[nit.git] / lib / standard / file.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2004-2008 Jean Privat <jean@pryen.org>
# Copyright 2008 Floréal Morandat <morandat@lirmm.fr>
# Copyright 2008 Jean-Sébastien Gélinas <calestar@gmail.com>
#
# This file is free software, which comes along with NIT.  This software is
# distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
# without  even  the implied warranty of  MERCHANTABILITY or  FITNESS FOR A
# PARTICULAR PURPOSE.  You can modify it is you want,  provided this header
# is kept unaltered, and a notification of the changes is added.
# You  are  allowed  to  redistribute it and sell it, alone or is a part of
# another product.

# File manipulations (create, read, write, etc.)
module file

intrude import stream
intrude import text::ropes
import text
import time
import gc

in "C Header" `{
        #include <dirent.h>
        #include <string.h>
        #include <sys/types.h>
        #include <sys/stat.h>
        #include <unistd.h>
        #include <stdio.h>
        #include <poll.h>
        #include <errno.h>
`}

# `Stream` used to interact with a File or FileDescriptor
abstract class FileStream
        super Stream
        # The path of the file.
        var path: nullable String = null

        # The FILE *.
        private var file: nullable NativeFile = null

        # The status of a file. see POSIX stat(2).
        #
        #     var f = new FileReader.open("/etc/issue")
        #     assert f.file_stat.is_file
        #
        # Return null in case of error
        fun file_stat: nullable FileStat
        do
                var stat = _file.file_stat
                if stat.address_is_null then return null
                return new FileStat(stat)
        end

        # File descriptor of this file
        fun fd: Int do return _file.fileno

        redef fun close
        do
                if _file == null then return
                if _file.address_is_null then
                        if last_error != null then return
                        last_error = new IOError("Cannot close unopened file")
                        return
                end
                var i = _file.io_close
                if i != 0 then
                        last_error = new IOError("Close failed due to error {sys.errno.strerror}")
                end
                _file = null
        end

        # Sets the buffering mode for the current FileStream
        #
        # If the buf_size is <= 0, its value will be 512 by default
        #
        # The mode is any of the buffer_mode enumeration in `Sys`:
        #       - buffer_mode_full
        #       - buffer_mode_line
        #       - buffer_mode_none
        fun set_buffering_mode(buf_size, mode: Int) do
                if buf_size <= 0 then buf_size = 512
                if _file.set_buffering_type(buf_size, mode) != 0 then
                        last_error = new IOError("Error while changing buffering type for FileStream, returned error {sys.errno.strerror}")
                end
        end
end

# `Stream` that can read from a File
class FileReader
        super FileStream
        super BufferedReader
        super PollableReader
        # Misc

        # Open the same file again.
        # The original path is reused, therefore the reopened file can be a different file.
        #
        #     var f = new FileReader.open("/etc/issue")
        #     var l = f.read_line
        #     f.reopen
        #     assert l == f.read_line
        fun reopen
        do
                if not eof and not _file.address_is_null then close
                last_error = null
                _file = new NativeFile.io_open_read(path.to_cstring)
                if _file.address_is_null then
                        last_error = new IOError("Error: Opening file at '{path.as(not null)}' failed with '{sys.errno.strerror}'")
                        end_reached = true
                        return
                end
                end_reached = false
                buffer_reset
        end

        redef fun close
        do
                super
                buffer_reset
                end_reached = true
        end

        redef fun fill_buffer
        do
                var nb = _file.io_read(_buffer, _buffer_capacity)
                if nb <= 0 then
                        end_reached = true
                        nb = 0
                end
                _buffer_length = nb
                _buffer_pos = 0
        end

        # End of file?
        redef var end_reached = false

        # Open the file at `path` for reading.
        #
        #     var f = new FileReader.open("/etc/issue")
        #     assert not f.end_reached
        #     f.close
        #
        # In case of error, `last_error` is set
        #
        #     f = new FileReader.open("/fail/does not/exist")
        #     assert f.end_reached
        #     assert f.last_error != null
        init open(path: String)
        do
                self.path = path
                prepare_buffer(10)
                _file = new NativeFile.io_open_read(path.to_cstring)
                if _file.address_is_null then
                        last_error = new IOError("Error: Opening file at '{path}' failed with '{sys.errno.strerror}'")
                        end_reached = true
                end
        end

        # Creates a new File stream from a file descriptor
        #
        # This is a low-level method.
        init from_fd(fd: Int) do
                self.path = ""
                prepare_buffer(1)
                _file = fd.fd_to_stream(read_only)
                if _file.address_is_null then
                        last_error = new IOError("Error: Converting fd {fd} to stream failed with '{sys.errno.strerror}'")
                        end_reached = true
                end
        end
end

