TUN-8726: implement compression routine to be used in diagnostic procedure

## Summary
Basic routine to compress the diagnostic files into the root of a zipfile.

Closes TUN-8726

Author: lmpn

diagnostic/diagnostic_utils.go

@@ -0,0 +1,69 @@
+package diagnostic
+
+import (
+	"archive/zip"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// CreateDiagnosticZipFile create a zip file with the contents from the all
+// files paths. The files will be written in the root of the zip file.
+// In case of an error occurs after whilst writing to the zip file
+// this will be removed.
+func CreateDiagnosticZipFile(base string, paths []string) (zipFileName string, err error) {
+	// Create a zip file with all files from paths added to the root
+	suffix := time.Now().Format(time.RFC3339)
+	zipFileName = base + "-" + suffix + ".zip"
+	zipFileName = strings.ReplaceAll(zipFileName, ":", "-")
+
+	archive, cerr := os.Create(zipFileName)
+	if cerr != nil {
+		return "", fmt.Errorf("error creating file %s: %w", zipFileName, cerr)
+	}
+
+	archiveWriter := zip.NewWriter(archive)
+
+	defer func() {
+		archiveWriter.Close()
+		archive.Close()
+
+		if err != nil {
+			os.Remove(zipFileName)
+		}
+	}()
+
+	for _, file := range paths {
+		if file == "" {
+			continue
+		}
+
+		var handle *os.File
+
+		handle, err = os.Open(file)
+		if err != nil {
+			return "", fmt.Errorf("error opening file %s: %w", zipFileName, err)
+		}
+
+		defer handle.Close()
+
+		// Keep the base only to not create sub directories in the
+		// zip file.
+		var writer io.Writer
+
+		writer, err = archiveWriter.Create(filepath.Base(file))
+		if err != nil {
+			return "", fmt.Errorf("error creating archive writer from %s: %w", file, err)
+		}
+
+		if _, err = io.Copy(writer, handle); err != nil {
+			return "", fmt.Errorf("error copying file %s: %w", file, err)
+		}
+	}
+
+	zipFileName = archive.Name()
+	return zipFileName, nil
+}