feat(sdk/rust): add optional feature for serde

This commit updates the Rust SDK to include two new functions that
integrates key/value with serde. Specifically:

- `set_json`: this function takes a key and a struct that can be
  serialized by serde into JSON, and that representation is added to the
  store
- `get_json`: this function takes a key, reads the key/value pair from
  the store, then deserializes it into the specified type

Considering that storing serialized state in Spin's key/value store is
one of the popular use cases for the API, these convenience functions
should simplify that operation.

This functionality is added as an optional feature in the SDK, so it
doesn't add to the binary size of the resulting component unless needed.

Signed-off-by: Radu Matei <radu.matei@fermyon.com>

Cargo.lock

@@ -4595,9 +4595,9 @@ dependencies = [
 
 [[package]]
 name = "serde"
-version = "1.0.154"
+version = "1.0.163"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8cdd151213925e7f1ab45a9bbfb129316bd00799784b174b7cc7bcd16961c49e"
+checksum = "2113ab51b87a539ae008b5c6c02dc020ffa39afd2d83cffcb3f4eb2722cebec2"
 dependencies = [
  "serde_derive",
 ]
@@ -4614,13 +4614,13 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.154"
+version = "1.0.163"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4fc80d722935453bcafdc2c9a73cd6fac4dc1938f0346035d84bf99fa9e33217"
+checksum = "8c805777e3930c8883389c602315a24224bcc738b63905ef87cd1420353ea93e"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 1.0.109",
+ "syn 2.0.8",
 ]
 
 [[package]]
@@ -4634,9 +4634,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.94"
+version = "1.0.96"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1c533a59c9d8a93a09c6ab31f0fd5e5f4dd1b8fc9434804029839884765d04ea"
+checksum = "057d394a50403bcac12672b2b18fb387ab6d289d957dab67dd201875391e52f1"
 dependencies = [
  "itoa",
  "ryu",
@@ -5282,6 +5282,8 @@ dependencies = [
  "form_urlencoded",
  "http",
  "routefinder",
+ "serde",
+ "serde_json",
  "spin-macro",
  "thiserror",
  "wit-bindgen-rust",

sdk/rust/Cargo.toml

@@ -17,7 +17,10 @@ spin-macro = { path = "macro" }
 thiserror = "1.0.37"
 wit-bindgen-rust = { git = "https://github.com/bytecodealliance/wit-bindgen", rev = "cb871cfa1ee460b51eb1d144b175b9aab9c50aba" }
 routefinder = "0.5.3"
+serde_json = {version = "1.0.96", optional = true}
+serde = {version = "1.0.163", optional = true}
 
 [features]
-default = [ "export-sdk-language" ]
+default = ["export-sdk-language"]
 export-sdk-language = []
+json = ["dep:serde", "dep:serde_json"]

sdk/rust/src/key_value.rs

@@ -8,6 +8,9 @@ wit_bindgen_rust::import!("../../wit/ephemeral/key-value.wit");
 
 use key_value::Store as RawStore;
 
+#[cfg(feature = "json")]
+use serde::{de::DeserializeOwned, Serialize};
+
 /// Errors which may be raised by the methods of `Store`
 pub type Error = key_value::Error;
 
@@ -61,6 +64,29 @@ impl Store {
     pub fn get_keys(&self) -> Result<Vec<String>, Error> {
         key_value::get_keys(self.0)
     }
+
+    #[cfg(feature = "json")]
+    /// Serialize the given data to JSON, then set it as the value for the specified `key`.
+    pub fn set_json<T: Serialize>(
+        &self,
+        key: impl AsRef<str>,
+        value: &T,
+    ) -> Result<(), anyhow::Error> {
+        Ok(key_value::set(
+            self.0,
+            key.as_ref(),
+            &serde_json::to_vec(value)?,
+        )?)
+    }
+
+    #[cfg(feature = "json")]
+    /// Deserialize an instance of type `T` from the value of `key`.
+    pub fn get_json<T: DeserializeOwned>(&self, key: impl AsRef<str>) -> Result<T, anyhow::Error> {
+        Ok(serde_json::from_slice(&key_value::get(
+            self.0,
+            key.as_ref(),
+        )?)?)
+    }
 }
 
 impl Drop for Store {