# `Stream` that can write to a File
class FileWriter
        super FileStream
        super Writer

        redef fun write_bytes(s) do
                if last_error != null then return
                if not _is_writable then
                        last_error = new IOError("cannot write to non-writable stream")
                        return
                end
                write_native(s.items, s.length)
        end

        redef fun write(s)
        do
                if last_error != null then return
                if not _is_writable then
                        last_error = new IOError("cannot write to non-writable stream")
                        return
                end
                for i in s.substrings do write_native(i.to_cstring, i.length)
        end

        redef fun write_byte(value)
        do
                if last_error != null then return
                if not _is_writable then
                        last_error = new IOError("Cannot write to non-writable stream")
                        return
                end
                if _file.address_is_null then
                        last_error = new IOError("Writing on a null stream")
                        _is_writable = false
                        return
                end

                var err = _file.write_byte(value)
                if err != 1 then
                        # Big problem
                        last_error = new IOError("Problem writing a byte: {err}")
                end
        end

        redef fun close
        do
                super
                _is_writable = false
        end
        redef var is_writable = false

        # Write `len` bytes from `native`.
        private fun write_native(native: NativeString, len: Int)
        do
                if last_error != null then return
                if not _is_writable then
                        last_error = new IOError("Cannot write to non-writable stream")
                        return
                end
                if _file.address_is_null then
                        last_error = new IOError("Writing on a null stream")
                        _is_writable = false
                        return
                end
                var err = _file.io_write(native, len)
                if err != len then
                        # Big problem
                        last_error = new IOError("Problem in writing : {err} {len} \n")
                end
        end

        # Open the file at `path` for writing.
        init open(path: String)
        do
                _file = new NativeFile.io_open_write(path.to_cstring)
                self.path = path
                _is_writable = true
                if _file.address_is_null then
                        last_error = new IOError("Error: Opening file at '{path}' failed with '{sys.errno.strerror}'")
                        is_writable = false
                end
        end

        # Creates a new File stream from a file descriptor
        init from_fd(fd: Int) do
                self.path = ""
                _file = fd.fd_to_stream(wipe_write)
                _is_writable = true
                 if _file.address_is_null then
                         last_error = new IOError("Error: Opening stream from file descriptor {fd} failed with '{sys.errno.strerror}'")
                        _is_writable = false
                end
        end
end

redef class Int
        # Creates a file stream from a file descriptor `fd` using the file access `mode`.
        #
        # NOTE: The `mode` specified must be compatible with the one used in the file descriptor.
        private fun fd_to_stream(mode: NativeString): NativeFile is extern "file_int_fdtostream"
end

# Constant for read-only file streams
private fun read_only: NativeString do return once "r".to_cstring

# Constant for write-only file streams
#
# If a stream is opened on a file with this method,
# it will wipe the previous file if any.
# Else, it will create the file.
private fun wipe_write: NativeString do return once "w".to_cstring

###############################################################################

# Standard input stream.
#
# The class of the default value of `sys.stdin`.
class Stdin
        super FileReader

        init do
                _file = new NativeFile.native_stdin
                path = "/dev/stdin"
                prepare_buffer(1)
        end

        redef fun poll_in `{
                struct pollfd fd = {0, POLLIN, 0};
                int res = poll(&fd, 1, 0);
                if (res == -1) {
                        perror("Error poll stdin");
                        exit(EXIT_FAILURE);
                }
                return res > 0;
        `}
end

# Standard output stream.
#
# The class of the default value of `sys.stdout`.
class Stdout
        super FileWriter
        init do
                _file = new NativeFile.native_stdout
                path = "/dev/stdout"
                _is_writable = true
                set_buffering_mode(256, sys.buffer_mode_line)
        end
end

# Standard error stream.
#
# The class of the default value of `sys.stderr`.
class Stderr
        super FileWriter
        init do
                _file = new NativeFile.native_stderr
                path = "/dev/stderr"
                _is_writable = true
        end
end

###############################################################################

redef class Writable
        # Like `write_to` but take care of creating the file
        fun write_to_file(filepath: String)
        do
                var stream = new FileWriter.open(filepath)
                write_to(stream)
                stream.close
        end
end

# Utility class to access file system services
#
# Usually created with `Text::to_path`.
class Path

        private var path: String

        # Path to this file
        redef fun to_s do return path

        # Name of the file name at `to_s`
        #
        # ~~~
        # var path = "/tmp/somefile".to_path
        # assert path.filename == "somefile"
        # ~~~
        var filename: String = path.basename("") is lazy

