Error handling improvements

README.md

@@ -40,7 +40,7 @@ pip3 install cargo-lambda
 
 See other installation options in [the Cargo Lambda documentation](https://www.cargo-lambda.info/guide/installation.html).
 
-### Your first function
+## Your first function
 
 To create your first function, run Cargo Lambda with the [subcommand `new`](https://www.cargo-lambda.info/commands/new.html). This command will generate a Rust package with the initial source code for your function:
 
@@ -71,6 +71,61 @@ async fn func(event: LambdaEvent<Value>) -> Result<Value, Error> {
 }
 ```
 
+## Understanding Lambda errors
+
+when a function invocation fails, AWS Lambda expects you to return an object that can be serialized into JSON structure with the error information. This structure is represented in the following example:
+
+```json
+{
+  "error_type": "the type of error raised",
+  "error_message": "a string description of the error"
+}
+```
+
+The Rust Runtime for Lambda uses a struct called `Diagnostic` to represent function errors internally. The runtime implements the converstion of several general errors types, like `std::error::Error`, into `Diagnostic`. For these general implementations, the `error_type` is the name of the value type returned by your function. For example, if your function returns `lambda_runtime::Error`, the `error_type` will be something like `alloc::boxed::Box<dyn core::error::Error + core::marker::Send + core::marker::Sync>`, which is not very descriptive.
+
+### Implement your own Diagnostic
+
+To get more descriptive `error_type` fields, you can implement `From` for your error type. That gives you full control on what the `error_type` is:
+
+```rust
+use lambda_runtime::{Diagnostic, Error, LambdaEvent};
+
+#[derive(Debug)]
+struct ErrorResponse(&'static str);
+
+impl From<ErrorResponse> for Diagnostic {
+    fn from(error: ErrorResponse) -> Diagnostic {
+        Diagnostic {
+            error_type: "MyErrorType".into(),
+            error_message: error.0.to_string(),
+        }
+    }
+}
+
+async fn handler(_event: LambdaEvent<()>) -> Result<(), ErrorResponse> {
+  Err(ErrorResponse("this is an error response"))
+}
+```
+
+We recommend you to use the [thiserror crate](https://crates.io/crates/thiserror) to declare your errors. You can see an example on how to integrate `thiserror` with the Runtime's diagnostics in our [example repository](https://github.com/awslabs/aws-lambda-rust-runtime/tree/main/examples/basic-error-thiserror)
+
+### Anyhow, Eyre, and Miette
+
+Popular error crates like Anyhow, Eyre, and Miette provide their own error types that encapsulate other errors. There is no direct transformation of those errors into `Diagnostic`, but we provide feature flags for each one of those crates to help you integrate them with your Lambda functions.
+
+If you enable the features `anyhow`, `eyre`, or `miette` in the `lambda_runtime` dependency of your package. The error types provided by those crates can have blanket transformations into `Diagnostic`. These features expose an `From<T> for Diagnostic` implementation that transforms those error types into a `Diagnostic`. This is an example that transforms an `anyhow::Error` into a `Diagnostic`:
+
+```rust
+use lambda_runtime::{Diagnostic, LambdaEvent};
+
+async fn handler(_event: LambdaEvent<Request>) -> Result<(), Diagnostic> {
+  Err(anyhow::anyhow!("this is an error").into())
+}
+```
+
+You can see more examples on how to use these error crates in our [example repository](https://github.com/awslabs/aws-lambda-rust-runtime/tree/main/examples/basic-error-error-crates-integration). 
+
 ## Building and deploying your Lambda functions
 
 If you already have Cargo Lambda installed in your machine, run the next command to build your function:

examples/basic-error-error-crates-integration/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "basic-error-error-crates-integration"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+anyhow = "1"
+eyre = "0.6.12"
+lambda_runtime = { path = "../../lambda-runtime", features = ["anyhow", "eyre", "miette"] }
+miette = "7.2.0"
+serde = "1"
+tokio = { version = "1", features = ["macros"] }

examples/basic-error-anyhow/README.md → examples/basic-error-error-crates-integration/README.md

@@ -1,6 +1,8 @@
-# AWS Lambda Function Error Handling With `anyhow` Crate Example
+# AWS Lambda Function Error Handling with several popular error crates.
 
-This example shows how to use external error types like `anyhow::Error`.
