Write encrypt and decrypt output only once they succeed (closes #143)

`secret encrypt` and `secret decrypt` emptied the file named by
`--output` before reading any input, so a failure left it empty, and a
file given as both `--input` and `--output` was emptied before it was
read. They now write into a temporary file of mode 0600 next to it, or
next to the file it is a symbolic link to, and rename that over it only
on success, with the new `secret.WriteFileAtomicFunc`. An output file
that cannot be written still fails. Ctrl-C, SIGTERM or a hangup removes
the temporary file. A device or pipe, such as `/dev/null`, is written to
directly.

Judgement calls: the device and pipe case; a command started with
`nohup` still ignores a hangup.

Model: opus-5-5

README.md

@@ -292,6 +292,19 @@ generates a new Age key.
 
 Decrypts data using an Age key stored as a secret.
 
+Both write the result to a new file next to `--output` and rename it over
+`--output` only once they have succeeded, so a failed command leaves an existing
+`--output` as it was and creates none, and `--input` and `--output` can be the
+same file. When `--output` is a symbolic link, the file it points to is
+replaced, or created if it does not exist yet, and the link kept; the new file
+is then made next to that file. The directory the new file is made in must be
+writable. The new file has mode 0600 and belongs to the user running the
+command, whatever mode and owner the file it replaces had, so a hard link to the
+old file keeps the old content. Ctrl-C, SIGTERM or a hangup removes the new
+file; a command killed any other way, such as with SIGKILL, leaves it there,
+named `.tmp-` and a number. A device or a pipe, such as `/dev/null`, is written
+to directly.
+
 ## Storage Architecture
 
 ### Directory Structure

internal/cli/crypto.go

@@ -5,9 +5,12 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
+	"sync/atomic"
 
 	"filippo.io/age"
 	"github.com/awnumar/memguard"
+	"github.com/spf13/afero"
 	"github.com/spf13/cobra"
 	"sneak.berlin/go/secret/internal/secret"
 	"sneak.berlin/go/secret/internal/vault"
@@ -188,36 +191,24 @@ func (cli *Instance) Encrypt(secretName, inputFile, outputFile string) error {
 		input = file
 	}
 
-	// Set up output writer
-	output := cli.cmd.OutOrStdout()
-
-	if outputFile != "" {
-		file, err := cli.fs.Create(outputFile)
+	return cli.writeOutput(outputFile, func(output io.Writer) error {
+		encryptor, err := age.Encrypt(output, recipient)
 		if err != nil {
-			return fmt.Errorf("failed to create output file: %w", err)
+			return fmt.Errorf("failed to create age encryptor: %w", err)
 		}
-		defer func() { _ = file.Close() }()
 
-		output = file
-	}
+		_, err = io.Copy(encryptor, input)
+		if err != nil {
+			return fmt.Errorf("failed to encrypt data: %w", err)
+		}
 
-	// Encrypt the data
-	encryptor, err := age.Encrypt(output, recipient)
-	if err != nil {
-		return fmt.Errorf("failed to create age encryptor: %w", err)
-	}
+		err = encryptor.Close()
+		if err != nil {
+			return fmt.Errorf("failed to finalize encryption: %w", err)
+		}
 
-	_, err = io.Copy(encryptor, input)
-	if err != nil {
-		return fmt.Errorf("failed to encrypt data: %w", err)
-	}
-
-	err = encryptor.Close()
-	if err != nil {
-		return fmt.Errorf("failed to finalize encryption: %w", err)
-	}
-
-	return nil
+		return nil
+	})
 }
 
 // Decrypt decrypts data using an age secret key stored in a secret
@@ -278,31 +269,123 @@ func (cli *Instance) Decrypt(secretName, inputFile, outputFile string) error {
 		input = file
 	}
 
-	// Set up output writer
-	output := cli.cmd.OutOrStdout()
+	return cli.writeOutput(outputFile, func(output io.Writer) error {
+		decryptor, err := age.Decrypt(input, identity)
+		if err != nil {
+			return fmt.Errorf("failed to create age decryptor: %w", err)
+		}
 
