cmd/age: clean up the terminal UI

cmd/age/age.go

@@ -10,7 +10,6 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"log"
 	"os"
 	"regexp"
 	"runtime/debug"
@@ -23,15 +22,6 @@ import (
 	"golang.org/x/term"
 )
 
-type multiFlag []string
-
-func (f *multiFlag) String() string { return fmt.Sprint(*f) }
-
-func (f *multiFlag) Set(value string) error {
-	*f = append(*f, value)
-	return nil
-}
-
 const usage = `Usage:
     age [--encrypt] (-r RECIPIENT | -R PATH)... [--armor] [-o OUTPUT] [INPUT]
     age [--encrypt] --passphrase [--armor] [-o OUTPUT] [INPUT]
@@ -77,8 +67,20 @@ Example:
 // golang.org/issue/29814 and golang.org/issue/29228.
 var Version string
 
+// stdinInUse is used to ensure only one of input, recipients, or identities
+// file is read from stdin. It's a singleton like os.Stdin.
+var stdinInUse bool
+
+type multiFlag []string
+
+func (f *multiFlag) String() string { return fmt.Sprint(*f) }
+
+func (f *multiFlag) Set(value string) error {
+	*f = append(*f, value)
+	return nil
+}
+
 func main() {
-	log.SetFlags(0)
 	flag.Usage = func() { fmt.Fprintf(os.Stderr, "%s\n", usage) }
 
 	if len(os.Args) == 1 {
@@ -119,6 +121,8 @@ func main() {
 			return
 		}
 		if buildInfo, ok := debug.ReadBuildInfo(); ok {
+			// TODO: use buildInfo.Settings to prepare a pseudoversion such as
+			// v0.0.0-20210817164053-32db794688a5+dirty on Go 1.18+.
 			fmt.Println(buildInfo.Main.Version)
 			return
 		}
@@ -255,7 +259,7 @@ func main() {
 }
 
 func passphrasePromptForEncryption() (string, error) {
-	pass, err := readPassphrase("Enter passphrase (leave empty to autogenerate a secure one):")
+	pass, err := readSecret("Enter passphrase (leave empty to autogenerate a secure one):")
 	if err != nil {
 		return "", fmt.Errorf("could not read passphrase: %v", err)
 	}
@@ -266,10 +270,14 @@ func passphrasePromptForEncryption() (string, error) {
 			words = append(words, randomWord())
 		}
 		p = strings.Join(words, "-")
-		// TODO: consider printing this to the terminal, instead of stderr.
+		// It's somewhat unfortunate that the prompt comes through the terminal,
-		fmt.Fprintf(os.Stderr, "Using the autogenerated passphrase %q.\n", p)
+		// while the autogenerated passphrase is printed to stderr. However,
+		// thinking about the terminal as a pinentry UI, it's better for the
+		// passphrase to stick around and be copy-pastable, than to show up in
+		// ephemeral UI.
+		printf("using autogenerated passphrase %q", p)
 	} else {
-		confirm, err := readPassphrase("Confirm passphrase:")
+		confirm, err := readSecret("Confirm passphrase:")
 		if err != nil {
 			return "", fmt.Errorf("could not read passphrase: %v", err)
 		}
@@ -390,7 +398,7 @@ func decrypt(keys []string, in io.Reader, out io.Writer) {
 }
 
 func passphrasePrompt() (string, error) {
-	pass, err := readPassphrase("Enter passphrase:")
+	pass, err := readSecret("Enter passphrase:")
 	if err != nil {
 		return "", fmt.Errorf("could not read passphrase: %v", err)
 	}
@@ -450,20 +458,3 @@ func (l *lazyOpener) Close() error {
 	}
 	return nil
 }
-
-func errorf(format string, v ...interface{}) {
-	log.Printf("age: error: "+format, v...)
-	log.Fatalf("age: report unexpected or unhelpful errors at https://filippo.io/age/report")
-}
-
-func warningf(format string, v ...interface{}) {
-	log.Printf("age: warning: "+format, v...)
-}
-
-func errorWithHint(error string, hints ...string) {
-	log.Printf("age: error: %s", error)
-	for _, hint := range hints {
-		log.Printf("age: hint: %s", hint)
-	}
-	log.Fatalf("age: report unexpected or unhelpful errors at https://filippo.io/age/report")
-}

cmd/age/encrypted_keys.go

@@ -8,13 +8,13 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"os"
-	"runtime"
 
 	"filippo.io/age"
-	"golang.org/x/term"
 )
 
