filling packed user

src/header.zig

@@ -1,5 +1,5 @@
 const std = @import("std");
-const shells = @import("shell.zig");
+const shell = @import("shell.zig");
 
 const HeaderSize = @sizeOf(Header);
 const Magic = [4]u8{ 0xf0, 0x9f, 0xa4, 0xb7 };
@@ -43,7 +43,7 @@ const Header = packed struct {
         if (self.bom != Bom) {
             return error.InvalidBom;
         }
-        if (self.num_shells > shells.MaxShells) {
+        if (self.num_shells > shell.MaxShells) {
             return error.TooManyShells;
         }
 
@@ -116,7 +116,7 @@ test "header pack, unpack and validation" {
 
     {
         var header = goodHeader;
-        header.num_shells = shells.MaxShells + 1;
+        header.num_shells = shell.MaxShells + 1;
         try testing.expectError(error.TooManyShells, Header.init(header.asArray()));
     }
 

src/user.zig

@@ -1,4 +1,7 @@
 const std = @import("std");
+const shell = @import("shell.zig");
+
+const Allocator = std.mem.Allocator;
 
 pub const PackedUserSize = @sizeOf(PackedUser);
 pub const PackedUser = packed struct {
@@ -13,6 +16,53 @@ pub const PackedUser = packed struct {
     gecos_len: u8,
 };
 
+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 {
+    allocator: Allocator,
+
+    pub fn init(allocator: Allocator) UserWriter {
+        return UserWriter{
+            .allocator = allocator,
+        };
+    }
+
+    pub fn fromUser(user: User, shellw: shell.ShellWriter) !PackedUser {
+        var shell_here: u1 = undefined;
+        var shell_len_or_place: u6 = undefined;
+        if (shellw.getIndex(user.shell)) |idx| {
+            shell_here = false;
+            shell_len_or_place = idx;
+        } else {
+            shell_here = true;
+            shell_len_or_place = user.shell.len;
+        }
+
+        var puser = PackedUser{
+            .uid = user.uid,
+            .gid = user.gid,
+            .additional_gids_offset = 0, // second pass
+            .shell_here = shell_here,
+            .shell_len_or_place = shell_len_or_place,
+            .homedir_len = undefined,
+            .username_is_a_suffix = undefined,
+            .username_offset_or_len = undefined,
+            .gecos_len = undefined,
+        };
+
+        _ = shellw;
+        return puser;
+    }
+};
+
 const testing = std.testing;
 
 test "PackedUser is byte-aligned" {