Merge pull request #9762 from jlowdermilk/negotiate-api-version

kubectl negotiates api version to use based on client,server supported versions

pkg/client/helper.go

@@ -30,8 +30,11 @@ import (
 	"time"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/latest"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/registered"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/runtime"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/version"
+	"github.com/golang/glog"
 )
 
 // Config holds the common attributes that can be passed to a Kubernetes client on
@@ -138,6 +141,9 @@ func New(c *Config) (*Client, error) {
 	return &Client{client}, nil
 }
 
+// MatchesServerVersion queries the server to compares the build version
+// (git hash) of the client with the server's build version. It returns an error
+// if it failed to contact the server or if the versions are not an exact match.
 func MatchesServerVersion(c *Config) error {
 	client, err := New(c)
 	if err != nil {
@@ -156,6 +162,66 @@ func MatchesServerVersion(c *Config) error {
 	return nil
 }
 
+// NegotiateVersion queries the server's supported api versions to find
+// a version that both client and server support.
+// - If no version is provided, try the client's registered versions in order of
+//   preference.
+// - If version is provided, but not default config (explicitly requested via
+//   commandline flag), and is unsupported by the server, print a warning to
+//   stderr and try client's registered versions in order of preference.
+// - If version is config default, and the server does not support it,
+//   return an error.
+func NegotiateVersion(c *Config, version string) (string, error) {
+	client, err := New(c)
+	if err != nil {
+		return "", err
+	}
+	clientVersions := util.StringSet{}
+	for _, v := range registered.RegisteredVersions {
+		clientVersions.Insert(v)
+	}
+	apiVersions, err := client.ServerAPIVersions()
+	if err != nil {
+		return "", fmt.Errorf("couldn't read version from server: %v\n", err)
+	}
+	serverVersions := util.StringSet{}
+	for _, v := range apiVersions.Versions {
+		serverVersions.Insert(v)
+	}
+	// If no version requested, use config version (may also be empty).
+	if len(version) == 0 {
+		version = c.Version
+	}
+	// If version explicitly requested verify that both client and server support it.
+	// If server does not support warn, but try to negotiate a lower version.
+	if len(version) != 0 {
+		if !clientVersions.Has(version) {
+			return "", fmt.Errorf("Client does not support API version '%s'. Client supported API versions: %v", version, clientVersions)
+
+		}
+		if serverVersions.Has(version) {
+			return version, nil
+		}
+		// If we are using an explicit config version the server does not support, fail.
+		if version == c.Version {
+			return "", fmt.Errorf("Server does not support API version '%s'.", version)
+		}
+	}
+
+	for _, clientVersion := range registered.RegisteredVersions {
+		if serverVersions.Has(clientVersion) {
+			// Version was not explicitly requested in command config (--api-version).
+			// Ok to fall back to a supported version with a warning.
+			if len(version) != 0 {
+				glog.Warningf("Server does not support API version '%s'. Falling back to '%s'.", version, clientVersion)
+			}
+			return clientVersion, nil
+		}
+	}
+	return "", fmt.Errorf("Failed to negotiate an api version. Server supports: %v. Client supports: %v.",
+		serverVersions, registered.RegisteredVersions)
+}
+
 // NewOrDie creates a Kubernetes client and panics if the provided API version is not recognized.
 func NewOrDie(c *Config) *Client {
 	client, err := New(c)