feat: add pgp card

src/card.rs

@@ -0,0 +1,13 @@
+use openpgp_card_pcsc::PcscBackend;
+use rust_util::{opt_result, opt_value_result, simple_error, warning, XResult};
+
+pub fn get_card() -> XResult<PcscBackend> {
+    let card_list = opt_result!(PcscBackend::cards(None), "Read OpenPGP card list failed: {}");
+    if card_list.is_empty() {
+        return simple_error!("Cannot find any card");
+    }
+    if card_list.len() > 1 {
+        warning!("Find {} OpenPGP cards, will use first card", card_list.len());
+    }
+    Ok(opt_value_result!(card_list.into_iter().next(), "SHOULD NOT HAPPEN, CANNOT FIND ANY CARD"))
+}