bazel-lib/docs/tar.md

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General-purpose rule to create tar archives.

Unlike [pkg_tar from rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/main/docs/latest.md#pkg_tar):

- It does not depend on any Python interpreter setup
- The "manifest" specification is a mature public API and uses a compact tabular format, fixing
  https://github.com/bazelbuild/rules_pkg/pull/238
- It doesn't rely custom program to produce the output, instead
  we rely on the well-known C++ program called "tar".
  Specifically, we use the BSD variant of tar since it provides a means
  of controlling mtimes, uid, symlinks, etc.

We also provide full control for tar'ring binaries including their runfiles.

The `tar` binary is hermetic and fully statically-linked.
It is fetched as a toolchain from https://github.com/aspect-build/bsdtar-prebuilt.

## Examples

See the [`tar` tests](/lib/tests/tar/BUILD.bazel) for examples of usage.

## Mutating the tar contents

The `mtree_spec` rule can be used to create an mtree manifest for the tar file.
Then you can mutate that spec using `mtree_mutate` and feed the result
as the `mtree` attribute of the `tar` rule.

For example, to set the owner uid of files in the tar, you could:

```starlark
_TAR_SRCS = ["//some:files"]

mtree_spec(
    name = "mtree",
    srcs = _TAR_SRCS,
)

mtree_mutate(
    name = "change_owner",
    mtree = ":mtree",
    owner = "1000",
)

tar(
    name = "tar",
    srcs = _TAR_SRCS,
    mtree = "change_owner",
)
```

TODO:
- Provide convenience for rules_pkg users to re-use or replace pkg_files trees

<a id="mtree_spec"></a>

## mtree_spec

<pre>
mtree_spec(<a href="#mtree_spec-name">name</a>, <a href="#mtree_spec-srcs">srcs</a>, <a href="#mtree_spec-out">out</a>)
</pre>

Create an mtree specification to map a directory hierarchy. See https://man.freebsd.org/cgi/man.cgi?mtree(8)

**ATTRIBUTES**


| Name  | Description | Type | Mandatory | Default |
| :------------- | :------------- | :------------- | :------------- | :------------- |
| <a id="mtree_spec-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
| <a id="mtree_spec-srcs"></a>srcs |  Files that are placed into the tar   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional |  `[]`  |
| <a id="mtree_spec-out"></a>out |  Resulting specification file to write   | <a href="https://bazel.build/concepts/labels">Label</a> | optional |  `None`  |


<a id="tar_rule"></a>

## tar_rule

<pre>
tar_rule(<a href="#tar_rule-name">name</a>, <a href="#tar_rule-srcs">srcs</a>, <a href="#tar_rule-out">out</a>, <a href="#tar_rule-args">args</a>, <a href="#tar_rule-compress">compress</a>, <a href="#tar_rule-mode">mode</a>, <a href="#tar_rule-mtree">mtree</a>)
</pre>

Rule that executes BSD `tar`. Most users should use the [`tar`](#tar) macro, rather than load this directly.

**ATTRIBUTES**


| Name  | Description | Type | Mandatory | Default |
| :------------- | :------------- | :------------- | :------------- | :------------- |
| <a id="tar_rule-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
| <a id="tar_rule-srcs"></a>srcs |  Files, directories, or other targets whose default outputs are placed into the tar.<br><br>If any of the srcs are binaries with runfiles, those are copied into the resulting tar as well.   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional |  `[]`  |
| <a id="tar_rule-out"></a>out |  Resulting tar file to write. If absent, `[name].tar` is written.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional |  `None`  |
| <a id="tar_rule-args"></a>args |  Additional flags permitted by BSD tar; see the man page.   | List of strings | optional |  `[]`  |
| <a id="tar_rule-compress"></a>compress |  Compress the archive file with a supported algorithm.   | String | optional |  `""`  |
| <a id="tar_rule-mode"></a>mode |  A mode indicator from the following list, copied from the tar manpage:<br><br>- create: Create a new archive containing the specified items. - append: Like `create`, but new entries are appended to the archive.      Note that this only works on uncompressed archives stored in regular files.      The -f option is required. - list: List  archive contents to stdout. - update: Like `append`, but new entries are added only if they have a      modification date newer than the corresponding entry in the archive.         Note that this only works on uncompressed archives stored in         regular files. The -f option     is required. - extract: Extract to disk from the archive. If a file with the same name         appears more than once in the archive, each copy  will  be  extracted,     with  later  copies  overwriting  (replacing) earlier copies.   | String | optional |  `"create"`  |
| <a id="tar_rule-mtree"></a>mtree |  An mtree specification file   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |


<a id="mtree_mutate"></a>

## mtree_mutate

<pre>
mtree_mutate(<a href="#mtree_mutate-name">name</a>, <a href="#mtree_mutate-mtree">mtree</a>, <a href="#mtree_mutate-strip_prefix">strip_prefix</a>, <a href="#mtree_mutate-package_dir">package_dir</a>, <a href="#mtree_mutate-mtime">mtime</a>, <a href="#mtree_mutate-owner">owner</a>, <a href="#mtree_mutate-ownername">ownername</a>, <a href="#mtree_mutate-awk_script">awk_script</a>, <a href="#mtree_mutate-kwargs">kwargs</a>)
</pre>

Modify metadata in an mtree file.

