How to convert RTF to plain text

Introduction

Converting from RTF with the Translator is straightforward. The following example shows a function that takes an RTF document, and strips out all the formatting and non-text objects to produce plain text.

As you can see it is as simple as loading the file and making a single function call.

Note: The main() function uses print() to log messages. When an Iguana channel is run print() messages are logged as informational messages. For more sophisticated logging you can use the iguana.logInfo(), iguana.logWarning(), iguana.logDebug() functions.

Source Code [top]

Here is the source code for the rtf module. To use it:

  1. Create a new shared module called “rtf” and copy paste in the code below.
  2. Add the code require(‘rtf’) at the top of the main module.
  3. Test using sample.rtf, or your own rtf file.

Code for main:

local rtf = require('rtf')

function main()
   io.input('sample.rtf')
   Rtf=io.read("*all")

   local text=rtf.toTxt(Rtf)
   trace(text)
end

Code for rtf module:

local rtf={}

-- 
-- Implementation
--  

-- A simple set implementation in Lua
local function Set (list)
  local set = {}
  for _, l in ipairs(list) do set[l] = true end
  return set
end

-- Which control sequences to ignore
local IgnoreSet = Set { 'info', 'fonttbl', 'colortbl', 'stylesheet', '*' }
local Out = '';
local StateStack = {};
local State;

-- States of the state machine
local PLAINTEXT = 1
local CONTROL = 2
local ARGUMENT = 3
local BACKSLASH = 4
local ESCAPED_CHAR = 5

-- Character destinationions
local USE = 0
local IGNORE = 1

-- To print an exception only the first time
local UnexpectedCharFound = false;

-- Sets current character destination (IGNORE or USE)
local function setDest (D)
   Dest = D    
end

local function pushState ()
   table.insert (StateStack, { ['Dest'] = Dest } )
end

local function popState ()
   local EL = table.remove (StateStack)
   setDest  (EL['Dest'])
end

-- Collect or ignore the character based on the current destination
local function putChar (C, B)
   if C == '\r' then
      C = '\n'
   end
   if Dest ~= IGNORE then
      Out = Out..C
   end
end

local function isAlpha (C)
   return string.match (C, "%a") ~= nil
end

local function isDigit (C)
   return string.match (C, "%d") ~= nil
end

local function isSpace (C)
   return string.match (C, "%s") ~= nil
end

-- Process an RTF control word
-- T is token
-- A is argument
local function doControl (T, A)
   if T == 'par' then
      putChar ('\n')
   elseif IgnoreSet[T] then
      setDest (IGNORE)
   end
end

local function feedChar (C, B)
   local function nextState (C, B, CheckSpace)
      if C == '\\' then
         State = BACKSLASH
      elseif C == '{' then
         pushState ()
      elseif C == '}' then
         popState ()
      else
         if not CheckSpace or not isSpace (C) then
            putChar (C, B)
         end
      end       
   end

   if State == PLAINTEXT then
      nextState (C, B, false)
   elseif State == BACKSLASH then
      if C == '\\' or C == '{' or C == '}' then
         putChar (C)
         State = PLAINTEXT
      else
         if isAlpha (C) or C == '*' or C == '-' or C == '|' then
            State = CONTROL
            Token = C
         elseif C == "'" then
            State = ESCAPED_CHAR
            EscapedChar = ''
         elseif C == '\\' or C == '{' or C == '}' then
            putChar (C)
            State = PLAINTEXT
         elseif C == '~' then
            putChar (' ')
            state = PLAINTEXT
         else
            if (UnexpectedCharFound ~= true) then
               print ('Exception: unxepected '..C..' after \\')
               UnexpectedCharFound = true
            end
         end           
      end
   elseif State == ESCAPED_CHAR then
      EscapedChar = EscapedChar..C
      if #EscapedChar == 2 then
         C = string.char (tonumber (EscapedChar, 16))
         putChar (C)
         State = PLAINTEXT
      end
   elseif State == CONTROL then
      if isAlpha (C) then
         Token = Token..C
      elseif isDigit (C) or C == '-' then
         State = ARGUMENT
         Arg = C
      else
         doControl (Token, Arg)
         State = PLAINTEXT
         nextState (C, B, true)
      end
   elseif State == ARGUMENT then
      if isDigit (C) then
         Arg = Arg .. C
      else
         State = PLAINTEXT
         doControl (Token, Arg)
         nextState (C, B, true)
      end
   end
end

-- 
-- Public API
-- 

-- Given an RTF document as a Lua string (Data), return the text
-- portion of the document.
function rtf.toTxt(Data)
   Out = ''
   StateStack = { }
   State = PLAINTEXT
   setDest (USE)

   Data = string.gsub (Data, '\r', '')
   Data = string.gsub (Data, '\n', '')

   local i = 1
   for i = 1, #Data do
      local B = string.byte (Data, i)
      feedChar (string.char (B), B)
   end
   return Out
end

return rtf

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