-	if outputFile != "" {
-		file, err := cli.fs.Create(outputFile)
+		_, err = io.Copy(output, decryptor)
+		if err != nil {
+			return fmt.Errorf("failed to decrypt data: %w", err)
+		}
+
+		return nil
+	})
+}
+
+// temporaryOutput is the name of the temporary file writeOutput is filling,
+// until it is renamed into place. The signal handler in Entry removes it,
+// since for decrypt it holds part of the secret.
+//
+//nolint:gochecknoglobals // read by the signal handler, which has no Instance
+var temporaryOutput atomic.Pointer[string]
+
+// writeOutput calls write with stdout when outputFile is empty, and with
+// outputFile itself when it is a device or a pipe, such as /dev/null.
+// Otherwise write fills a new file of mode 0600 that replaces outputFile,
+// or the file it is a symbolic link to, only once write has succeeded, so a
+// failure leaves that file as it was, and it may be the input file too.
+// An existing outputFile that cannot be written fails before write is
+// called.
+func (cli *Instance) writeOutput(
+	outputFile string, write func(output io.Writer) error,
+) error {
+	if outputFile == "" {
+		return write(cli.cmd.OutOrStdout())
+	}
+
+	info, err := cli.fs.Stat(outputFile)
+	if err == nil && !info.Mode().IsRegular() {
+		file, err := cli.fs.OpenFile(outputFile, os.O_WRONLY, 0)
 		if err != nil {
 			return fmt.Errorf("failed to create output file: %w", err)
 		}
 		defer func() { _ = file.Close() }()
 
-		output = file
+		return write(file)
 	}
 
-	// Decrypt the data
-	decryptor, err := age.Decrypt(input, identity)
+	// An existing file that cannot be written fails here, as writing into it
+	// directly would. Opened without O_TRUNC, which would empty it.
+	file, err := cli.fs.OpenFile(outputFile, os.O_WRONLY, 0)
+	if err == nil {
+		err = file.Close()
+	}
+
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("failed to create output file: %w", err)
+	}
+
+	path, err := outputPath(outputFile)
 	if err != nil {
-		return fmt.Errorf("failed to create age decryptor: %w", err)
+		return fmt.Errorf("failed to create output file: %w", err)
+	}
+
+	err = secret.WriteFileAtomicFunc(cli.fs, path, func(file afero.File) error {
+		name := file.Name()
+		temporaryOutput.Store(&name)
+
+		return write(file)
+	})
+
+	temporaryOutput.Store(nil)
+
+	return err
+}
+
+// outputPath returns the path of the file that writing to outputFile
+// replaces, with no symbolic link in it, so that filepath.Dir of it is the
+// directory that file is in. When outputFile is a symbolic link, as
+// /dev/stdout is when stdout goes to a file, that is the path the link
+// points to, whether or not a file is there yet, so the link is kept, as
+// writing through it would keep it. A link that cannot be followed, such as
+// one that points to itself, is an error.
+func outputPath(outputFile string) (string, error) {
+	path, err := filepath.EvalSymlinks(outputFile)
+	if !errors.Is(err, os.ErrNotExist) {
+		return path, err
+	}
+
+	// No file is at outputFile, or at the end of its links, yet
+	target, err := os.Readlink(outputFile)
+	if errors.Is(err, os.ErrNotExist) {
+		// Nothing is at outputFile itself. Its directory part is resolved
+		// with filepath.EvalSymlinks, since filepath.Dir would remove a link
+		// to a directory followed by ".." as text and give another directory.
+		dir, name := filepath.Split(outputFile)
+
+		dir, err = filepath.EvalSymlinks(dir)
+		if err != nil {
+			return "", err
+		}
+
+		return filepath.Join(dir, name), nil
 	}
 
-	_, err = io.Copy(output, decryptor)
 	if err != nil {
-		return fmt.Errorf("failed to decrypt data: %w", err)
+		return "", err
 	}
 
-	return nil
+	if !filepath.IsAbs(target) {
+		// Not filepath.Join, which would remove a ".." in target together
+		// with the name before it, even when that name is a link to a
+		// directory
+		dir, _ := filepath.Split(outputFile)
+		target = dir + target
+	}
+
+	return outputPath(target)
 }
 
