Add allowed prefixes for RPC methods

Introduce a check to validate that RPC method names start with any of the specified allowed prefixes. Update the code to use `HashSet` for efficient prefix storage and add default allowed prefixes when initializing the application state.

src/main.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 use actix_web::{error, web, App, Error, HttpResponse, HttpServer};
 use anyhow::Context;
@@ -83,6 +83,15 @@ async fn rpc_call(
                 }
             };
 
+            // Check if the method starts with an allowed prefix
+            if !chain_state.allowed_prefixes.iter().any(|prefix| method.starts_with(prefix)) {
+                ordered_requests_result.push(Some(JsonRpcResponse::from_error(
+                    Some(id),
+                    DefinedError::MethodNotFound,
+                )));
+                continue;
+            }
+
             macro_rules! push_uncached_request_and_continue {
                 () => {{
                     let rpc_request = RpcRequest::new_uncachable(index, id, method, params);
@@ -382,6 +391,7 @@ async fn main() -> std::io::Result<()> {
             rpc_url: rpc_url.clone(),
             handlers: Default::default(),
             cache_factory,
+            allowed_prefixes: vec!["eth_".to_string(), "alchemy_".to_string(), "net_".to_string()],
         };
 
         for factory in &handler_factories {
@@ -472,6 +482,7 @@ struct ChainState {
     rpc_url: Url,
     cache_factory: Box<dyn CacheBackendFactory>,
     handlers: HashMap<String, HandlerEntry>,
+    allowed_prefixes: Vec<String>,
 }
 
 struct HandlerEntry {