Add previous container state manifest

This commit is a prerequisite to issue #4176 in the rpm-ostree repo,
implementing the `rpm-ostree upgrade --check` feature for ostree native
containers.

A previous_state `LayeredImageState` object is added to the
`PreparedImport` object, used to store the previous container state when
importing a container image.

A `export_as_string()` function is added to the `ManifestDiff` object to
allow rpm-ostree to print the manifest diff on the client side. The code
is exactly the same as the existing `print()` function for
`ManifestDiff`, except it returns a string instead of printing out the
diff in the terminal.

lib/src/cli.rs

@@ -16,7 +16,7 @@ use tokio::sync::mpsc::Receiver;
 
 use crate::commit::container_commit;
 use crate::container::store::{ImportProgress, LayerProgress, PreparedImport};
-use crate::container::{self as ostree_container};
+use crate::container::{self as ostree_container, ManifestDiff};
 use crate::container::{Config, ImageReference, OstreeImageReference};
 use ostree_container::store::{ImageImporter, PrepareResult};
 
@@ -613,6 +613,10 @@ async fn container_store(
     if let Some(warning) = prep.deprecated_warning() {
         print_deprecated_warning(warning).await;
     }
+    if let Some(previous_state) = prep.previous_state.as_ref() {
+        let diff = ManifestDiff::new(&previous_state.manifest, &prep.manifest);
+        diff.print();
+    }
     print_layer_status(&prep);
     let printer = (!quiet).then(|| {
         let layer_progress = imp.request_progress();

lib/src/container/mod.rs

@@ -324,6 +324,23 @@ impl<'a> ManifestDiff<'a> {
         println!("Removed layers:   {n_removed:<4}  Size: {removed_size_str}");
         println!("Added layers:     {n_added:<4}  Size: {added_size_str}");
     }
+
+    /// Exports the total, removed and added content between two OCI images as a string
+    pub fn export_as_string(&self) -> String {
+        fn layersum<'a, I: Iterator<Item = &'a oci_spec::image::Descriptor>>(layers: I) -> u64 {
+            layers.map(|layer| layer.size() as u64).sum()
+        }
+        let new_total = self.to.layers().len();
+        let new_total_size = glib::format_size(layersum(self.to.layers().iter()));
+        let n_removed = self.removed.len();
+        let n_added = self.added.len();
+        let removed_size = layersum(self.removed.iter().copied());
+        let removed_size_str = glib::format_size(removed_size);
+        let added_size = layersum(self.added.iter().copied());
+        let added_size_str = glib::format_size(added_size);
+        let result = format!("Total new layers: {new_total:<4}  Size: {new_total_size}\nRemoved layers:   {n_removed:<4}  Size: {removed_size_str}\nAdded layers:     {n_added:<4}  Size: {added_size_str}");
+        return result
+    }
 }
 
 /// Apply default configuration for container image pulls to an existing configuration.

lib/src/container/store.rs

@@ -191,6 +191,8 @@ pub struct PreparedImport {
     pub manifest: oci_image::ImageManifest,
     /// The deserialized configuration.
     pub config: oci_image::ImageConfiguration,
+    /// The previous manifest
+    pub previous_state: Option<Box<LayeredImageState>>,
     /// The previously stored manifest digest.
     pub previous_manifest_digest: Option<String>,
     /// The previously stored image ID.
@@ -532,7 +534,7 @@ impl ImageImporter {
 
         // Query for previous stored state
 
-        let (previous_manifest_digest, previous_imageid) =
+        let (previous_state, previous_imageid) =
             if let Some(previous_state) = try_query_image_ref(&self.repo, &self.imgref.imgref)? {
                 // If the manifest digests match, we're done.
                 if previous_state.manifest_digest == manifest_digest {
@@ -543,10 +545,8 @@ impl ImageImporter {
                 if previous_imageid == new_imageid {
                     return Ok(PrepareResult::AlreadyPresent(previous_state));
                 }
-                (
-                    Some(previous_state.manifest_digest),
-                    Some(previous_imageid.to_string()),
-                )
+                let previous_imageid = previous_imageid.to_string();
+                (Some(previous_state), Some(previous_imageid))
             } else {
                 (None, None)
             };
@@ -567,10 +567,12 @@ impl ImageImporter {
             .map(query)
             .collect::<Result<Vec<_>>>()?;
 
+        let previous_manifest_digest = previous_state.as_ref().map(|s| s.manifest_digest.clone());
         let imp = PreparedImport {
             manifest,
             manifest_digest,
             config,
+            previous_state,
             previous_manifest_digest,
             previous_imageid,
             ostree_layers: component_layers,