tarreader.lua

--
-- tarreader.lua
--
-- Copyright (c) 2018 rxi
--
-- Permission is hereby granted, free of charge, to any person obtaining a copy
-- of this software and associated documentation files (the "Software"), to
-- deal in the Software without restriction, including without limitation the
-- rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
-- sell copies of the Software, and to permit persons to whom the Software is
-- furnished to do so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in
-- all copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-- FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
-- IN THE SOFTWARE.
--


local TarReader = {}
TarReader.__index = TarReader


local FileStream = {}
FileStream.__index = FileStream


function FileStream.new(filename)
  local file = assert( io.open(filename, "rb") )
  local self = setmetatable({}, FileStream)
  self.file = file
  return self
end


function FileStream:read(n)
  return self.file:read(n)
end


function FileStream:seek(n)
  self.file:seek("set", n)
end


function FileStream:close()
  self.file:close()
end


local function round_up(n, incr)
  return n + (incr - n % incr) % incr;
end


local function read_string(stream, n)
  return stream:read(n):gsub("%z", "")
end


local function read_header(stream)
  return {
    name     =           read_string(stream, 100 ),
    mode     = tonumber( read_string(stream, 8   ), 8),
    owner    = tonumber( read_string(stream, 8   ), 8),
    group    =           read_string(stream, 8   ),
    size     = tonumber( read_string(stream, 12  ), 8),
    mtime    = tonumber( read_string(stream, 12  ), 8),
    checksum =           read_string(stream, 8   ),
    type     =           read_string(stream, 1   ),
    linkname =           read_string(stream, 100 ),
  }
end


function TarReader.new(stream)
  if type(stream) == "string" then
    stream = FileStream.new(stream)
  end

  local self = setmetatable({}, TarReader)
  self.stream = assert(stream)
  return self
end


function TarReader:close()
  self.stream:close()
end


function TarReader:each()
  local pos = 0

  return function()
    self.stream:seek(pos)
    local header = read_header(self.stream)
    header.position = pos + 512

    if header.name == "" then
      return nil
    end

    pos = pos + 512 + round_up(header.size, 512)
    return header
  end
end


function TarReader:read(filename)
  for header in self:each() do
    if header.name == filename then
      self.stream:seek(header.position)
      return self.stream:read(header.size)
    end
  end

  return nil, "could not find file"
end


return TarReader