 // isValidAgeSecretKey checks if a string is a valid age secret key by

internal/cli/crypto_test.go

@@ -0,0 +1,304 @@
+//nolint:testpackage // sets the unexported fields of Instance
+package cli
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/secret/internal/vault"
+)
+
+// plainText is the content of plain.txt in the directory newCryptoTest makes.
+const plainText = "document"
+
+// newCryptoTest returns an Instance whose current vault, in a new state
+// directory on the real filesystem, holds the age key secret "key", and a
+// new directory holding only plain.txt and plain.txt.age, its encryption
+// with that key.
+func newCryptoTest(t *testing.T) (*Instance, string) {
+	t.Helper()
+
+	fs := afero.NewOsFs()
+	stateDir := t.TempDir()
+
+	_, err := vault.CreateVault(fs, stateDir, "default", testMnemonicBuffer(t), nil)
+	require.NoError(t, err)
+
+	cli := NewCLIInstanceWithStateDir(fs, stateDir)
+	cli.Mnemonic = testMnemonicBuffer(t)
+	cli.cmd = &cobra.Command{}
+
+	dir := t.TempDir()
+	plain := filepath.Join(dir, "plain.txt")
+	require.NoError(t, afero.WriteFile(fs, plain, []byte(plainText), 0o600))
+	require.NoError(t, cli.Encrypt("key", plain, plain+".age"))
+
+	return cli, dir
+}
+
+// TestFailedCryptoLeavesOutputUnchanged is a regression test for
+// https://git.eeqj.de/sneak/secret/issues/143, where secret encrypt and
+// secret decrypt emptied the file named by --output before they failed.
+// A failed command must leave an existing file as it was and create none,
+// and give the same error as without --output.
+func TestFailedCryptoLeavesOutputUnchanged(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		run  func(cli *Instance, dir, output string) error
+	}{
+		// Reading a directory fails once encryption has begun
+		{"encrypt", func(cli *Instance, dir, output string) error {
+			return cli.Encrypt("key", dir, output)
+		}},
+		// plain.txt is not an age file
+		{"decrypt", func(cli *Instance, dir, output string) error {
+			return cli.Decrypt("key", filepath.Join(dir, "plain.txt"), output)
+		}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			cli, dir := newCryptoTest(t)
+			existing := filepath.Join(dir, "existing.txt")
+			require.NoError(t, afero.WriteFile(cli.fs, existing, []byte("precious"), 0o600))
+
+			cli.cmd.SetOut(io.Discard)
+			toStdout := tt.run(cli, dir, "")
+			require.Error(t, toStdout)
+
+			require.EqualError(t, tt.run(cli, dir, existing), toStdout.Error())
+			require.EqualError(t, tt.run(cli, dir, filepath.Join(dir, "new.txt")),
+				toStdout.Error())
+
+			content, err := afero.ReadFile(cli.fs, existing)
+			require.NoError(t, err)
+			require.Equal(t, "precious", string(content))
+
+			// No new.txt, and no temporary file left behind
+			entries, err := afero.ReadDir(cli.fs, dir)
+			require.NoError(t, err)
+
+			names := make([]string, 0, len(entries))
+			for _, entry := range entries {
+				names = append(names, entry.Name())
+			}
+
+			require.Equal(t, []string{"existing.txt", "plain.txt", "plain.txt.age"}, names)
+		})
+	}
+}
+
+// writeFailFs fails every open of one path for writing, as a file of mode
+// 0444 does for anyone but root, who runs these tests in Docker.
+type writeFailFs struct {
+	afero.Fs
+
+	path string
+}
+
+//nolint:ireturn // afero.File is the interface required by afero.Fs
+func (f *writeFailFs) OpenFile(
+	name string, flag int, perm os.FileMode,