        # Does the file at `path` exists?
        fun exists: Bool do return stat != null

        # Information on the file at `self` following symbolic links
        #
        # Returns `null` if there is no file at `self`.
        #
        #     assert "/etc/".to_path.stat.is_dir
        #     assert "/etc/issue".to_path.stat.is_file
        #     assert "/fail/does not/exist".to_path.stat == null
        #
        # ~~~
        # var p = "/tmp/".to_path
        # var stat = p.stat
        # if stat != null then # Does `p` exist?
        #     print "It's size is {stat.size}"
        #     if stat.is_dir then print "It's a directory"
        # end
        # ~~~
        fun stat: nullable FileStat
        do
                var stat = path.to_cstring.file_stat
                if stat.address_is_null then return null
                return new FileStat(stat)
        end

        # Information on the file or link at `self`
        #
        # Do not follow symbolic links.
        fun link_stat: nullable FileStat
        do
                var stat = path.to_cstring.file_lstat
                if stat.address_is_null then return null
                return new FileStat(stat)
        end

        # Delete a file from the file system, return `true` on success
        fun delete: Bool do return path.to_cstring.file_delete

        # Copy content of file at `path` to `dest`
        #
        # Require: `exists`
        fun copy(dest: Path)
        do
                var input = open_ro
                var output = dest.open_wo

                while not input.eof do
                        var buffer = input.read(1024)
                        output.write buffer
                end

                input.close
                output.close
        end

        # Open this file for reading
        #
        # Require: `exists and not link_stat.is_dir`
        fun open_ro: FileReader
        do
                # TODO manage streams error when they are merged
                return new FileReader.open(path)
        end

        # Open this file for writing
        #
        # Require: `not exists or not stat.is_dir`
        fun open_wo: FileWriter
        do
                # TODO manage streams error when they are merged
                return new FileWriter.open(path)
        end

        # Read all the content of the file
        #
        # ~~~
        # var content = "/etc/issue".to_path.read_all
        # print content
        # ~~~
        #
        # See `Reader::read_all` for details.
        fun read_all: String do return read_all_bytes.to_s

        fun read_all_bytes: Bytes
        do
                var s = open_ro
                var res = s.read_all_bytes
                s.close
                return res
        end

        # Read all the lines of the file
        #
        # ~~~
        # var lines = "/etc/passwd".to_path.read_lines
        #
        # print "{lines.length} users"
        #
        # for l in lines do
        #     var fields = l.split(":")
        #     print "name={fields[0]} uid={fields[2]}"
        # end
        # ~~~
        #
        # See `Reader::read_lines` for details.
        fun read_lines: Array[String]
        do
                var s = open_ro
                var res = s.read_lines
                s.close
                return res
        end

        # Return an iterator on each line of the file
        #
        # ~~~
        # for l in "/etc/passwd".to_path.each_line do
        #     var fields = l.split(":")
        #     print "name={fields[0]} uid={fields[2]}"
        # end
        # ~~~
        #
        # Note: the stream is automatically closed at the end of the file (see `LineIterator::close_on_finish`)
        #
        # See `Reader::each_line` for details.
        fun each_line: LineIterator
        do
                var s = open_ro
                var res = s.each_line
                res.close_on_finish = true
                return res
        end


        # Lists the name of the files contained within the directory at `path`
        #
        # Require: `exists and is_dir`
        fun files: Array[Path]
        do
                var files = new Array[Path]
                for filename in path.files do
                        files.add new Path(path / filename)
                end
                return files
        end

        # Delete a directory and all of its content, return `true` on success
        #
        # Does not go through symbolic links and may get stuck in a cycle if there
        # is a cycle in the file system.
        fun rmdir: Bool
        do
                var ok = true
                for file in self.files do
                        var stat = file.link_stat
                        if stat.is_dir then
                                ok = file.rmdir and ok
                        else
                                ok = file.delete and ok
                        end
                end

                # Delete the directory itself
                if ok then ok = path.to_cstring.rmdir and ok

                return ok
        end

        redef fun ==(other) do return other isa Path and path.simplify_path == other.path.simplify_path
        redef fun hash do return path.simplify_path.hash
end

# Information on a file
#
# Created by `Path::stat` and `Path::link_stat`.
#
# The information within this class is gathered when the instance is initialized
# it will not be updated if the targeted file is modified.
class FileStat
        super Finalizable

        # TODO private init

        # The low-level status of a file
        #
        # See: POSIX stat(2)
        private var stat: NativeFileStat

        private var finalized = false

        redef fun finalize
        do
                if not finalized then
                        stat.free
                        finalized = true
                end
        end

        # Returns the last access time in seconds since Epoch
        fun last_access_time: Int
        do
                assert not finalized
                return stat.atime
        end

        # Returns the last access time
        #
        # alias for `last_access_time`
        fun atime: Int do return last_access_time

        # Returns the last modification time in seconds since Epoch
        fun last_modification_time: Int
        do
                assert not finalized
                return stat.mtime
        end

