Pass on resolved USB path to extensions

To avoid reimplementing the device selection logic in extensions, we
introduce a new environment variable NITROCLI_RESOLVED_USB_PATH that is
set to the USB path of the single matching Nitrokey device. If no device
matches, or if there are multiple matching devices, the variable
is not set.

CHANGELOG.md

@@ -1,6 +1,8 @@
 Unreleased
 ----------
 - Enabled usage of empty PWS slot fields
+- Added `NITROCLI_RESOLVED_USB_PATH` environment variable to be used by
+ extensions
 - Allowed entering of `base32` encoded strings containing spaces
 - Fixed pinentry dialog highlighting some messages incorrectly as errors
 - Bumped `nitrokey` dependency to `0.9.0`

doc/nitrocli.1

@@ -1,4 +1,4 @@
-.TH NITROCLI 1 2020-10-11
+.TH NITROCLI 1 2021-04-14
 .SH NAME
 nitrocli \- access Nitrokey devices
 .SH SYNOPSIS
@@ -427,12 +427,18 @@ The program conveys basic configuration information to any extension being
 started this way. Specifically, it will set each environment variable as
 described in the Configuration subsection of the Environment section above, if
 the corresponding \fBnitrocli\fR program configuration was set. In addition, the
-following variable will be set unconditionally:
+following variables will be set:
 .TP
 .B NITROCLI_BINARY
 The absolute path to the \fBnitrocli\fR binary through which the extension was
 invoked. This path may be used to recursively invoke \fBnitrocli\fR to implement
 certain functionality.
+.TP
+.B NITROCLI_RESOLVED_USB_PATH
+The USB path of the device that \fBnitrocli\fR would connect to based on the
+\fB\-\-model\fR, \fB\-\-serial-number\fR, and \fB\-\-usb-path\fR options.
+If there is no matching Nitrokey device, or if multiple devices match the
+options, the environment variable is not set.
 
 .P
 All other variables present in the environment will be passed through to the

src/commands.rs

@@ -1170,6 +1170,10 @@ pub fn extension(ctx: &mut Context<'_>, args: Vec<ffi::OsString>) -> anyhow::Res
  // a cargo test context.
  let mut cmd = process::Command::new(&ext_path);
 
+ if let Ok(device_info) = find_device(&ctx.config) {
+ let _ = cmd.env(crate::NITROCLI_RESOLVED_USB_PATH, device_info.path);
+ }
+
  if let Some(model) = ctx.config.model {
  let _ = cmd.env(crate::NITROCLI_MODEL, model.to_string());
  }

src/main.rs

@@ -74,6 +74,7 @@ use structopt::clap::SubCommand;
 use structopt::StructOpt;
 
 const NITROCLI_BINARY: &str = "NITROCLI_BINARY";
+const NITROCLI_RESOLVED_USB_PATH: &str = "NITROCLI_RESOLVED_USB_PATH";
 const NITROCLI_MODEL: &str = "NITROCLI_MODEL";
 const NITROCLI_USB_PATH: &str = "NITROCLI_USB_PATH";
 const NITROCLI_VERBOSITY: &str = "NITROCLI_VERBOSITY";