added significantly larger file support to libmtar, as well as versioning support

lib/libmtar.lua

@@ -1,4 +1,8 @@
 local mtar = {}
+local versions = {}
+versions[0] = {nlf = ">I2", flf = ">I2"} -- original version format
+versions[1] = {nlf = ">I2", flf = ">I8"} -- extended file size format
+mtar.versions = versions
 
 local function cleanPath(path)
  local pt = {}
@@ -12,8 +16,9 @@ local function cleanPath(path)
  return table.concat(pt,"/")
 end
 
-function mtar.genHeader(fname,len) -- string number -- string -- generate a header for file *fname* when provided with file length *len*
- return string.format("%s%s%s", string.pack(">I2",fname:len()), fname, string.pack(">I2",len))
+function mtar.genHeader(fname,len,version) -- string number -- string -- generate a header for file *fname* when provided with file length *len*
+ version=version or 1
+ return string.format("\255\255%s%s%s%s", string.char(version), string.pack(versions[version].nlf,fname:len()), fname, string.pack(versions[version].flf,len))
 end
 
 function mtar.iter(stream) -- table -- function -- Given buffer *stream*, returns an iterator suitable for use with *for* that returns, for each iteration, the file name, a function to read from the file, and the length of the file.
@@ -27,14 +32,17 @@ function mtar.iter(stream) -- table -- function -- Given buffer *stream*, return
   while remain > 0 do
    remain=remain-#stream:read(math.min(remain,2048))
   end
+  local version = 0
   local nlen = string.unpack(">I2", stream:read(2) or "\0\0")
   if nlen == 0 then
    return
+  elseif nlen == 65535 then -- versioned header
+   version = string.byte(stream:read(1))
+   nlen = string.unpack(versions[version].nlf, stream:read(string.packsize(versions[version].nlf)))
   end
   local name = cleanPath(stream:read(nlen))
-  local fsize = string.unpack(">I2", stream:read(2))
-  remain = fsize
-  return name, read, fsize
+  remain = string.unpack(versions[version].flf, stream:read(string.packsize(versions[version].flf)))
+  return name, read, remain
  end
 end