        # Returns the last modification time
        #
        # alias for `last_modification_time`
        fun mtime: Int do return last_modification_time


        # Size of the file at `path`
        fun size: Int
        do
                assert not finalized
                return stat.size
        end

        # Is self a regular file and not a device file, pipe, socket, etc.?
        fun is_file: Bool
        do
                assert not finalized
                return stat.is_reg
        end

        # Alias for `is_file`
        fun is_reg: Bool do return is_file

        # Is this a directory?
        fun is_dir: Bool
        do
                assert not finalized
                return stat.is_dir
        end

        # Is this a symbolic link?
        fun is_link: Bool
        do
                assert not finalized
                return stat.is_lnk
        end

        # FIXME Make the following POSIX only? or implement in some other way on Windows

        # Returns the last status change time in seconds since Epoch
        fun last_status_change_time: Int
        do
                assert not finalized
                return stat.ctime
        end

        # Returns the last status change time
        #
        # alias for `last_status_change_time`
        fun ctime: Int do return last_status_change_time

        # Returns the permission bits of file
        fun mode: Int
        do
                assert not finalized
                return stat.mode
        end

        # Is this a character device?
        fun is_chr: Bool
        do
                assert not finalized
                return stat.is_chr
        end

        # Is this a block device?
        fun is_blk: Bool
        do
                assert not finalized
                return stat.is_blk
        end

        # Is this a FIFO pipe?
        fun is_fifo: Bool
        do
                assert not finalized
                return stat.is_fifo
        end

        # Is this a UNIX socket
        fun is_sock: Bool
        do
                assert not finalized
                return stat.is_sock
        end
end

redef class Text
        # Access file system related services on the path at `self`
        fun to_path: Path do return new Path(to_s)
end

redef class String
        # return true if a file with this names exists
        fun file_exists: Bool do return to_cstring.file_exists

        # The status of a file. see POSIX stat(2).
        fun file_stat: nullable FileStat
        do
                var stat = to_cstring.file_stat
                if stat.address_is_null then return null
                return new FileStat(stat)
        end

        # The status of a file or of a symlink. see POSIX lstat(2).
        fun file_lstat: nullable FileStat
        do
                var stat = to_cstring.file_lstat
                if stat.address_is_null then return null
                return new FileStat(stat)
        end

        # Remove a file, return true if success
        fun file_delete: Bool do return to_cstring.file_delete

        # Copy content of file at `self` to `dest`
        fun file_copy_to(dest: String) do to_path.copy(dest.to_path)

        # Remove the trailing extension `ext`.
        #
        # `ext` usually starts with a dot but could be anything.
        #
        #     assert "file.txt".strip_extension(".txt")  == "file"
        #     assert "file.txt".strip_extension("le.txt")  == "fi"
        #     assert "file.txt".strip_extension("xt")  == "file.t"
        #
        # if `ext` is not present, `self` is returned unmodified.
        #
        #     assert "file.txt".strip_extension(".tar.gz")  == "file.txt"
        fun strip_extension(ext: String): String
        do
                if has_suffix(ext) then
                        return substring(0, length - ext.length)
                end
                return self
        end

        # Extract the basename of a path and remove the extension
        #
        #     assert "/path/to/a_file.ext".basename(".ext")         == "a_file"
        #     assert "path/to/a_file.ext".basename(".ext")          == "a_file"
        #     assert "path/to".basename(".ext")                     == "to"
        #     assert "path/to/".basename(".ext")                    == "to"
        #     assert "path".basename("")                        == "path"
        #     assert "/path".basename("")                       == "path"
        #     assert "/".basename("")                           == "/"
        #     assert "".basename("")                            == ""
        fun basename(ext: String): String
        do
                var l = length - 1 # Index of the last char
                while l > 0 and self.chars[l] == '/' do l -= 1 # remove all trailing `/`
                if l == 0 then return "/"
                var pos = chars.last_index_of_from('/', l)
                var n = self
                if pos >= 0 then
                        n = substring(pos+1, l-pos)
                end
                return n.strip_extension(ext)
        end

        # Extract the dirname of a path
        #
        #     assert "/path/to/a_file.ext".dirname         == "/path/to"
        #     assert "path/to/a_file.ext".dirname          == "path/to"
        #     assert "path/to".dirname                     == "path"
        #     assert "path/to/".dirname                    == "path"
        #     assert "path".dirname                        == "."
        #     assert "/path".dirname                       == "/"
        #     assert "/".dirname                           == "/"
        #     assert "".dirname                            == "."
        fun dirname: String
        do
                var l = length - 1 # Index of the last char
                while l > 0 and self.chars[l] == '/' do l -= 1 # remove all trailing `/`
                var pos = chars.last_index_of_from('/', l)
                if pos > 0 then
                        return substring(0, pos)
                else if pos == 0 then
                        return "/"
                else
                        return "."
                end
        end

