ensure aborted transactions don't get written

gg-txn/src/main.rs

@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 
-use nebkor_maelstrom::{mk_payload, Body, Message, Node, Runner};
+use nebkor_maelstrom::{mk_payload, Body, ErrorCode, Message, Node, Runner};
 use serde_json::Value;
 
 type Txn = Vec<TxnOp>;
@@ -44,6 +44,7 @@ impl TANode {
     fn transact(&mut self, txn: &Txn) -> (Txn, Txn) {
         let mut out = Txn::with_capacity(txn.len());
         let mut yo = Txn::new();
+        let mut new = HashMap::new();
         for txn_op in txn.iter() {
             let op = txn_op.op.as_str();
             match op {
@@ -57,7 +58,7 @@ impl TANode {
                     out.push(op);
                 }
                 "w" => {
-                    self.store.insert(txn_op.key, txn_op.value.unwrap());
+                    new.insert(txn_op.key, txn_op.value.unwrap());
                     yo.push(txn_op.clone());
                     out.push(txn_op.clone());
                 }
@@ -67,13 +68,13 @@ impl TANode {
             }
         }
 
-        (out, yo)
+        // if the transaction were aborted, we'd not want to commit it by inserting from
+        // `new` here
+        for (k, v) in new.into_iter() {
+            self.store.insert(k, v);
         }
 
-    fn handle_yo(&mut self, txn: &Txn) {
+        (out, yo)
-        for op in txn.iter() {
-            self.store.insert(op.key, op.value.unwrap());
-        }
     }
 }
 
@@ -86,15 +87,26 @@ impl Node for TANode {
                 let txn = get_txn(&msg);
 
                 let (txn, yo) = self.transact(&txn);
+                // simulated aborted transaction for G1a-resistance
+                if txn.is_empty() {
+                    let mut error = Body::from_type("error");
+                    let ec =
+                        ErrorCode::Definite(nebkor_maelstrom::protocol::DefiniteError::TxnConflict);
+                    error.code = Some(ec);
+                    error.text = Some("shit's fucked".into());
+                    runner.reply(&msg, error);
+                    return;
+                }
                 gossip(runner, &yo);
                 let payload = mk_payload(&[("txn", txn.serialize())]);
                 let body = Body::from_type("txn_ok").with_payload(payload);
                 runner.reply(&msg, body);
             }
-
             "yo" => {
                 let txn = get_txn(&msg);
-                self.handle_yo(&txn);
+                for op in txn.iter() {
+                    self.store.insert(op.key, op.value.unwrap());
+                }
             }
             _ => {
                 eprintln!("unknown message type {typ}")