Return error when loading fails instead of panicking

This refactoring changes the public API of the `openvino` crate to add a new error type, `LoadingError`, as well as a wrapper type, `SetupError`, to disambiguate between that and `InferenceError`. The `Core::new` function changes to return the wrapper, `SetupError`, since it could fail while loading the OpenVINO shared libraries.

Author: abrown

crates/openvino/src/core.rs

@@ -2,9 +2,12 @@
 //! [API](https://docs.openvinotoolkit.org/latest/ie_c_api/modules.html).
 
 use crate::blob::Blob;
-use crate::network::{CNNNetwork, ExecutableNetwork};
 use crate::tensor_desc::TensorDesc;
 use crate::{cstr, drop_using_function, try_unsafe, util::Result};
+use crate::{
+    error::{LoadingError, SetupError},
+    network::{CNNNetwork, ExecutableNetwork},
+};
 use crate::{Layout, Precision};
 use openvino_sys::{
     self, ie_config_t, ie_core_create, ie_core_free, ie_core_load_network, ie_core_read_network,
@@ -19,17 +22,18 @@ drop_using_function!(Core, ie_core_free);
 
 impl Core {
     /// Construct a new OpenVINO [Core]--this is the primary entrypoint for constructing and using
-    /// inference networks.
-    pub fn new(xml_config_file: Option<&str>) -> Result<Core> {
-        openvino_sys::library::load().expect("unable to load shared library");
+    /// inference networks. Because this function may load OpenVINO's shared libraries at runtime,
+    /// there are more ways than usual that this function can fail (e.g., [LoadingError]s).
+    pub fn new(xml_config_file: Option<&str>) -> std::result::Result<Core, SetupError> {
+        openvino_sys::library::load().or_else(|e| Err(LoadingError::SystemFailure(e)))?;
 
         let file = match xml_config_file {
             None => format!(
                 "{}/plugins.xml",
                 openvino_sys::library::find()
-                    .expect("unable to find path to OpenVINO libraries")
+                    .ok_or(LoadingError::CannotFindPath)?
                     .parent()
-                    .expect("unable to get the parent of the linked OpenVINO library")
+                    .ok_or(LoadingError::NoParentDirectory)?
                     .display()
             ),
             Some(f) => f.to_string(),

crates/openvino/src/error.rs

@@ -1,12 +1,8 @@
 use thiserror::Error;
 
-/// See
+/// Enumerate errors returned by the OpenVINO implementation. See
 /// [IEStatusCode](https://docs.openvinotoolkit.org/latest/ie_c_api/ie__c__api_8h.html#a391683b1e8e26df8b58d7033edd9ee83).
-///
-/// TODO Replace this in bindgen with
-/// [newtype_enum](https://docs.rs/bindgen/0.54.1/bindgen/struct.Builder.html#method.newtype_enum)
-/// or
-/// [rustified_enum](https://docs.rs/bindgen/0.54.1/bindgen/struct.Builder.html#method.rustified_enum).
+/// TODO This could be auto-generated (https://github.com/intel/openvino-rs/issues/20).
 #[derive(Debug, Error)]
 pub enum InferenceError {
     #[error("general error")]
@@ -58,3 +54,25 @@ impl InferenceError {
         }
     }
 }
+
+/// Enumberate setup failures: in some cases, this library calls library loading code that may fail
+/// in a different way (i.e., [LoadingError]) than the calls in to the OpenVINO libraries (i.e.,
+/// [InferenceError]).
+#[derive(Debug, Error)]
+pub enum SetupError {
+    #[error("inference error")]
+    Inference(#[from] InferenceError),
+    #[error("library loading error")]
+    Loading(#[from] LoadingError),
+}
+
+/// Enumerate the ways that library loading can fail.
+#[derive(Debug, Error)]
+pub enum LoadingError {
+    #[error("system failed to load shared libraries (see https://github.com/intel/openvino-rs/blob/main/crates/openvino-finder): {0}")]
+    SystemFailure(String),
+    #[error("cannot find path to shared libraries (see https://github.com/intel/openvino-rs/blob/main/crates/openvino-finder)")]
+    CannotFindPath,
+    #[error("no parent directory found for shared library path")]
+    NoParentDirectory,
+}

crates/openvino/src/lib.rs

@@ -8,7 +8,7 @@ mod util;
 
 pub use crate::core::Core;
 pub use blob::Blob;
-pub use error::InferenceError;
+pub use error::{InferenceError, LoadingError, SetupError};
 pub use network::{CNNNetwork, ExecutableNetwork};
 // Re-publish some OpenVINO enums with a conventional Rust naming (see
 // `crates/openvino-sys/build.rs`).