**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="mtree_mutate-name"></a>name |  name of the target, output will be `[name].mtree`.   |  none |
| <a id="mtree_mutate-mtree"></a>mtree |  input mtree file, typically created by `mtree_spec`.   |  none |
| <a id="mtree_mutate-strip_prefix"></a>strip_prefix |  prefix to remove from all paths in the tar. Files and directories not under this prefix are dropped.   |  `None` |
| <a id="mtree_mutate-package_dir"></a>package_dir |  directory prefix to add to all paths in the tar.   |  `None` |
| <a id="mtree_mutate-mtime"></a>mtime |  new modification time for all entries.   |  `None` |
| <a id="mtree_mutate-owner"></a>owner |  new uid for all entries.   |  `None` |
| <a id="mtree_mutate-ownername"></a>ownername |  new uname for all entries.   |  `None` |
| <a id="mtree_mutate-awk_script"></a>awk_script |  may be overridden to change the script containing the modification logic.   |  `"@aspect_bazel_lib//lib/private:modify_mtree.awk"` |
| <a id="mtree_mutate-kwargs"></a>kwargs |  additional named parameters to genrule   |  none |


<a id="tar"></a>

## tar

<pre>
tar(<a href="#tar-name">name</a>, <a href="#tar-mtree">mtree</a>, <a href="#tar-stamp">stamp</a>, <a href="#tar-kwargs">kwargs</a>)
</pre>

Wrapper macro around [`tar_rule`](#tar_rule).

### Options for mtree

mtree provides the "specification" or manifest of a tar file.
See https://man.freebsd.org/cgi/man.cgi?mtree(8)
Because BSD tar doesn't have a flag to set modification times to a constant,
we must always supply an mtree input to get reproducible builds.
See https://reproducible-builds.org/docs/archives/ for more explanation.

1. By default, mtree is "auto" which causes the macro to create an `mtree_spec` rule.

2. `mtree` may be supplied as an array literal of lines, e.g.

```
mtree =[
    "usr/bin uid=0 gid=0 mode=0755 type=dir",
    "usr/bin/ls uid=0 gid=0 mode=0755 time=0 type=file content={}/a".format(package_name()),
],
```

For the format of a line, see "There are four types of lines in a specification" on the man page for BSD mtree,
https://man.freebsd.org/cgi/man.cgi?mtree(8)

3. `mtree` may be a label of a file containing the specification lines.


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="tar-name"></a>name |  name of resulting `tar_rule`   |  none |
| <a id="tar-mtree"></a>mtree |  "auto", or an array of specification lines, or a label of a file that contains the lines. Subject to [$(location)](https://bazel.build/reference/be/make-variables#predefined_label_variables) and ["Make variable"](https://bazel.build/reference/be/make-variables) substitution.   |  `"auto"` |
| <a id="tar-stamp"></a>stamp |  should mtree attribute be stamped   |  `0` |
| <a id="tar-kwargs"></a>kwargs |  additional named parameters to pass to `tar_rule`   |  none |


<a id="tar_lib.common.add_compression_args"></a>

## tar_lib.common.add_compression_args

<pre>
tar_lib.common.add_compression_args(<a href="#tar_lib.common.add_compression_args-compress">compress</a>, <a href="#tar_lib.common.add_compression_args-args">args</a>)
</pre>



**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="tar_lib.common.add_compression_args-compress"></a>compress |  <p align="center"> - </p>   |  none |
| <a id="tar_lib.common.add_compression_args-args"></a>args |  <p align="center"> - </p>   |  none |


<a id="tar_lib.implementation"></a>

## tar_lib.implementation

<pre>
tar_lib.implementation(<a href="#tar_lib.implementation-ctx">ctx</a>)
</pre>



**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="tar_lib.implementation-ctx"></a>ctx |  <p align="center"> - </p>   |  none |


<a id="tar_lib.mtree_implementation"></a>

## tar_lib.mtree_implementation

<pre>
tar_lib.mtree_implementation(<a href="#tar_lib.mtree_implementation-ctx">ctx</a>)
</pre>



**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="tar_lib.mtree_implementation-ctx"></a>ctx |  <p align="center"> - </p>   |  none |