e2e-framework: add an EmbeddedFileSource to sources

The data structure would wrap an embedded filesystem andthe root
directory relative to which the embedded filesystem is constructed.

Signed-off-by: Nabarun Pal <pal.nabarun95@gmail.com>

test/e2e/framework/testfiles/testdata/a/foo.txt

@@ -0,0 +1 @@
+Hello World

test/e2e/framework/testfiles/testfiles.go

@@ -25,8 +25,10 @@ limitations under the License.
 package testfiles
 
 import (
+	"embed"
 	"errors"
 	"fmt"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path"
@@ -176,3 +178,48 @@ func (b BindataFileSource) DescribeFiles() string {
 	description := strings.Join(lines, "\n   ")
 	return description
 }
+
+// EmbeddedFileSource handles files stored in a package generated with bindata.
+type EmbeddedFileSource struct {
+	EmbeddedFS embed.FS
+	Root       string
+	fileList   []string
+}
+
+// ReadTestFile looks for an embedded file with the given path.
+func (e EmbeddedFileSource) ReadTestFile(filepath string) ([]byte, error) {
+	relativePath := strings.TrimPrefix(filepath, fmt.Sprintf("%s/", e.Root))
+
+	b, err := e.EmbeddedFS.ReadFile(relativePath)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	return b, nil
+}
+
+// DescribeFiles explains that it is looking inside an embedded filesystem
+func (e EmbeddedFileSource) DescribeFiles() string {
+	var lines []string
+	lines = append(lines, "The following files are embedded into the test executable:")
+
+	if len(e.fileList) == 0 {
+		e.populateFileList()
+	}
+	lines = append(lines, e.fileList...)
+
+	return strings.Join(lines, "\n\t")
+}
+
+func (e *EmbeddedFileSource) populateFileList() {
+	fs.WalkDir(e.EmbeddedFS, ".", func(path string, d fs.DirEntry, err error) error {
+		if !d.IsDir() {
+			e.fileList = append(e.fileList, filepath.Join(e.Root, path))
+		}
+
+		return nil
+	})
+}

test/e2e/framework/testfiles/testfiles_test.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package testfiles
+
+import (
+	"embed"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	fooContents = `Hello World
+`
+	fooPath = "testdata/a/foo.txt"
+
+	notExistsPath = "testdata/b"
+
+	expectedDescription = `The following files are embedded into the test executable:
+	testdata/a/foo.txt`
+)
+
+//go:embed testdata/a
+var testFS embed.FS
+
+func getTestEmbeddedSource() *EmbeddedFileSource {
+	return &EmbeddedFileSource{
+		EmbeddedFS: testFS,
+	}
+}
+
+func TestEmbeddedFileSource(t *testing.T) {
+	s := getTestEmbeddedSource()
+
+	// read a file which exists and compare the contents
+	b, err := s.ReadTestFile(fooPath)
+
+	assert.NoError(t, err)
+	assert.Equal(t, fooContents, string(b))
+
+	// read a non-existent file and ensure that the returned value is empty and error is nil
+	// Note: this is done so that the next file source can be tried by the caller
+	b, err = s.ReadTestFile(notExistsPath)
+	assert.NoError(t, err)
+	assert.Empty(t, b)
+
+	// describing the test filesystem should list down all files
+	assert.Equal(t, expectedDescription, s.DescribeFiles())
+}