buildcache extractall: extract directly into spec.prefix (#37441)

- Run `mkdirp` on `spec.prefix`
- Extract directly into `spec.prefix`
  1. No need for `$store/tmp.xxx` where we extract the tarball directly, pray that it has one subdir `<name>-<version>-<hash>`, and then `rm -rf` the package prefix followed by `mv`.
  2. No need to clean up this temp dir in `spack clean`.
  3. Instead figure out package directory prefix from the tarball contents, and strip the tarinfo entries accordingly (kinda like tar --strip-components but more strict)
- Set package dir permissions
- Don't error during error handling when files cannot removed
- No need to "enrich" spec.json with this tarball-toplevel-path

After this PR, we can in fact tarball packages relative to `/` instead of `spec.prefix/..`, which makes it possible to use Spack tarballs as container layers, where relocation is impossible, and rootfs tarballs are expected.

5 files changed, 159 insertions, 60 deletions

diff --git a/lib/spack/docs/signing.rst b/lib/spack/docs/signing.rst
index f88b87f07e..dc44eaec1d 100644
--- a/lib/spack/docs/signing.rst
+++ b/lib/spack/docs/signing.rst
@@ -217,13 +217,7 @@ file would live in the ``build_cache`` directory of a binary mirror::
     "binary_cache_checksum": {
       "hash_algorithm": "sha256",
       "hash": "4f1e46452c35a5e61bcacca205bae1bfcd60a83a399af201a29c95b7cc3e1423"
-     },
-
-    "buildinfo": {
-      "relative_prefix":
-      "linux-ubuntu18.04-haswell/gcc-7.5.0/zlib-1.2.12-llv2ysfdxnppzjrt5ldybb5c52qbmoow",
-      "relative_rpaths": false
-    }
+     }
   }
 
   -----BEGIN PGP SIGNATURE-----
diff --git a/lib/spack/spack/binary_distribution.py b/lib/spack/spack/binary_distribution.py
index b0c72b9740..339fafb2ea 100644
--- a/lib/spack/spack/binary_distribution.py
+++ b/lib/spack/spack/binary_distribution.py
@@ -52,6 +52,7 @@ import spack.util.spack_yaml as syaml
 import spack.util.url as url_util
 import spack.util.web as web_util
 from spack.caches import misc_cache_location
+from spack.package_prefs import get_package_dir_permissions, get_package_group
 from spack.relocate_text import utf8_paths_to_single_binary_regex
 from spack.spec import Spec
 from spack.stage import Stage
@@ -1312,15 +1313,7 @@ def _build_tarball_in_stage_dir(spec: Spec, out_url: str, stage_dir: str, option
         else:
             raise ValueError("{0} not a valid spec file type".format(spec_file))
     spec_dict["buildcache_layout_version"] = 1
-    bchecksum = {}
-    bchecksum["hash_algorithm"] = "sha256"
-    bchecksum["hash"] = checksum
-    spec_dict["binary_cache_checksum"] = bchecksum
-    # Add original install prefix relative to layout root to spec.json.
-    # This will be used to determine is the directory layout has changed.
-    buildinfo = {}
-    buildinfo["relative_prefix"] = os.path.relpath(spec.prefix, spack.store.STORE.layout.root)
-    spec_dict["buildinfo"] = buildinfo
+    spec_dict["binary_cache_checksum"] = {"hash_algorithm": "sha256", "hash": checksum}
 
     with open(specfile_path, "w") as outfile:
         # Note: when using gpg clear sign, we need to avoid long lines (19995 chars).
@@ -1799,6 +1792,27 @@ def _extract_inner_tarball(spec, filename, extract_to, unsigned, remote_checksum
     return tarfile_path
 
