Make CLI functions return error instead of fatal out (#1379)

Before this PR, CLI functions fatal out when encountering error
instead of returning it. Such behavior makes it hard to reuse 
the functions nor writing unit tests. This PR aims to make functions 
return errors instead of error out.

pkg/fission-cli/cmd/package/util/util.go

@@ -26,11 +26,11 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/pkg/errors"
 	uuid "github.com/satori/go.uuid"
 
 	fv1 "github.com/fission/fission/pkg/apis/fission.io/v1"
 	"github.com/fission/fission/pkg/controller/client"
-	"github.com/fission/fission/pkg/fission-cli/util"
 	storageSvcClient "github.com/fission/fission/pkg/storagesvc/client"
 	"github.com/fission/fission/pkg/types"
 	"github.com/fission/fission/pkg/utils"
@@ -46,18 +46,25 @@ func UploadArchiveFile(ctx context.Context, client *client.Client, fileName stri
 
 	if size < types.ArchiveLiteralSizeLimit {
 		archive.Type = fv1.ArchiveTypeLiteral
-		archive.Literal = GetContents(fileName)
+		archive.Literal, err = GetContents(fileName)
+		if err != nil {
+			return nil, err
+		}
 	} else {
 		u := strings.TrimSuffix(client.Url, "/") + "/proxy/storage"
 		ssClient := storageSvcClient.MakeClient(u)
 
 		// TODO add a progress bar
 		id, err := ssClient.Upload(ctx, fileName, nil)
-		util.CheckErr(err, fmt.Sprintf("upload file %v", fileName))
+		if err != nil {
+			return nil, errors.Wrapf(err, "error uploading file %v", fileName)
+		}
 
 		storageSvc, err := client.GetSvcURL("application=fission-storage")
 		storageSvcURL := "http://" + storageSvc
-		util.CheckErr(err, "get fission storage service name")
+		if err != nil {
+			return nil, errors.Wrapf(err, "error getting fission storage service name")
+		}
 
 		// We make a new client with actual URL of Storage service so that the URL is not
 		// pointing to 127.0.0.1 i.e. proxy. DON'T reuse previous ssClient
@@ -68,7 +75,9 @@ func UploadArchiveFile(ctx context.Context, client *client.Client, fileName stri
 		archive.URL = archiveURL
 
 		csum, err := utils.GetFileChecksum(fileName)
-		util.CheckErr(err, fmt.Sprintf("calculate checksum for file %v", fileName))
+		if err != nil {
+			return nil, errors.Wrapf(err, "calculate checksum for file %v", fileName)
+		}
 
 		archive.Checksum = *csum
 	}
@@ -76,32 +85,37 @@ func UploadArchiveFile(ctx context.Context, client *client.Client, fileName stri
 	return &archive, nil
 }
 
-func GetContents(filePath string) []byte {
-	var code []byte
-	var err error
-
-	code, err = ioutil.ReadFile(filePath)
-	util.CheckErr(err, fmt.Sprintf("read %v", filePath))
-	return code
+func GetContents(filePath string) ([]byte, error) {
+	code, err := ioutil.ReadFile(filePath)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error reading %v", filePath)
+	}
+	return code, nil
 }
 
 // DownloadToTempFile fetches archive file from arbitrary url
 // and write it to temp file for further usage
-func DownloadToTempFile(fileUrl string) string {
+func DownloadToTempFile(fileUrl string) (string, error) {
 	reader, err := DownloadURL(fileUrl)
-	util.CheckErr(err, fmt.Sprintf("download from url: %v", fileUrl))
+	if err != nil {
+		return "", errors.Wrapf(err, "error downloading from url: %v", fileUrl)
+	}
 	defer reader.Close()
 
 	tmpDir, err := utils.GetTempDir()
-	util.CheckErr(err, "create temp directory")
+	if err != nil {
+		return "", errors.Wrapf(err, "error creating temp directory %v", tmpDir)
+	}
 
 	tmpFilename := uuid.NewV4().String()
 	destination := filepath.Join(tmpDir, tmpFilename)
 
 	err = WriteArchiveToFile(destination, reader)
-	util.CheckErr(err, "write archive to file")
+	if err != nil {
+		return "", errors.Wrapf(err, "error writing archive to file %v", destination)
+	}
 
-	return destination
+	return destination, nil
 }
 
 // DownloadURL downloads file from given url
@@ -146,16 +160,18 @@ func WriteArchiveToFile(fileName string, reader io.Reader) error {
 }
 
 // DownloadStoragesvcURL downloads and return archive content with given storage service url
-func DownloadStoragesvcURL(client *client.Client, fileUrl string) io.ReadCloser {
+func DownloadStoragesvcURL(client *client.Client, fileUrl string) (io.ReadCloser, error) {
 	u, err := url.ParseRequestURI(fileUrl)
 	if err != nil {
-		return nil
+		return nil, err
 	}
 
 	// replace in-cluster storage service host with controller server url
 	fileDownloadUrl := strings.TrimSuffix(client.Url, "/") + "/proxy/storage/" + u.RequestURI()
 	reader, err := DownloadURL(fileDownloadUrl)
+	if err != nil {
+		return nil, errors.Wrapf(err, fmt.Sprintf("error downloading from storage service url: %v", fileUrl))
+	}
 
-	util.CheckErr(err, fmt.Sprintf("download from storage service url: %v", fileUrl))
-	return reader
+	return reader, nil
 }