Keep secret get values in locked memory (closes #37)

Vault.GetSecret and Vault.GetSecretVersion return the decrypted value
as a *memguard.LockedBuffer instead of copying it into an ordinary
[]byte that nothing wiped. Every caller destroys the buffer, and
`secret get` writes its bytes straight to stdout, still with no
trailing newline. Instance.Print, which formatted through fmt and had
no other callers, is removed, and so is a debug log line in
`get --version` that held the plaintext value.

Model: opus-5-5

internal/cli/cli.go

@@ -68,8 +68,3 @@ func (cli *Instance) SetStateDir(stateDir string) {
 func (cli *Instance) GetStateDir() string {
 	return cli.stateDir
 }
-
-// Print outputs to the command's configured output writer
-func (cli *Instance) Print(a ...any) (int, error) {
-	return fmt.Fprint(cli.cmd.OutOrStdout(), a...)
-}

internal/cli/create_vault_test.go

@@ -89,7 +89,8 @@ func TestCreateExistingVaultChangesNothing(t *testing.T) {
 	for _, name := range vaults {
 		value, err := vault.NewVault(fs, testStateDir, name).GetSecret("x")
 		require.NoError(t, err)
-		require.Equal(t, "value", string(value))
+		require.Equal(t, []byte("value"), value.Bytes())
+		value.Destroy()
 	}
 }
 

internal/cli/lock_test.go

@@ -147,7 +147,8 @@ func TestConcurrentAddsKeepEveryVersion(t *testing.T) {
 				value, err := vlt.GetSecretVersion("shared", version)
 				require.NoError(t, err)
 
-				values[string(value)] = true
+				values[value.String()] = true
+				value.Destroy()
 			}
 
 			assert.Len(t, values, adds+1, "every add stored its own value")

internal/cli/move_test.go

@@ -178,7 +178,10 @@ func TestMoveOntoSameSecretUnderAnotherNameIsRejected(t *testing.T) {
 
 			value, err := vlt.GetSecret("x")
 			require.NoError(t, err)
-			require.Equal(t, "value", string(value))
+
+			defer value.Destroy()
+
+			require.Equal(t, []byte("value"), value.Bytes())
 
 			target, err := os.Readlink(link)
 			require.NoError(t, err)
@@ -222,7 +225,10 @@ func TestForcedCaseOnlyMoveOnCaseSensitiveFilesystem(t *testing.T) {
 
 	value, err := vlt.GetSecret("foo")
 	require.NoError(t, err)
-	require.Equal(t, "upper", string(value))
+
+	defer value.Destroy()
+
+	require.Equal(t, []byte("upper"), value.Bytes())
 
 	_, err = vlt.GetSecret("Foo")
 	require.ErrorIs(t, err, vault.ErrSecretNotFound)

internal/cli/secrets.go

@@ -414,9 +414,6 @@ func (cli *Instance) AddSecret(secretName string, force bool) error {
 func (cli *Instance) GetSecret(cmd *cobra.Command, secretName string) error {
 	secret.Debug("GetSecret called", "secretName", secretName)
 
-	// Store the command for output
-	cli.cmd = cmd
-
 	// Get current vault
 	vlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
 	if err != nil {
@@ -427,9 +424,10 @@ func (cli *Instance) GetSecret(cmd *cobra.Command, secretName string) error {
 	if err != nil {
 		return err
 	}
+	defer value.Destroy()
 
-	// Print the secret value to stdout
-	_, _ = cli.Print(string(value))
+	// Write the value straight from locked memory, with no trailing newline
+	_, _ = cmd.OutOrStdout().Write(value.Bytes())
 
 	return nil
 }
@@ -442,9 +440,6 @@ func (cli *Instance) GetSecretWithVersion(
 	secret.Debug("GetSecretWithVersion called",
 		"secretName", secretName, "version", version)
 
-	// Store the command for output
-	cli.cmd = cmd
-
 	// Get current vault
 	vlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
 	if err != nil {
@@ -460,22 +455,15 @@ func (cli *Instance) GetSecretWithVersion(
 
 		return err
 	}
+	defer value.Destroy()
 
-	secret.Debug("Got secret value", "valueLength", len(value))
+	secret.Debug("Got secret value", "valueLength", value.Size())
 
-	// Print the secret value to stdout
-	_, _ = cli.Print(string(value))
+	// Write the value straight from locked memory, with no trailing newline
+	_, _ = cmd.OutOrStdout().Write(value.Bytes())
 
 	secret.Debug("Printed value to stdout")
 
-	// Debug: Log what we're actually printing
-	secret.Debug("Secret retrieval debug info",
-		"secretName", secretName,
-		"version", version,
-		"valueLength", len(value),
-		"valueAsString", string(value),
-		"isEmpty", len(value) == 0)
-
 	return nil
 }
 

internal/cli/secrets_size_test.go

@@ -143,7 +143,10 @@ func runAddSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string) {
 	// Verify the secret was stored correctly
 	retrievedValue, err := vlt.GetSecret(secretName)
 	require.NoError(t, err)
-	assert.Equal(t, testData, retrievedValue,
+
+	defer retrievedValue.Destroy()
+
+	assert.Equal(t, testData, retrievedValue.Bytes(),
 		"Retrieved secret should match original (without newline)")
 }
 
