Introduce TryInto<T> trait

This change introduces a new trait, TryInto, to the crate. In the future
this trait will allow us to keep a flexible set of error result types
from the various try_with_* functions, which use a certain nitrokey
error variant to check for the entry of a wrong secret.
Note that while a TryInto trait exists in Rust's standard library, that
was not found to be helpful because we have no way to define it for
nitrkey crate's error type. Because of that, we will always have a
mismatch between our internal error and std::convert::Infallible.

2 files changed, 42 insertions, 19 deletions

diff --git a/nitrocli/src/commands.rs b/nitrocli/src/commands.rs
index 6285c90..ccbff69 100644
--- a/nitrocli/src/commands.rs
+++ b/nitrocli/src/commands.rs
@@ -30,6 +30,7 @@ use nitrokey::Device;
 use nitrokey::GenerateOtp;
 
 use crate::args;
+use crate::error;
 use crate::error::Error;
 use crate::pinentry;
 use crate::Result;
@@ -188,7 +189,7 @@ fn get_volume_status(status: &nitrokey::VolumeStatus) -> &'static str {
 /// the first try, this function will call `op` with `data`.  At the
 /// second or third try, it will call `op` with the data returned by the
 /// previous call to `op`.
-fn try_with_pin_and_data_with_pinentry<D, F, R>(
+fn try_with_pin_and_data_with_pinentry<D, F, R, E>(
   ctx: &mut args::ExecCtx<'_>,
   pin_entry: &pinentry::PinEntry,
   msg: &'static str,
@@ -196,7 +197,8 @@ fn try_with_pin_and_data_with_pinentry<D, F, R>(
   mut op: F,
 ) -> Result<R>
 where
-  F: FnMut(D, &str) -> result::Result<R, (D, nitrokey::CommandError)>,
+  F: FnMut(D, &str) -> result::Result<R, (D, E)>,
+  E: error::TryInto<nitrokey::CommandError>,
 {
   let mut data = data;
   let mut retry = 3;
@@ -205,26 +207,29 @@ where
     let pin = pinentry::inquire(ctx, pin_entry, pinentry::Mode::Query, error_msg)?;
     match op(data, &pin) {
       Ok(result) => return Ok(result),
-      Err((new_data, err)) => match err {
-        nitrokey::CommandError::WrongPassword => {
-          pinentry::clear(pin_entry)?;
-          retry -= 1;
-
-          if retry > 0 {
-            error_msg = Some("Wrong password, please reenter");
-            data = new_data;
-            continue;
+      Err((new_data, err)) => match err.try_into() {
+        Ok(err) => match err {
+          nitrokey::CommandError::WrongPassword => {
+            pinentry::clear(pin_entry)?;
+            retry -= 1;
+
+            if retry > 0 {
+              error_msg = Some("Wrong password, please reenter");
+              data = new_data;
+              continue;
+            }
+            return Err(get_error(msg, err));
           }
-          return Err(get_error(msg, err));
-        }
-        err => return Err(get_error(msg, err)),
+          err => return Err(get_error(msg, err)),
+        },
+        Err(err) => return Err(err),
       },
     };
   }
 }
 
 /// Try to execute the given function with a PIN.
-fn try_with_pin_and_data<D, F, R>(
+fn try_with_pin_and_data<D, F, R, E>(
   ctx: &mut args::ExecCtx<'_>,
   pin_entry: &pinentry::PinEntry,
   msg: &'static str,
@@ -232,7 +237,8 @@ fn try_with_pin_and_data<D, F, R>(
   mut op: F,
 ) -> Result<R>
 where
-  F: FnMut(D, &str) -> result::Result<R, (D, nitrokey::CommandError)>,
+  F: FnMut(D, &str) -> result::Result<R, (D, E)>,
+  E: Into<Error> + error::TryInto<nitrokey::CommandError>,
 {
   let pin = match pin_entry.pin_type() {
     pinentry::PinType::Admin => &ctx.admin_pin,
@@ -246,7 +252,7 @@ where
         msg
       ))
     })?;
-    op(data, &pin).map_err(|(_, err)| get_error(msg, err))
+    op(data, &pin).map_err(|(_, err)| err.into())
   } else {
     try_with_pin_and_data_with_pinentry(ctx, pin_entry, msg, data, op)
   }
@@ -256,14 +262,15 @@ where
 ///
 /// This function behaves exactly as `try_with_pin_and_data`, but
 /// it refrains from passing any data to it.
-fn try_with_pin<F>(
+fn try_with_pin<F, E>(
   ctx: &mut args::ExecCtx<'_>,
   pin_entry: &pinentry::PinEntry,
   msg: &'static str,
   mut op: F,
 ) -> Result<()>
 where
-  F: FnMut(&str) -> result::Result<(), nitrokey::CommandError>,
+  F: FnMut(&str) -> result::Result<(), E>,
+  E: Into<Error> + error::TryInto<nitrokey::CommandError>,
 {
   try_with_pin_and_data(ctx, pin_entry, msg, (), |data, pin| {
     op(pin).map_err(|err| (data, err))
diff --git a/nitrocli/src/error.rs b/nitrocli/src/error.rs
index 1346526..d1eb2eb 100644
--- a/nitrocli/src/error.rs
+++ b/nitrocli/src/error.rs
@@ -22,6 +22,22 @@ use std::io;
 use std::str;
 use std::string;
 
+/// A trait used to simplify error handling in conjunction with the
+/// try_with_* functions we use for repeatedly asking the user for a
+/// secret.
+pub trait TryInto<T> {
+  fn try_into(self) -> Result<T, Error>;
+}
+
+impl<T, U> TryInto<U> for T
+where
+  T: Into<U>,
+{
+  fn try_into(self) -> Result<U, Error> {
+    Ok(self.into())
+  }
+}
+
 #[derive(Debug)]
 pub enum Error {
   ArgparseError(i32),