diff --git a/luametalatex-callbacks.lua b/luametalatex-callbacks.lua
index 58ed8c0..fefb603 100644
--- a/luametalatex-callbacks.lua
+++ b/luametalatex-callbacks.lua
@@ -87,3 +87,27 @@ callback_register('handle_error_hook', function()
   until false
   return 3
 end)
+
+-- Now overwrite the callback functionality. Our system is based on the ssumption there there are
+-- no unknown callback names, just callbacks very unlikely to ever be called. That doesn't lead to
+-- good error checking, but we expect this to be overwritten by LaTeX anyway.
+
+local callback_find = callback.find
+local rawset = rawset
+local callbacks = setmetatable({}, {
+  __index = function(cbs, name)
+    return callback_find(name)
+  end,
+  __newindex = function(cbs, name, new)
+    return callback_register(name, new) or rawset(cbs, name, new)
+  end,
+})
+
+function callback.register(name, new)
+  callbacks[name] = new
+end
+function callback.find(name)
+  return callbacks[name]
+end
+
+return callbacks
diff --git a/luametalatex-font-enc.lua b/luametalatex-font-enc.lua
index 3ff9ed4..b8d2a32 100644
--- a/luametalatex-font-enc.lua
+++ b/luametalatex-font-enc.lua
@@ -1,3 +1,5 @@
+local readfile = require'luametalatex-readfile'
+
 local white = (lpeg.S'\0\9\10\12\13\32' + '%' * (1 - lpeg.S'\r\n')^0)^1
 local regular = 1-lpeg.S'()<>[]{}/%\0\9\10\12\13\32'
 local name = lpeg.C(regular^1)
@@ -5,8 +7,7 @@ local lname = '/' * name / 1
 local namearray = lpeg.Ct('['*white^0*lpeg.Cg(lname*white^0, 0)^-1*(lname*white^0)^0*']')
 local encfile = white^0*lname*white^0*namearray*white^0*'def'*white^0*-1
 return function(filename)
-  local file = io.open(filename, 'r')
-  local name, encoding = encfile:match(file:read'a')
-  file:close()
+  local file <close> = readfile('enc', filename, nil, 'r')
+  local name, encoding = encfile:match(file())
   return encoding, name
 end
diff --git a/luametalatex-font-t1.lua b/luametalatex-font-t1.lua
index 4a5baf0..b5ad593 100644
--- a/luametalatex-font-t1.lua
+++ b/luametalatex-font-t1.lua
@@ -140,11 +140,9 @@ local function parse_maintable(offset, str)
   return continue_maintable(offset, str, {})
 end
 
-return function(filename)
-  local file = io.open(filename, 'rb')
-  local preface, private = string.unpack("<xxs4xxs4", file:read'a')
+return function(data)
+  local preface, private = string.unpack("<xxs4xxs4", data)
   private = decrypt(55665, 4, private)
-  file:close()
   local after = parse_maintable(1, preface .. private)
   local lenIV = after.Private.lenIV or 4
   local chars = after.CharStrings
diff --git a/luametalatex-pdf-font-cff.lua b/luametalatex-pdf-font-cff.lua
index 1c47629..11c4da7 100644
--- a/luametalatex-pdf-font-cff.lua
+++ b/luametalatex-pdf-font-cff.lua
@@ -1,3 +1,5 @@
+local readfile = require'luametalatex-readfile'
+
 local sfnt = require'luametalatex-font-sfnt'
 local stdStrings = require'luametalatex-font-cff-data'
 local offsetfmt = ">I%i"
@@ -576,15 +578,11 @@ function myfunc(buf, i0, fontid, usedcids, encoding, trust_widths)
   end
   return require'luametalatex-font-cff'(top), bbox
 end
--- local file = io.open(arg[1])
--- local buf = file:read'a'
--- file:close()
--- io.open(arg[3], 'w'):write(myfunc(buf, 1, 1, nil, {{3}, {200}, {1000}, {1329}, {1330}, {1331}})):close()
+
 return function(filename, fontid, encoding) return function(fontdir, usedcids)
-  local file = io.open(filename, 'rb')
-  local buf = file:read'a'
+  local file <close> = readfile('subset', filename, nil)
+  local buf = file()
   local i = 1
-  file:close()
   local magic = buf:sub(1, 4)
   if magic == "ttcf" or magic == "OTTO" then
     -- assert(not encoding) -- nil or false
@@ -598,4 +596,3 @@ return function(filename, fontid, encoding) return function(fontdir, usedcids)