        # Return the canonicalized absolute pathname (see POSIX function `realpath`)
        fun realpath: String do
                var cs = to_cstring.file_realpath
                var res = cs.to_s_with_copy
                # cs.free_malloc # FIXME memory leak
                return res
        end

        # Simplify a file path by remove useless `.`, removing `//`, and resolving `..`
        #
        # * `..` are not resolved if they start the path
        # * starting `.` is simplified unless the path is empty
        # * starting `/` is not removed
        # * trailing `/` is removed
        #
        # Note that the method only work on the string:
        #
        #  * no I/O access is performed
        #  * the validity of the path is not checked
        #
        # ~~~
        # assert "some/./complex/../../path/from/../to/a////file//".simplify_path            ==  "path/to/a/file"
        # assert "../dir/file".simplify_path       ==  "../dir/file"
        # assert "dir/../../".simplify_path        ==  ".."
        # assert "dir/..".simplify_path            ==  "."
        # assert "//absolute//path/".simplify_path ==  "/absolute/path"
        # assert "//absolute//../".simplify_path   ==  "/"
        # assert "/".simplify_path                 == "/"
        # assert "../".simplify_path               == ".."
        # assert "./".simplify_path                == "."
        # assert "././././././".simplify_path      == "."
        # assert "./../dir".simplify_path                  == "../dir"
        # assert "./dir".simplify_path                     == "dir"
        # ~~~
        fun simplify_path: String
        do
                var a = self.split_with("/")
                var a2 = new Array[String]
                for x in a do
                        if x == "." and not a2.is_empty then continue # skip `././`
                        if x == "" and not a2.is_empty then continue # skip `//`
                        if x == ".." and not a2.is_empty and a2.last != ".." then
                                if a2.last == "." then # do not skip `./../`
                                        a2.pop # reduce `./../` in `../`
                                else # reduce `dir/../` in `/`
                                        a2.pop
                                        continue
                                end
                        else if not a2.is_empty and a2.last == "." then
                                a2.pop # reduce `./dir` in `dir`
                        end
                        a2.push(x)
                end
                if a2.is_empty then return "."
                if a2.length == 1 and a2.first == "" then return "/"
                return a2.join("/")
        end

        # Correctly join two path using the directory separator.
        #
        # Using a standard "{self}/{path}" does not work in the following cases:
        #
        # * `self` is empty.
        # * `path` starts with `'/'`.
        #
        # This method ensures that the join is valid.
        #
        #     assert "hello".join_path("world")   == "hello/world"
        #     assert "hel/lo".join_path("wor/ld") == "hel/lo/wor/ld"
        #     assert "".join_path("world")        == "world"
        #     assert "hello".join_path("/world")  == "/world"
        #     assert "hello/".join_path("world")  == "hello/world"
        #     assert "hello/".join_path("/world") == "/world"
        #
        # Note: You may want to use `simplify_path` on the result.
        #
        # Note: This method works only with POSIX paths.
        fun join_path(path: String): String
        do
                if path.is_empty then return self
                if self.is_empty then return path
                if path.chars[0] == '/' then return path
                if self.last == '/' then return "{self}{path}"
                return "{self}/{path}"
        end

        # Convert the path (`self`) to a program name.
        #
        # Ensure the path (`self`) will be treated as-is by POSIX shells when it is
        # used as a program name. In order to do that, prepend `./` if needed.
        #
        #     assert "foo".to_program_name == "./foo"
        #     assert "/foo".to_program_name == "/foo"
        #     assert "".to_program_name == "./" # At least, your shell will detect the error.
        fun to_program_name: String do
                if self.has_prefix("/") then
                        return self
                else
                        return "./{self}"
                end
        end

        # Alias for `join_path`
        #
        #     assert "hello" / "world"      ==  "hello/world"
        #     assert "hel/lo" / "wor/ld"    ==  "hel/lo/wor/ld"
        #     assert "" / "world"           ==  "world"
        #     assert "/hello" / "/world"    ==  "/world"
        #
        # This operator is quite useful for chaining changes of path.
        # The next one being relative to the previous one.
        #
        #     var a = "foo"
        #     var b = "/bar"
        #     var c = "baz/foobar"
        #     assert a/b/c == "/bar/baz/foobar"
        fun /(path: String): String do return join_path(path)

