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LibCore: Add FilePermissionsMask
This class parses UNIX file permissions definitions in numeric (octal) or symbolic (ugoa+rwx) format and can apply them on a given file mode.
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151
Userland/Libraries/LibCore/FilePermissionsMask.cpp
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151
Userland/Libraries/LibCore/FilePermissionsMask.cpp
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/*
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* Copyright (c) 2021, Xavier Defrang <xavier.defrang@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Assertions.h>
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#include <AK/CharacterTypes.h>
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#include <AK/StringUtils.h>
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#include <LibCore/FilePermissionsMask.h>
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namespace Core {
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enum State {
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Reference,
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Mode
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};
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enum ClassFlag {
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Other = 1,
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Group = 2,
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User = 4
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};
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enum Operation {
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Add,
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Remove,
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Assign,
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};
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ErrorOr<FilePermissionsMask> FilePermissionsMask::parse(StringView string)
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{
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return (!string.is_empty() && is_ascii_digit(string[0]))
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? from_numeric_notation(string)
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: from_symbolic_notation(string);
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}
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ErrorOr<FilePermissionsMask> FilePermissionsMask::from_numeric_notation(StringView string)
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{
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mode_t mode = AK::StringUtils::convert_to_uint_from_octal<u16>(string).value_or(01000);
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if (mode > 0777)
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return Error::from_string_literal("invalid octal representation"sv);
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return FilePermissionsMask().assign_permissions(mode);
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}
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ErrorOr<FilePermissionsMask> FilePermissionsMask::from_symbolic_notation(StringView string)
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{
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auto mask = FilePermissionsMask();
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u8 state = State::Reference;
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u8 classes = 0;
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u8 operation = 0;
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for (auto ch : string) {
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switch (state) {
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case State::Reference: {
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// one or more [ugoa] terminated by one operator [+-=]
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if (ch == 'u')
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classes |= ClassFlag::User;
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else if (ch == 'g')
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classes |= ClassFlag::Group;
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else if (ch == 'o')
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classes |= ClassFlag::Other;
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else if (ch == 'a')
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classes = ClassFlag::User | ClassFlag::Group | ClassFlag::Other;
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else {
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if (classes == 0)
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return Error::from_string_literal("invalid access class: expected 'u', 'g', 'o' or 'a' "sv);
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if (ch == '+')
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operation = Operation::Add;
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else if (ch == '-')
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operation = Operation::Remove;
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else if (ch == '=')
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operation = Operation::Assign;
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else
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return Error::from_string_literal("invalid operation: expected '+', '-' or '='"sv);
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state = State::Mode;
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}
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break;
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}
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case State::Mode: {
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// one or more [rwx] terminated by a comma
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// End of mode part, expect reference next
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if (ch == ',') {
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state = State::Reference;
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classes = operation = 0;
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continue;
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}
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mode_t write_bits = 0;
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if (ch == 'r')
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write_bits = 4;
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else if (ch == 'w')
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write_bits = 2;
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else if (ch == 'x')
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write_bits = 1;
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else
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return Error::from_string_literal("invalid symbolic permission"sv);
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mode_t clear_bits = operation == Operation::Assign ? 7 : write_bits;
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// Update masks one class at a time in other, group, user order
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for (auto cls = classes; cls != 0; cls >>= 1) {
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if (cls & 1) {
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if (operation == Operation::Add || operation == Operation::Assign)
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mask.add_permissions(write_bits);
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if (operation == Operation::Remove || operation == Operation::Assign)
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mask.remove_permissions(clear_bits);
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}
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write_bits <<= 3;
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clear_bits <<= 3;
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}
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break;
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}
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default:
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VERIFY_NOT_REACHED();
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}
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}
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return mask;
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}
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FilePermissionsMask& FilePermissionsMask::assign_permissions(mode_t mode)
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{
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m_write_mask = mode;
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m_clear_mask = 0777;
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return *this;
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}
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FilePermissionsMask& FilePermissionsMask::add_permissions(mode_t mode)
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{
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m_write_mask |= mode;
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return *this;
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}
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FilePermissionsMask& FilePermissionsMask::remove_permissions(mode_t mode)
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{
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m_clear_mask |= mode;
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return *this;
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}
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}
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