cmd/age: buffer armored ciphertext before prompting

A partial solution, still missing bracketed paste support.

Updates #364

cmd/age/age.go

@@ -234,6 +234,16 @@ func main() {
 		in = f
 	} else {
 		stdinInUse = true
+		if decryptFlag && term.IsTerminal(int(os.Stdin.Fd())) {
+			// If the input comes from a TTY, assume it's armored, and buffer up
+			// to the END line (or EOF/EOT) so that a password prompt or the
+			// output don't get in the way of typing the input. See Issue 364.
+			buf, err := bufferTerminalInput(in)
+			if err != nil {
+				errorf("failed to buffer terminal input: %v", err)
+			}
+			in = buf
+		}
 	}
 	if name := outFlag; name != "" && name != "-" {
 		f := newLazyOpener(name)

cmd/age/testdata/encrypted_keys.txt

@@ -1,4 +1,5 @@
-# TODO: age-encrypted private keys, multiple identities, -i ordering, -e -i
+# TODO: age-encrypted private keys, multiple identities, -i ordering, -e -i,
+# age file password prompt during encryption
 
 [windows] skip # no pty support
 
@@ -48,6 +49,16 @@ pty terminal
 ! age -d -i key_rsa_other rsa_other.age
 stderr 'mismatched private and public SSH key'
 
+# buffer armored ciphertext before prompting if stdin is the terminal
+pty terminal
+age -e -i key_ed25519 -a -o test.age input
+exec cat test.age terminal # concatenated ciphertext + password
+pty -stdin stdout
+age -d -i key_ed25519
+ptyout 'Enter passphrase'
+! stderr .
+cmp stdout input
+
 -- input --
 test
 -- terminal --

cmd/age/testdata/terminal.txt

@@ -37,6 +37,16 @@ pty terminal
 age -d test.age
 cmp stdout input
 
+# buffer armored ciphertext before prompting if stdin is the terminal
+pty terminal
+age -p -a -o test.age input
+exec cat test.age terminal # concatenated ciphertext + password
+pty -stdin stdout
+age -d
+ptyout 'Enter passphrase'
+! stderr .
+cmp stdout input
+
 -- input --
 test
 -- terminal --

cmd/age/tui.go

@@ -14,6 +14,7 @@ package main
 //     No capitalized initials and no periods at the end.
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -21,6 +22,7 @@ import (
 	"os"
 	"runtime"
 
+	"filippo.io/age/armor"
 	"filippo.io/age/internal/plugin"
 	"golang.org/x/term"
 )
@@ -205,3 +207,20 @@ var pluginTerminalUI = &plugin.ClientUI{
 		printf("waiting on %s plugin...", name)
 	},
 }
+
+func bufferTerminalInput(in io.Reader) (io.Reader, error) {
+	buf := &bytes.Buffer{}
+	if _, err := buf.ReadFrom(ReaderFunc(func(p []byte) (n int, err error) {
+		if bytes.Contains(buf.Bytes(), []byte(armor.Footer+"\n")) {
+			return 0, io.EOF
+		}
+		return in.Read(p)
+	})); err != nil {
+		return nil, err
+	}
+	return buf, nil
+}
+
+type ReaderFunc func(p []byte) (n int, err error)
+
+func (f ReaderFunc) Read(p []byte) (n int, err error) { return f(p) }