tink template create now accepts data from STDIN (#133)

At present, we create a template as shown below:
```
$ tink template create --name example --path /tmp/example.tmpl 
```

With the code changes in place, a user can now pipe the template data from a file. For example, if the data is saved in `/tmp/example.tmpl`, you can create a template with either of the following:
```
$ cat /tmp/example.tmpl | tink template create -n example
$ tink template create --name example --path /tmp/example.tmpl
```

Signed-off-by: Gaurav Gahlot <[email protected]>

cmd/tink-cli/cmd/template/create.go

@@ -3,6 +3,7 @@ package template
 import (
 	"context"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
@@ -22,54 +23,80 @@ var (
 
 // createCmd represents the create subcommand for template command
 var createCmd = &cobra.Command{
-	Use:     "create",
-	Short:   "create a workflow template ",
-	Example: "tink template create [flags]",
+	Use:   "create",
+	Short: "create a workflow template ",
+	Example: `tink template create [flags]
+cat /tmp/example.tmpl | tink template create -n example`,
+	PreRunE: func(c *cobra.Command, args []string) error {
+		if !isInputFromPipe() {
+			path, _ := c.Flags().GetString(fPath)
+			if path == "" {
+				return fmt.Errorf("either pipe the template or provide the required '--path' flag")
+			}
+		}
+		return nil
+	},
 	Run: func(c *cobra.Command, args []string) {
-		validateTemplate()
-		createTemplate(c, args)
+		var reader io.Reader
+		if isInputFromPipe() {
+			reader = os.Stdin
+		} else {
+			f, err := os.Open(filePath)
+			if err != nil {
+				log.Println(err)
+			}
+			reader = f
+		}
+
+		data := readAll(reader)
+		if data != nil {
+			if err := tryParseTemplate(data); err != nil {
+				log.Println(err)
+				return
+			}
+			createTemplate(data)
+		}
 	},
 }
 
+func readAll(reader io.Reader) []byte {
+	data, err := ioutil.ReadAll(reader)
+	if err != nil {
+		log.Println(err)
+	}
+	return data
+}
+
 func addFlags() {
 	flags := createCmd.PersistentFlags()
 	flags.StringVarP(&filePath, "path", "p", "", "path to the template file")
 	flags.StringVarP(&templateName, "name", "n", "", "unique name for the template (alphanumeric)")
-
-	createCmd.MarkPersistentFlagRequired(fPath)
 	createCmd.MarkPersistentFlagRequired(fName)
 }
 
-func validateTemplate() {
-	_, err := tt.ParseFiles(filePath)
-	if err != nil {
-		log.Fatalln(err)
+func tryParseTemplate(data []byte) error {
+	tmpl := *tt.New("")
+	if _, err := tmpl.Parse(string(data)); err != nil {
+		return err
 	}
+	return nil
 }
 
-func readTemplateData() []byte {
-	f, err := os.Open(filePath)
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer f.Close()
-
-	data, err := ioutil.ReadAll(f)
-	if err != nil {
-		log.Fatal(err)
-	}
-	return data
-}
-
-func createTemplate(c *cobra.Command, args []string) {
-	req := template.WorkflowTemplate{Name: templateName, Data: readTemplateData()}
+func createTemplate(data []byte) {
+	req := template.WorkflowTemplate{Name: templateName, Data: data}
 	res, err := client.TemplateClient.CreateTemplate(context.Background(), &req)
 	if err != nil {
-		log.Fatal(err)
+		log.Println(err)
+		return
 	}
 	fmt.Println("Created Template: ", res.Id)
 }
 
+func isInputFromPipe() bool {
+	fileInfo, _ := os.Stdin.Stat()
+	return fileInfo.Mode()&os.ModeCharDevice == 0
+}
+
 func init() {
 	addFlags()
 	SubCommands = append(SubCommands, createCmd)

cmd/tink-cli/cmd/template/update.go

@@ -3,7 +3,9 @@ package template
 import (
 	"context"
 	"fmt"
+	"io/ioutil"
 	"log"
+	"os"
 
 	uuid "github.com/satori/go.uuid"
 	"github.com/spf13/cobra"
@@ -47,8 +49,14 @@ func updateTemplate(id string) {
 	if filePath == "" && templateName != "" {
 		req.Name = templateName
 	} else if filePath != "" && templateName == "" {
-		validateTemplate()
-		req.Data = readTemplateData()
+		data := readTemplateData()
+		if data != nil {
+			if err := tryParseTemplate(data); err != nil {
+				log.Println(err)
+				return
+			}
+			req.Data = data
+		}
 	} else {
 		req.Name = templateName
 		req.Data = readTemplateData()
@@ -61,6 +69,20 @@ func updateTemplate(id string) {
 	fmt.Println("Updated Template: ", id)
 }
 
+func readTemplateData() []byte {
+	f, err := os.Open(filePath)
+	if err != nil {
+		log.Println(err)
+	}
+	defer f.Close()
+
+	data, err := ioutil.ReadAll(f)
+	if err != nil {
+		log.Println(err)
+	}
+	return data
+}
+
 func init() {
 	flags := updateCmd.PersistentFlags()
 	flags.StringVarP(&filePath, "path", "p", "", "path to the template file")