rust/rpmostree-client: parse OCI deployment manifest

When the deployment is an OCI image, the base_commit_meta
field contains nested escaped JSON.

Add a method to get the base oci manifest deserialized into an
ImageManifest from the oci-spec rust crate.

Fixes #5196

rust/rpmostree-client/Cargo.toml

@@ -12,6 +12,7 @@ publish = false
 
 [dependencies]
 anyhow = "1.0.94"
+oci-spec = "0.7.1"
 serde = { version = "1.0.217", features = ["derive"] }
 serde_derive = "1.0.118"
 serde_json = "1.0.135"

rust/rpmostree-client/src/lib.rs

@@ -2,7 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use anyhow::Context;
-use serde_derive::Deserialize;
+use oci_spec;
+use serde::Deserialize;
 use std::collections::HashMap;
 use std::process::Command;
 
@@ -97,6 +98,22 @@ impl Deployment {
             Err(format!("No {} metadata key", k).into())
         }
     }
+
+    pub fn get_base_manifest(&self) -> Result<Option<oci_spec::image::ImageManifest>> {
+        if self.container_image_reference.is_none() {
+            return Ok(None);
+        }
+
+        let manifest = self.base_commit_meta.get("ostree.manifest");
+        if let Some(inner) = manifest {
+            let deser = String::deserialize(inner)?;
+            let manifest: oci_spec::image::ImageManifest = serde_json::from_str(deser.as_str())?;
+
+            return Ok(Some(manifest));
+        };
+
+        Ok(None)
+    }
 }
 
 impl CliClient {