+// LazyScryptIdentity is an age.Identity that requests a passphrase only if it
+// encounters an scrypt stanza. After obtaining a passphrase, it delegates to
+// ScryptIdentity.
 type LazyScryptIdentity struct {
 	Passphrase func() (string, error)
 }
@@ -102,37 +102,3 @@ func (i *EncryptedIdentity) decrypt() error {
 	i.identities, err = parseIdentities(d)
 	return err
 }
-
-// readPassphrase reads a passphrase from the terminal. It does not read from a
-// non-terminal stdin, so it does not check stdinInUse.
-func readPassphrase(prompt string) ([]byte, error) {
-	var in, out *os.File
-	if runtime.GOOS == "windows" {
-		var err error
-		in, err = os.OpenFile("CONIN$", os.O_RDWR, 0)
-		if err != nil {
-			return nil, err
-		}
-		defer in.Close()
-		out, err = os.OpenFile("CONOUT$", os.O_WRONLY, 0)
-		if err != nil {
-			return nil, err
-		}
-		defer out.Close()
-	} else if tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0); err == nil {
-		defer tty.Close()
-		in, out = tty, tty
-	} else {
-		if !term.IsTerminal(int(os.Stdin.Fd())) {
-			return nil, fmt.Errorf("standard input is not a terminal, and /dev/tty is not available: %v", err)
-		}
-		in, out = os.Stdin, os.Stderr
-	}
-	fmt.Fprintf(out, "%s ", prompt)
-	// Use CRLF to work around an apparent bug in WSL2's handling of CONOUT$.
-	// Only when running a Windows binary from WSL2, the cursor would not go
-	// back to the start of the line with a simple LF. Honestly, it's impressive
-	// CONIN$ and CONOUT$ even work at all inside WSL2.
-	defer fmt.Fprintf(out, "\r\n")
-	return term.ReadPassword(int(in.Fd()))
-}

cmd/age/parse.go

@@ -20,9 +20,6 @@ import (
 	"golang.org/x/crypto/ssh"
 )
 
-// stdinInUse is set in main. It's a singleton like os.Stdin.
-var stdinInUse bool
-
 type gitHubRecipientError struct {
 	username string
 }
@@ -171,7 +168,7 @@ func parseIdentitiesFile(name string) ([]age.Identity, error) {
 		return []age.Identity{&EncryptedIdentity{
 			Contents: contents,
 			Passphrase: func() (string, error) {
-				pass, err := readPassphrase(fmt.Sprintf("Enter passphrase for identity file %q:", name))
+				pass, err := readSecret(fmt.Sprintf("Enter passphrase for identity file %q:", name))
 				if err != nil {
 					return "", fmt.Errorf("could not read passphrase: %v", err)
 				}
@@ -261,7 +258,7 @@ func parseSSHIdentity(name string, pemBytes []byte) ([]age.Identity, error) {
 			}
 		}
 		passphrasePrompt := func() ([]byte, error) {
-			pass, err := readPassphrase(fmt.Sprintf("Enter passphrase for %q:", name))
+			pass, err := readSecret(fmt.Sprintf("Enter passphrase for %q:", name))
 			if err != nil {
 				return nil, fmt.Errorf("could not read passphrase for %q: %v", name, err)
 			}
@@ -303,23 +300,3 @@ Ensure %q exists, or convert the private key %q to a modern format with "ssh-key
 	}
 	return pubKey, nil
 }
-
-func pluginDisplayMessage(name string) func(string) error {
-	return func(message string) error {
-		fmt.Fprintf(os.Stderr, "[age-plugin-%s] %v\n", name, message)
-		return nil
-	}
-}
-
-func pluginRequestSecret(name string) func(string, bool) (string, error) {
-	return func(message string, _ bool) (string, error) {
-		fmt.Fprintf(os.Stderr, "[age-plugin-%s] %v\n", name, message)
-		prompt := fmt.Sprintf("[age-plugin-%s] Enter value:", name)
-		secret, err := readPassphrase(prompt)
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "Could not read value for age-plugin-%s: %v", name, err)
-			return "", err
-		}
-		return string(secret), nil
-	}
-}

