oci: introduce WithSpecFromFile combinator

We introduce a WithSpecFromFile option combinator to allow creation
simpler creation of OCI specs from a file name. Often used as the first
option in a `SpecOpts` slice, it simplifies choosing between a local
file and the built-in default.

The code in `ctr run` has been updated to use the new option, with out
changing the order of operations or functionality present there.

Signed-off-by: Stephen Day <stephen.day@getcruise.com>

cmd/ctr/commands/run/run.go

@@ -19,9 +19,7 @@ package run
 import (
 	gocontext "context"
 	"encoding/csv"
-	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"strings"
 
 	"github.com/containerd/console"
@@ -37,17 +35,6 @@ import (
 	"github.com/urfave/cli"
 )
 
-func loadSpec(path string, s *specs.Spec) error {
-	raw, err := ioutil.ReadFile(path)
-	if err != nil {
-		return errors.New("cannot load spec config file")
-	}
-	if err := json.Unmarshal(raw, s); err != nil {
-		return errors.Errorf("decoding spec config file failed, current supported OCI runtime-spec : v%s", specs.Version)
-	}
-	return nil
-}
-
 func withMounts(context *cli.Context) oci.SpecOpts {
 	return func(ctx gocontext.Context, client oci.Client, container *containers.Container, s *specs.Spec) error {
 		mounts := make([]specs.Mount, 0)

cmd/ctr/commands/run/run_unix.go

@@ -52,6 +52,13 @@ func NewContainer(ctx gocontext.Context, client *containerd.Client, context *cli
 		cOpts []containerd.NewContainerOpts
 		spec  containerd.NewContainerOpts
 	)
+
+	if context.IsSet("config") {
+		opts = append(opts, oci.WithSpecFromFile(context.String("config")))
+	} else {
+		opts = append(opts, oci.WithDefaultSpec())
+	}
+
 	opts = append(opts, oci.WithEnv(context.StringSlice("env")))
 	opts = append(opts, withMounts(context))
 	cOpts = append(cOpts, containerd.WithContainerLabels(commands.LabelArgs(context.StringSlice("label"))))
@@ -117,15 +124,10 @@ func NewContainer(ctx gocontext.Context, client *containerd.Client, context *cli
 	if context.IsSet("gpus") {
 		opts = append(opts, nvidia.WithGPUs(nvidia.WithDevices(context.Int("gpus")), nvidia.WithAllCapabilities))
 	}
-	if context.IsSet("config") {
-		var s specs.Spec
-		if err := loadSpec(context.String("config"), &s); err != nil {
-			return nil, err
-		}
-		spec = containerd.WithSpec(&s, opts...)
-	} else {
-		spec = containerd.WithNewSpec(opts...)
-	}
+
+	var s specs.Spec
+	spec = containerd.WithSpec(&s, opts...)
+
 	cOpts = append(cOpts, spec)
 
 	// oci.WithImageConfig (WithUsername, WithUserID) depends on rootfs snapshot for resolving /etc/passwd.

cmd/ctr/commands/run/run_windows.go

@@ -63,6 +63,13 @@ func NewContainer(ctx gocontext.Context, client *containerd.Client, context *cli
 		cOpts []containerd.NewContainerOpts
 		spec  containerd.NewContainerOpts
 	)
+
+	if context.IsSet("config") {
+		opts = append(opts, oci.WithSpecFromFile(context.String("config")))
+	} else {
+		opts = append(opts, oci.WithDefaultSpec())
+	}
+
 	opts = append(opts, oci.WithImageConfig(image))
 	opts = append(opts, oci.WithEnv(context.StringSlice("env")))
 	opts = append(opts, withMounts(context))
@@ -74,15 +81,8 @@ func NewContainer(ctx gocontext.Context, client *containerd.Client, context *cli
 		opts = append(opts, oci.WithProcessCwd(cwd))
 	}
 
-	if context.IsSet("config") {
-		var s specs.Spec
-		if err := loadSpec(context.String("config"), &s); err != nil {
-			return nil, err
-		}
-		spec = containerd.WithSpec(&s, opts...)
-	} else {
-		spec = containerd.WithNewSpec(opts...)
-	}
+	var s specs.Spec
+	spec = containerd.WithSpec(&s, opts...)
 
 	cOpts = append(cOpts, containerd.WithContainerLabels(commands.LabelArgs(context.StringSlice("label"))))
 	cOpts = append(cOpts, containerd.WithImage(image))