Port argument handling to argparse

This patch replaces the macro for argument parsing with
`argparse::ArgumentParser` from the argparse crate.  It moves the
application logic to the `commands` module and the argument parsing to
the `options` module.  An enum is used to represent the available
commands.  The code is based on the `subcommands.rs` example shipped
with argparse.

4 files changed, 173 insertions, 32 deletions

diff --git a/nitrocli/CHANGELOG.md b/nitrocli/CHANGELOG.md
index 1beabf2..2d43788 100644
--- a/nitrocli/CHANGELOG.md
+++ b/nitrocli/CHANGELOG.md
@@ -12,7 +12,8 @@ Unreleased
   version of the crate, and minimum version of `rustc` required
 - Fixed wrong messages in the pinentry dialog that were caused by unescaped
   spaces in a string
-- Added `argparse` dependency in version `0.2.2`
+- Use the `argparse` crate to parse the command-line arguments
+  - Added `argparse` dependency in version `0.2.2`
 
 
 0.1.3
diff --git a/nitrocli/src/args.rs b/nitrocli/src/args.rs
new file mode 100644
index 0000000..07a3e6a
--- /dev/null
+++ b/nitrocli/src/args.rs
@@ -0,0 +1,153 @@
+// args.rs
+
+// *************************************************************************
+// * Copyright (C) 2018 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::fmt;
+use std::io;
+use std::result;
+use std::str;
+
+use crate::commands;
+use crate::error::Error;
+
+type Result<T> = result::Result<T, Error>;
+
+/// A top-level command for nitrocli.
+#[derive(Debug)]
+pub enum Command {
+  Clear,
+  Close,
+  Open,
+  Status,
+}
+
+impl Command {
+  /// Execute this command with the given arguments.
+  pub fn execute(&self, args: Vec<String>) -> Result<()> {
+    match *self {
+      Command::Clear => clear(args),
+      Command::Close => close(args),
+      Command::Open => open(args),
+      Command::Status => status(args),
+    }
+  }
+}
+
+impl fmt::Display for Command {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    write!(
+      f,
+      "{}",
+      match *self {
+        Command::Clear => "clear",
+        Command::Close => "close",
+        Command::Open => "open",
+        Command::Status => "status",
+      }
+    )
+  }
+}
+
+impl str::FromStr for Command {
+  type Err = ();
+
+  fn from_str(s: &str) -> result::Result<Self, Self::Err> {
+    match s {
+      "clear" => Ok(Command::Clear),
+      "close" => Ok(Command::Close),
+      "open" => Ok(Command::Open),
+      "status" => Ok(Command::Status),
+      _ => Err(()),
+    }
+  }
+}
+
+fn parse(parser: &argparse::ArgumentParser<'_>, args: Vec<String>) -> Result<()> {
+  if let Err(err) = parser.parse(args, &mut io::stdout(), &mut io::stderr()) {
+    Err(Error::ArgparseError(err))
+  } else {
+    Ok(())
+  }
+}
+
+/// Inquire the status of the nitrokey.
+fn status(args: Vec<String>) -> Result<()> {
+  let mut parser = argparse::ArgumentParser::new();
+  parser.set_description("Print the status of the connected Nitrokey Storage");
+  parse(&parser, args)?;
+
+  commands::status()
+}
+
+/// Open the encrypted volume on the nitrokey.
+fn open(args: Vec<String>) -> Result<()> {
+  let mut parser = argparse::ArgumentParser::new();
+  parser.set_description("Opens the encrypted volume on a Nitrokey Storage");
+  parse(&parser, args)?;
+
+  commands::open()
+}
+
+/// Close the previously opened encrypted volume.
+fn close(args: Vec<String>) -> Result<()> {
+  let mut parser = argparse::ArgumentParser::new();
+  parser.set_description("Closes the encrypted volume on a Nitrokey Storage");
+  parse(&parser, args)?;
+
+  commands::close()
+}
+
+/// Clear the PIN stored when opening the nitrokey's encrypted volume.
+fn clear(args: Vec<String>) -> Result<()> {
+  let mut parser = argparse::ArgumentParser::new();
+  parser.set_description("Clears the cached passphrase");
+  parse(&parser, args)?;
+
+  commands::clear()
+}
+
+/// Parse the command-line arguments and return the selected command and
+/// the remaining arguments for the command.
+fn parse_arguments(args: Vec<String>) -> Result<(Command, Vec<String>)> {
+  let mut command = Command::Status;
+  let mut subargs = vec![];
+  let mut parser = argparse::ArgumentParser::new();
+  parser.set_description("Provides access to a Nitrokey device");
+  let _ = parser.refer(&mut command).required().add_argument(
+    "command",
+    argparse::Store,
+    "The command to execute (clear|close|open|status)",
+  );
+  let _ = parser.refer(&mut subargs).add_argument(
+    "arguments",
+    argparse::List,
+    "The arguments for the command",
+  );
+  parser.stop_on_first_argument(true);
+  parse(&parser, args)?;
+  drop(parser);
+
+  subargs.insert(0, format!("nitrocli {}", command));
+  Ok((command, subargs))
+}
+
+/// Parse the command-line arguments and execute the selected command.
+pub fn handle_arguments(args: Vec<String>) -> Result<()> {
+  let (command, args) = parse_arguments(args)?;
+  command.execute(args)
+}
diff --git a/nitrocli/src/error.rs b/nitrocli/src/error.rs
index d755cac..d86a635 100644
--- a/nitrocli/src/error.rs
+++ b/nitrocli/src/error.rs
@@ -23,6 +23,7 @@ use std::string;
 