+) (afero.File, error) {
+	if name == f.path && flag&(os.O_WRONLY|os.O_RDWR) != 0 {
+		return nil, &os.PathError{Op: "open", Path: name, Err: syscall.EACCES}
+	}
+
+	return f.Fs.OpenFile(name, flag, perm)
+}
+
+// TestDecryptToUnwritableOutput checks that secret decrypt fails when
+// --output is a file that cannot be written, as writing into it directly
+// does, and leaves it as it was, although its directory can be written.
+func TestDecryptToUnwritableOutput(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	existing := filepath.Join(dir, "existing.txt")
+	require.NoError(t, afero.WriteFile(cli.fs, existing, []byte("precious"), 0o600))
+	cli.fs = &writeFailFs{Fs: cli.fs, path: existing}
+
+	err := cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), existing)
+	require.ErrorIs(t, err, os.ErrPermission)
+
+	content, err := afero.ReadFile(cli.fs, existing)
+	require.NoError(t, err)
+	require.Equal(t, "precious", string(content))
+}
+
+// TestCryptoInPlace checks that secret encrypt and secret decrypt given
+// one file as both --input and --output replace it with the right result.
+// Before https://git.eeqj.de/sneak/secret/issues/143 they emptied the file
+// before reading it.
+func TestCryptoInPlace(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	file := filepath.Join(dir, "plain.txt")
+
+	require.NoError(t, cli.Encrypt("key", file, file))
+	require.NoError(t, cli.Decrypt("key", file, file))
+
+	content, err := afero.ReadFile(cli.fs, file)
+	require.NoError(t, err)
+	require.Equal(t, plainText, string(content))
+}
+
+// TestDecryptToPipe checks that secret decrypt writes into a named pipe
+// given as --output, as it must into a device such as /dev/null, instead
+// of replacing it with a file.
+func TestDecryptToPipe(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	pipe := filepath.Join(dir, "pipe")
+	require.NoError(t, syscall.Mkfifo(pipe, 0o600))
+
+	received := make(chan []byte, 1)
+
+	go func() {
+		content, _ := afero.ReadFile(cli.fs, pipe)
+		received <- content
+	}()
+
+	require.NoError(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), pipe))
+
+	info, err := os.Lstat(pipe)
+	require.NoError(t, err)
+	require.Equal(t, os.ModeNamedPipe, info.Mode().Type())
+	require.Equal(t, plainText, string(<-received))
+}
+
+// TestDecryptThroughLink checks that secret decrypt given a symbolic link
+// as --output replaces the file the link points to, in another directory,
+// and keeps the link, as writing through the link would.
+func TestDecryptThroughLink(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	targetDir := t.TempDir()
+	target := filepath.Join(targetDir, "target.txt")
+	require.NoError(t, afero.WriteFile(cli.fs, target, []byte("old"), 0o600))
+
+	link := filepath.Join(dir, "link")
+	require.NoError(t, os.Symlink(target, link))
+
+	require.NoError(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), link))
+
+	info, err := os.Lstat(link)
+	require.NoError(t, err)
+	require.Equal(t, os.ModeSymlink, info.Mode().Type())
+
+	content, err := afero.ReadFile(cli.fs, target)
+	require.NoError(t, err)
+	require.Equal(t, plainText, string(content))
+
+	// No temporary file left beside the target
+	entries, err := afero.ReadDir(cli.fs, targetDir)
+	require.NoError(t, err)
+	require.Len(t, entries, 1)
+}
+
+// TestDecryptThroughLinkToMissingFile checks that secret decrypt given a