 
+def _tar_strip_component(tar: tarfile.TarFile, prefix: str):
+    """Strip the top-level directory `prefix` from the member names in a tarfile."""
+    # Including trailing /, otherwise we end up with absolute paths.
+    regex = re.compile(re.escape(prefix) + "/*")
+
+    # Remove the top-level directory from the member (link)names.
+    # Note: when a tarfile is created, relative in-prefix symlinks are
+    # expanded to matching member names of tarfile entries. So, we have
+    # to ensure that those are updated too.
+    # Absolute symlinks are copied verbatim -- relocation should take care of
+    # them.
+    for m in tar.getmembers():
+        result = regex.match(m.name)
+        assert result is not None
+        m.name = m.name[result.end() :]
+        if m.linkname:
+            result = regex.match(m.linkname)
+            if result:
+                m.linkname = m.linkname[result.end() :]
+
+
 def extract_tarball(spec, download_result, unsigned=False, force=False):
     """
     extract binary tarball for given package into install area
@@ -1809,6 +1823,14 @@ def extract_tarball(spec, download_result, unsigned=False, force=False):
         else:
             raise NoOverwriteException(str(spec.prefix))
 
+    # Create the install prefix
+    fsys.mkdirp(
+        spec.prefix,
+        mode=get_package_dir_permissions(spec),
+        group=get_package_group(spec),
+        default_perms="parents",
+    )
+
     specfile_path = download_result["specfile_stage"].save_filename
 
     with open(specfile_path, "r") as inputfile:
@@ -1862,42 +1884,23 @@ def extract_tarball(spec, download_result, unsigned=False, force=False):
                 tarfile_path, size, contents, "sha256", expected, local_checksum
             )
 
-    new_relative_prefix = str(os.path.relpath(spec.prefix, spack.store.STORE.layout.root))
-    # if the original relative prefix is in the spec file use it
-    buildinfo = spec_dict.get("buildinfo", {})
-    old_relative_prefix = buildinfo.get("relative_prefix", new_relative_prefix)
-    rel = buildinfo.get("relative_rpaths")
-    info = "old relative prefix %s\nnew relative prefix %s\nrelative rpaths %s"
-    tty.debug(info % (old_relative_prefix, new_relative_prefix, rel), level=2)
-
-    # Extract the tarball into the store root, presumably on the same filesystem.
-    # The directory created is the base directory name of the old prefix.
-    # Moving the old prefix name to the new prefix location should preserve
-    # hard links and symbolic links.
-    extract_tmp = os.path.join(spack.store.STORE.layout.root, ".tmp")
-    mkdirp(extract_tmp)
-    extracted_dir = os.path.join(extract_tmp, old_relative_prefix.split(os.path.sep)[-1])
-
-    with closing(tarfile.open(tarfile_path, "r")) as tar:
-        try:
-            tar.extractall(path=extract_tmp)
-        except Exception as e:
-            _delete_staged_downloads(download_result)
-            shutil.rmtree(extracted_dir)
-            raise e
     try:
-        shutil.move(extracted_dir, spec.prefix)
-    except Exception as e:
+        with closing(tarfile.open(tarfile_path, "r")) as tar:
+            # Remove install prefix from tarfil to extract directly into spec.prefix
+            _tar_strip_component(tar, prefix=_ensure_common_prefix(tar))
+            tar.extractall(path=spec.prefix)
+    except Exception:
+        shutil.rmtree(spec.prefix, ignore_errors=True)
         _delete_staged_downloads(download_result)
-        shutil.rmtree(extracted_dir)
-        raise e
+        raise
+
     os.remove(tarfile_path)
     os.remove(specfile_path)
 
     try:
         relocate_package(spec)
     except Exception as e:
-        shutil.rmtree(spec.prefix)
+        shutil.rmtree(spec.prefix, ignore_errors=True)
         raise e
     else:
         manifest_file = os.path.join(
@@ -1910,12 +1913,29 @@ def extract_tarball(spec, download_result, unsigned=False, force=False):
             tty.warn("No manifest file in tarball for spec %s" % spec_id)
     finally:
         if tmpdir:
-            shutil.rmtree(tmpdir)
+            shutil.rmtree(tmpdir, ignore_errors=True)
         if os.path.exists(filename):
             os.remove(filename)
         _delete_staged_downloads(download_result)
 
