Read email addresses from $CERTSPOTTER_CONFIG_DIR/email_recipients

cmd/certspotter/main.go

@@ -10,6 +10,7 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"errors"
 	"flag"
@@ -102,6 +103,9 @@ func defaultWatchListPathIfExists() string {
 func defaultScriptDir() string {
 	return filepath.Join(defaultConfigDir(), "hooks.d")
 }
+func defaultEmailFile() string {
+	return filepath.Join(defaultConfigDir(), "email_recipients")
+}
 
 func simplifyError(err error) error {
 	var pathErr *fs.PathError
@@ -121,6 +125,25 @@ func readWatchListFile(filename string) (monitor.WatchList, error) {
 	return monitor.ReadWatchList(file)
 }
 
+func readEmailFile(filename string) ([]string, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, simplifyError(err)
+	}
+	defer file.Close()
+
+	var emails []string
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+		emails = append(emails, line)
+	}
+	return emails, err
+}
+
 func appendFunc(slice *[]string) func(string) error {
 	return func(value string) error {
 		*slice = append(*slice, value)
@@ -183,9 +206,19 @@ func main() {
 		HealthCheckInterval: flags.healthcheck,
 	}
 
-	if len(config.Email) == 0 && config.Script == "" && !fileExists(config.ScriptDir) && config.Stdout == false {
+	emailFileExists := false
+	if emailRecipients, err := readEmailFile(defaultEmailFile()); err == nil {
+		emailFileExists = true
+		config.Email = append(config.Email, emailRecipients...)
+	} else if !errors.Is(err, fs.ErrNotExist) {
+		fmt.Fprintf(os.Stderr, "%s: error reading email recipients file %q: %s\n", programName, defaultEmailFile(), err)
+		os.Exit(1)
+	}
+
+	if len(config.Email) == 0 && !emailFileExists && config.Script == "" && !fileExists(config.ScriptDir) && config.Stdout == false {
 		fmt.Fprintf(os.Stderr, "%s: no notification methods were specified\n", programName)
 		fmt.Fprintf(os.Stderr, "Please specify at least one of the following notification methods:\n")
+		fmt.Fprintf(os.Stderr, " - Place one or more email addresses in %s (one address per line)\n", defaultEmailFile())
 		fmt.Fprintf(os.Stderr, " - Place one or more executable scripts in the %s directory\n", config.ScriptDir)
 		fmt.Fprintf(os.Stderr, " - Specify an email address using the -email flag\n")
 		fmt.Fprintf(os.Stderr, " - Specify the path to an executable script using the -script flag\n")