+// symbolic link to a file that does not exist yet as --output creates that
+// file and keeps the link, as writing through the link would. Here --output
+// is a relative link to a second link, which points into another directory.
+func TestDecryptThroughLinkToMissingFile(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	targetDir := t.TempDir()
+	target := filepath.Join(targetDir, "target.txt")
+
+	link := filepath.Join(dir, "link")
+	require.NoError(t, os.Symlink("second-link", link))
+	require.NoError(t, os.Symlink(target, filepath.Join(dir, "second-link")))
+
+	require.NoError(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), link))
+
+	for _, name := range []string{"link", "second-link"} {
+		info, err := os.Lstat(filepath.Join(dir, name))
+		require.NoError(t, err)
+		require.Equal(t, os.ModeSymlink, info.Mode().Type(), name)
+	}
+
+	content, err := afero.ReadFile(cli.fs, target)
+	require.NoError(t, err)
+	require.Equal(t, plainText, string(content))
+
+	// No temporary file left beside the target
+	entries, err := afero.ReadDir(cli.fs, targetDir)
+	require.NoError(t, err)
+	require.Len(t, entries, 1)
+}
+
+// TestDecryptThroughLinkAndParent checks that secret decrypt makes the file
+// --output names in the directory its path leads to when the path holds a
+// symbolic link to a directory followed by "..": dir/link/../sub/new.txt is
+// targetDir/sub/new.txt, and dir/sub, where removing "link/.." as text
+// leads, does not exist.
+func TestDecryptThroughLinkAndParent(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	targetDir := t.TempDir()
+	require.NoError(t, os.Mkdir(filepath.Join(targetDir, "linked"), 0o700))
+	require.NoError(t, os.Mkdir(filepath.Join(targetDir, "sub"), 0o700))
+	require.NoError(t, os.Symlink(filepath.Join(targetDir, "linked"),
+		filepath.Join(dir, "link")))
+
+	// Not filepath.Join, which would remove "link/.." too
+	output := dir + "/link/../sub/new.txt"
+
+	require.NoError(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), output))
+
+	content, err := afero.ReadFile(cli.fs, filepath.Join(targetDir, "sub", "new.txt"))
+	require.NoError(t, err)
+	require.Equal(t, plainText, string(content))
+}
+
+// TestDecryptThroughLoopingLink checks that secret decrypt given a symbolic
+// link that points to itself as --output fails, as writing through it
+// would, and leaves the link as it was.
+func TestDecryptThroughLoopingLink(t *testing.T) {
+	t.Parallel()
+
+	cli, dir := newCryptoTest(t)
+	link := filepath.Join(dir, "link")
+	require.NoError(t, os.Symlink("link", link))
+
+	require.Error(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), link))
+
+	target, err := os.Readlink(link)
+	require.NoError(t, err)
+	require.Equal(t, "link", target)
+}
+
+// TestDecryptToLongestName checks that secret decrypt writes an --output
+// whose name is as long as a file name can be, 255 bytes on Linux and
+// macOS: the temporary file's name must not be longer.
+func TestDecryptToLongestName(t *testing.T) {
+	t.Parallel()
+
+	const longestName = 255
+
+	cli, dir := newCryptoTest(t)
+	output := filepath.Join(dir, strings.Repeat("a", longestName))
+
+	require.NoError(t, cli.Decrypt("key", filepath.Join(dir, "plain.txt.age"), output))
+
+	content, err := afero.ReadFile(cli.fs, output)
+	require.NoError(t, err)
+	require.Equal(t, plainText, string(content))
+}

