nydus-image: enhance unpack command to support extracting files to dir

When --output is specified as a directory, the nydus-image unpack
command will return an error, which is not convenient for users.

This patch enhances this command to allow --output to be passed into a
dir. In this case, nydus-image will extract all files into this dir.

Signed-off-by: Qinqi Qu <[email protected]>

src/bin/nydus-image/main.rs

@@ -720,7 +720,7 @@ fn prepare_cmd_args(bti_string: &'static str) -> App {
             .arg(
                 Arg::new("output")
                     .long("output")
-                    .help("path for output tar file")
+                    .help("Path for output tar file, If it is a directory, extract all files to there.")
                     .required(true),
             ),
     )
@@ -1365,9 +1365,9 @@ impl Command {
         };
 
         OCIUnpacker::new(bootstrap, backend, output)
-            .with_context(|| "fail to create unpacker")?
+            .with_context(|| "failed to create unpacker")?
             .unpack(config)
-            .with_context(|| "fail to unpack")
+            .with_context(|| format!("failed to unpack image to: {}", output))
     }
 
     fn check(matches: &ArgMatches, build_info: &BuildTimeInfo) -> Result<()> {

src/bin/nydus-image/unpack/mod.rs

@@ -3,7 +3,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 use std::collections::HashMap;
-use std::fs::{File, OpenOptions};
+use std::fs::{create_dir_all, remove_file, File, OpenOptions};
 use std::io::Read;
 use std::path::{Path, PathBuf};
 use std::rc::Rc;
@@ -18,7 +18,7 @@ use nydus_rafs::{
 };
 use nydus_storage::backend::BlobBackend;
 use nydus_storage::device::BlobInfo;
-use tar::{Builder, Header};
+use tar::{Archive, Builder, Header};
 
 use self::pax::{
     OCIBlockBuilder, OCICharBuilder, OCIDirBuilder, OCIFifoBuilder, OCILinkBuilder, OCIRegBuilder,
@@ -32,7 +32,7 @@ pub trait Unpacker {
     fn unpack(&self, config: Arc<ConfigV2>) -> Result<()>;
 }
 
-///  A unpacker with the ability to convert bootstrap file and blob file to tar
+///  A unpacker with the ability to convert bootstrap file and blob file to tar or dir.
 pub struct OCIUnpacker {
     bootstrap: PathBuf,
     blob_backend: Option<Arc<dyn BlobBackend + Send + Sync>>,
@@ -66,23 +66,54 @@ impl OCIUnpacker {
     }
 }
 
+// If output ends with path separator, then it is a dir.
+// Output a tar file first, and untar it later.
+fn get_unpack_path(bootstrap: PathBuf, output: PathBuf) -> Result<(bool, PathBuf)> {
+    let is_dir = output
+        .to_string_lossy()
+        .ends_with(std::path::MAIN_SEPARATOR);
+    let mut tar_path = output.clone();
+    if is_dir {
+        if !output.exists() {
+            create_dir_all(&output)?;
+        }
+        let mut base_name = output.as_os_str().to_os_string();
+        base_name.push(bootstrap.file_name().unwrap_or_default());
+        base_name.push(".tar");
+        tar_path = PathBuf::from(base_name);
+    }
+
+    Ok((is_dir, tar_path))
+}
+
 impl Unpacker for OCIUnpacker {
     fn unpack(&self, config: Arc<ConfigV2>) -> Result<()> {
         debug!(
-            "oci unpacker, bootstrap file: {:?}, output file: {:?}",
+            "oci unpacker, bootstrap file: {:?}, output path: {:?}",
             self.bootstrap, self.output
         );
 
         let rafs = self.load_rafs(config)?;
 
+        let (is_dir, tar_path) = get_unpack_path(self.bootstrap.clone(), self.output.clone())?;
+
         let mut builder = self
             .builder_factory
-            .create(&rafs, &self.blob_backend, &self.output)?;
+            .create(&rafs, &self.blob_backend, &tar_path)?;
 
         for (node, path) in RafsIterator::new(&rafs) {
             builder.append(node, &path)?;
         }
 
+        // untar this tar file to self.output dir
+        if is_dir {
+            let file = File::open(&tar_path)?;
+            let mut tar = Archive::new(file);
+            tar.unpack(&self.output)?;
+            remove_file(&tar_path)?;
+        }
+
+        info!("successfully unpack image to: {}", self.output.display());
         Ok(())
     }
 }
@@ -230,3 +261,34 @@ impl TarBuilder for OCITarBuilder {
         bail!("node {:?} can not be unpacked", path)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_get_unpack_path() {
+        let bootstrap = PathBuf::from("bootstrap");
+        let output = PathBuf::from("target.tar");
+        let (is_dir, tar_path) = get_unpack_path(bootstrap, output).unwrap();
+        assert!(!is_dir);
+        assert_eq!(tar_path, PathBuf::from("target.tar"));
+
+        let bootstrap = PathBuf::from("test/bootstrap");
+        let output = PathBuf::from("target/");
+        let (is_dir, tar_path) = get_unpack_path(bootstrap, output).unwrap();
+        assert!(is_dir);
+        assert_eq!(tar_path, PathBuf::from("target/bootstrap.tar"));
+
+        let bootstrap = PathBuf::from("/run/test/bootstrap.meta");
+        let output = PathBuf::from("target/");
+        let (is_dir, tar_path) = get_unpack_path(bootstrap, output).unwrap();
+        assert!(is_dir);
+        assert_eq!(tar_path, PathBuf::from("target/bootstrap.meta.tar"));
+
+        let bootstrap = PathBuf::from("/run/test/bootstrap.meta");
+        let output = PathBuf::from("/run/");
+        let (is_dir, tar_path) = get_unpack_path(bootstrap, output).unwrap();
+        assert!(is_dir);
+        assert_eq!(tar_path, PathBuf::from("/run/bootstrap.meta.tar"));
+    }
+}