LCOW: API: Add platform to /images/create and /build

Signed-off-by: John Howard <jhoward@microsoft.com>

This PR has the API changes described in https://github.com/moby/moby/issues/34617.
Specifically, it adds an HTTP header "X-Requested-Platform" which is a JSON-encoded
OCI Image-spec `Platform` structure.

In addition, it renames (almost all) uses of a string variable platform (and associated)
methods/functions to os. This makes it much clearer to disambiguate with the swarm
"platform" which is really os/arch. This is a stepping stone to getting the daemon towards
fully multi-platform/arch-aware, and makes it clear when "operating system" is being
referred to rather than "platform" which is misleadingly used - sometimes in the swarm
meaning, but more often as just the operating system.
Upstream-commit: 0380fbff37922cadf294851b1546f4c212c7f364
Component: engine

components/engine/pkg/system/init_windows.go

@@ -2,17 +2,16 @@ package system
 
 import "os"
 
-// LCOWSupported determines if Linux Containers on Windows are supported.
-// Note: This feature is in development (06/17) and enabled through an
-// environment variable. At a future time, it will be enabled based
-// on build number. @jhowardmsft
+// lcowSupported determines if Linux Containers on Windows are supported.
 var lcowSupported = false
 
 // InitLCOW sets whether LCOW is supported or not
+// TODO @jhowardmsft.
+// 1. Replace with RS3 RTM build number.
+// 2. Remove the getenv check when image-store is coalesced as shouldn't be needed anymore.
 func InitLCOW(experimental bool) {
-	// LCOW initialization
-	if experimental && os.Getenv("LCOW_SUPPORTED") != "" {
+	v := GetOSVersion()
+	if experimental && v.Build > 16270 && os.Getenv("LCOW_SUPPORTED") != "" {
 		lcowSupported = true
 	}
-
 }

components/engine/pkg/system/lcow.go

@@ -0,0 +1,71 @@
+package system
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+
+	specs "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// IsPlatformEmpty determines if an OCI image-spec platform structure is not populated.
+// TODO This is a temporary function - can be replaced by parsing from
+// https://github.com/containerd/containerd/pull/1403/files at a later date.
+// @jhowardmsft
+func IsPlatformEmpty(platform specs.Platform) bool {
+	if platform.Architecture == "" &&
+		platform.OS == "" &&
+		len(platform.OSFeatures) == 0 &&
+		platform.OSVersion == "" &&
+		platform.Variant == "" {
+		return true
+	}
+	return false
+}
+
+// ValidatePlatform determines if a platform structure is valid.
+// TODO This is a temporary function - can be replaced by parsing from
+// https://github.com/containerd/containerd/pull/1403/files at a later date.
+// @jhowardmsft
+func ValidatePlatform(platform *specs.Platform) error {
+	platform.Architecture = strings.ToLower(platform.Architecture)
+	platform.OS = strings.ToLower(platform.OS)
+	if platform.Architecture != "" && platform.Architecture != runtime.GOARCH {
+		return fmt.Errorf("invalid platform architecture %q", platform.Architecture)
+	}
+	if platform.OS != "" {
+		if !(platform.OS == runtime.GOOS || (LCOWSupported() && platform.OS == "linux")) {
+			return fmt.Errorf("invalid platform os %q", platform.OS)
+		}
+	}
+	if len(platform.OSFeatures) != 0 {
+		return fmt.Errorf("invalid platform osfeatures %q", platform.OSFeatures)
+	}
+	if platform.OSVersion != "" {
+		return fmt.Errorf("invalid platform osversion %q", platform.OSVersion)
+	}
+	if platform.Variant != "" {
+		return fmt.Errorf("invalid platform variant %q", platform.Variant)
+	}
+	return nil
+}
+
+// ParsePlatform parses a platform string in the format os[/arch[/variant]
+// into an OCI image-spec platform structure.
+// TODO This is a temporary function - can be replaced by parsing from
+// https://github.com/containerd/containerd/pull/1403/files at a later date.
+// @jhowardmsft
+func ParsePlatform(in string) *specs.Platform {
+	p := &specs.Platform{}
+	elements := strings.SplitN(strings.ToLower(in), "/", 3)
+	if len(elements) == 3 {
+		p.Variant = elements[2]
+	}
+	if len(elements) >= 2 {
+		p.Architecture = elements[1]
+	}
+	if len(elements) >= 1 {
+		p.OS = elements[0]
+	}
+	return p
+}

components/engine/pkg/system/path.go

@@ -14,9 +14,9 @@ const defaultUnixPathEnv = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/s
 // DefaultPathEnv is unix style list of directories to search for
 // executables. Each directory is separated from the next by a colon
 // ':' character .
-func DefaultPathEnv(platform string) string {
+func DefaultPathEnv(os string) string {
 	if runtime.GOOS == "windows" {
-		if platform != runtime.GOOS && LCOWSupported() {
+		if os != runtime.GOOS {
 			return defaultUnixPathEnv
 		}
 		// Deliberately empty on Windows containers on Windows as the default path will be set by