secret get fails when it cannot write the value (closes #155)

GetSecret and GetSecretWithVersion discarded the result of writing the
value to stdout, so a full disk or a failing stdout left the caller with
an empty or cut-short file and exit status 0. The write error is now
returned, so the command prints it and exits 1.

Deviation: a stdout the shell closed before `secret` started still exits
0, because the Go runtime opens /dev/null in its place and the write
there succeeds.

Model: opus-5-5

README.md

@@ -142,7 +142,8 @@ contain `//`, or have `..` as a path segment.
 
 #### `secret get <secret-name> [--version <version>]`
 
-Retrieves and outputs a secret value to stdout.
+Retrieves and outputs a secret value to stdout. If the value cannot be written,
+as when stdout is a file on a full disk, it prints the error and exits 1.
 
 - `--version, -v`: Get a specific version (default: current)
 

TODO.md

@@ -18,6 +18,14 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-14: `secret get` fails when it cannot write the value to stdout
+  (https://git.eeqj.de/sneak/secret/issues/155). The write's error was ignored,
+  so a script that sent the value to a file on a full disk saw `secret get`
+  succeed and was left with an empty or cut-short file. That error is now the
+  command's error, and `secret get` exits 1. A stdout the shell closed (`>&-`)
+  still gives exit 0, because the Go runtime opens `/dev/null` in its place
+  before `secret` starts and the write there succeeds.
+
 - 2026-10-14: Removing the current unlocker no longer leaves the vault unable to
   open through the unlockers it still has
   (https://git.eeqj.de/sneak/secret/issues/137). `current-unlocker` went on

internal/cli/secrets.go

@@ -443,7 +443,10 @@ func (cli *Instance) GetSecret(cmd *cobra.Command, secretName string) error {
 	defer value.Destroy()
 
 	// Write the value straight from locked memory, with no trailing newline
-	_, _ = cmd.OutOrStdout().Write(value.Bytes())
+	_, err = cmd.OutOrStdout().Write(value.Bytes())
+	if err != nil {
+		return fmt.Errorf("failed to write secret value: %w", err)
+	}
 
 	return nil
 }
@@ -478,7 +481,10 @@ func (cli *Instance) GetSecretWithVersion(
 	secret.Debug("Got secret value", "valueLength", value.Size())
 
 	// Write the value straight from locked memory, with no trailing newline
-	_, _ = cmd.OutOrStdout().Write(value.Bytes())
+	_, err = cmd.OutOrStdout().Write(value.Bytes())
+	if err != nil {
+		return fmt.Errorf("failed to write secret value: %w", err)
+	}
 
 	secret.Debug("Printed value to stdout")
 

internal/cli/version_test.go

@@ -8,6 +8,7 @@
 // - TestPromoteNonExistentVersion: Tests error handling for invalid promotion
 // - TestGetSecretWithVersion: Tests `secret get --version` flag functionality
 // - TestGetSecretWritesBinaryValue: Tests `secret get` output of binary values
+// - TestGetSecretReturnsWriteError: Tests `secret get` when stdout fails
 // - TestVersionCommandStructure: Tests command structure and help text
 // - TestListVersionsEmptyOutput: Tests edge case with no versions
 //
@@ -20,6 +21,7 @@ package cli
 
 import (
 	"bytes"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -360,6 +362,45 @@ func TestGetSecretWritesBinaryValue(t *testing.T) {
 	assert.Equal(t, value, buf.Bytes())
 }
 
+// TestGetSecretReturnsWriteError checks that `secret get`, with and without
+// a version, returns the error of a failed write of the value.
+func TestGetSecretReturnsWriteError(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	cli := NewCLIInstanceWithStateDir(fs, testStateDir)
+	cli.Mnemonic = testMnemonicBuffer(t)
+
+	setupTestVault(t, fs)
+
+	vlt, err := vault.GetCurrentVault(fs, testStateDir)
+	require.NoError(t, err)
+
+	addTestSecret(t, vlt, []byte("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)
+
+	// Stdout is a file closed before the value is written to it
+	out, err := os.Create(filepath.Join(t.TempDir(), "stdout"))
+	require.NoError(t, err)
+	require.NoError(t, out.Close())
+
+	cmd := newRootCmd()
+	cmd.SetOut(out)
+
+	err = cli.GetSecret(cmd, "test/secret")
+	require.ErrorIs(t, err, os.ErrClosed)
+
+	err = cli.GetSecretWithVersion(cmd, "test/secret", versions[0])
+	require.ErrorIs(t, err, os.ErrClosed)
+}
+
 //nolint:paralleltest // reads process environment to determine the state dir
 func TestVersionCommandStructure(t *testing.T) {
 	// Test that version commands are properly structured