Platforms: Add From/ToProto helpers for types

Helpers to convert from a slice of platforms to our protobuf representation
and vice-versa appear a couple times. It seems sane to just expose this facility
in the platforms pkg.

Signed-off-by: Danny Canter <danny@dcantah.dev>

services/introspection/local.go

@@ -24,9 +24,9 @@ import (
 	"sync"
 
 	api "github.com/containerd/containerd/api/services/introspection/v1"
-	"github.com/containerd/containerd/api/types"
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/filters"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	ptypes "github.com/containerd/containerd/protobuf/types"
 	"github.com/containerd/containerd/services"
@@ -189,15 +189,6 @@ func adaptPlugin(o interface{}) filters.Adaptor {
 func pluginsToPB(plugins []*plugin.Plugin) []*api.Plugin {
 	var pluginsPB []*api.Plugin
 	for _, p := range plugins {
-		var platforms []*types.Platform
-		for _, p := range p.Meta.Platforms {
-			platforms = append(platforms, &types.Platform{
-				OS:           p.OS,
-				Architecture: p.Architecture,
-				Variant:      p.Variant,
-			})
-		}
-
 		var requires []string
 		for _, r := range p.Registration.Requires {
 			requires = append(requires, r.String())
@@ -231,7 +222,7 @@ func pluginsToPB(plugins []*plugin.Plugin) []*api.Plugin {
 			Type:         p.Registration.Type.String(),
 			ID:           p.Registration.ID,
 			Requires:     requires,
-			Platforms:    platforms,
+			Platforms:    platforms.ToProto(p.Meta.Platforms),
 			Capabilities: p.Meta.Capabilities,
 			Exports:      p.Meta.Exports,
 			InitErr:      initErr,