 
+def _ensure_common_prefix(tar: tarfile.TarFile) -> str:
+    # Get the shortest length directory.
+    common_prefix = min((e.name for e in tar.getmembers() if e.isdir()), key=len, default=None)
+
+    if common_prefix is None:
+        raise ValueError("Tarball does not contain a common prefix")
+
+    # Validate that each file starts with the prefix
+    for member in tar.getmembers():
+        if not member.name.startswith(common_prefix):
+            raise ValueError(
+                f"Tarball contains file {member.name} outside of prefix {common_prefix}"
+            )
+
+    return common_prefix
+
+
 def install_root_node(spec, unsigned=False, force=False, sha256=None):
     """Install the root node of a concrete spec from a buildcache.
 
diff --git a/lib/spack/spack/cmd/clean.py b/lib/spack/spack/cmd/clean.py
index 44e7f8e49e..93edcd712f 100644
--- a/lib/spack/spack/cmd/clean.py
+++ b/lib/spack/spack/cmd/clean.py
@@ -114,11 +114,7 @@ def clean(parser, args):
     if args.stage:
         tty.msg("Removing all temporary build stages")
         spack.stage.purge()
-        # Temp directory where buildcaches are extracted
-        extract_tmp = os.path.join(spack.store.STORE.layout.root, ".tmp")
-        if os.path.exists(extract_tmp):
-            tty.debug("Removing {0}".format(extract_tmp))
-            shutil.rmtree(extract_tmp)
+
     if args.downloads:
         tty.msg("Removing cached downloads")
         spack.caches.fetch_cache.destroy()
diff --git a/lib/spack/spack/schema/buildcache_spec.py b/lib/spack/spack/schema/buildcache_spec.py
index eeeb6dc085..7c74c7f4eb 100644
--- a/lib/spack/spack/schema/buildcache_spec.py
+++ b/lib/spack/spack/schema/buildcache_spec.py
@@ -6,7 +6,7 @@
 """Schema for a buildcache spec.yaml file
 
 .. literalinclude:: _spack_root/lib/spack/spack/schema/buildcache_spec.py
-   :lines: 14-
+   :lines: 13-
 """
 import spack.schema.spec
 
@@ -16,15 +16,8 @@ schema = {
     "type": "object",
     "additionalProperties": False,
     "properties": {
-        "buildinfo": {
-            "type": "object",
-            "additionalProperties": False,
-            "required": ["relative_prefix"],
-            "properties": {
-                "relative_prefix": {"type": "string"},
-                "relative_rpaths": {"type": "boolean"},
-            },
-        },
+        # `buildinfo` is no longer needed as of Spack 0.21
+        "buildinfo": {"type": "object"},
         "spec": {
             "type": "object",
             "additionalProperties": True,
diff --git a/lib/spack/spack/test/bindist.py b/lib/spack/spack/test/bindist.py
index 4ef280469b..b778651455 100644
--- a/lib/spack/spack/test/bindist.py
+++ b/lib/spack/spack/test/bindist.py
@@ -12,6 +12,7 @@ import tarfile
 import urllib.error
 import urllib.request
 import urllib.response
+from pathlib import PurePath
 
 import py
 import pytest
@@ -177,6 +178,33 @@ def install_dir_non_default_layout(tmpdir):
         spack.store.STORE.layout = real_layout
 