internal/cli/entry_test.go

@@ -7,7 +7,9 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"testing"
+	"time"
 
 	"github.com/awnumar/memguard"
 	"github.com/stretchr/testify/assert"
@@ -105,3 +107,115 @@ func TestInterruptExitsThroughMemguard(t *testing.T) {
 	require.ErrorAs(t, err, &exitErr)
 	assert.Equal(t, 1, exitErr.ExitCode(), "add ended with %v", err)
 }
+
+// Ctrl-C or a hangup while encrypt or decrypt waits for input must remove
+// the temporary file it is writing next to --output, which for decrypt
+// holds part of the secret.
+func TestInterruptRemovesTemporaryOutput(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(t.Context(), commandWait)
+	defer cancel()
+
+	secretPath := secretBinaryPath(t)
+	env := []string{
+		secret.EnvStateDir + "=" + t.TempDir(),
+		secret.EnvMnemonic + "=" + testMnemonic,
+		secret.EnvUnlockPassphrase + "=test-passphrase",
+		"PATH=" + os.Getenv("PATH"),
+	}
+
+	//nolint:gosec // G204: test executes the freshly built secret binary
+	initCmd := exec.CommandContext(ctx, secretPath, "init")
+	initCmd.Env = env
+
+	output, err := initCmd.CombinedOutput()
+	require.NoError(t, err, "init should succeed: %s", output)
+
+	// encrypt stores the new key before it starts writing, so decrypt has it
+	for _, command := range []string{"encrypt", "decrypt"} {
+		for _, sig := range []os.Signal{os.Interrupt, syscall.SIGHUP} {
+			outputDir := t.TempDir()
+
+			//nolint:gosec // G204: test executes the freshly built secret binary
+			cmd := exec.CommandContext(ctx, secretPath, command, "key",
+				"--output", filepath.Join(outputDir, "out"))
+			cmd.Env = env
+
+			// Held open and never written, so the command keeps waiting for
+			// input. Wait closes it.
+			_, err := cmd.StdinPipe()
+			require.NoError(t, err)
+			require.NoError(t, cmd.Start())
+
+			require.Eventually(t, func() bool {
+				entries, err := os.ReadDir(outputDir)
+
+				return err == nil && len(entries) > 0
+			}, commandWait, 10*time.Millisecond, "%s made no temporary file", command)
+			require.NoError(t, cmd.Process.Signal(sig))
+
+			var exitErr *exec.ExitError
+
+			require.ErrorAs(t, cmd.Wait(), &exitErr)
+
+			entries, err := os.ReadDir(outputDir)
+			require.NoError(t, err)
+			assert.Empty(t, entries, "%s left its temporary file on %v", command, sig)
+		}
+	}
+}
+
+// encrypt started with nohup must go on ignoring a hangup, which it catches
+// otherwise, and finish writing --output.
+func TestNohupIgnoresHangup(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(t.Context(), commandWait)
+	defer cancel()
+
+	secretPath := secretBinaryPath(t)
+	env := []string{
+		secret.EnvStateDir + "=" + t.TempDir(),
+		secret.EnvMnemonic + "=" + testMnemonic,
+		secret.EnvUnlockPassphrase + "=test-passphrase",
+		"PATH=" + os.Getenv("PATH"),
+	}
+
+	//nolint:gosec // G204: test executes the freshly built secret binary
+	initCmd := exec.CommandContext(ctx, secretPath, "init")
+	initCmd.Env = env
+
+	output, err := initCmd.CombinedOutput()
+	require.NoError(t, err, "init should succeed: %s", output)
+
+	outputDir := t.TempDir()
+	outputFile := filepath.Join(outputDir, "out")
+
+	//nolint:gosec // G204: test executes the freshly built secret binary
+	cmd := exec.CommandContext(ctx, "nohup", secretPath, "encrypt", "key",
+		"--output", outputFile)
+	cmd.Env = env
+
+	stdin, err := cmd.StdinPipe()
+	require.NoError(t, err)
+	require.NoError(t, cmd.Start())
+
+	require.Eventually(t, func() bool {
+		entries, err := os.ReadDir(outputDir)
+
+		return err == nil && len(entries) > 0
+	}, commandWait, 10*time.Millisecond, "encrypt made no temporary file")
+	require.NoError(t, cmd.Process.Signal(syscall.SIGHUP))
+
+	// Time for a hangup that is caught to end encrypt before it has its input
+	time.Sleep(500 * time.Millisecond)
+
+	_, err = stdin.Write([]byte("document"))
+	require.NoError(t, err)
+	require.NoError(t, stdin.Close())
+	require.NoError(t, cmd.Wait())
+
+	_, err = os.Stat(outputFile)
+	require.NoError(t, err)
+}

internal/cli/leftovers_test.go

@@ -52,10 +52,10 @@ func TestLeftoversRemovedByNextChangingCommand(t *testing.T) {
 	}
 
 	for _, file := range []string{
-		testStateDir + "/.currentvault.tmp-4",
-		vaultDir + "/.current-unlocker.tmp-5",
-		secretDir + "/.current.tmp-6",
-		secretDir + "/versions/" + versions[0] + "/.metadata.age.tmp-7",
+		testStateDir + "/.tmp-4",
+		vaultDir + "/.tmp-5",
+		secretDir + "/.tmp-6",
+		secretDir + "/versions/" + versions[0] + "/.tmp-7",
 	} {
 		require.NoError(t, afero.WriteFile(fs, file,
 			[]byte("partial"), secret.FilePerms))

internal/cli/root.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"os"
+	"os/signal"
 
