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turbonss/src/user.zig

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const std = @import("std");
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const Allocator = std.mem.Allocator;
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const cast = std.math.cast;
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pub const PackedUserSize = @divExact(@bitSizeOf(PackedUser), 8);
pub const PackedUser = packed struct {
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uid: u32,
gid: u32,
additional_gids_offset: u29,
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shell_here: bool,
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shell_len_or_idx: u6,
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home_len: u6,
name_is_a_suffix: bool,
name_len: u5,
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gecos_len: u8,
};
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pub const User = struct {
uid: u32,
gid: u32,
name: []const u8,
gecos: []const u8,
home: []const u8,
shell: []const u8,
};
// UserWriter accepts a naive User struct and returns a PackedUser
pub const UserWriter = struct {
// shellIndexFnType is a signature for a function that accepts a shell
// string and returns it's index in the global shell section. Passing a
// function makes tests easier, and removes the Shell dependency of this
// module.
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const shellIndexFnType = fn ([]const u8) ?u6;
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allocator: Allocator,
shellIndexFn: shellIndexFnType,
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pub fn init(allocator: Allocator, shellIndexFn: shellIndexFnType) UserWriter {
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return UserWriter{
.allocator = allocator,
.shellIndexFn = shellIndexFn,
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};
}
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const fromUserErr = std.mem.Allocator.Error || error{InvalidRecord};
pub fn fromUser(self: *UserWriter, user: User) fromUserErr![]const u8 {
const home_len = std.math.cast(u6, user.home.len - 1) catch return error.InvalidRecord;
const name_len = cast(u5, user.name.len - 1) catch return error.InvalidRecord;
const shell_len = cast(u6, user.shell.len - 1) catch return error.InvalidRecord;
const gecos_len = cast(u8, user.gecos.len) catch return error.InvalidRecord;
var bindata_len: u32 = home_len;
var puser = PackedUser{
.uid = @as(u32, user.uid),
.gid = @as(u32, user.gid),
.additional_gids_offset = std.math.maxInt(u29), // needs second pass
.shell_here = undefined,
.shell_len_or_idx = undefined,
.home_len = home_len,
.name_is_a_suffix = undefined,
.name_len = name_len,
.gecos_len = gecos_len,
};
if (std.mem.endsWith(u8, user.home, user.name)) {
puser.name_is_a_suffix = true;
} else {
puser.name_is_a_suffix = false;
bindata_len += name_len;
}
bindata_len += gecos_len;
if (self.shellIndexFn(user.shell)) |idx| {
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puser.shell_here = false;
puser.shell_len_or_idx = idx;
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} else {
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puser.shell_here = true;
puser.shell_len_or_idx = shell_len;
bindata_len += shell_len;
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}
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var result = try self.allocator.alloc(u8, PackedUserSize + bindata_len);
const userPointer = @ptrCast([*]const u8, &puser);
{
var i: u32 = 0;
while (i < PackedUserSize) {
result[i] = userPointer[i];
i += 1;
}
}
std.mem.copy(u8, result, user.home);
if (!puser.name_is_a_suffix) {
std.mem.copy(u8, result, user.name);
}
std.mem.copy(u8, result, user.gecos);
if (puser.shell_here) {
std.mem.copy(u8, result, user.shell);
}
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return result;
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}
};
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const testing = std.testing;
test "PackedUser is byte-aligned" {
try testing.expectEqual(0, @rem(@bitSizeOf(PackedUser), 8));
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}
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fn testShellIndex(shell: []const u8) ?u6 {
if (std.mem.eql(u8, shell, "/bin/bash")) {
return 0;
} else if (std.mem.eql(u8, shell, "/bin/zsh")) {
return 1;
}
return null;
}
test "construct PackedUser blob" {
var writer = UserWriter.init(testing.allocator, testShellIndex);
const user1 = User{
.uid = 1000,
.gid = 1000,
.name = "vidmantas",
.gecos = "Vidmantas Kaminskas",
.home = "/home/vidmantas",
.shell = "/bin/bash",
};
const user2 = User{
.uid = 1001,
.gid = 1001,
.name = "svc-foo",
.gecos = "Service Account",
.home = "/home/service1",
.shell = "/usr/bin/nologin",
};
const puser1 = try writer.fromUser(user1);
const puser2 = try writer.fromUser(user2);
defer testing.allocator.free(puser1);
defer testing.allocator.free(puser2);
}