        # Returns the relative path needed to go from `self` to `dest`.
        #
        #     assert "/foo/bar".relpath("/foo/baz") == "../baz"
        #     assert "/foo/bar".relpath("/baz/bar") == "../../baz/bar"
        #
        # If `self` or `dest` is relative, they are considered relatively to `getcwd`.
        #
        # In some cases, the result is still independent of the current directory:
        #
        #     assert "foo/bar".relpath("..") == "../../.."
        #
        # In other cases, parts of the current directory may be exhibited:
        #
        #     var p = "../foo/bar".relpath("baz")
        #     var c = getcwd.basename("")
        #     assert p == "../../{c}/baz"
        #
        # For path resolution independent of the current directory (eg. for paths in URL),
        # or to use an other starting directory than the current directory,
        # just force absolute paths:
        #
        #     var start = "/a/b/c/d"
        #     var p2 = (start/"../foo/bar").relpath(start/"baz")
        #     assert p2 == "../../d/baz"
        #
        #
        # Neither `self` or `dest` has to be real paths or to exist in directories since
        # the resolution is only done with string manipulations and without any access to
        # the underlying file system.
        #
        # If `self` and `dest` are the same directory, the empty string is returned:
        #
        #     assert "foo".relpath("foo") == ""
        #     assert "foo/../bar".relpath("bar") == ""
        #
        # The empty string and "." designate both the current directory:
        #
        #     assert "".relpath("foo/bar")  == "foo/bar"
        #     assert ".".relpath("foo/bar") == "foo/bar"
        #     assert "foo/bar".relpath("")  == "../.."
        #     assert "/" + "/".relpath(".") == getcwd
        fun relpath(dest: String): String
        do
                var cwd = getcwd
                var from = (cwd/self).simplify_path.split("/")
                if from.last.is_empty then from.pop # case for the root directory
                var to = (cwd/dest).simplify_path.split("/")
                if to.last.is_empty then to.pop # case for the root directory

                # Remove common prefixes
                while not from.is_empty and not to.is_empty and from.first == to.first do
                        from.shift
                        to.shift
                end

                # Result is going up in `from` with ".." then going down following `to`
                var from_len = from.length
                if from_len == 0 then return to.join("/")
                var up = "../"*(from_len-1) + ".."
                if to.is_empty then return up
                var res = up + "/" + to.join("/")
                return res
        end

        # Create a directory (and all intermediate directories if needed)
        #
        # Return an error object in case of error.
        #
        #    assert "/etc/".mkdir != null
        fun mkdir: nullable Error
        do
                var dirs = self.split_with("/")
                var path = new FlatBuffer
                if dirs.is_empty then return null
                if dirs[0].is_empty then
                        # it was a starting /
                        path.add('/')
                end
                var error: nullable Error = null
                for d in dirs do
                        if d.is_empty then continue
                        path.append(d)
                        path.add('/')
                        var res = path.to_s.to_cstring.file_mkdir
                        if not res and error == null then
                                error = new IOError("Cannot create directory `{path}`: {sys.errno.strerror}")
                        end
                end
                return error
        end

        # Delete a directory and all of its content, return `true` on success
        #
        # Does not go through symbolic links and may get stuck in a cycle if there
        # is a cycle in the filesystem.
        #
        # Return an error object in case of error.
        #
        #     assert "/fail/does not/exist".rmdir != null
        fun rmdir: nullable Error
        do
                var res = to_path.rmdir
                if res then return null
                var error = new IOError("Cannot change remove `{self}`: {sys.errno.strerror}")
                return error
        end

        # Change the current working directory
        #
        #     "/etc".chdir
        #     assert getcwd == "/etc"
        #     "..".chdir
        #     assert getcwd == "/"
        #
        # Return an error object in case of error.
        #
        #     assert "/etc".chdir == null
        #     assert "/fail/does no/exist".chdir != null
        #     assert getcwd == "/etc" # unchanger
        fun chdir: nullable Error
        do
                var res = to_cstring.file_chdir
                if res then return null
                var error = new IOError("Cannot change directory to `{self}`: {sys.errno.strerror}")
                return error
        end

        # Return right-most extension (without the dot)
        #
        # Only the last extension is returned.
        # There is no special case for combined extensions.
        #
        #     assert "file.txt".file_extension      == "txt"
        #     assert "file.tar.gz".file_extension   == "gz"
        #
        # For file without extension, `null` is returned.
        # Hoever, for trailing dot, `""` is returned.
        #
        #     assert "file".file_extension          == null
        #     assert "file.".file_extension         == ""
        #
        # The starting dot of hidden files is never considered.
        #
        #     assert ".file.txt".file_extension     == "txt"
        #     assert ".file".file_extension         == null
        fun file_extension: nullable String
        do
                var last_slash = chars.last_index_of('.')
                if last_slash > 0 then
                        return substring( last_slash+1, length )
                else
                        return null
                end
        end

