LTN12 wrappers for POSIX read and write.

readme.md

Because they use the Lua io interface, the built in ltn12.source.file and ltn12.sink.file inherit C's stdio.h semantics.

This may not be desirable, for example, if the source is stdin connected to an interactive stream where we want to process chunks as soon as possible, and we wish to avoid buffering (stdin:setvbuf('no')). In this case ltn12.source.file(stdin) will block until exactly ltn12.BLOCKSIZE bytes (usually 2048) are read from the stream. ltn12_posix.source(0) will instead return a chunk as soon as one is available for reading, however many bytes it may be, as per POSIX read semantics.

local ltn12 = require('ltn12')
local ltn12_posix = require('ltn12-posix')
local fcntl = require('posix.fcntl')

-- copy a file
ltn12.pump.all(
  ltn12_posix.source(fcntl.open('original.png', 'r')),
  ltn12_posix.sink(fcntl.open('copy.png', 'w'))
)

ltn12-posix.lua

local unistd = require('posix.unistd')
local ltn12 = require('ltn12')

local _M = {}

-- creates a source from a file descriptor
function _M.source(fd, err)
    if fd then
        return function ()
            local chunk = unistd.read(fd, ltn12.BLOCKSIZE) -- [TODO] stat(fd).st_blksize?
            if not chunk or chunk == '' then
                err = select(2, unistd.close(fd))
            end
            return chunk, err
        end
    else
        return ltn12.source.error(err or 'unable to open file')
    end
end

-- creates a sink from a file descriptor
function _M.sink(fd, err)
    if fd then
        return function (chunk, err)
            if not chunk then
                return unistd.close(fd)
            else
                return unistd.write(fd, chunk)
            end
        end
    else
        return ltn12.sink.error(err or 'unable to open file')
    end
end

return _M