   fontdir.bbox = bbox
   return content
 end end
--- io.open(arg[3], 'w'):write(myfunc(buf, 1, 1, require'parseEnc'(arg[2]), {{string.byte'a'}, {string.byte'b'}, {string.byte'-'}})):close()
diff --git a/luametalatex-pdf-font-map.lua b/luametalatex-pdf-font-map.lua
index 4c27d38..d4016de 100644
--- a/luametalatex-pdf-font-map.lua
+++ b/luametalatex-pdf-font-map.lua
@@ -1,3 +1,5 @@
+local readfile = require'luametalatex-readfile'
+
 local purenumber = lpeg.R'09'^1
 local optoperator = lpeg.C(lpeg.S'+-='^-1)*lpeg.C(lpeg.P(1)^0)
 local commentchar = lpeg.S' %*;#'+-1
@@ -38,9 +40,8 @@ local function mapfile(filename, operator)
   if not operator then
     operator, filename = optoperator:match(filename)
   end
-  local file = io.open(kpse.find_file(filename, 'map'), 'r')
+  local file <close> = readfile('map', filename, 'map', 'r')
   for line in file:lines() do mapline(line, operator) end
-  file:close()
 end
 local function reset()
   for k in next, fontmap do
diff --git a/luametalatex-pdf-font-t1.lua b/luametalatex-pdf-font-t1.lua
index 12a55d5..b65d106 100644
--- a/luametalatex-pdf-font-t1.lua
+++ b/luametalatex-pdf-font-t1.lua
@@ -1,11 +1,13 @@
+local readfile = require'luametalatex-readfile'
+
 -- Some helpers:
--- A kpse wrapper
 local serialize_cff = require'luametalatex-font-cff'
 local serializet2 = require'luametalatex-font-t2'
 local parseT1 = require'luametalatex-font-t1'
 local t1tot2 = require'luametalatex-font-t1tot2'
 return function(filename, reencode)
-  local parsed_t1 = parseT1(filename)
+  local file <close> = readfile('subset', filename, nil)
+  local parsed_t1 = parseT1(file())
   return function(f, usedcids)
     f.bbox = parsed_t1.FontBBox
     local fonttable = {
diff --git a/luametalatex-pdf-font-ttf.lua b/luametalatex-pdf-font-ttf.lua
index 2b03eee..8d6d086 100644
--- a/luametalatex-pdf-font-ttf.lua
+++ b/luametalatex-pdf-font-ttf.lua
@@ -1,3 +1,5 @@
+local readfile = require'luametalatex-readfile'
+
 local sfnt = require'luametalatex-font-sfnt'
 local stdnames = require'luametalatex-font-ttf-data'
 local function round(x)
@@ -15,7 +17,6 @@ local function addglyph(glyph, usedcids, cidtogid)
     while offset do
       local flags, component = string.unpack(">I2I2", glyph, offset)
       local gid = cidtogid[component]
-      print(glyph, component, gid)
       if not gid then
         gid = #usedcids
         usedcids[gid+1] = {component}
@@ -68,11 +69,10 @@ local function readpostnames(buf, i, usedcids, encoding)
   return newusedcids
 end
 return function(filename, fontid, reencode)
-  local file = io.open(filename, 'rb')
-  local buf = file:read'a'
-  file:close()
+  local file <close> = readfile('subset', filename, nil)
+  local buf = file()
   local magic, tables = sfnt.parse(buf, 1, fontid)
-  if magic ~=  "\0\1\0\0" then error[[Invalid TTF font]] end
+  if magic ~= "\0\1\0\0" then error[[Invalid TTF font]] end
   -- TODO: Parse post table and add reencoding support
   -- if tables.post and string.unpack(">I4", buf, tables.post[1]) == 0x00020000 and reencode then
   --   local encoding = require'parseEnc'(reencode)
diff --git a/luametalatex-pdf-image-png.lua b/luametalatex-pdf-image-png.lua
index 500a557..36d1332 100644
--- a/luametalatex-pdf-image-png.lua
+++ b/luametalatex-pdf-image-png.lua
@@ -1,3 +1,4 @@
+local readfile = require'luametalatex-readfile'
 local strip_floats = require'luametalatex-pdf-utils'.strip_floats
 
 local function ignore() end
@@ -204,12 +205,11 @@ end
 local png_functions = {}
 
 function png_functions.scan(img)
-  local file = io.open(img.filepath, 'rb')
+  local file <close> = readfile('image', img.filepath, nil)
   if not file then
     error[[PDF image could not be opened.]]
