129 lines
3.3 KiB
Zig
129 lines
3.3 KiB
Zig
const std = @import("std");
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const shell = @import("shell.zig");
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const HeaderSize = @sizeOf(Header);
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const Magic = [4]u8{ 0xf0, 0x9f, 0xa4, 0xb7 };
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const Version = 0;
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const Bom = 0x1234;
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pub const SectionLength = 64;
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const InvalidHeader = error{
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InvalidMagic,
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InvalidVersion,
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InvalidBom,
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TooManyShells,
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InvalidOffset,
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};
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const Header = packed struct {
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magic: [4]u8,
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version: u8,
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bom: u16,
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num_shells: u8,
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num_users: u32,
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num_groups: u32,
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offset_bdz_uid2user: u32,
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offset_bdz_groupname2group: u32,
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offset_bdz_username2user: u32,
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offset_idx: u32,
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offset_groups: u32,
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offset_users: u32,
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offset_groupmembers: u32,
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offset_additional_gids: u32,
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pub fn init(blob: [HeaderSize]u8) InvalidHeader!Header {
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const self = @bitCast(Header, blob);
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for (Magic) |item, index| {
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if (self.magic[index] != item) return error.InvalidMagic;
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}
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if (self.version != 0) {
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return error.InvalidVersion;
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}
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if (self.bom != Bom) {
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return error.InvalidBom;
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}
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if (self.num_shells > shell.MaxShells) {
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return error.TooManyShells;
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}
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const offsets = [_]u32{
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self.offset_bdz_uid2user,
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self.offset_bdz_groupname2group,
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self.offset_bdz_username2user,
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self.offset_idx,
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self.offset_groups,
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self.offset_users,
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self.offset_groupmembers,
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self.offset_additional_gids,
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};
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for (offsets) |offset| {
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if (offset & (SectionLength - 1) != 0) {
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return error.InvalidOffset;
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}
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}
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return self;
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}
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pub fn asArray(self: *const Header) [HeaderSize]u8 {
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return @bitCast([HeaderSize]u8, self.*);
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}
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};
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const testing = std.testing;
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test "header is byte-aligned" {
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try testing.expectEqual(HeaderSize * 8, @bitSizeOf(Header));
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}
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test "Section length is a power of two" {
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try testing.expect(std.math.isPowerOfTwo(SectionLength));
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}
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test "header pack, unpack and validation" {
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const goodHeader = Header{
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.magic = Magic,
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.version = Version,
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.bom = Bom,
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.num_shells = 0,
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.num_users = 0,
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.num_groups = 0,
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.offset_bdz_uid2user = 0,
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.offset_bdz_groupname2group = 0,
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.offset_bdz_username2user = 0,
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.offset_idx = 0,
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.offset_groups = 0,
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.offset_users = 0,
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.offset_groupmembers = 0,
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.offset_additional_gids = 0,
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};
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const gotHeader = try Header.init(goodHeader.asArray());
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try testing.expectEqual(goodHeader, gotHeader);
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{
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var header = goodHeader;
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header.magic[0] = 0;
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try testing.expectError(error.InvalidMagic, Header.init(header.asArray()));
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}
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{
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var header = goodHeader;
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header.bom = 0x3412;
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try testing.expectError(error.InvalidBom, Header.init(header.asArray()));
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}
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{
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var header = goodHeader;
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header.num_shells = shell.MaxShells + 1;
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try testing.expectError(error.TooManyShells, Header.init(header.asArray()));
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}
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{
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var header = goodHeader;
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header.offset_bdz_uid2user = 65;
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try testing.expectError(error.InvalidOffset, Header.init(header.asArray()));
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}
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}
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