        # Returns entries contained within the directory represented by self.
        #
        #     var files = "/etc".files
        #     assert files.has("issue")
        #
        # Returns an empty array in case of error
        #
        #     files = "/etc/issue".files
        #     assert files.is_empty
        #
        # TODO find a better way to handle errors and to give them back to the user.
        fun files: Array[String]
        do
                var res = new Array[String]
                var d = new NativeDir.opendir(to_cstring)
                if d.address_is_null then return res

                loop
                        var de = d.readdir
                        if de.address_is_null then break
                        var name = de.to_s_with_copy
                        if name == "." or name == ".." then continue
                        res.add name
                end
                d.closedir

                return res
        end
end

redef class NativeString
        private fun file_exists: Bool `{
                FILE *hdl = fopen(self,"r");
                if(hdl != NULL){
                        fclose(hdl);
                }
                return hdl != NULL;
        `}

        private fun file_stat: NativeFileStat `{
                struct stat buff;
                if(stat(self, &buff) != -1) {
                        struct stat* stat_element;
                        stat_element = malloc(sizeof(struct stat));
                        return memcpy(stat_element, &buff, sizeof(struct stat));
                }
                return 0;
        `}

        private fun file_lstat: NativeFileStat `{
                struct stat* stat_element;
                int res;
                stat_element = malloc(sizeof(struct stat));
                res = lstat(self, stat_element);
                if (res == -1) return NULL;
                return stat_element;
        `}
        private fun file_mkdir: Bool is extern "string_NativeString_NativeString_file_mkdir_0"
        private fun rmdir: Bool `{ return !rmdir(self); `}
        private fun file_delete: Bool is extern "string_NativeString_NativeString_file_delete_0"
        private fun file_chdir: Bool is extern "string_NativeString_NativeString_file_chdir_0"
        private fun file_realpath: NativeString is extern "file_NativeString_realpath"
end

# This class is system dependent ... must reify the vfs
private extern class NativeFileStat `{ struct stat * `}
        # Returns the permission bits of file
        fun mode: Int is extern "file_FileStat_FileStat_mode_0"
        # Returns the last access time
        fun atime: Int is extern "file_FileStat_FileStat_atime_0"
        # Returns the last status change time
        fun ctime: Int is extern "file_FileStat_FileStat_ctime_0"
        # Returns the last modification time
        fun mtime: Int is extern "file_FileStat_FileStat_mtime_0"
        # Returns the size
        fun size: Int is extern "file_FileStat_FileStat_size_0"

        # Returns true if it is a regular file (not a device file, pipe, sockect, ...)
        fun is_reg: Bool `{ return S_ISREG(self->st_mode); `}

        # Returns true if it is a directory
        fun is_dir: Bool `{ return S_ISDIR(self->st_mode); `}

        # Returns true if it is a character device
        fun is_chr: Bool `{ return S_ISCHR(self->st_mode); `}

        # Returns true if it is a block device
        fun is_blk: Bool `{ return S_ISBLK(self->st_mode); `}

        # Returns true if the type is fifo
        fun is_fifo: Bool `{ return S_ISFIFO(self->st_mode); `}

        # Returns true if the type is a link
        fun is_lnk: Bool `{ return S_ISLNK(self->st_mode); `}

        # Returns true if the type is a socket
        fun is_sock: Bool `{ return S_ISSOCK(self->st_mode); `}
end

# Instance of this class are standard FILE * pointers
private extern class NativeFile `{ FILE* `}
        fun io_read(buf: NativeString, len: Int): Int is extern "file_NativeFile_NativeFile_io_read_2"
        fun io_write(buf: NativeString, len: Int): Int is extern "file_NativeFile_NativeFile_io_write_2"
        fun write_byte(value: Int): Int `{
                unsigned char b = (unsigned char)value;
                return fwrite(&b, 1, 1, self);
        `}
        fun io_close: Int is extern "file_NativeFile_NativeFile_io_close_0"
        fun file_stat: NativeFileStat `{
                struct stat buff;
                if(fstat(fileno(self), &buff) != -1) {
                        struct stat* stat_element;
                        stat_element = malloc(sizeof(struct stat));
                        return memcpy(stat_element, &buff, sizeof(struct stat));
                }
                return 0;
        `}

        fun fileno: Int `{ return fileno(self); `}

        # Flushes the buffer, forcing the write operation
        fun flush: Int is extern "fflush"
        # Used to specify how the buffering will be handled for the current stream.
        fun set_buffering_type(buf_length: Int, mode: Int): Int is extern "file_NativeFile_NativeFile_set_buffering_type_0"

        new io_open_read(path: NativeString) is extern "file_NativeFileCapable_NativeFileCapable_io_open_read_1"
        new io_open_write(path: NativeString) is extern "file_NativeFileCapable_NativeFileCapable_io_open_write_1"
        new native_stdin is extern "file_NativeFileCapable_NativeFileCapable_native_stdin_0"
        new native_stdout is extern "file_NativeFileCapable_NativeFileCapable_native_stdout_0"
        new native_stderr is extern "file_NativeFileCapable_NativeFileCapable_native_stderr_0"
end

