\"}
  '{"a}": 1}',  -- Should become Lua {"a}" = 1}
  '["key": "value"]',  -- error
  '["\\u0041"]',  -- Should become Lua {"A"}
  '["\\uD800"]',  -- error
  '["\\uD834\\uDD1EX"]',  -- Should become Lua {"\240\157\132\158X"}
}
function test()
  print("Tests running")
  local i,v,res,status
  for i,v in pairs(TESTS) do
    print("----------------------------")
    print(v)
    status,res = parse(v)
    if not status then print( res) end
    if(status) then
      print(generate(res))
    else
      print("Error:".. res)
    end
  end
end

return _ENV;