Introduce support for user-provided extensions

This change introduces support for discovering and executing
user-provided extensions to the program. Extensions are useful for
allowing users to provide additional functionality on top of the
nitrocli proper. Implementation wise we stick to an approach similar to
git or cargo subcommands in nature: we search the directories listed in
the PATH environment variable for a file that starts with "nitrocli-",
followed by the extension name. This file is then executed. It is
assumed that the extension recognizes (or at least not prohibits) the
following arguments: --nitrocli (providing the path to the nitrocli
binary), --model (with the model passed to the main program), and
--verbosity (the verbosity level).

4 files changed, 242 insertions, 0 deletions

diff --git a/src/tests/extension_model_test.py b/src/tests/extension_model_test.py
new file mode 100644
index 0000000..651c8e7
--- /dev/null
+++ b/src/tests/extension_model_test.py
@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+
+from argparse import (
+  ArgumentParser,
+)
+from enum import (
+  Enum,
+)
+from sys import (
+  argv,
+  exit,
+)
+
+
+class Action(Enum):
+  """An action to perform."""
+  NITROCLI = "nitrocli"
+  MODEL = "model"
+  VERBOSITY = "verbosity"
+
+  @classmethod
+  def all(cls):
+    """Return the list of all the enum members' values."""
+    return [x.value for x in cls.__members__.values()]
+
+
+def main(args):
+  """The extension's main function."""
+  parser = ArgumentParser()
+  parser.add_argument(choices=Action.all(), dest="what")
+  parser.add_argument("--nitrocli", action="store", default=None)
+  parser.add_argument("--model", action="store", default=None)
+  # We deliberately store the argument to this option as a string
+  # because we can differentiate between None and a valid value, in
+  # order to verify that it really is supplied.
+  parser.add_argument("--verbosity", action="store", default=None)
+
+  namespace = parser.parse_args(args[1:])
+  if namespace.what == Action.NITROCLI.value:
+    print(namespace.nitrocli)
+  elif namespace.what == Action.MODEL.value:
+    print(namespace.model)
+  elif namespace.what == Action.VERBOSITY.value:
+    print(namespace.verbosity)
+  else:
+    return 1
+
+  return 0
+
+
+if __name__ == "__main__":
+  exit(main(argv))
diff --git a/src/tests/extensions.rs b/src/tests/extensions.rs
new file mode 100644
index 0000000..9e70181
--- /dev/null
+++ b/src/tests/extensions.rs
@@ -0,0 +1,65 @@
+// extensions.rs
+
+// *************************************************************************
+// * Copyright (C) 2020 Daniel Mueller (deso@posteo.net)                   *
+// *                                                                       *
+// * This program is free software: you can redistribute it and/or modify  *
+// * it under the terms of the GNU General Public License as published by  *
+// * the Free Software Foundation, either version 3 of the License, or     *
+// * (at your option) any later version.                                   *
+// *                                                                       *
+// * This program is distributed in the hope that it will be useful,       *
+// * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+// * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+// * GNU General Public License for more details.                          *
+// *                                                                       *
+// * You should have received a copy of the GNU General Public License     *
+// * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+// *************************************************************************
+
+use std::env;
+use std::fs;
+use std::io;
+
+use super::*;
+
+use crate::commands::resolve_extension;
+use crate::Error;
+
+#[test]
+fn discover_extensions() -> crate::Result<()> {
+  let dir1 = tempfile::tempdir()?;
+  let dir2 = tempfile::tempdir()?;
+
+  {
+    let ext1_path = dir1.path().join("nitrocli-ext1");
+    let ext2_path = dir1.path().join("nitrocli-ext2");
+    let ext3_path = dir2.path().join("nitrocli-super-1337-extensions111one");
+    let _ext1 = fs::File::create(&ext1_path)?;
+    let _ext2 = fs::File::create(&ext2_path)?;
+    let _ext3 = fs::File::create(&ext3_path)?;
+
+    let path = env::join_paths(&[dir1.path(), dir2.path()]).map_err(|err| err.to_string())?;
+    assert_eq!(
+      resolve_extension(&path, ffi::OsStr::new("ext1"))?,
+      ext1_path
+    );
+    assert_eq!(
+      resolve_extension(&path, ffi::OsStr::new("ext2"))?,
+      ext2_path
+    );
+    assert_eq!(
+      resolve_extension(&path, ffi::OsStr::new("super-1337-extensions111one"))?,
+      ext3_path
+    );
+
+    match resolve_extension(&ffi::OsStr::new(""), ffi::OsStr::new("ext1")) {
+      Err(Error::IoError(err)) if err.kind() == io::ErrorKind::NotFound => {
+        let expected = io::Error::new(io::ErrorKind::NotFound, "extension nitrocli-ext1 not found");
+        assert_eq!(err.to_string(), expected.to_string())
+      }
+      r => panic!("Unexpected variant found: {:?}", r),
+    }
+  }
+  Ok(())
+}
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
index e86f42f..e0ee876 100644
--- a/src/tests/mod.rs
+++ b/src/tests/mod.rs
@@ -24,6 +24,7 @@ use nitrokey_test::test as test_device;
 
 mod config;
 mod encrypted;
+mod extensions;
 mod hidden;
 mod list;
 mod lock;
@@ -93,6 +94,15 @@ impl Builder {
     self
   }
 
