add CLI to update license headers

internal/copyright/header.txt

@@ -0,0 +1,3 @@
+Unless explicitly stated otherwise all files in this repository are licensed under the MIT License.
+
+This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2021 Datadog, Inc.

internal/copyright/main.go

@@ -0,0 +1,167 @@
+package main
+
+import (
+	"bufio"
+	_ "embed"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type (
+	// task that adds license header to source
+	// files, if they don't already exist
+	addLicenseHeaderTask struct {
+		license string  // license header string to add
+		config  *config // root directory of the project source
+	}
+
+	// command line config params
+	config struct {
+		licenseFile string
+		scanDir     string
+		verifyOnly  bool
+	}
+)
+
+var (
+	//go:embed header.txt
+	headerText     string
+	headerPrefixes = []string{"The MIT License", "Unless explicitly stated"}
+)
+
+var (
+	// directories to be excluded
+	dirBlocklist = []string{".gen/", ".git/", ".vscode/", ".idea/"}
+	// default perms for the newly created files
+	defaultFilePerms = os.FileMode(0644)
+)
+
+// command line utility that adds license header
+// to the source files. Usage as follows:
+//
+//  ./cmd/tools/copyright/licensegen.go
+func main() {
+	var cfg config
+	flag.StringVar(&cfg.scanDir, "scanDir", ".", "directory to scan")
+	flag.BoolVar(&cfg.verifyOnly, "verifyOnly", false, "don't automatically add headers, just verify all files")
+	flag.Parse()
+
+	task := newAddLicenseHeaderTask(&cfg)
+	if err := task.run(); err != nil {
+		fmt.Println(err)
+		os.Exit(-1)
+	}
+}
+
+func newAddLicenseHeaderTask(cfg *config) *addLicenseHeaderTask {
+	return &addLicenseHeaderTask{
+		config: cfg,
+	}
+}
+
+func (task *addLicenseHeaderTask) run() error {
+	license, err := commentOutLines(headerText)
+	if err != nil {
+		return fmt.Errorf("copyright header failed to comment out lines, err=%v", err.Error())
+	}
+	task.license = license
+
+	if err := filepath.Walk(task.config.scanDir, task.handleFile); err != nil {
+		return fmt.Errorf("copyright header check failed, err=%v", err.Error())
+	}
+	return nil
+}
+
+func (task *addLicenseHeaderTask) handleFile(path string, fileInfo os.FileInfo, err error) error {
+	if err != nil {
+		return err
+	}
+
+	if fileInfo.IsDir() {
+		return nil
+	}
+
+	if !mustProcessPath(path) {
+		return nil
+	}
+
+	if !strings.HasSuffix(fileInfo.Name(), ".go") {
+		return nil
+	}
+
+	// Used as part of the cli to write licence headers on files, does not use user supplied input so marked as nosec
+	// #nosec
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+
+	scanner := bufio.NewScanner(f)
+	readLineSucc := scanner.Scan()
+	if !readLineSucc {
+		return fmt.Errorf("fail to read first line of file %v", path)
+	}
+	firstLine := strings.TrimSpace(scanner.Text())
+	if err := scanner.Err(); err != nil {
+		return err
+	}
+	f.Close()
+
+	for _, prefix := range headerPrefixes {
+		if strings.Contains(firstLine, prefix) {
+			return nil // file already has the copyright header
+		}
+	}
+
+	// at this point, src file is missing the header
+	if task.config.verifyOnly {
+		if !isFileAutogenerated(path) {
+			return fmt.Errorf("%v missing license header", path)
+		}
+	}
+
+	// Used as part of the cli to write licence headers on files, does not use user supplied input so marked as nosec
+	// #nosec
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+
+	return ioutil.WriteFile(path, []byte(task.license+string(data)), defaultFilePerms)
+}
+
+func isFileAutogenerated(path string) bool {
+	return false
+}
+
+func mustProcessPath(path string) bool {
+	for _, d := range dirBlocklist {
+		if strings.HasPrefix(path, d) {
+			return false
+		}
+	}
+	return true
+}
+
+func commentOutLines(str string) (string, error) {
+	var lines []string
+	scanner := bufio.NewScanner(strings.NewReader(str))
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			lines = append(lines, "//\n")
+		} else {
+			lines = append(lines, fmt.Sprintf("// %s\n", line))
+		}
+	}
+	lines = append(lines, "\n")
+
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
+	return strings.Join(lines, ""), nil
+}