cmd/age/tui.go

@@ -0,0 +1,113 @@
+// Copyright 2021 The age Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// This file implements the terminal UI of cmd/age. The rules are:
+//
+//   - Anything that requires user interaction goes to the terminal,
+//     and is erased afterwards if possible. This UI would be possible
+//     to replace with a pinentry with no output or UX changes.
+//
+//   - Everything else goes to standard error with an "age:" prefix.
+//     No capitalized initials and no periods at the end.
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"runtime"
+
+	"golang.org/x/term"
+)
+
+// l is a logger with no prefixes.
+var l = log.New(os.Stderr, "", 0)
+
+func printf(format string, v ...interface{}) {
+	l.Printf("age: "+format, v...)
+}
+
+func errorf(format string, v ...interface{}) {
+	l.Printf("age: error: "+format, v...)
+	l.Fatalf("age: report unexpected or unhelpful errors at https://filippo.io/age/report")
+}
+
+func warningf(format string, v ...interface{}) {
+	l.Printf("age: warning: "+format, v...)
+}
+
+func errorWithHint(error string, hints ...string) {
+	l.Printf("age: error: %s", error)
+	for _, hint := range hints {
+		l.Printf("age: hint: %s", hint)
+	}
+	l.Fatalf("age: report unexpected or unhelpful errors at https://filippo.io/age/report")
+}
+
+// Terminal escape codes to erase the previous line.
+const (
+	CUI = "\033["   // Control Sequence Introducer
+	CPL = CUI + "F" // Cursor Previous Line
+	EL  = CUI + "K" // Erase in Line
+	CHA = CUI + "G" // Cursor Horizontal Absolute
+)
+
+// readSecret reads a value from the terminal with no echo. The prompt is
+// ephemeral. readSecret does not read from a non-terminal stdin, so it does not
+// check stdinInUse.
+func readSecret(prompt string) ([]byte, error) {
+	var in, out *os.File
+	if runtime.GOOS == "windows" {
+		var err error
+		in, err = os.OpenFile("CONIN$", os.O_RDWR, 0)
+		if err != nil {
+			return nil, err
+		}
+		defer in.Close()
+		out, err = os.OpenFile("CONOUT$", os.O_WRONLY, 0)
+		if err != nil {
+			return nil, err
+		}
+		defer out.Close()
+	} else if tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0); err == nil {
+		defer tty.Close()
+		in, out = tty, tty
+	} else {
+		if !term.IsTerminal(int(os.Stdin.Fd())) {
+			return nil, fmt.Errorf("standard input is not a terminal, and /dev/tty is not available: %v", err)
+		}
+		in, out = os.Stdin, os.Stderr
+	}
+
+	fmt.Fprintf(out, "%s ", prompt)
+
+	// First, open a new line (since the return character is not echoed, like
+	// the password), which is guaranteed to work everywhere. Then, try to erase
+	// the line above with escape codes. (We use CRLF instead of LF to work
+	// around an apparent bug in WSL2's handling of CONOUT$. Only when running a
+	// Windows binary from WSL2, the cursor would not go back to the start of
+	// the line with a simple LF. Honestly, it's impressive CONIN$ and CONOUT$
+	// even work at all inside WSL2.)
+	defer fmt.Fprintf(out, "\r\n"+CPL+EL)
+
+	return term.ReadPassword(int(in.Fd()))
+}
+
+func pluginDisplayMessage(name string) func(string) error {
+	return func(message string) error {
+		printf("%s plugin: %s", name, message)
+		return nil
+	}
+}
+
+func pluginRequestSecret(name string) func(string, bool) (string, error) {
+	return func(message string, _ bool) (string, error) {
+		secret, err := readSecret(message)
+		if err != nil {
+			return "", fmt.Errorf("could not read value for age-plugin-%s: %v", name, err)
+		}
+		return string(secret), nil
+	}
+}

go.mod

@@ -5,6 +5,6 @@ go 1.17
 require (
 	filippo.io/edwards25519 v1.0.0-rc.1
 	golang.org/x/crypto v0.0.0-20210817164053-32db794688a5
-	golang.org/x/term v0.0.0-20210615171337-6886f2dfbf5b
 	golang.org/x/sys v0.0.0-20210903071746-97244b99971b
+	golang.org/x/term v0.0.0-20210615171337-6886f2dfbf5b
 )

internal/plugin/client.go

@@ -66,7 +66,7 @@ func (r *Recipient) Name() string {
 func (r *Recipient) Wrap(fileKey []byte) (stanzas []*age.Stanza, err error) {
 	defer func() {
 		if err != nil {
-			err = fmt.Errorf("age-plugin-%s: %w", r.name, err)
+			err = fmt.Errorf("%s plugin: %w", r.name, err)
 		}
 	}()
 
@@ -254,7 +254,7 @@ func (i *Identity) Recipient() *Recipient {
 func (i *Identity) Unwrap(stanzas []*age.Stanza) (fileKey []byte, err error) {
 	defer func() {
 		if err != nil {
-			err = fmt.Errorf("age-plugin-%s: %w", i.name, err)
+			err = fmt.Errorf("%s plugin: %w", i.name, err)
 		}
 	}()
 
@@ -418,10 +418,12 @@ func openClientConnection(name, protocol string) (*clientConnection, error) {
 	if os.Getenv("AGEDEBUG") == "plugin" {
 		cc.Reader = io.TeeReader(cc.Reader, os.Stderr)
 		cc.Writer = io.MultiWriter(cc.Writer, os.Stderr)
+		cmd.Stderr = os.Stderr
 	}
 
-	cmd.Stderr = &cc.stderr
+	// We don't want the plugins to rely on the working directory for anything
-
+	// as different clients might treat it differently, so we set it to an empty
+	// temporary directory.
 	cmd.Dir = os.TempDir()
 
 	if err := cmd.Start(); err != nil {