container: Add support for copying optionally-present keys

This is to aid coreos/coreos-assembler#3214
which is trying to inject the metadata key `fedora-coreos.stream`
into the container image.  However, this value will only be
present in Fedora derivatives, and not RHEL/CentOS.

Add support for copying a key only if present, instead of
erroring if it's missing.

lib/src/cli.rs

@@ -126,6 +126,10 @@ pub(crate) enum ContainerOpts {
         #[clap(name = "copymeta", long)]
         copy_meta_keys: Vec<String>,
 
+        /// Propagate an optionally-present OSTree commit metadata key to container label
+        #[clap(name = "copymeta-opt", long)]
+        copy_meta_opt_keys: Vec<String>,
+
         /// Corresponds to the Dockerfile `CMD` instruction.
         #[clap(long)]
         cmd: Option<Vec<String>>,
@@ -531,12 +535,14 @@ async fn container_import(
 }
 
 /// Export a container image with an encapsulated ostree commit.
+#[allow(clippy::too_many_arguments)]
 async fn container_export(
     repo: &ostree::Repo,
     rev: &str,
     imgref: &ImageReference,
     labels: BTreeMap<String, String>,
     copy_meta_keys: Vec<String>,
+    copy_meta_opt_keys: Vec<String>,
     cmd: Option<Vec<String>>,
     compression_fast: bool,
 ) -> Result<()> {
@@ -546,6 +552,7 @@ async fn container_export(
     };
     let opts = crate::container::ExportOpts {
         copy_meta_keys,
+        copy_meta_opt_keys,
         skip_compression: compression_fast, // TODO rename this in the struct at the next semver break
         ..Default::default()
     };
@@ -723,6 +730,7 @@ where
                 imgref,
                 labels,
                 copy_meta_keys,
+                copy_meta_opt_keys,
                 cmd,
                 compression_fast,
             } => {
@@ -742,6 +750,7 @@ where
                     &imgref,
                     labels?,
                     copy_meta_keys,
+                    copy_meta_opt_keys,
                     cmd,
                     compression_fast,
                 )

lib/src/container/encapsulate.rs

@@ -65,6 +65,7 @@ pub struct Config {
 fn commit_meta_to_labels<'a>(
     meta: &glib::VariantDict,
     keys: impl IntoIterator<Item = &'a str>,
+    opt_keys: impl IntoIterator<Item = &'a str>,
     labels: &mut HashMap<String, String>,
 ) -> Result<()> {
     for k in keys {
@@ -74,6 +75,14 @@ fn commit_meta_to_labels<'a>(
             .ok_or_else(|| anyhow!("Could not find commit metadata key: {}", k))?;
         labels.insert(k.to_string(), v);
     }
+    for k in opt_keys {
+        let v = meta
+            .lookup::<String>(k)
+            .context("Expected string for commit metadata value")?;
+        if let Some(v) = v {
+            labels.insert(k.to_string(), v);
+        }
+    }
     // Copy standard metadata keys `ostree.bootable` and `ostree.linux`.
     // Bootable is an odd one out in being a boolean.
     if let Some(v) = meta.lookup::<bool>(*ostree::METADATA_KEY_BOOTABLE)? {
@@ -217,6 +226,7 @@ fn build_oci(
     commit_meta_to_labels(
         &commit_meta,
         opts.copy_meta_keys.iter().map(|k| k.as_str()),
+        opts.copy_meta_opt_keys.iter().map(|k| k.as_str()),
         labels,
     )?;
 
@@ -361,6 +371,8 @@ pub struct ExportOpts {
     pub skip_compression: bool,
     /// A set of commit metadata keys to copy as image labels.
     pub copy_meta_keys: Vec<String>,
+    /// A set of optionally-present commit metadata keys to copy as image labels.
+    pub copy_meta_opt_keys: Vec<String>,
     /// Maximum number of layers to use
     pub max_layers: Option<NonZeroU32>,
     /// The container image layout

lib/tests/it/main.rs

@@ -525,6 +525,7 @@ async fn impl_test_container_import_export(
         .transpose()?;
     let opts = ExportOpts {
         copy_meta_keys: vec!["buildsys.checksum".to_string()],
+        copy_meta_opt_keys: vec!["nosuchvalue".to_string()],
         format: export_format,
         ..Default::default()
     };