Make secret unlocker add pgp work on Linux (closes #88)

CreatePGPUnlocker got the vault's long-term key from the keychain
unlocker's helper, which on every platform but macOS is a stub that
always fails. It now calls the vault's GetOrDeriveLongTermKey, as adding
a passphrase unlocker does: from the mnemonic, checked against the
vault, or else from the current unlocker. That method joins
VaultInterface. The test GPG key gains an encryption subkey, and a new
test adds a PGP unlocker with the long-term key from the mnemonic and
from a passphrase unlocker, then reads a secret through it.

Model: opus-5-5

internal/cli/unlockers_add_test.go

@@ -5,18 +5,88 @@ import (
 	"path/filepath"
 	"testing"
 
+	"git.eeqj.de/sneak/secret/internal/secret"
+	"git.eeqj.de/sneak/secret/internal/vault"
+	"github.com/awnumar/memguard"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
 // unknownTestGPGUserID is a GPG user ID that no key in the test keyring has.
 const unknownTestGPGUserID = "not-in-keyring@example.com"
 
+// The secret TestAddPGPUnlocker stores, then reads through the new unlocker.
+const (
+	addTestSecretName  = "api-key"
+	addTestSecretValue = "value"
+)
+
+// TestAddPGPUnlocker adds a PGP unlocker for a throwaway GPG key to a vault
+// with a passphrase unlocker, getting the vault's long-term key from the
+// mnemonic or, with the mnemonic unset, from the passphrase unlocker. It
+// then reads a secret with neither the mnemonic nor the passphrase set, so
+// through the new unlocker, which the add selects.
+func TestAddPGPUnlocker(t *testing.T) {
+	newTestGPGKey(t)
+
+	tests := []struct {
+		name string
+		// mnemonic is the mnemonic set while the unlocker is added.
+		mnemonic string
+	}{
+		{"long-term key from the mnemonic", testMnemonic},
+		{"long-term key from the current unlocker", ""},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Setenv(secret.EnvMnemonic, testMnemonic)
+			t.Setenv(secret.EnvUnlockPassphrase, testPassphrase)
+
+			fs := afero.NewMemMapFs()
+			vlt, err := vault.CreateVault(fs, listTestStateDir, listTestVaultName)
+			require.NoError(t, err)
+
+			err = vlt.AddSecret(addTestSecretName,
+				memguard.NewBufferFromBytes([]byte(addTestSecretValue)), false)
+			require.NoError(t, err)
+
+			_, err = vlt.CreatePassphraseUnlocker(
+				memguard.NewBufferFromBytes([]byte(testPassphrase)))
+			require.NoError(t, err)
+
+			t.Setenv(secret.EnvMnemonic, test.mnemonic)
+
+			instance, cmd := newTestInstance(fs)
+			cmd.Flags().String("keyid", unreadableTestGPGUserID, "")
+			require.NoError(t, instance.UnlockersAdd(unlockerTypePGP, cmd))
+
+			t.Setenv(secret.EnvMnemonic, "")
+			t.Setenv(secret.EnvUnlockPassphrase, "")
+
+			reopened := vault.NewVault(fs, listTestStateDir, listTestVaultName)
+
+			current, err := reopened.GetCurrentUnlocker()
+			require.NoError(t, err)
+			assert.Equal(t, unlockerTypePGP, current.GetType())
+
+			value, err := reopened.GetSecret(addTestSecretName)
+			require.NoError(t, err)
+
+			defer value.Destroy()
+
+			assert.Equal(t, addTestSecretValue, value.String())
+		})
+	}
+}
+
 // TestAddPGPUnlockerUnknownKey asserts that adding a PGP unlocker for a key
 // the keyring does not hold fails at looking up the key's fingerprint and
 // leaves no new unlocker directory. The error must come from the lookup: a
 // lookup moved after anything is written would also come after getting the
-// vault's long-term key, which fails first on every platform but macOS
-// (https://git.eeqj.de/sneak/secret/issues/88).
+// vault's long-term key, which fails first here: this vault's unlockers hold
+// no keys.
 //
 //nolint:paralleltest // t.Setenv (GNUPGHOME) forbids parallel tests
 func TestAddPGPUnlockerUnknownKey(t *testing.T) {

internal/cli/unreadable_dir_test.go

@@ -122,7 +122,8 @@ func assertDirEntries(t *testing.T, fs afero.Fs, dir string, want ...string) {
 }
 
 // newTestGPGKey points GNUPGHOME at a fresh directory, generates a GPG key
-// without a passphrase there, and returns the key's fingerprint.
+// without a passphrase there, with a subkey for encryption, and returns the
+// key's fingerprint.
 func newTestGPGKey(t *testing.T) string {
 	t.Helper()
 
@@ -151,6 +152,14 @@ func newTestGPGKey(t *testing.T) string {
 	fingerprint, err := secret.ResolveGPGKeyFingerprint(unreadableTestGPGUserID)
 	require.NoError(t, err)
 
+	//nolint:gosec // G204: fingerprint is the test key's, as gpg printed it
+	output, err = exec.CommandContext(t.Context(), "gpg", "--batch",
+		"--pinentry-mode", "loopback", "--passphrase", "",
+		"--quick-add-key", fingerprint, "cv25519", "encr", "never",
+	).CombinedOutput()
+	require.NoError(t, err, "adding the test GPG key's encryption subkey: %s",
+		output)
+
 	return fingerprint
 }