Put ExampleError in the sample crate

flutter_ffi_plugin/example/native/hub/src/sample_functions.rs

@@ -91,7 +91,7 @@ pub async fn stream_fractal() {
                 Ok(inner) => inner,
                 Err(_) => continue,
             };
-            if let Some(fractal_image) = received_frame {
+            if let Ok(fractal_image) = received_frame {
                 // Stream the image data to Dart.
                 SampleFractal {
                     current_scale,

flutter_ffi_plugin/example/native/sample_crate/src/error.rs

@@ -0,0 +1,18 @@
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub struct ExampleError(pub Box<dyn Error + Send + Sync>);
+
+impl fmt::Display for ExampleError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let source = self.0.as_ref();
+        write!(f, "An error occured inside the example code.\n{source}")
+    }
+}
+
+impl Error for ExampleError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        Some(self.0.as_ref())
+    }
+}

flutter_ffi_plugin/example/native/sample_crate/src/fractal.rs

@@ -2,6 +2,7 @@
 //! Copied and modified from
 //! https://github.com/abour/fractal repository.
 
+use crate::error::ExampleError;
 use image::ImageEncoder;
 
 const WIDTH: u32 = 384;
@@ -10,7 +11,7 @@ const BUF_SIZE: u32 = WIDTH * HEIGHT * 3;
 const SIZE: f64 = 0.000000001;
 const MAX_ITER: u32 = 1000;
 
-pub fn draw_fractal_image(scale: f64) -> Option<Vec<u8>> {
+pub fn draw_fractal_image(scale: f64) -> Result<Vec<u8>, ExampleError> {
     let point_x: f64 = -0.5557506;
     let point_y: f64 = -0.55560;
     let mut buffer: Vec<u8> = vec![0; BUF_SIZE as usize];
@@ -27,8 +28,8 @@ pub fn draw_fractal_image(scale: f64) -> Option<Vec<u8>> {
     );
 
     match result {
-        Ok(_) => Some(image_data),
-        Err(_) => None,
+        Ok(_) => Ok(image_data),
+        Err(error) => Err(ExampleError(error.into())),
     }
 }
 

flutter_ffi_plugin/example/native/sample_crate/src/lib.rs

@@ -1,20 +1,22 @@
 //! This crate is written for Rinf demonstrations.
 
-mod common;
+mod error;
 mod fractal;
 
-use common::*;
+use error::ExampleError;
 
 pub use fractal::draw_fractal_image;
 
 // `machineid_rs` only supports desktop platforms.
 #[cfg(any(target_os = "windows", target_os = "macos", target_os = "linux"))]
-pub fn get_hardward_id() -> Result<String> {
+pub fn get_hardward_id() -> Result<String, ExampleError> {
     let mut builder = machineid_rs::IdBuilder::new(machineid_rs::Encryption::MD5);
     builder
         .add_component(machineid_rs::HWIDComponent::SystemID)
         .add_component(machineid_rs::HWIDComponent::CPUCores);
-    let hwid = builder.build("mykey")?;
+    let hwid = builder
+        .build("mykey")
+        .map_err(|error| ExampleError(error.into()))?;
     Ok(hwid)
 }
 #[cfg(not(any(target_os = "windows", target_os = "macos", target_os = "linux")))]
@@ -29,7 +31,12 @@ pub fn get_current_time() -> DateTime<offset::Local> {
 }
 
 // `reqwest` supports all platforms, including web.
-pub async fn fetch_from_web_api(url: &str) -> Result<String> {
-    let fetched = reqwest::get(url).await?.text().await?;
+pub async fn fetch_from_web_api(url: &str) -> Result<String, ExampleError> {
+    let fetched = reqwest::get(url)
+        .await
+        .map_err(|error| ExampleError(error.into()))?
+        .text()
+        .await
+        .map_err(|error| ExampleError(error.into()))?;
     Ok(fetched)
 }