mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-28 08:36:15 +02:00
eb7d7780b1
This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
43 lines
1.6 KiB
Markdown
43 lines
1.6 KiB
Markdown
# Nix Archive (NAR) format
|
||
|
||
This is the complete specification of the [Nix Archive] format.
|
||
The Nix Archive format closely follows the abstract specification of a [file system object] tree,
|
||
because it is designed to serialize exactly that data structure.
|
||
|
||
[Nix Archive]: @docroot@/store/file-system-object/content-address.md#nix-archive
|
||
[file system object]: @docroot@/store/file-system-object.md
|
||
|
||
The format of this specification is close to [Extended Backus–Naur form](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form), with the exception of the `str(..)` function / parameterized rule, which length-prefixes and pads strings.
|
||
This makes the resulting binary format easier to parse.
|
||
|
||
Regular users do *not* need to know this information.
|
||
But for those interested in exactly how Nix works, e.g. if they are reimplementing it, this information can be useful.
|
||
|
||
```ebnf
|
||
nar = str("nix-archive-1"), nar-obj;
|
||
|
||
nar-obj = str("("), nar-obj-inner, str(")");
|
||
|
||
nar-obj-inner
|
||
= str("type"), str("regular") regular
|
||
| str("type"), str("symlink") symlink
|
||
| str("type"), str("directory") directory
|
||
;
|
||
|
||
regular = [ str("executable"), str("") ], str("contents"), str(contents);
|
||
|
||
symlink = str("target"), str(target);
|
||
|
||
(* side condition: directory entries must be ordered by their names *)
|
||
directory = { directory-entry };
|
||
|
||
directory-entry = str("entry"), str("("), str("name"), str(name), str("node"), nar-obj, str(")");
|
||
```
|
||
|
||
The `str` function / parameterized rule is defined as follows:
|
||
|
||
- `str(s)` = `int(|s|), pad(s);`
|
||
|
||
- `int(n)` = the 64-bit little endian representation of the number `n`
|
||
|
||
- `pad(s)` = the byte sequence `s`, padded with 0s to a multiple of 8 byte
|