Add scaffolding for the list command

This patch adds the basic scaffolding for the list command which will
list all attached Nitrokey devices.

CHANGELOG.md

@@ -1,5 +1,6 @@
 Unreleased
 ----------
+- Added the `list` command that lists all attached Nitrokey devices
 - Reworked argument handling:
   - Added `structopt` dependency in version `0.3.7`
   - Replaced `argparse` with `structopt`

README.md

@@ -13,6 +13,7 @@ Storage][nitrokey-storage] devices.
 
 
 The following commands are currently supported:
+- list: List all attached Nitrokey devices.
 - status: Report status information about the Nitrokey.
 - lock: Lock the Nitrokey.
 - config: Access the Nitrokey's configuration

src/args.rs

@@ -117,6 +117,8 @@ Command! {Command, [
   Encrypted(EncryptedArgs) => |ctx, args: EncryptedArgs| args.subcmd.execute(ctx),
   /// Interacts with the device's hidden volume
   Hidden(HiddenArgs) => |ctx, args: HiddenArgs| args.subcmd.execute(ctx),
+  /// Lists the attached Nitrokey devices
+  List(ListArgs) => |ctx, args: ListArgs| commands::list(ctx, args.no_connect),
   /// Locks the connected Nitrokey device
   Lock => commands::lock,
   /// Accesses one-time passwords
@@ -263,6 +265,13 @@ struct HiddenCreateArgs {
   end: u8,
 }
 
+#[derive(Debug, PartialEq, structopt::StructOpt)]
+struct ListArgs {
+  /// Only print the information that is available without connecting to a device
+  #[structopt(short, long)]
+  no_connect: bool,
+}
+
 #[derive(Debug, PartialEq, structopt::StructOpt)]
 struct OtpArgs {
   #[structopt(subcommand)]

src/commands.rs

@@ -376,6 +376,11 @@ pub fn status(ctx: &mut args::ExecCtx<'_>) -> Result<()> {
   })
 }
 
+/// List the attached Nitrokey devices.
+pub fn list(_ctx: &mut args::ExecCtx<'_>, _no_connect: bool) -> Result<()> {
+  unimplemented!();
+}
+
 /// Perform a factory reset.
 pub fn reset(ctx: &mut args::ExecCtx<'_>) -> Result<()> {
   with_device(ctx, |ctx, mut device| {