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.

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

@@ -1,8 +1,8 @@
 use std::{
     ffi::{OsStr, OsString},
     fmt::Write as _,
-    fs::{self, OpenOptions},
-    io::{BufRead as _, BufReader, Write as _},
+    fs::{self, File, OpenOptions},
+    io::{BufRead as _, BufReader, Cursor, Read as _, Write as _},
     ops::Deref as _,
     path::{self, Path, PathBuf},
     process::{Child, ChildStdin, Command, Output, Stdio},
@@ -300,29 +300,43 @@ 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);
+                // This would've been easier if `ar` crate was providing some iterator
+                // over entries...
+                // https://github.com/mdsteele/rust-ar/issues/15
+                let mut inner_archive = None;
+                while let Some(entry) = archive_reader.next_entry() {
+                    let mut 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 mut buf = Vec::with_capacity(entry.header().size() as usize);
+                        let _bytes_read = entry.read_to_end(&mut buf)?;
+                        inner_archive = Some(buf);
+                        break;
+                    }
+                }
+                let Some(inner_archive) = inner_archive else {
+                    bail!(
+                        "cound not find the `data.tar.xz` archive inside the deb package {}",
+                        archive.display()
+                    );
+                };
+                let inner_archive_reader = xz2::read::XzDecoder::new(Cursor::new(inner_archive));
+                let mut inner_archive_reader = tar::Archive::new(inner_archive_reader);
+                inner_archive_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}");
-                }
 
                 let mut kernel_images = Vec::new();
                 let mut configs = Vec::new();