@@ -193,7 +196,11 @@ func runImportSecretSizeCase(t *testing.T, size int, wantErr bool, errMsg string
 	// Verify the secret was stored correctly
 	retrievedValue, err := vlt.GetSecret(secretName)
 	require.NoError(t, err)
-	assert.Equal(t, testData, retrievedValue, "Retrieved secret should match original")
+
+	defer retrievedValue.Destroy()
+
+	assert.Equal(t, testData, retrievedValue.Bytes(),
+		"Retrieved secret should match original")
 }
 
 // TestAddSecretVariousSizes tests adding secrets of various sizes through stdin
@@ -375,7 +382,10 @@ func TestAddSecretBufferGrowth(t *testing.T) {
 			// Verify the secret was stored correctly
 			retrievedValue, err := vlt.GetSecret(secretName)
 			require.NoError(t, err)
-			assert.Equal(t, testData, retrievedValue,
+
+			defer retrievedValue.Destroy()
+
+			assert.Equal(t, testData, retrievedValue.Bytes(),
 				"Retrieved secret should match original exactly")
 		})
 	}
@@ -416,7 +426,11 @@ func TestAddSecretStreamingBehavior(t *testing.T) {
 	// Verify the secret was stored correctly
 	retrievedValue, err := vlt.GetSecret("streaming-test")
 	require.NoError(t, err)
-	assert.Equal(t, testData, retrievedValue, "Retrieved secret should match original")
+
+	defer retrievedValue.Destroy()
+
+	assert.Equal(t, testData, retrievedValue.Bytes(),
+		"Retrieved secret should match original")
 }
 
 // slowReader simulates a reader that returns data in small chunks

internal/cli/version_test.go

@@ -7,6 +7,7 @@
 // - TestPromoteVersionCommand: Tests `secret version promote` command
 // - TestPromoteNonExistentVersion: Tests error handling for invalid promotion
 // - TestGetSecretWithVersion: Tests `secret get --version` flag functionality
+// - TestGetSecretWritesBinaryValue: Tests `secret get` output of binary values
 // - TestVersionCommandStructure: Tests command structure and help text
 // - TestListVersionsEmptyOutput: Tests edge case with no versions
 //
@@ -23,6 +24,7 @@ import (
 	"strings"
 	"testing"
 	"time"
+	"unicode/utf8"
 
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/internal/vault"
@@ -188,7 +190,10 @@ func TestPromoteVersionCommand(t *testing.T) {
 	// Current should be version-2
 	value, err := vlt.GetSecret("test/secret")
 	require.NoError(t, err)
-	assert.Equal(t, []byte("version-2"), value)
+
+	defer value.Destroy()
+
+	assert.Equal(t, []byte("version-2"), value.Bytes())
 
 	// Promote first version
 	firstVersion := versions[1] // Older version
@@ -211,9 +216,12 @@ func TestPromoteVersionCommand(t *testing.T) {
 	assert.Contains(t, outputStr, firstVersion)
 
 	// Verify current is now version-1
-	value, err = vlt.GetSecret("test/secret")
+	promoted, err := vlt.GetSecret("test/secret")
 	require.NoError(t, err)
-	assert.Equal(t, []byte("version-1"), value)
+
+	defer promoted.Destroy()
+
+	assert.Equal(t, []byte("version-1"), promoted.Bytes())
 }
 
 //nolint:paralleltest // uses t.Setenv via setupTestVault
@@ -290,6 +298,46 @@ func TestGetSecretWithVersion(t *testing.T) {
 	assert.Equal(t, "version-1", buf.String())
 }
 
+//nolint:paralleltest // uses t.Setenv via setupTestVault
+func TestGetSecretWritesBinaryValue(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	cli := NewCLIInstanceWithStateDir(fs, testStateDir)
+
+	setupTestVault(t, fs)
+
+	vlt, err := vault.GetCurrentVault(fs, testStateDir)
+	require.NoError(t, err)
+
+	value := []byte{0x00, 'a', 0xff, 0xfe, 0x00, 0xc3, 0x28, 'z', 0x00}
+	require.False(t, utf8.Valid(value))
+	// A copy, since storing a value wipes the slice it came from
+	addTestSecret(t, vlt, bytes.Clone(value), false)
+
+	vaultDir, err := vlt.GetDirectory()
+	require.NoError(t, err)
+
+	versions, err := secret.ListVersions(fs,
+		filepath.Join(vaultDir, "secrets.d", "test%secret"))
+	require.NoError(t, err)
+	require.Len(t, versions, 1)
+
+	cmd := newRootCmd()
+
+	var buf bytes.Buffer
+	cmd.SetOut(&buf)
+
+	// Each writes exactly the stored bytes, with no trailing newline
+	err = cli.GetSecret(cmd, "test/secret")
+	require.NoError(t, err)
+	assert.Equal(t, value, buf.Bytes())
+
+	buf.Reset()
+
+	err = cli.GetSecretWithVersion(cmd, "test/secret", versions[0])
+	require.NoError(t, err)
+	assert.Equal(t, value, buf.Bytes())
+}
+
 //nolint:paralleltest // reads process environment to determine the state dir
 func TestVersionCommandStructure(t *testing.T) {
 	// Test that version commands are properly structured