Add get_[inputs|outputs]_len to CNNNetwork (#34)

This change is an adaptation of #33 that allows for the same kind of functionality. It also adds tests checking the newly-added functions. With this in place, users will be able to set input layouts with something like:

```rust
for i in 0..network.get_inputs_len() {
  let name = network.get_input_name(i)?;
  network.set_input_layout(&name, Layout::NHWC)?;
}
```

Author: abrown

crates/openvino/src/error.rs

@@ -3,7 +3,7 @@ use thiserror::Error;
 /// Enumerate errors returned by the OpenVINO implementation. See
 /// [IEStatusCode](https://docs.openvinotoolkit.org/latest/ie_c_api/ie__c__api_8h.html#a391683b1e8e26df8b58d7033edd9ee83).
 /// TODO This could be auto-generated (https://github.com/intel/openvino-rs/issues/20).
-#[derive(Debug, Error)]
+#[derive(Debug, Error, PartialEq)]
 pub enum InferenceError {
     #[error("general error")]
     GeneralError,

crates/openvino/src/network.rs

@@ -1,13 +1,14 @@
 //! Contains the network representations in OpenVINO:
-//!  - [CNNNetwork] is the OpenVINO represenation of a neural network
+//!  - [CNNNetwork] is the OpenVINO representation of a neural network
 //!  - [ExecutableNetwork] is the compiled representation of a [CNNNetwork] for a device.
 
 use crate::request::InferRequest;
 use crate::{cstr, drop_using_function, try_unsafe, util::Result};
 use crate::{Layout, Precision, ResizeAlgorithm};
 use openvino_sys::{
     ie_exec_network_create_infer_request, ie_exec_network_free, ie_executable_network_t,
-    ie_network_free, ie_network_get_input_name, ie_network_get_output_name, ie_network_name_free,
+    ie_network_free, ie_network_get_input_name, ie_network_get_inputs_number,
+    ie_network_get_output_name, ie_network_get_outputs_number, ie_network_name_free,
     ie_network_set_input_layout, ie_network_set_input_precision,
     ie_network_set_input_resize_algorithm, ie_network_set_output_precision, ie_network_t,
 };
@@ -21,6 +22,20 @@ pub struct CNNNetwork {
 drop_using_function!(CNNNetwork, ie_network_free);
 
 impl CNNNetwork {
+    /// Retrieve the number of network inputs.
+    pub fn get_inputs_len(&self) -> Result<usize> {
+        let mut num: usize = 0;
+        try_unsafe!(ie_network_get_inputs_number(self.instance, &mut num))?;
+        Ok(num)
+    }
+
+    /// Retrieve the number of network outputs.
+    pub fn get_outputs_len(&self) -> Result<usize> {
+        let mut num: usize = 0;
+        try_unsafe!(ie_network_get_outputs_number(self.instance, &mut num))?;
+        Ok(num)
+    }
+
     /// Retrieve the name identifying the input tensor at `index`.
     pub fn get_input_name(&self, index: usize) -> Result<String> {
         let mut cname = std::ptr::null_mut();

crates/openvino/tests/setup.rs

@@ -10,5 +10,9 @@ fn read_network() {
     let mut core = Core::new(None).unwrap();
     let model = fs::read(Fixture::graph()).unwrap();
     let weights = fs::read(Fixture::weights()).unwrap();
-    core.read_network_from_buffer(&model, &weights).unwrap();
+    let network = core.read_network_from_buffer(&model, &weights).unwrap();
+
+    // Check the number of inputs and outputs.
+    assert_eq!(network.get_inputs_len(), Ok(1));
+    assert_eq!(network.get_outputs_len(), Ok(1));
 }