Resolve api spec based on swagger version

Currently the Kubernetes API version used is defaulted to 1.7.0 if the
--api-spec flag is not populated. This change will attempt to retrieve
the swagger.json version of the server instead.

Signed-off-by: Jessica Yuen <im.jessicayuen@gmail.com>

client/client.go

@@ -16,9 +16,15 @@
 package client
 
 import (
+	"encoding/json"
 	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
 	"os"
+	"path"
 	"reflect"
+	"time"
 
 	"github.com/ksonnet/ksonnet/metadata"
 	str "github.com/ksonnet/ksonnet/strings"
@@ -61,6 +67,59 @@ func InitClient(env string) (dynamic.ClientPool, discovery.DiscoveryInterface, s
 	return clientConfig.RestClient(&env)
 }
 
+// GetAPISpec reads the kubernetes API version from this client's swagger.json.
+// We anticipate the swagger.json to be located at <server>/swagger.json.
+// If no swagger is found, or we are unable to authenticate to the server, we
+// will default to version:v1.7.0.
+func (c *Config) GetAPISpec(server string) string {
+	const (
+		defaultVersion = "version:v1.7.0"
+	)
+
+	type Info struct {
+		Version string `json:"version"`
+	}
+
+	type Spec struct {
+		Info Info `json:"info"`
+	}
+
+	u, err := url.Parse(server)
+	u.Path = path.Join(u.Path, "swagger.json")
+	url := u.String()
+
+	client := http.Client{
+		Timeout: time.Second * 2,
+	}
+
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		log.Debugf("Failed to create request at %s\n%s", url, err.Error())
+		return defaultVersion
+	}
+
+	res, err := client.Do(req)
+	if err != nil {
+		log.Debugf("Failed to open swagger at %s\n%s", url, err.Error())
+		return defaultVersion
+	}
+
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		log.Debugf("Failed to read swagger at %s\n%s", url, err.Error())
+		return defaultVersion
+	}
+
+	spec := Spec{}
+	jsonErr := json.Unmarshal(body, &spec)
+	if jsonErr != nil {
+		log.Debugf("Failed to parse swagger at %s\n%s", url, err.Error())
+		return defaultVersion
+	}
+
+	return fmt.Sprintf("version:%s", spec.Info.Version)
+}
+
 // Namespace returns the namespace for the provided ClientConfig.
 func (c *Config) Namespace() (string, error) {
 	ns, _, err := c.Config.Namespace()

cmd/env.go

@@ -140,6 +140,9 @@ var envAddCmd = &cobra.Command{
 		if err != nil {
 			return err
 		}
+		if specFlag == "" {
+			specFlag = envClientConfig.GetAPISpec(server)
+		}
 
 		c, err := kubecfg.NewEnvAddCmd(name, server, namespace, specFlag, manager)
 		if err != nil {

cmd/init.go

@@ -23,7 +23,6 @@ import (
 
 	"github.com/ksonnet/ksonnet/client"
 	"github.com/ksonnet/ksonnet/pkg/kubecfg"
-	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 )
 
@@ -39,7 +38,7 @@ var (
 func init() {
 	RootCmd.AddCommand(initCmd)
 	// TODO: We need to make this default to checking the `kubeconfig` file.
-	initCmd.PersistentFlags().String(flagAPISpec, "version:v1.7.0",
+	initCmd.PersistentFlags().String(flagAPISpec, "",
 		"Manually specified Kubernetes API version. The corresponding OpenAPI spec is used to generate ksonnet's Kubernetes libraries")
 
 	initClientConfig = client.NewDefaultClientConfig()
@@ -72,17 +71,19 @@ var initCmd = &cobra.Command{
 			return err
 		}
 
-		specFlag, err := flags.GetString(flagAPISpec)
+		server, namespace, err := resolveEnvFlags(flags)
 		if err != nil {
 			return err
 		}
 
-		server, namespace, err := resolveEnvFlags(flags)
+		specFlag, err := flags.GetString(flagAPISpec)
 		if err != nil {
 			return err
 		}
+		if specFlag == "" {
+			specFlag = initClientConfig.GetAPISpec(server)
+		}
 
-		log.Infof("Creating a new app '%s' at path '%s'", appName, appRoot)
 		c, err := kubecfg.NewInitCmd(appName, appRoot, &specFlag, &server, &namespace)
 		if err != nil {
 			return err

docs/cli-reference/ks_init.md

@@ -81,7 +81,7 @@ ks init app-name --dir=custom-location
 ### Options
 
 ```
-      --api-spec string                Manually specified Kubernetes API version. The corresponding OpenAPI spec is used to generate ksonnet's Kubernetes libraries (default "version:v1.7.0")
+      --api-spec string                Manually specified Kubernetes API version. The corresponding OpenAPI spec is used to generate ksonnet's Kubernetes libraries
       --as string                      Username to impersonate for the operation
       --as-group stringArray           Group to impersonate for the operation, this flag can be repeated to specify multiple groups.
       --certificate-authority string   Path to a cert file for the certificate authority