feat: oci: support --env option in --oci mode

* Merge image config ENV and env vars requested by user with the --env
  CLI option.
* Set default SINGULARITY_CONTAINER and SINGULARITY_NAME env variables.
* Set default LD_LIBRARY_PATH to be used later for library
  injection (this is a singularity default).

Fixes sylabs#1029

internal/pkg/runtime/launcher/oci/launcher_linux.go

@@ -127,9 +127,6 @@ func checkOpts(lo launcher.Options) error {
 		badOpt = append(badOpt, "Proot")
 	}
 
-	if len(lo.Env) > 0 {
-		badOpt = append(badOpt, "Env")
-	}
 	if lo.EnvFile != "" {
 		badOpt = append(badOpt, "EnvFile")
 	}
@@ -230,8 +227,9 @@ func checkOpts(lo launcher.Options) error {
 }
 
 // createSpec produces an OCI runtime specification, suitable to launch a
-// container. This spec excludes ProcessArgs, as these have to be computed where
-// the image config is available, to account for the image's CMD / ENTRYPOINT.
+// container. This spec excludes ProcessArgs and Env, as these have to be
+// computed where the image config is available, to account for the image's CMD
+// / ENTRYPOINT / ENV.
 func (l *Launcher) createSpec() (*specs.Spec, error) {
 	spec := minimalSpec()
 
@@ -318,12 +316,20 @@ func (l *Launcher) Exec(ctx context.Context, image string, process string, args
 		return fmt.Errorf("while creating OCI spec: %w", err)
 	}
 
+	// Assemble the runtime & user-requested environment, which will be merged
+	// with the image ENV and set in the container at runtime.
+	rtEnv := defaultEnv(image, bundleDir)
+	// --env flag
+	rtEnv = mergeMap(rtEnv, l.cfg.Env)
+	// TODO - --env-file, SINGULARITYENV_
+
 	b, err := native.New(
 		native.OptBundlePath(bundleDir),
 		native.OptImageRef(image),
 		native.OptSysCtx(sysCtx),
 		native.OptImgCache(imgCache),
 		native.OptProcessArgs(process, args),
+		native.OptProcessEnv(rtEnv),
 	)
 	if err != nil {
 		return err
@@ -351,3 +357,10 @@ func (l *Launcher) Exec(ctx context.Context, image string, process string, args
 	}
 	return err
 }
+
+func mergeMap(a map[string]string, b map[string]string) map[string]string {
+	for k, v := range b {
+		a[k] = v
+	}
+	return a
+}

internal/pkg/runtime/launcher/oci/process_linux.go

@@ -137,3 +137,12 @@ func (l *Launcher) getReverseUserMaps() (uidMap, gidMap []specs.LinuxIDMapping,
 
 	return uidMap, gidMap, nil
 }
+
+// defaultEnv returns default environment variables set in the container.
+func defaultEnv(image, bundle string) map[string]string {
+	return map[string]string{
+		"LD_LIBRARY_PATH":       "/.singularity.d/libs",
+		"SINGULARITY_CONTAINER": bundle,
+		"SINGULARITY_NAME":      image,
+	}
+}

pkg/ocibundle/native/bundle_linux.go

@@ -53,6 +53,8 @@ type Bundle struct {
 	process string
 	// args are the command arguments, which may override the image's CMD.
 	args []string
+	// env is the container environment to set, which will be merged with the image's env.
+	env map[string]string
 	// Generic bundle properties
 	ocibundle.Bundle
 }
@@ -104,6 +106,14 @@ func OptProcessArgs(process string, args []string) Option {
 	}
 }
 
+// OptEnv sets the environment to be set, merged with the image ENV.
+func OptProcessEnv(env map[string]string) Option {
+	return func(b *Bundle) error {
+		b.env = env
+		return nil
+	}
+}
+
 // New returns a bundle interface to create/delete an OCI bundle from an OCI image ref.
 func New(opts ...Option) (ocibundle.Bundle, error) {
 	b := Bundle{
@@ -156,6 +166,8 @@ func (b *Bundle) Create(ctx context.Context, ociConfig *specs.Spec) error {
 	// consult the image Config to handle combining ENTRYPOINT/CMD with user
 	// provided args.
 	b.setProcessArgs(g)
+	// Ditto for environment handling (merge image and user/rt requested).
+	b.setProcessEnv(g)
 
 	return b.writeConfig(g)
 }
@@ -185,6 +197,20 @@ func (b *Bundle) setProcessArgs(g *generate.Generator) {
 	g.SetProcessArgs(processArgs)
 }
 
+func (b *Bundle) setProcessEnv(g *generate.Generator) {
+	if g.Config == nil {
+		g.Config = &specs.Spec{}
+	}
+	if g.Config.Process == nil {
+		g.Config.Process = &specs.Process{}
+	}
+	g.Config.Process.Env = b.imageSpec.Config.Env
+
+	for k, v := range b.env {
+		g.AddProcessEnv(k, v)
+	}
+}
+
 func (b *Bundle) writeConfig(g *generate.Generator) error {
 	return tools.SaveBundleConfig(b.bundlePath, g)
 }