feat: create json-rpc mock builder (ethereum#1378)

ethportal-api/src/types/jsonrpc/json_rpc_mock.rs

@@ -0,0 +1,97 @@
+use serde::Serialize;
+use serde_json::Value;
+use tokio::sync::mpsc;
+
+use super::request::JsonRpcRequest;
+
+type FilterFn<T> = Box<dyn Fn(&T) -> bool + Send>;
+
+/// Defines whether and how to respond to the request.
+struct Interaction<T> {
+    request_selector_fn: FilterFn<T>,
+    response: Result<Value, String>,
+}
+
+impl<T> Interaction<T> {
+    /// Returns `Some(response)` if selector returns `true`, `None` otherwise.
+    fn maybe_respond(&self, request: &T) -> Option<Result<Value, String>> {
+        if (self.request_selector_fn)(request) {
+            Some(self.response.clone())
+        } else {
+            None
+        }
+    }
+}
+
+/// Builder for mocking the JSPN-RPC handler.
+pub struct MockJsonRpcBuilder<T> {
+    interactions: Vec<Interaction<T>>,
+}
+
+impl<T: PartialEq + Send + 'static> MockJsonRpcBuilder<T> {
+    pub fn new() -> Self {
+        Self {
+            interactions: vec![],
+        }
+    }
+
+    pub fn with_response(mut self, request: T, response: impl Serialize) -> Self {
+        self.interactions.push(Interaction {
+            request_selector_fn: Box::new(move |r| r == &request),
+            response: serde_json::to_value(response).map_err(|err| err.to_string()),
+        });
+        self
+    }
+
+    pub fn with_error(mut self, request: T, error: impl ToString) -> Self {
+        self.interactions.push(Interaction {
+            request_selector_fn: Box::new(move |r| r == &request),
+            response: Err(error.to_string()),
+        });
+        self
+    }
+
+    pub fn with_custom_trigger(
+        mut self,
+        trigger_fn: FilterFn<T>,
+        response: Result<Value, String>,
+    ) -> Self {
+        self.interactions.push(Interaction {
+            request_selector_fn: trigger_fn,
+            response,
+        });
+        self
+    }
+
+    pub fn or_else(mut self, response: impl Serialize) -> mpsc::UnboundedSender<JsonRpcRequest<T>> {
+        self.interactions.push(Interaction {
+            request_selector_fn: Box::new(|_| true),
+            response: serde_json::to_value(response).map_err(|err| err.to_string()),
+        });
+        self.or_fail()
+    }
+
+    pub fn or_fail(self) -> mpsc::UnboundedSender<JsonRpcRequest<T>> {
+        let (tx, mut rx) = mpsc::unbounded_channel::<JsonRpcRequest<T>>();
+        tokio::spawn(async move {
+            while let Some(request) = rx.recv().await {
+                let response = self
+                    .interactions
+                    .iter()
+                    .find_map(|interaction| interaction.maybe_respond(&request.endpoint))
+                    .unwrap_or_else(|| Err("No expected response found".to_string()));
+                request
+                    .resp
+                    .send(response)
+                    .expect("Something should receive response");
+            }
+        });
+        tx
+    }
+}
+
+impl<T: PartialEq + Send + 'static> Default for MockJsonRpcBuilder<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}

ethportal-api/src/types/jsonrpc/mod.rs

@@ -1,3 +1,4 @@
 pub mod endpoints;
+pub mod json_rpc_mock;
 pub mod params;
 pub mod request;