Ability to override version of terraform used

README.md

@@ -39,7 +39,7 @@ Execute from the working directory:
 docker run --rm \
   -v $(pwd):$(pwd) \
   -w $(pwd) \
-  jmccann/drone-terraform:1 --plan
+  jmccann/drone-terraform:latest --plan
 ```
 
 ## Drone 0.4

main.go

@@ -90,6 +90,11 @@ func main() {
 			Usage:  "destory all resurces",
 			EnvVar: "PLUGIN_DESTROY",
 		},
+		cli.StringFlag{
+			Name:   "tf.version",
+			Usage:  "terraform version to use",
+			EnvVar: "PLUGIN_TF_VERSION",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -137,6 +142,9 @@ func run(c *cli.Context) error {
 			VarFiles:    c.StringSlice("var_files"),
 			Destroy:     c.Bool("destroy"),
 		},
+		Terraform: Terraform{
+			Version: c.String("tf.version"),
+		},
 	}
 
 	return plugin.Exec()

plugin.go

@@ -43,17 +43,29 @@ type (
 	// Plugin represents the plugin instance to be executed
 	Plugin struct {
 		Config    Config
+		Terraform Terraform
 	}
 )
 
 // Exec executes the plugin
 func (p Plugin) Exec() error {
+	// Install specified version of terraform
+	if p.Terraform.Version != "" {
+		err := installTerraform(p.Terraform.Version)
+
+		if err != nil {
+			return err
+		}
+	}
+
 	if p.Config.RoleARN != "" {
 		assumeRole(p.Config.RoleARN)
 	}
 
 	var commands []*exec.Cmd
 
+	commands = append(commands, exec.Command("terraform", "version"))
+
 	CopyTfEnv()
 
 	if p.Config.Cacert != "" {

terraform.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"archive/zip"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+)
+
+type (
+	// Terraform holds input parameters for terraform
+	Terraform struct {
+		Version string
+	}
+)
+
+func installTerraform(version string) error {
+	err := downloadTerraform(version)
+	if err != nil {
+		return nil
+	}
+
+	return Unzip("/var/tmp/terraform.zip", "/bin")
+}
+
+func downloadTerraform(version string) error {
+	return downloadFile("/var/tmp/terraform.zip", fmt.Sprintf("https://releases.hashicorp.com/terraform/%s/terraform_%s_linux_amd64.zip", version, version))
+}
+
+func downloadFile(filepath string, url string) error {
+	// Create the file
+	out, err := os.Create(filepath)
+	if err != nil  {
+		return err
+	}
+	defer out.Close()
+
+	// Get the data
+	resp, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	// Writer the body to file
+	_, err = io.Copy(out, resp.Body)
+	if err != nil  {
+		return err
+	}
+
+	return nil
+}
+
+func Unzip(src, dest string) error {
+	r, err := zip.OpenReader(src)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err := r.Close(); err != nil {
+			panic(err)
+		}
+	}()
+
+	os.MkdirAll(dest, 0755)
+
+	// Closure to address file descriptors issue with all the deferred .Close() methods
+	extractAndWriteFile := func(f *zip.File) error {
+		rc, err := f.Open()
+		if err != nil {
+			return err
+		}
+		defer func() {
+			if err := rc.Close(); err != nil {
+				panic(err)
+			}
+		}()
+
+		path := filepath.Join(dest, f.Name)
+
+		if f.FileInfo().IsDir() {
+			os.MkdirAll(path, f.Mode())
+		} else {
+			os.MkdirAll(filepath.Dir(path), f.Mode())
+			f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
+			if err != nil {
+				return err
+			}
+			defer func() {
+				if err := f.Close(); err != nil {
+					panic(err)
+				}
+			}()
+
+			_, err = io.Copy(f, rc)
+			if err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	for _, f := range r.File {
+		err := extractAndWriteFile(f)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}