lnd: allow reading aezeed mnemonic and passphrase from env variables

Author: guggero

lnd/aezeed.go

@@ -15,6 +15,11 @@ import (
 	"golang.org/x/crypto/ssh/terminal"
 )
 
+const (
+	memonicEnvName    = "AEZEED_MNEMONIC"
+	passphraseEnvName = "AEZEED_PASSPHRASE"
+)
+
 var (
 	numberDotsRegex = regexp.MustCompile("[\\d.\\-\\n\\r\\t]*")
 	multipleSpaces  = regexp.MustCompile(" [ ]+")
@@ -23,12 +28,21 @@ var (
 func ReadAezeed(params *chaincfg.Params) (*hdkeychain.ExtendedKey, time.Time,
 	error) {
 
-	// We'll now prompt the user to enter in their 24-word mnemonic.
-	fmt.Printf("Input your 24-word mnemonic separated by spaces: ")
-	reader := bufio.NewReader(os.Stdin)
-	mnemonicStr, err := reader.ReadString('\n')
-	if err != nil {
-		return nil, time.Unix(0, 0), err
+	// To automate things with chantools, we also offer reading the seed
+	// from environment variables.
+	mnemonicStr := strings.TrimSpace(os.Getenv(memonicEnvName))
+
+	// If nothing is set in the environment, read the seed from the
+	// terminal.
+	if mnemonicStr == "" {
+		var err error
+		// We'll now prompt the user to enter in their 24-word mnemonic.
+		fmt.Printf("Input your 24-word mnemonic separated by spaces: ")
+		reader := bufio.NewReader(os.Stdin)
+		mnemonicStr, err = reader.ReadString('\n')
+		if err != nil {
+			return nil, time.Unix(0, 0), err
+		}
 	}
 
 	// We'll trim off extra spaces, and ensure the mnemonic is all
@@ -53,23 +67,46 @@ func ReadAezeed(params *chaincfg.Params) (*hdkeychain.ExtendedKey, time.Time,
 			len(cipherSeedMnemonic), 24)
 	}
 
-	// Additionally, the user may have a passphrase, that will also
-	// need to be provided so the daemon can properly decipher the
-	// cipher seed.
-	fmt.Printf("Input your cipher seed passphrase (press enter if " +
-		"your seed doesn't have a passphrase): ")
-	passphrase, err := terminal.ReadPassword(int(syscall.Stdin)) // nolint
-	if err != nil {
-		return nil, time.Unix(0, 0), err
+	// Additionally, the user may have a passphrase, that will also need to
+	// be provided so the daemon can properly decipher the cipher seed.
+	// Try the environment variable first.
+	passphrase := strings.TrimSpace(os.Getenv(passphraseEnvName))
+
+	// Because we cannot differentiate between an empty and a non-existent
+	// environment variable, we need a special character that indicates that
+	// no passphrase should be used. We use a single dash (-) for that as
+	// that would be too short for a passphrase anyway.
+	var passphraseBytes []byte
+	switch {
+	// The user indicated in the environment variable that no passphrase
+	// should be used. We don't set any value.
+	case passphrase == "-":
+
+	// The environment variable didn't contain anything, we'll read the
+	// passphrase from the terminal.
+	case passphrase == "":
+		fmt.Printf("Input your cipher seed passphrase (press enter " +
+			"if your seed doesn't have a passphrase): ")
+		var err error
+		passphraseBytes, err = terminal.ReadPassword(
+			int(syscall.Stdin), // nolint
+		)
+		if err != nil {
+			return nil, time.Unix(0, 0), err
+		}
+		fmt.Println()
+
+	// There was a password in the environment, just convert it to bytes.
+	default:
+		passphraseBytes = []byte(passphrase)
 	}
-	fmt.Println()
 
 	var mnemonic aezeed.Mnemonic
 	copy(mnemonic[:], cipherSeedMnemonic)
 
 	// If we're unable to map it back into the ciphertext, then either the
 	// mnemonic is wrong, or the passphrase is wrong.
-	cipherSeed, err := mnemonic.ToCipherSeed(passphrase)
+	cipherSeed, err := mnemonic.ToCipherSeed(passphraseBytes)
 	if err != nil {
 		return nil, time.Unix(0, 0), fmt.Errorf("failed to decrypt "+
 			"seed with passphrase: %v", err)