image: resolve --image via the Docker daemon API instead of the CLI

crates/sandlock-cli/src/main.rs

@@ -105,8 +105,12 @@ struct RunArgs {
     #[arg(short = 'i', long)]
     interactive: bool,
 
-    /// Use a local Docker image as chroot rootfs
-    #[arg(long)]
+    /// Use a local Docker image as chroot rootfs, given by reference
+    /// (e.g. `python:3.12-slim`, a digest, or an image id). The image
+    /// must already be present in local Docker storage; sandlock never
+    /// pulls from a registry. Requires a running Docker daemon and an
+    /// accessible socket; the run fails early if neither is reachable.
+    #[arg(long, value_name = "IMAGE")]
     image: Option<String>,
 
     /// Dry-run: run the command, show filesystem changes, then discard
@@ -429,13 +433,13 @@ async fn run_command(args: RunArgs) -> Result<i32> {
     // the shared image cache directly.
     let image_cmd: Option<Vec<String>>;
     if let Some(ref img) = args.image {
-        let rootfs = sandlock_core::image::extract(img, None)?;
+        let rootfs = sandlock_core::image::extract(img, None).await?;
         builder = builder.chroot(&rootfs).fs_read("/");
         if pb.workdir.is_none() {
             builder = builder.workdir(&rootfs);
         }
         if args.cmd.is_empty() {
-            image_cmd = Some(sandlock_core::image::inspect_cmd(img)?);
+            image_cmd = Some(sandlock_core::image::inspect_cmd(img).await?);
         } else {
             image_cmd = None;
         }

crates/sandlock-core/Cargo.toml

@@ -12,7 +12,7 @@ description = "Lightweight process sandbox using Landlock, seccomp-bpf, and secc
 libc = "0.2"
 syscalls = { version = "0.8", default-features = false }
 nix = { version = "0.29", features = ["process", "signal", "fs", "ioctl", "poll"] }
-tokio = { version = "1", features = ["rt", "net", "time", "sync", "macros", "io-util"] }
+tokio = { version = "1", features = ["rt", "net", "time", "sync", "macros", "io-util", "fs"] }
 serde = { version = "1", features = ["derive"] }
 thiserror = "2"
 rand = "0.8"
@@ -26,7 +26,10 @@ toml = "0.8"
 jiff = "0.2"
 pathdiff = "0.2"
 hudsucker = "0.22"
+tar = "0.4"
 clap = { version = "4", features = ["derive"], optional = true }
+bollard = "0.21"
+futures-util = "0.3"
 
 [features]
 default = []