 
+@pytest.fixture(scope="function")
+def dummy_prefix(tmpdir):
+    """Dummy prefix used for testing tarball creation, validation, extraction"""
+    p = tmpdir.mkdir("prefix")
+    assert os.path.isabs(p)
+
+    p.mkdir("bin")
+    p.mkdir("share")
+    p.mkdir(".spack")
+
+    app = p.join("bin", "app")
+    relative_app_link = p.join("bin", "relative_app_link")
+    absolute_app_link = p.join("bin", "absolute_app_link")
+    data = p.join("share", "file")
+
+    with open(app, "w") as f:
+        f.write("hello world")
+
+    with open(data, "w") as f:
+        f.write("hello world")
+
+    os.symlink("app", relative_app_link)
+    os.symlink(app, absolute_app_link)
+
+    return str(p)
+
+
 args = ["file"]
 if sys.platform == "darwin":
     args.extend(["/usr/bin/clang++", "install_name_tool"])
@@ -966,3 +994,71 @@ def test_tarball_normalized_permissions(tmpdir):
 
     # not-executable-by-user files should be 0o644
     assert path_to_member["pkg/share/file"].mode == 0o644
+
+
+def test_tarball_common_prefix(dummy_prefix, tmpdir):
+    """Tests whether Spack can figure out the package directory
+    from the tarball contents, and strip them when extracting."""
+
+    # When creating a tarball, Python (and tar) use relative paths,
+    # Absolute paths become relative to `/`, so drop the leading `/`.
+    assert os.path.isabs(dummy_prefix)
+    expected_prefix = PurePath(dummy_prefix).as_posix().lstrip("/")
+
+    with tmpdir.as_cwd():
+        # Create a tarball (using absolute path for prefix dir)
+        with tarfile.open("example.tar", mode="w") as tar:
+            tar.add(name=dummy_prefix)
+
+        # Open, verify common prefix, and extract it.
+        with tarfile.open("example.tar", mode="r") as tar:
+            common_prefix = bindist._ensure_common_prefix(tar)
+            assert common_prefix == expected_prefix
+
+            # Strip the prefix from the tar entries
+            bindist._tar_strip_component(tar, common_prefix)
+
+            # Extract into prefix2
+            tar.extractall(path="prefix2")
+
+        # Verify files are all there at the correct level.
+        assert set(os.listdir("prefix2")) == {"bin", "share", ".spack"}
+        assert set(os.listdir(os.path.join("prefix2", "bin"))) == {
+            "app",
+            "relative_app_link",
+            "absolute_app_link",
+        }
+        assert set(os.listdir(os.path.join("prefix2", "share"))) == {"file"}
+
+        # Relative symlink should still be correct
+        assert os.readlink(os.path.join("prefix2", "bin", "relative_app_link")) == "app"
+
+        # Absolute symlink should remain absolute -- this is for relocation to fix up.
+        assert os.readlink(os.path.join("prefix2", "bin", "absolute_app_link")) == os.path.join(
+            dummy_prefix, "bin", "app"
+        )
+
+
+def test_tarfile_without_common_directory_prefix_fails(tmpdir):
+    """A tarfile that only contains files without a common package directory
+    should fail to extract, as we won't know where to put the files."""
+    with tmpdir.as_cwd():
+        # Create a broken tarball with just a file, no directories.
+        with tarfile.open("empty.tar", mode="w") as tar:
+            tar.addfile(tarfile.TarInfo(name="example/file"), fileobj=io.BytesIO(b"hello"))
+
+        with pytest.raises(ValueError, match="Tarball does not contain a common prefix"):
+            bindist._ensure_common_prefix(tarfile.open("empty.tar", mode="r"))
+
+
+def test_tarfile_with_files_outside_common_prefix(tmpdir, dummy_prefix):
+    """If a file is outside of the common prefix, we should fail."""
+    with tmpdir.as_cwd():
+        with tarfile.open("broken.tar", mode="w") as tar:
+            tar.add(name=dummy_prefix)
+            tar.addfile(tarfile.TarInfo(name="/etc/config_file"), fileobj=io.BytesIO(b"hello"))
+
+        with pytest.raises(
+            ValueError, match="Tarball contains file /etc/config_file outside of prefix"
+        ):
+            bindist._ensure_common_prefix(tarfile.open("broken.tar", mode="r"))