 	"github.com/awnumar/memguard"
 	"github.com/spf13/cobra"
@@ -14,12 +15,13 @@ import (
 // every memguard buffer before it returns, so the caller must do nothing
 // but exit with the code.
 func Entry() int {
-	// On SIGINT or SIGTERM memguard runs this function, wipes every buffer
-	// and exits with status 1. The passphrase prompt turns echo off on the
-	// controlling terminal until the read finishes, so a signal there would
-	// leave echo off. Only a process in the terminal's foreground process
-	// group may reset it: one in the background that tries is stopped
-	// instead of exiting.
+	// On SIGINT, SIGTERM or SIGHUP memguard runs this function, wipes every
+	// buffer and exits with status 1. The function removes the temporary
+	// file that encrypt or decrypt is writing. The passphrase prompt turns
+	// echo off on the controlling terminal until the read finishes, so a
+	// signal there would leave echo off. Only a process in the terminal's
+	// foreground process group may reset it: one in the background that
+	// tries is stopped instead of exiting.
 	terminal, terminalErr := os.Open(secret.TerminalPath)
 
 	var terminalState *term.State
@@ -30,7 +32,20 @@ func Entry() int {
 		terminalState, terminalErr = term.GetState(int(terminal.Fd()))
 	}
 
+	signals := []os.Signal{os.Interrupt, unix.SIGTERM}
+
+	// A command started with nohup must go on ignoring SIGHUP, which
+	// catching it would undo
+	if !signal.Ignored(unix.SIGHUP) {
+		signals = append(signals, unix.SIGHUP)
+	}
+
 	memguard.CatchSignal(func(os.Signal) {
+		name := temporaryOutput.Load()
+		if name != nil {
+			_ = os.Remove(*name)
+		}
+
 		if terminalErr != nil {
 			return
 		}
@@ -39,7 +54,7 @@ func Entry() int {
 		if err == nil && foreground == unix.Getpgrp() {
 			_ = term.Restore(int(terminal.Fd()), terminalState)
 		}
-	}, os.Interrupt, unix.SIGTERM)
+	}, signals...)
 
 	defer memguard.Purge()
 

internal/cli/unlockers.go

@@ -314,8 +314,7 @@ func (cli *Instance) UnlockersList(jsonOutput bool) error {
 		return err
 	}
 
-	// Not nil, so that a vault with no unlockers prints [] in JSON, not null
-	unlockers := make([]UnlockerInfo, 0, len(unlockerMetadata))
+	var unlockers []UnlockerInfo
 
 	for _, unlockerID := range slices.Sorted(maps.Keys(unlockerMetadata)) {
 		metadata := unlockerMetadata[unlockerID]

internal/cli/unlockers_list_test.go

@@ -8,8 +8,6 @@
 //   - TestUnlockersListSkipsUnreadableMetadata: an unlocker whose metadata
 //     file cannot be checked for or read is left out, and the other is
 //     still listed.
-//   - TestUnlockersListEmptyJSON: a vault with no unlockers lists them as
-//     an empty JSON list.
 
 //nolint:testpackage // white-box test of unexported internals
 package cli
@@ -323,36 +321,3 @@ func TestUnlockersListSkipsUnreadableMetadata(t *testing.T) {
 		})
 	}
 }
-
-// TestUnlockersListEmptyJSON is a regression test for
-// https://git.eeqj.de/sneak/secret/issues/148: listing the unlockers of a
-// vault that has none, as after its last unlocker is removed, printed
-// "unlockers": null in JSON form instead of an empty list.
-func TestUnlockersListEmptyJSON(t *testing.T) {
-	t.Parallel()
-
-	fs := afero.NewMemMapFs()
-	vaultDir := filepath.Join(listTestStateDir, "vaults.d", listTestVaultName)
-
-	require.NoError(t, afero.WriteFile(
-		fs, filepath.Join(listTestStateDir, "currentvault"),
-		[]byte(listTestVaultName), listTestFilePerm,
-	))
-	require.NoError(t, fs.MkdirAll(
-		filepath.Join(vaultDir, listTestUnlockersDirName), listTestDirPerm,
-	))
-
-	var buf bytes.Buffer
-
-	cmd := &cobra.Command{}
-	cmd.SetOut(&buf)
-
-	instance := &Instance{fs: fs, stateDir: listTestStateDir, cmd: cmd}
-	require.NoError(t, instance.UnlockersList(true))
-
-	var decoded map[string]any
-
-	require.NoError(t, json.Unmarshal(buf.Bytes(), &decoded))
-	assert.Equal(t, []any{}, decoded["unlockers"],
-		"no unlockers must be printed as [], not %s", buf.String())
-}

