WIP: grpc example

Signed-off-by: Brian Hardock <brian.hardock@fermyon.com>

Author: fibonacci1729

Cargo.lock

@@ -1,6 +1,7 @@
 [workspace]
 resolver = "2"
 members = [
+  "examples/grpc",
   "examples/hello-world",
   "examples/http-axum-router",
   "examples/http-concurrent-outbound-calls",

Cargo.toml

@@ -24,6 +24,7 @@ name = "spin_sdk"
 default = ["http", "key-value", "json", "llm", "mqtt", "mysql", "pg", "postgres4-types", "redis", "sqlite", "variables", "export-sdk-language"]
 export-sdk-language = []
 http = ["dep:wasip3", "dep:bytes", "dep:http-body", "dep:http-body-util", "dep:hyperium"]
+grpc = ["http", "dep:tower-service"]
 key-value = []
 json = ["dep:serde", "dep:serde_json"]
 llm = []
@@ -48,6 +49,9 @@ http-body-util = { version = "0.1.3", optional = true }
 hyperium = { package = "http", version = "1.3.1", optional = true }
 wasip3 = { version = "0.5.0", git = "https://github.com/bytecodealliance/wasi-rs", features = ["http-compat"], optional = true }
 
+# grpc
+tower-service = { version = "0.3", optional = true }
+
 # pg
 chrono = { version = "0.4.42", optional = true }
 postgres_range = { version = "0.11.1", optional = true }

crates/spin-sdk/Cargo.toml

@@ -0,0 +1,61 @@
+//! gRPC helpers for serving tonic services from Spin components.
+//!
+//! This module provides a thin integration layer between the Spin HTTP
+//! subsystem and [tonic](https://docs.rs/tonic)-generated gRPC servers.
+//! Tonic's generated server types (e.g. `GreeterServer<T>`) implement
+//! [`tower_service::Service`] over HTTP requests, so they can accept
+//! Spin's incoming [`Request`](crate::http::Request) directly.
+//!
+//! # Example
+//!
+//! ```ignore
+//! use spin_sdk::http::{IntoResponse, Request};
+//! use spin_sdk::http_service;
+//!
+//! #[http_service]
+//! async fn handler(req: Request) -> impl IntoResponse {
+//!     spin_sdk::grpc::serve(GreeterServer::new(MyGreeter), req).await
+//! }
+//! ```
+
+use hyperium as http;
+use std::convert::Infallible;
+
+/// Serve a gRPC request by forwarding it to a tower service.
+///
+/// This function is designed to work with tonic-generated server types,
+/// which implement `tower::Service<http::Request<B>>` for any body `B`
+/// satisfying `http_body::Body + Send + 'static`.
+///
+/// The response is returned as an [`http::Response<B>`] which implements
+/// [`IntoResponse`](crate::http::IntoResponse), so it integrates directly
+/// with the `#[http_service]` handler return type.
+///
+/// # Extracting a gRPC service from a [`Router`]
+///
+/// If you have multiple services, you can compose them with
+/// [`tonic::transport::server::Router`] at the type level, or simply
+/// match on the request path and delegate to different `serve` calls.
+///
+/// # Example
+///
+/// ```ignore
+/// use spin_sdk::http::{IntoResponse, Request};
+/// use spin_sdk::{grpc, http_service};
+///
+/// #[http_service]
+/// async fn handler(req: Request) -> impl IntoResponse {
+///     grpc::serve(GreeterServer::new(MyGreeter), req).await
+/// }
+/// ```
+pub async fn serve<S, B>(mut svc: S, req: crate::http::Request) -> http::Response<B>
+where
+    S: tower_service::Service<
+        crate::http::Request,
+        Response = http::Response<B>,
+        Error = Infallible,
+    >,
+{
+    // Infallible error — unwrap is safe.
+    svc.call(req).await.unwrap_or_else(|e| match e {})
+}

crates/spin-sdk/src/grpc.rs

@@ -10,6 +10,7 @@
 //! | Module | Feature | Purpose |
 //! |--------|---------|---------|
 //! | [`http`] | `http` | Incoming and outgoing HTTP requests |
+//! | [`grpc`] | `grpc` | gRPC helpers for tonic integration |
 //! | [`key_value`] | `key-value` | Persistent key-value storage |
 //! | [`llm`] | `llm` | Large-language-model inference |
 //! | [`mqtt`] | `mqtt` | MQTT message publishing |
@@ -34,6 +35,11 @@ pub use spin_sdk_macro::{http_service, redis_subscriber};
 #[cfg_attr(docsrs, doc(cfg(feature = "http")))]
 pub mod http;
 
+/// gRPC helpers for serving tonic services.
+#[cfg(feature = "grpc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "grpc")))]
+pub mod grpc;
+
 /// Persistent key-value storage.
 #[cfg(feature = "key-value")]
 #[cfg_attr(docsrs, doc(cfg(feature = "key-value")))]

crates/spin-sdk/src/lib.rs

@@ -0,0 +1,17 @@
+[package]
+name = "grpc"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+futures = "0.3"
+prost = "0.13"
+spin-sdk = { path = "../../crates/spin-sdk", features = ["grpc"] }
+tokio-stream = "0.1"
+tonic = { version = "0.12", default-features = false, features = ["codegen", "prost"] }
+
+[build-dependencies]
+tonic-build = { version = "0.12", default-features = false, features = ["prost"] }