Fix handling of empty user input in pinentry module

As it turns out, the pinentry program responds slightly differently to a
request to enter a password/PIN when the user enters one vs. when he/she
just continues, leaving the input empty, as is illustrated here:

When the user enters 'hello':
  > $ gpg-connect-agent 'GET_PASSPHRASE --data cacheid errormsg prompt description' '/bye'
  > D hello
  > OK

When the user enters nothing:
  > $ gpg-connect-agent 'GET_PASSPHRASE --data cacheid errormsg prompt description' '/bye'
  > OK

So far we always expected a two line response, with the first line
containing the 'D ' prefix, which prevents us from handling empty input
properly.
This change fixes this shortcoming by adding a case for it.

Fixes #176

CHANGELOG.md

@@ -14,6 +14,7 @@ Unreleased
  extensions
 - Allowed entering of `base32` encoded strings containing spaces
 - Fixed pinentry dialog highlighting some messages incorrectly as errors
+- Fixed handling of empty user input through pinentry
 - Switched to using GitHub Actions as the project's CI pipeline
 - Updated minimum supported Rust version to `1.43.0`
 - Bumped `nitrokey` dependency to `0.9.0`

src/pinentry.rs

@@ -1,6 +1,6 @@
 // pinentry.rs
 
-// Copyright (C) 2017-2020 The Nitrocli Developers
+// Copyright (C) 2017-2021 The Nitrocli Developers
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 use std::borrow;
@@ -187,6 +187,9 @@ fn parse_pinentry_pin<R>(response: R) -> anyhow::Result<String>
 where
  R: AsRef<str>,
 {
+ const DATA_PREFIX: &str = "D ";
+ const ERR_PREFIX: &str = "ERR ";
+
  let string = response.as_ref();
  let lines: Vec<&str> = string.lines().collect();
 
@@ -195,19 +198,20 @@ where
  // > OK
  // or potentially:
  // > ERR 83886179 Operation cancelled <Pinentry>
- if lines.len() == 2 && lines[1] == "OK" && lines[0].starts_with("D ") {
- // We got the only valid answer we accept.
- let (_, pass) = lines[0].split_at(2);
- return Ok(pass.to_string());
- }
-
- // Check if we are dealing with a special "ERR " line and report that
- // specially.
- if !lines.is_empty() && lines[0].starts_with("ERR ") {
- let (_, error) = lines[0].split_at(4);
- anyhow::bail!("{}", error);
+ //
+ // Furthermore, in case of an empty password we'd get just an OK.
+ match lines.as_slice() {
+ ["OK"] => Ok(String::new()),
+ [line, "OK"] if line.starts_with(DATA_PREFIX) => {
+ let (_, pass) = line.split_at(DATA_PREFIX.len());
+ Ok(pass.to_string())
+ }
+ [line] if line.starts_with(ERR_PREFIX) => {
+ let (_, error) = line.split_at(ERR_PREFIX.len());
+ anyhow::bail!("{}", error);
+ }
+ _ => anyhow::bail!("Unexpected response: {}", string),
  }
- anyhow::bail!("Unexpected response: {}", string)
 }
 
 /// Inquire a secret from the user.
@@ -333,6 +337,14 @@ where
 mod tests {
  use super::*;
 
+ #[test]
+ fn parse_pinentry_pin_empty() {
+ let response = "OK\n";
+ let expected = "";
+
+ assert_eq!(parse_pinentry_pin(response).unwrap(), expected)
+ }
+
  #[test]
  fn parse_pinentry_pin_good() {
  let response = "D passphrase\nOK\n";