feat: update WIT with new guest function web helper. add example function. (#19)

Author: tylerburdsall

momento-functions-host/src/web_extensions.rs

@@ -5,9 +5,18 @@
 use momento_functions_wit::function_web::momento::functions::web_function_support;
 
 /// Returns the headers for the web function, if any are present.
+/// This consumes the headers and takes ownership of the value; multiple calls after will always
+/// yield `None`.
 pub fn headers() -> Vec<(String, String)> {
     web_function_support::headers()
         .into_iter()
         .map(|web_function_support::Header { name, value }| (name, value))
         .collect()
 }
+
+/// Returns the metadata within the caller's token, if present.
+/// This consumes the metadata and takes ownership of the value; multiple calls after will always
+/// yield `None`.
+pub fn token_metadata() -> Option<String> {
+    web_function_support::token_metadata()
+}

momento-functions-wit/wit/guest-function-web.wit

@@ -1,7 +1,7 @@
 
 interface guest-function-web {
     use web-function-support.{header};
-    
+
     post: func(payload: list<u8>) -> response;
 
     record response {
@@ -12,8 +12,12 @@ interface guest-function-web {
 }
 
 interface web-function-support {
+    /// Returns a list of headers used in the function. Can only be called once, consumes ownership.
     headers: func() -> list<header>;
+    /// Returns a list of query parameters used in the function. Can only be called once, consumes ownership.
     query-parameters: func() -> list<query-parameter>;
+    /// Returns the metadata provided in the caller's token, if present. Can only be called once, consumes ownership.
+    token-metadata: func() -> option<string>;
 
     record header {
         name: string,

momento-functions/Cargo.toml

@@ -70,6 +70,10 @@ crate-type = ["cdylib"]
 name = "web-function-json-greeter"
 crate-type = ["cdylib"]
 
+[[example]]
+name = "web-function-token-metadata"
+crate-type = ["cdylib"]
+
 [[example]]
 name = "environment-variables"
 crate-type = ["cdylib"]

momento-functions/examples/web-function-token-metadata.rs

@@ -0,0 +1,23 @@
+use momento_functions_host::encoding::Json;
+
+#[derive(serde::Serialize)]
+struct Response {
+    message: String,
+}
+
+momento_functions::post!(token_metadata);
+/// Using the provided host support, this function returns the caller's provided metadata within the `token_id` field
+/// of the Momento key. When calling `GenerateApiToken` or `GenerateDisposableToken`, you can provide
+/// data serialized as a `String` in the `token_id` field.
+fn token_metadata(_: Vec<u8>) -> Json<Response> {
+    let maybe_token_metadata = momento_functions_host::web_extensions::token_metadata();
+    if let Some(metadata) = maybe_token_metadata {
+        Json(Response {
+            message: format!("Token metadata provided: {}", metadata),
+        })
+    } else {
+        Json(Response {
+            message: "No metadata provided, try invoking with a Momento key that was generated with a populated 'token_id' field".to_string(),
+        })
+    }
+}