File LFS module

Since Origin / Contributor Maintainer Source
2020-11-30 vsky279 vsky279 file_lfs.lua

Provides access to arbitrary files stored in LFS.

An arbitrary file can be stored in LFS and still can be accessed using file functions. This module is an overlay over file base functions providing access to such LFS files.

The module tries to be transparent as much as possible so it makes no difference where LFS file or standard SPIFFS file is accessed. LFS file is read only. If the file is open for writing a standard SPIFFS file is opened instead. Both basic and object model can be used to access LFS file (see file module documentation).

resource.lua file

Files to be stored in LFS needs to be preprocessed, i.e. a Lua file with its contents needs to be generated. This file called resource.lua is then included in the LFS image. A Lua script make_resource.lua can be used to generate resource.lua script.

A structure of the resource.lua file is simple. It returns a string, i.e. file content, depending on filename parameter passed to it. It returns table with list of files stored when called without any parameter.

local arg = ...
if arg == "index.html" then return "<!DOCTYPE html><html><body>Hi, there!</body></html>" end
if arg == "favicon.ico" then return ""\000\000\000\000\000\000..." end
if arg == nil then return {"index.html", "favicon.ico"} end

make_resource.lua script

Lua script to be run on PC to generate resource.lua file.


 ./make_resource.lua [-o outputfile] file1 [file2]

### Example
Create `resource.lua` file with all files in the `resource` directory
./make_resource resource/*

Basic usage

file = require("file_lfs")

f ="index.html") -- let's assume the above resource.lua file is embedded in LFS
-- prints: <!DOCTYPE html><html><body>Hi, there!</body></html>

f ="init.lua")
-- init.lua file is not stored in LFS (does not have entry in resource.lua stored in LFS) -> SPIFFS files is opened instead

Methods implemented - basically all file module functions are available though only some of them work with LFS files. The other functions are just passed through to the base file functions.


Lists all files in the file system. It works almost in the same way as file.list()


file.list([pattern], [SPIFFs_only])


  • pattern only files matching the Lua pattern will be returned
  • SPIFFs_only if not nil LFS files won't be included in the result (LFS files are returned only if the parameter is nil)


a Lua table which contains all {file name: file size} pairs, if no pattern given. If a pattern is given, only those file names matching the pattern (interpreted as a traditional Lua pattern, not, say, a UNIX shell glob) will be included in the resulting table. file.list will throw any errors encountered during pattern matching.


Renames a file. If a file is currently open, it will be closed first. It works almost in the same way as file.rename()


file.rename(oldname, newname)


  • oldname old file name
  • newname new file name


true on success, false when the file is stored in LFS (so read-only) or on error

Opens a LFS file included in LFS in the resource.lua file. If it cannot be found in LFS not standard function is called. LFS file is opened only when "r" access is requested.

Syntax, mode)


  • filename file to be opened
  • mode:
    • "r": read mode (the default). If file of the same name is present in SPIFFS then SPIFFS file is opened instead of LFS file.
    • "w": write mode - as LFS file is read-only a SPIFFS file of the same name is created and opened for writing.
    • "r+", "w+", "a", "a+": as LFS file is read-only and all these modes allow file updates the LFS file is copied to SPIFFS and then it is opened with correspondig open mode.


LFS file object (Lua table) or SPIFFS file object if file opened ok. nil if file not opened, or not exists (read modes)., file.obj:read()

Read content from the open file. It has the same parameters and returns values as / file.obj:read()




  • n_or_char:
    • if nothing passed in, then read up to FILE_READ_CHUNK bytes or the entire file (whichever is smaller).
    • if passed a number n, then read up to n bytes or the entire file (whichever is smaller).
    • if passed a string containing the single character char, then read until char appears next in the file, FILE_READ_CHUNK bytes have been read, or EOF is reached.


File content as a string, or nil when EOF

file.readline(), file.obj:readline()

Read the next line from the open file. Lines are defined as zero or more bytes ending with a EOL ('\n') byte. If the next line is longer than 1024, this function only returns the first 1024 bytes. It has the same parameters and return values as file.readline() / file.obj:readline()







File content in string, line by line, including EOL('\n'). Return nil when EOF., file.obj:seek()

Sets and gets the file position, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence. It has the same parameters and return values as / file.obj:seek()

Syntax[whence [, offset]])

fd:seek([whence [, offset]])


  • whence
    • "set": base is position 0 (beginning of the file)
    • "cur": base is current position (default value)
    • "end": base is end of file
  • offset default 0

If no parameters are given, the function simply returns the current file offset.


the resulting file position, or nil on error


Get attribtues of a file or directory in a table. Elements of the table are:

  • size file size in bytes
  • name file name
  • time table with time stamp information. Default is 1970-01-01 00:00:00 in case time stamps are not supported (on SPIFFS).

    • year
    • mon
    • day
    • hour
    • min
    • sec
  • is_dir flag true if item is a directory, otherwise false

  • is_rdonly flag true if item is read-only, otherwise false
  • is_hidden flag true if item is hidden, otherwise false
  • is_sys flag true if item is system, otherwise false
  • is_arch flag true if item is archive, otherwise false
  • is_LFS flag true if item is stored in LFS, otherwise it is not present in the file.stat() result table - the only difference to file.stat()




filename file name


table containing file attributes