# Standard `DIR*` pointer
private extern class NativeDir `{ DIR* `}

        # Open a directory
        new opendir(path: NativeString) `{ return opendir(path); `}

        # Close a directory
        fun closedir `{ closedir(self); `}

        # Read the next directory entry
        fun readdir: NativeString `{
                struct dirent *de;
                de = readdir(self);
                if (!de) return NULL;
                return de->d_name;
        `}
end

redef class Sys

        # Standard input
        var stdin: PollableReader = new Stdin is protected writable, lazy

        # Standard output
        var stdout: Writer = new Stdout is protected writable, lazy

        # Standard output for errors
        var stderr: Writer = new Stderr is protected writable, lazy

        # Enumeration for buffer mode full (flushes when buffer is full)
        fun buffer_mode_full: Int is extern "file_Sys_Sys_buffer_mode_full_0"
        # Enumeration for buffer mode line (flushes when a `\n` is encountered)
        fun buffer_mode_line: Int is extern "file_Sys_Sys_buffer_mode_line_0"
        # Enumeration for buffer mode none (flushes ASAP when something is written)
        fun buffer_mode_none: Int is extern "file_Sys_Sys_buffer_mode_none_0"

        # returns first available stream to read or write to
        # return null on interruption (possibly a signal)
        protected fun poll( streams : Sequence[FileStream] ) : nullable FileStream
        do
                var in_fds = new Array[Int]
                var out_fds = new Array[Int]
                var fd_to_stream = new HashMap[Int,FileStream]
                for s in streams do
                        var fd = s.fd
                        if s isa FileReader then in_fds.add( fd )
                        if s isa FileWriter then out_fds.add( fd )

                        fd_to_stream[fd] = s
                end

                var polled_fd = intern_poll( in_fds, out_fds )

                if polled_fd == null then
                        return null
                else
                        return fd_to_stream[polled_fd]
                end
        end

        private fun intern_poll(in_fds: Array[Int], out_fds: Array[Int]): nullable Int
        import Array[Int].length, Array[Int].[], Int.as(nullable Int) `{
                int in_len, out_len, total_len;
                struct pollfd *c_fds;
                int i;
                int first_polled_fd = -1;
                int result;

                in_len = Array_of_Int_length( in_fds );
                out_len = Array_of_Int_length( out_fds );
                total_len = in_len + out_len;
                c_fds = malloc( sizeof(struct pollfd) * total_len );

                /* input streams */
                for ( i=0; i<in_len; i ++ ) {
                        int fd;
                        fd = Array_of_Int__index( in_fds, i );

                        c_fds[i].fd = fd;
                        c_fds[i].events = POLLIN;
                }

                /* output streams */
                for ( i=0; i<out_len; i ++ ) {
                        int fd;
                        fd = Array_of_Int__index( out_fds, i );

                        c_fds[i].fd = fd;
                        c_fds[i].events = POLLOUT;
                }

                /* poll all fds, unlimited timeout */
                result = poll( c_fds, total_len, -1 );

                if ( result > 0 ) {
                        /* analyse results */
                        for ( i=0; i<total_len; i++ )
                                if ( c_fds[i].revents & c_fds[i].events || /* awaited event */
                                         c_fds[i].revents & POLLHUP ) /* closed */
                                {
                                        first_polled_fd = c_fds[i].fd;
                                        break;
                                }

                        return Int_as_nullable( first_polled_fd );
                }
                else if ( result < 0 )
                        fprintf( stderr, "Error in Stream:poll: %s\n", strerror( errno ) );

                return null_Int();
        `}

end

# Print `objects` on the standard output (`stdout`).
fun printn(objects: Object...)
do
        sys.stdout.write(objects.plain_to_s)
end

# Print an `object` on the standard output (`stdout`) and add a newline.
fun print(object: Object)
do
        sys.stdout.write(object.to_s)
        sys.stdout.write("\n")
end

# Print `object` on the error output (`stderr` or a log system)
fun print_error(object: Object)
do
        sys.stderr.write object.to_s
        sys.stderr.write "\n"
end

# Read a character from the standard input (`stdin`).
fun getc: Char
do
        var c = sys.stdin.read_char
        if c == null then return '\1'
        return c
end

# Read a line from the standard input (`stdin`).
fun gets: String
do
        return sys.stdin.read_line
end

# Return the working (current) directory
fun getcwd: String do return file_getcwd.to_s
private fun file_getcwd: NativeString is extern "string_NativeString_NativeString_file_getcwd_0"