[WIP] Dynamically download kubectl client

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/spf13/cobra v1.0.0
 	github.com/stretchr/testify v1.5.1
 	github.com/xeipuuv/gojsonschema v1.2.0
+	golang.org/x/mod v0.2.0
 	gopkg.in/yaml.v2 v2.2.4
 )
 

go.sum

@@ -464,6 +464,7 @@ golang.org/x/lint v0.0.0-20190301231843-5614ed5bae6f/go.mod h1:UVdnD1Gm6xHRNCYTk
 golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
 golang.org/x/lint v0.0.0-20190930215403-16217165b5de/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
 golang.org/x/mod v0.0.0-20190513183733-4bf6d317e70e/go.mod h1:mXi4GBBbnImb6dmsKGUJ2LatrhH/nqhxcFungHvyanc=
+golang.org/x/mod v0.2.0 h1:KU7oHjnv3XNWfa5COkzUifxZmxp1TyI7ImMXqFxLwvQ=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20170114055629-f2499483f923/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180218175443-cbe0f9307d01/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=

pkg/kubernetes/helpers.go

@@ -11,6 +11,8 @@ type TestMixin struct {
 	TestContext *context.TestContext
 }
 
+const MockkubectlClientVersion string = "v1.15.5"
+
 func NewTestMixin(t *testing.T) *TestMixin {
 	c := context.NewTestContext(t)
 	m := New()

pkg/kubernetes/init.go

@@ -0,0 +1,127 @@
+package kubernetes
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"time"
+
+	"github.com/pkg/errors"
+	"golang.org/x/mod/semver"
+)
+
+type KubectlVersion struct {
+	ClientVersion struct {
+		Major        string    `json:"major"`
+		Minor        string    `json:"minor"`
+		GitVersion   string    `json:"gitVersion"`
+		GitCommit    string    `json:"gitCommit"`
+		GitTreeState string    `json:"gitTreeState"`
+		BuildDate    time.Time `json:"buildDate"`
+		GoVersion    string    `json:"goVersion"`
+		Compiler     string    `json:"compiler"`
+		Platform     string    `json:"platform"`
+	} `json:"clientVersion"`
+	ServerVersion struct {
+		Major        string    `json:"major"`
+		Minor        string    `json:"minor"`
+		GitVersion   string    `json:"gitVersion"`
+		GitCommit    string    `json:"gitCommit"`
+		GitTreeState string    `json:"gitTreeState"`
+		BuildDate    time.Time `json:"buildDate"`
+		GoVersion    string    `json:"goVersion"`
+		Compiler     string    `json:"compiler"`
+		Platform     string    `json:"platform"`
+	} `json:"serverVersion"`
+}
+
+func (m *Mixin) init() error {
+
+	serverVersion, err := getServerVersion(m)
+
+	if err != nil {
+		return err
+	}
+
+	if semver.Compare(m.KubernetesClientVersion, serverVersion) == -1 && serverVersion != "" {
+
+		// Here we are triggering the download
+		fmt.Fprintf(m.Out, "Kubectl server version (%s) does not match client version (%s); downloading a compatible client.\n",
+			serverVersion, m.KubernetesClientVersion)
+		// try to install the new client
+		err := installClient(m, serverVersion)
+		if err != nil {
+			return errors.Wrap(err, "unable to install a compatible kubectl client")
+		}
+	}
+
+	return err
+}
+
+func installClient(m *Mixin, version string) error {
+
+	url := fmt.Sprintf("https://storage.googleapis.com/kubernetes-release/release/%s/bin/linux/amd64/kubectl", version)
+
+	// Fetch kubectl from url
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return errors.Wrap(err, "failed to construct GET request for fetching kubectl client binary")
+	}
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return errors.Wrapf(err, "failed to download kubectl client binary via url: %s", url)
+	}
+	defer res.Body.Close()
+
+	// Create a temp dir
+	tmpDir, err := m.FileSystem.TempDir("", "tmp")
+	if err != nil {
+		return errors.Wrap(err, "unable to create a temporary directory for downloading the kubectl client binary")
+	}
+	defer os.RemoveAll(tmpDir)
+
+	// Create the local binary
+	kubectlBinPath, err := m.FileSystem.Create(filepath.Join(tmpDir, "kubectlBin"))
+	if err != nil {
+		return errors.Wrap(err, "unable to create a local file for the kubectl client binary")
+	}
+
+	// Copy response body to local binary
+	_, err = io.Copy(kubectlBinPath, res.Body)
+	if err != nil {
+		return errors.Wrap(err, "unable to copy the kubectl client binary to the local binary file")
+	}
+
+	// Move the kubectl binary into the appropriate location
+	binPath := "/usr/local/bin/kubectl"
+	err = m.FileSystem.Rename(fmt.Sprintf("%s", kubectlBinPath.Name()), binPath)
+	if err != nil {
+		return errors.Wrapf(err, "unable to install the kubectl client binary to %q", binPath)
+	}
+	return nil
+}
+
+func getServerVersion(m *Mixin) (string, error) {
+
+	var stderr bytes.Buffer
+	currentKubectl := KubectlVersion{}
+
+	cmd := exec.Command("kubectl", "version", "-o", "json")
+	cmd.Stderr = &stderr
+	// Execute the command and the version output
+	outputBytes, err := cmd.Output()
+	if err != nil {
+		return "", errors.Wrapf(err, "unable to determine kubernetes server version: %s", stderr.String())
+	}
+	// Rebuild version json object
+	json.Unmarshal(outputBytes, &currentKubectl)
+
+	version := currentKubectl.ServerVersion.GitVersion
+
+	return version, nil
+}

pkg/kubernetes/kubernetes.go

@@ -1,5 +1,4 @@
 //go:generate packr2
-
 package kubernetes
 
 import (