+  /// Set the `PATH` used for looking up extensions.
+  fn path<P>(mut self, path: P) -> Self
+  where
+    P: Into<ffi::OsString>,
+  {
+    self.0.path = Some(path.into());
+    self
+  }
+
   /// Set the password to use for certain operations.
   fn password<P>(mut self, password: P) -> Self
   where
@@ -110,6 +120,7 @@ impl Builder {
 
 struct Nitrocli {
   model: Option<nitrokey::Model>,
+  path: Option<ffi::OsString>,
   admin_pin: Option<ffi::OsString>,
   user_pin: Option<ffi::OsString>,
   new_admin_pin: Option<ffi::OsString>,
@@ -121,6 +132,7 @@ impl Nitrocli {
   pub fn new() -> Self {
     Self {
       model: None,
+      path: None,
       admin_pin: Some(nitrokey::DEFAULT_ADMIN_PIN.into()),
       user_pin: Some(nitrokey::DEFAULT_USER_PIN.into()),
       new_admin_pin: None,
@@ -174,6 +186,7 @@ impl Nitrocli {
     let ctx = &mut crate::RunCtx {
       stdout: &mut stdout,
       stderr: &mut stderr,
+      path: self.path.clone(),
       admin_pin: self.admin_pin.clone(),
       user_pin: self.user_pin.clone(),
       new_admin_pin: self.new_admin_pin.clone(),
diff --git a/src/tests/run.rs b/src/tests/run.rs
index 22e7004..f8470ad 100644
--- a/src/tests/run.rs
+++ b/src/tests/run.rs
@@ -17,6 +17,11 @@
 // * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
 // *************************************************************************
 
+use std::fs;
+use std::io::Write;
+use std::os::unix::fs::OpenOptionsExt;
+use std::path;
+
 use super::*;
 
 #[test]
@@ -108,3 +113,110 @@ fn version_option() {
   test(&re, "--version");
   test(&re, "-V");
 }
+
+#[test]
+fn extension() -> crate::Result<()> {
+  let ext_dir = tempfile::tempdir()?;
+  {
+    let mut ext = fs::OpenOptions::new()
+      .create(true)
+      .mode(0o755)
+      .write(true)
+      .open(ext_dir.path().join("nitrocli-ext"))?;
+
+    ext.write_all(
+      br#"#!/usr/bin/env python
+print("success")
+"#,
+    )?;
+  }
+
+  let path = ext_dir.path().as_os_str().to_os_string();
+  let out = Nitrocli::make().path(path).build().handle(&["ext"])?;
+  assert_eq!(out, "success\n");
+  Ok(())
+}
+
+#[test]
+fn extension_failure() -> crate::Result<()> {
+  let ext_dir = tempfile::tempdir()?;
+  {
+    let mut ext = fs::OpenOptions::new()
+      .create(true)
+      .mode(0o755)
+      .write(true)
+      .open(ext_dir.path().join("nitrocli-ext"))?;
+
+    ext.write_all(
+      br#"#!/usr/bin/env python
+import sys
+sys.exit(42);
+"#,
+    )?;
+  }
+
+  let path = ext_dir.path().as_os_str().to_os_string();
+  let err = Nitrocli::make()
+    .path(path)
+    .build()
+    .handle(&["ext"])
+    .unwrap_err();
+
+  match err {
+    crate::Error::ExtensionFailed(ext, rc) => {
+      assert_eq!(ext, ext_dir.path().join("nitrocli-ext"));
+      assert_eq!(rc, Some(42));
+    }
+    _ => panic!("Unexpected error variant found: {:?}", err),
+  };
+  Ok(())
+}
+
+#[test_device]
+fn extension_arguments(model: nitrokey::Model) -> crate::Result<()> {
+  fn test<F>(model: nitrokey::Model, what: &str, args: &[&str], check: F) -> crate::Result<()>
+  where
+    F: FnOnce(&str) -> bool,
+  {
+    let ext_dir = tempfile::tempdir()?;
+    {
+      let mut ext = fs::OpenOptions::new()
+        .create(true)
+        .mode(0o755)
+        .write(true)
+        .open(ext_dir.path().join("nitrocli-ext"))?;
+
+      ext.write_all(include_bytes!("extension_model_test.py"))?;
+    }
+
+    let mut args = args.to_vec();
+    args.append(&mut vec!["ext", what]);
+
+    let path = ext_dir.path().as_os_str().to_os_string();
+    let out = Nitrocli::make()
+      .model(model)
+      .path(path)
+      .build()
+      .handle(&args)?;
+
+    assert!(check(&out), out);
+    Ok(())
+  }
+
+  test(model, "model", &[], |out| {
+    out == model.to_string().to_lowercase() + "\n"
+  })?;
+  test(model, "nitrocli", &[], |out| {
+    path::Path::new(out)
+      .file_stem()
+      .unwrap()
+      .to_str()
+      .unwrap()
+      .trim()
+      .contains("nitrocli")
+  })?;
+  test(model, "verbosity", &[], |out| out == "0\n")?;
+  test(model, "verbosity", &["-v"], |out| out == "1\n")?;
+  test(model, "verbosity", &["-v", "--verbose"], |out| out == "2\n")?;
+  Ok(())
+}