utils/fs/lua_module.cpp

// Copyright 2011 The Kyua Authors.
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#include "utils/fs/lua_module.hpp"

extern "C" {
#include <dirent.h>
}

#include <cerrno>
#include <cstring>
#include <stdexcept>
#include <string>

#include <lutok/operations.hpp>
#include <lutok/stack_cleaner.hpp>
#include <lutok/state.ipp>

#include "utils/format/macros.hpp"
#include "utils/fs/operations.hpp"
#include "utils/fs/path.hpp"
#include "utils/sanity.hpp"

namespace fs = utils::fs;


namespace {


/// Given a path, qualifies it with the module's start directory if necessary.
///
/// \param state The Lua state.
/// \param path The path to qualify.
///
/// \return The original path if it was absolute; otherwise the original path
/// appended to the module's start directory.
///
/// \throw std::runtime_error If the module's state has been corrupted.
static fs::path
qualify_path(lutok::state& state, const fs::path& path)
{
    lutok::stack_cleaner cleaner(state);

    if (path.is_absolute()) {
        return path;
    } else {
        state.get_global("_fs_start_dir");
        if (!state.is_string(-1))
            throw std::runtime_error("Missing _fs_start_dir global variable; "
                                     "state corrupted?");
        return fs::path(state.to_string(-1)) / path;
    }
}


/// Safely gets a path from the Lua state.
///
/// \param state The Lua state.
/// \param index The position in the Lua stack that contains the path to query.
///
/// \return The queried path.
///
/// \throw fs::error If the value is not a valid path.
/// \throw std::runtime_error If the value on the Lua stack is not convertible
///     to a path.
static fs::path
to_path(lutok::state& state, const int index)
{
    if (!state.is_string(index))
        throw std::runtime_error("Need a string parameter");
    return fs::path(state.to_string(index));
}


/// Lua binding for fs::path::basename.
///
/// \pre stack(-1) The input path.
/// \post stack(-1) The basename of the input path.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_basename(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path = to_path(state, -1);
    state.push_string(path.leaf_name().c_str());
    cleaner.forget();
    return 1;
}


/// Lua binding for fs::path::dirname.
///
/// \pre stack(-1) The input path.
/// \post stack(-1) The directory part of the input path.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_dirname(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path = to_path(state, -1);
    state.push_string(path.branch_path().c_str());
    cleaner.forget();
    return 1;
}


/// Lua binding for fs::path::exists.
///
/// \pre stack(-1) The input path.
/// \post stack(-1) Whether the input path exists or not.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_exists(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path = qualify_path(state, to_path(state, -1));
    state.push_boolean(fs::exists(path));
    cleaner.forget();
    return 1;
}


/// Lua binding for the files iterator.
///
/// This function takes an open directory from the closure of the iterator and
/// returns the next entry.  See lua_fs_files() for the iterator generator
/// function.
///
/// \pre upvalue(1) The userdata containing an open DIR* object.
///
/// \param state The lua state.
///
/// \return The number of result values, i.e. 0 if there are no more entries or
/// 1 if an entry has been read.
static int
files_iterator(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    DIR** dirp = state.to_userdata< DIR* >(state.upvalue_index(1));
    const struct dirent* entry = ::readdir(*dirp);
    if (entry == NULL)
        return 0;
    else {
        state.push_string(entry->d_name);
        cleaner.forget();
        return 1;
    }
}


/// Lua binding for the destruction of the files iterator.
///
/// This function takes an open directory and closes it.  See lua_fs_files() for
/// the iterator generator function.
///
/// \pre stack(-1) The userdata containing an open DIR* object.
/// \post The DIR* object is closed.
///
/// \param state The lua state.
///
/// \return The number of result values, i.e. 0.
static int
files_gc(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    PRE(state.is_userdata(-1));

    DIR** dirp = state.to_userdata< DIR* >(-1);
    // For some reason, this may be called more than once.  I don't know why
    // this happens, but we must protect against it.
    if (*dirp != NULL) {
        ::closedir(*dirp);
        *dirp = NULL;
    }

    return 0;
}


/// Lua binding to create an iterator to scan the contents of a directory.
///
/// \pre stack(-1) The input path.
/// \post stack(-1) The iterator function.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_files(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path = qualify_path(state, to_path(state, -1));

    DIR** dirp = state.new_userdata< DIR* >();

    state.new_table();
    state.push_string("__gc");
    state.push_cxx_function(files_gc);
    state.set_table(-3);

    state.set_metatable(-2);

    *dirp = ::opendir(path.c_str());
    if (*dirp == NULL) {
        const int original_errno = errno;
        throw std::runtime_error(F("Failed to open directory: %s") %
                                 std::strerror(original_errno));
    }

    state.push_cxx_closure(files_iterator, 1);

    cleaner.forget();
    return 1;
}


/// Lua binding for fs::path::is_absolute.
///
/// \pre stack(-1) The input path.
/// \post stack(-1) Whether the input path is absolute or not.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_is_absolute(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path = to_path(state, -1);

    state.push_boolean(path.is_absolute());
    cleaner.forget();
    return 1;
}


/// Lua binding for fs::path::operator/.
///
/// \pre stack(-2) The first input path.
/// \pre stack(-1) The second input path.
/// \post stack(-1) The concatenation of the two paths.
///
/// \param state The Lua state.
///
/// \return The number of result values, i.e. 1.
static int
lua_fs_join(lutok::state& state)
{
    lutok::stack_cleaner cleaner(state);

    const fs::path path1 = to_path(state, -2);
    const fs::path path2 = to_path(state, -1);
    state.push_string((path1 / path2).c_str());
    cleaner.forget();
    return 1;
}


}  // anonymous namespace


/// Creates a Lua 'fs' module with a default start directory of ".".
///
/// \post The global 'fs' symbol is set to a table that contains functions to a
/// variety of utilites from the fs C++ module.
///
/// \param s The Lua state.
void
fs::open_fs(lutok::state& s)
{
    open_fs(s, fs::current_path());
}


/// Creates a Lua 'fs' module with an explicit start directory.
///
/// \post The global 'fs' symbol is set to a table that contains functions to a
/// variety of utilites from the fs C++ module.
///
/// \param s The Lua state.
/// \param start_dir The start directory to use in all operations that reference
///     the underlying file sytem.
void
fs::open_fs(lutok::state& s, const fs::path& start_dir)
{
    lutok::stack_cleaner cleaner(s);

    s.push_string(start_dir.str());
    s.set_global("_fs_start_dir");

    std::map< std::string, lutok::cxx_function > members;
    members["basename"] = lua_fs_basename;
    members["dirname"] = lua_fs_dirname;
    members["exists"] = lua_fs_exists;
    members["files"] = lua_fs_files;
    members["is_absolute"] = lua_fs_is_absolute;
    members["join"] = lua_fs_join;
    lutok::create_module(s, "fs", members);
}