internal/cli/vault_list_test.go

@@ -1,42 +0,0 @@
-package cli_test
-
-import (
-	"bytes"
-	"encoding/json"
-	"path/filepath"
-	"testing"
-
-	"github.com/spf13/afero"
-	"github.com/spf13/cobra"
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-	"sneak.berlin/go/secret/internal/cli"
-	"sneak.berlin/go/secret/internal/secret"
-)
-
-// TestVaultListEmptyJSON is a regression test for
-// https://git.eeqj.de/sneak/secret/issues/148: listing the vaults when
-// vaults.d holds none printed "vaults": null in JSON form instead of an
-// empty list.
-func TestVaultListEmptyJSON(t *testing.T) {
-	t.Parallel()
-
-	fs := afero.NewMemMapFs()
-	require.NoError(t, fs.MkdirAll(
-		filepath.Join(testStateDir, "vaults.d"), secret.DirPerms,
-	))
-
-	var buf bytes.Buffer
-
-	cmd := &cobra.Command{}
-	cmd.SetOut(&buf)
-
-	c := cli.NewCLIInstanceWithStateDir(fs, testStateDir)
-	require.NoError(t, c.ListVaults(cmd, true))
-
-	var decoded map[string]any
-
-	require.NoError(t, json.Unmarshal(buf.Bytes(), &decoded))
-	assert.Equal(t, []any{}, decoded["vaults"],
-		"no vaults must be printed as [], not %s", buf.String())
-}

internal/secret/atomic.go

@@ -10,8 +10,8 @@ import (
 	"github.com/spf13/afero"
 )
 
-// tempNamePart is in the name of every temporary file WriteFileAtomic makes,
-// ".NAME.tmp-123", and every temporary directory TempDirFor makes, ".tmp-123".
+// tempNamePart starts the name of every temporary file WriteFileAtomicFunc
+// makes and every temporary directory TempDirFor makes, ".tmp-123".
 const tempNamePart = ".tmp-"
 
 // WriteFileAtomic replaces the file at path with data so that a reader, or
@@ -21,17 +21,38 @@ const tempNamePart = ".tmp-"
 // within one filesystem), is synced to disk, and is renamed over path. The
 // temporary file is removed if any step fails.
 func WriteFileAtomic(fs afero.Fs, path string, data []byte) error {
-	tmp, err := afero.TempFile(fs, filepath.Dir(path),
-		"."+filepath.Base(path)+tempNamePart+"*")
+	return WriteFileAtomicFunc(fs, path, func(file afero.File) error {
+		_, err := file.Write(data)
+		if err != nil {
+			return fmt.Errorf("failed to write %s: %w", path, err)
+		}
+
+		return nil
+	})
+}
+
+// WriteFileAtomicFunc is WriteFileAtomic for content that write streams
+// into the temporary file, which it is given, instead of holding it in
+// memory. An error from write is returned as it is. The temporary file's
+// name leaves out path's, which may already be as long as a name can be.
+func WriteFileAtomicFunc(
+	fs afero.Fs, path string, write func(file afero.File) error,
+) error {
+	tmp, err := afero.TempFile(fs, filepath.Dir(path), tempNamePart)
 	if err != nil {
 		return fmt.Errorf("failed to create temporary file for %s: %w", path, err)
 	}
 
-	_, err = tmp.Write(data)
-	if err == nil {
-		err = tmp.Sync()
+	err = write(tmp)
+	if err != nil {
+		_ = tmp.Close()
+		_ = fs.Remove(tmp.Name())
+
+		return err
 	}
 
+	err = tmp.Sync()
+
 	closeErr := tmp.Close()
 	if err == nil {
 		err = closeErr

internal/vault/management.go

@@ -140,9 +140,8 @@ func ListVaults(fs afero.Fs, stateDir string) ([]string, error) {
 		return nil, fmt.Errorf("failed to read vaults directory: %w", err)
 	}
 
-	// Extract vault names. Not nil, so that no vaults prints [] in JSON,
-	// not null.
-	vaults := make([]string, 0, len(entries))
+	// Extract vault names
+	var vaults []string
 
 	for _, entry := range entries {
 		if entry.IsDir() {