+This example shows how to use external error types like `anyhow::Error`, `eyre::Report`, and `miette::Report`.
+
+To use the integrations with these crates, you need to enable to respective feature flag in the runtime which provides the implemetation of `into_diagnostic` for specific error types provided by these crates.
 
 ## Build & Deploy
 

examples/basic-error-error-crates-integration/src/main.rs

@@ -0,0 +1,44 @@
+use lambda_runtime::{run, service_fn, Diagnostic, Error, LambdaEvent};
+use serde::Deserialize;
+
+#[derive(Deserialize)]
+#[serde(rename_all = "camelCase")]
+enum ErrorType {
+    Anyhow,
+    Eyre,
+    Miette,
+}
+
+#[derive(Deserialize)]
+struct Request {
+    error_type: ErrorType,
+}
+
+fn anyhow_error() -> anyhow::Result<()> {
+    anyhow::bail!("This is an error message from Anyhow");
+}
+
+fn eyre_error() -> eyre::Result<()> {
+    eyre::bail!("This is an error message from Eyre");
+}
+
+fn miette_error() -> miette::Result<()> {
+    miette::bail!("This is an error message from Miette");
+}
+
+/// Transform an anyhow::Error, eyre::Report, or miette::Report into a lambda_runtime::Diagnostic.
+/// It does it by enabling the feature `anyhow`, `eyre` or `miette` in the runtime dependency.
+/// Those features enable the implementation of `From<T> for Diagnostic` 
+/// for `anyhow::Error`, `eyre::Report`, and `miette::Report`.
+async fn function_handler(event: LambdaEvent<Request>) -> Result<(), Diagnostic> {
+    match event.payload.error_type {
+        ErrorType::Anyhow => anyhow_error().map_err(|e| e.into()),
+        ErrorType::Eyre => eyre_error().map_err(|e| e.into()),
+        ErrorType::Miette => miette_error().map_err(|e| e.into()),
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Error> {
+    run(service_fn(function_handler)).await
+}

examples/basic-error-diagnostic/Cargo.toml → examples/basic-error-thiserror/Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-name = "basic-error-diagnostic"
+name = "basic-error-thiserror"
 version = "0.1.0"
 edition = "2021"
 

examples/basic-error-diagnostic/src/main.rs → examples/basic-error-thiserror/src/main.rs

@@ -13,8 +13,8 @@ pub enum ExecutionError {
     Unexpected(String),
 }
 
-impl<'a> From<ExecutionError> for Diagnostic<'a> {
-    fn from(value: ExecutionError) -> Diagnostic<'a> {
+impl From<ExecutionError> for Diagnostic {
+    fn from(value: ExecutionError) -> Diagnostic {
         let (error_type, error_message) = match value {
             ExecutionError::DatabaseError(err) => ("Retryable", err.to_string()),
             ExecutionError::Unexpected(err) => ("NonRetryable", err.to_string()),

lambda-http/Cargo.toml

@@ -23,6 +23,9 @@ apigw_websockets = []
 alb = []
 pass_through = []
 tracing = ["lambda_runtime/tracing"]
+anyhow = ["lambda_runtime/anyhow"]
+eyre = ["lambda_runtime/eyre"]
+miette = ["lambda_runtime/miette"]
 
 [dependencies]
 base64 = { workspace = true }

lambda-http/src/lib.rs

@@ -194,7 +194,7 @@ where
     S: Service<Request, Response = R, Error = E>,
     S::Future: Send + 'a,
     R: IntoResponse,
-    E: std::fmt::Debug + for<'b> Into<Diagnostic<'b>>,
+    E: std::fmt::Debug + Into<Diagnostic>,
 {
     lambda_runtime::run(Adapter::from(handler)).await
 }

lambda-http/src/streaming.rs

@@ -20,7 +20,7 @@ pub async fn run_with_streaming_response<'a, S, B, E>(handler: S) -> Result<(),
 where
     S: Service<Request, Response = Response<B>, Error = E>,
     S::Future: Send + 'a,
-    E: Debug + for<'b> Into<Diagnostic<'b>>,
+    E: Debug + Into<Diagnostic>,
     B: Body + Unpin + Send + 'static,
     B::Data: Into<Bytes> + Send,
     B::Error: Into<Error> + Send + Debug,

lambda-runtime/Cargo.toml

@@ -17,11 +17,16 @@ readme = "../README.md"
 default = ["tracing"]
 tracing = ["lambda_runtime_api_client/tracing"]
 opentelemetry = ["opentelemetry-semantic-conventions"]
+anyhow = ["dep:anyhow"]
+eyre = ["dep:eyre"]
+miette = ["dep:miette"]
 
 [dependencies]
+anyhow = { version = "1.0.86", optional = true }
 async-stream = "0.3"
 base64 = { workspace = true }
 bytes = { workspace = true }
+eyre = { version = "0.6.12", optional = true }
 futures = { workspace = true }
 http = { workspace = true }
 http-body = { workspace = true }
@@ -35,6 +40,7 @@ hyper-util = { workspace = true, features = [
     "tokio",
 ] }
 lambda_runtime_api_client = { version = "0.11.1", path = "../lambda-runtime-api-client", default-features = false }
+miette = { version = "7.2.0", optional = true }
 opentelemetry-semantic-conventions = { version = "0.14", optional = true }
 pin-project = "1"
 serde = { version = "1", features = ["derive", "rc"] }