 #[derive(Debug)]
 pub enum Error {
+  ArgparseError(i32),
   IoError(io::Error),
   Utf8Error(string::FromUtf8Error),
   Error(String),
@@ -43,6 +44,7 @@ impl From<string::FromUtf8Error> for Error {
 impl fmt::Display for Error {
   fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     match *self {
+      Error::ArgparseError(_) => write!(f, "Could not parse arguments"),
       Error::Utf8Error(_) => write!(f, "Encountered UTF-8 conversion error"),
       Error::IoError(ref e) => write!(f, "IO error: {}", e.get_ref().unwrap()),
       Error::Error(ref e) => write!(f, "{}", e),
diff --git a/nitrocli/src/main.rs b/nitrocli/src/main.rs
index 86e9188..8a20494 100644
--- a/nitrocli/src/main.rs
+++ b/nitrocli/src/main.rs
@@ -68,6 +68,7 @@
 //! Nitrocli is a program providing a command line interface to certain
 //! commands of the Nitrokey Storage device.
 
+mod args;
 mod commands;
 mod error;
 mod pinentry;
@@ -75,43 +76,27 @@ mod pinentry;
 use std::process;
 use std::result;
 
-use nitrokey;
-
 use crate::error::Error;
 
 type Result<T> = result::Result<T, Error>;
 
-// A macro for generating a match of the different supported commands.
-// Each supplied command is converted into a string and matched against.
-macro_rules! commands {
-  ( $str:expr, [ $( $command:expr), *] ) => {
-    match &*$str.to_string() {
-      $(
-        stringify!($command) => {
-          if let Err(err) = $command() {
-            println!("{}", err);
-            return 1
-          }
-          return 0
-        },
-      )*
-      x => {
-        println!("Invalid command: {}", x);
-        println!("Available commands: {}", stringify!( $($command)* ));
-        return 1
-      },
-    }
-  }
-}
-
 fn run() -> i32 {
-  let argv: Vec<String> = std::env::args().collect();
-  if argv.len() != 2 {
-    println!("Usage: {} <command>", argv[0]);
-    return 1;
+  let args = std::env::args().collect();
+  match args::handle_arguments(args) {
+    Ok(()) => 0,
+    Err(err) => match err {
+      Error::ArgparseError(err) => match err {
+        // argparse printed the help message
+        0 => 0,
+        // argparse printed an error message
+        _ => 1,
+      },
+      _ => {
+        println!("{}", err);
+        1
+      }
+    },
   }
-
-  commands!(&argv[1], [commands::status, commands::open, commands::close, commands::clear]);
 }
 
 fn main() {