xtask: Allow to run VM integration tests without dpkg

Debian packages are just nested archives, where the outer one is ar
and the inner one is lzma2 tarball. Use Rust crates to unpack them.

Co-authored-by: Tamir Duberstein <tamird@gmail.com>

Cargo.toml

@@ -62,6 +62,7 @@ rust-version = "1.85.0"
 # them to do that, but in the meantime we need to be careful.
 [workspace.dependencies]
 anyhow = { version = "1", default-features = false }
+ar = { version = "0.9", default-features = false }
 assert_matches = { version = "1.5.0", default-features = false }
 base64 = { version = "0.22.1", default-features = false }
 bindgen = { version = "0.72", default-features = false }

xtask/Cargo.toml

@@ -15,6 +15,7 @@ workspace = true
 
 [dependencies]
 anyhow = { workspace = true, features = ["std"] }
+ar = { workspace = true }
 aya-tool = { path = "../aya-tool", version = "0.1.0", default-features = false }
 cargo_metadata = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
@@ -30,3 +31,4 @@ syn = { workspace = true }
 tar = { workspace = true }
 tempfile = { workspace = true }
 walkdir = { workspace = true }
+xz2 = { workspace = true }

xtask/src/run.rs

@@ -1,7 +1,7 @@
 use std::{
     ffi::{OsStr, OsString},
     fmt::Write as _,
-    fs::{self, OpenOptions},
+    fs::{self, File, OpenOptions},
     io::{BufRead as _, BufReader, Write as _},
     ops::Deref as _,
     path::{self, Path, PathBuf},
@@ -300,29 +300,37 @@ pub(crate) fn run(opts: Options) -> Result<()> {
                 fs::create_dir_all(&archive_dir)
                     .with_context(|| format!("failed to create {}", archive_dir.display()))?;
 
-                let mut dpkg = Command::new("dpkg-deb");
-                dpkg.arg("--fsys-tarfile")
-                    .arg(archive)
-                    .stdout(Stdio::piped());
-                let mut dpkg_child = dpkg
-                    .spawn()
-                    .with_context(|| format!("failed to spawn {dpkg:?}"))?;
-                let Child { stdout, .. } = &mut dpkg_child;
-                let stdout = stdout.take().unwrap();
-                let mut archive_reader = tar::Archive::new(stdout);
-                archive_reader.unpack(&archive_dir).with_context(|| {
+                let archive_reader = File::open(archive).with_context(|| {
+                    format!("failed to open the deb package {}", archive.display())
+                })?;
+                let mut archive_reader = ar::Archive::new(archive_reader);
+                // `ar` entries are borrowed from the reader, so the reader
+                // cannot implement `Iterator` (because `Iterator::Item` is not
+                // a GAT).
+                //
+                // https://github.com/mdsteele/rust-ar/issues/15
+                let mut entries = 0;
+                while let Some(entry) = archive_reader.next_entry() {
+                    let entry = entry.with_context(|| {
+                        format!(
+                            "failed to read an entry of the deb package {}",
+                            archive.display()
+                        )
+                    })?;
+                    if entry.header().identifier() == b"data.tar.xz" {
+                        let entry_reader = xz2::read::XzDecoder::new(entry);
+                        let mut entry_reader = tar::Archive::new(entry_reader);
+                        entry_reader.unpack(&archive_dir).with_context(|| {
                             format!(
                                 "failed to unpack archive {} to {}",
                                 archive.display(),
                                 archive_dir.display()
                             )
                         })?;
-                let status = dpkg_child
-                    .wait()
-                    .with_context(|| format!("failed to wait for {dpkg:?}"))?;
-                if !status.success() {
-                    bail!("{dpkg:?} exited with {status}");
+                        entries += 1;
+                    }
                 }
+                assert_eq!(entries, 1);
 
                 let mut kernel_images = Vec::new();
                 let mut configs = Vec::new();