   end
-  local buf = file:read'a'
-  file:close()
+  local buf = file()
   local t = run(buf, 1, #buf, 'IDAT')
   img.pages = 1
   img.page = 1
@@ -228,9 +228,8 @@ local intents = {[0]=
 }
 local function srgb_lookup(pfile, intent)
   if not srgb_colorspace then
-    local f = io.open(kpse.find_file'sRGB.icc.zlib', 'rb')
-    local profile = f:read'a'
-    f:close()
+    local file <close> = readfile('silent', 'sRGB.icc.zlib', 'other binary files')
+    local profile = file()
     local objnum = pfile:stream(nil, '/Filter/FlateDecode/N ' .. tostring(colortype & 2 == 2 and '3' or '1'), t.iCCP, nil, true)
     srgb_colorspace = string.format('[/ICCBased %i 0 R]', objnum)
   end
@@ -259,12 +258,11 @@ local function rawimage(t, content)
 end
 
 function png_functions.write(pfile, img)
-  local file = io.open(img.filepath, 'rb')
+  local file <close> = readfile('silent', img.filepath, nil)
   if not file then
     error[[PDF image could not be opened.]]
   end
-  local buf = file:read'a'
-  file:close()
+  local buf = file()
   local t = run(buf, 1, #buf, 'IEND')
   local colorspace
   local intent = ''
diff --git a/luametalatex-pdf.lua b/luametalatex-pdf.lua
index d157741..89b731d 100644
--- a/luametalatex-pdf.lua
+++ b/luametalatex-pdf.lua
@@ -1,3 +1,5 @@
+local readfile = require'luametalatex-readfile'
+
 local format = string.format
 local byte = string.byte
 local pack = string.pack
@@ -23,9 +25,8 @@ local function stream(pdf, num, dict, content, isfile, raw)
   end
   pdf[num] = {offset = pdf.file:seek()}
   if isfile then
-    local f = io.open(content, 'rb')
-    content = f:read'a'
-    f:close()
+    local file <close> = readfile('pdf_stream', content, nil)
+    content = file()
   end
   local level = not raw and pdfvariable.compresslevel or 0
   local filter = ''
@@ -56,9 +57,8 @@ local function indirect(pdf, num, content, isfile, objstream)
     error[[Invalid object]]
   end
   if isfile then
-    local f = io.open(content, 'rb')
-    content = f:read'a'
-    f:close()
+    local file <close> = readfile('pdf_dict', content, nil)
+    content = file()
   end
   if objstream ~= false and pdfvariable.objcompresslevel ~= 0 then
     objstream = objstream or true
diff --git a/luametalatex-readfile.lua b/luametalatex-readfile.lua
new file mode 100644
index 0000000..c1c113b
--- /dev/null
+++ b/luametalatex-readfile.lua
@@ -0,0 +1,48 @@
+local io_open = io.open
+local write = texio.write
+local find_file = kpse.find_file
+
+local callbacks = require'luametalatex-callbacks'
+
+local categories = { data = 1, map = 2, image = 3, subset = 4, font = 5, enc = 6, pdf_stream = 7, pdf_stream = 8, silent = 9}
+local start_categories = { [0] = '?', '(', '{', '<', '<', '<<' }
+local stop_categories  = { [0] = '?', ')', '}', '>', '>', '>>' }
+
+local function stop_file(t)
+  local cb = callbacks.stop_file
+  if cb then
+    cb(t.category)
+  else
+    write(stop_categories[t.category] or '')
+  end
+  t.file:close()
+end
+
+local meta = {
+  __close = stop_file,
+  __call = function(t) return t.file:read'a' end,
+  close = stop_file,
+  lines = function(t, ...) return t.file:lines(...) end,
+}
+meta.__index = meta
+
+return function(category, name, kpse, mode)
+  category = tonumber(category) or categories[category] or 0
+  if kpse then
+    name = find_file(name, kpse)
+  end
+  if not name then return name end
+  local f, msg = io_open(name, mode or 'rb')
+  if f then
+    local cb = callbacks.start_file
+    if cb then
+      cb(category, name)
+    else
+      local start_mark = start_categories[category]
+      if start_mark then
+        write(start_mark .. name)
+      end
+    end
+  end
+  return f and setmetatable({category = category, file = f}, meta), msg
+end