From 3f7bdaa64b1eab6936fe14977aa6add62dff4ea5 Mon Sep 17 00:00:00 2001
From: Luke Parker <lukeparker5132@gmail.com>
Date: Mon, 13 Nov 2023 00:17:58 -0500
Subject: [PATCH] Make the output distribution cache only available under a
 feature

Enables a mode with reduced memory usage *and* increased safety given current
unsafety of the cache.

Relevant to https://github.com/serai-dex/serai/issues/415.
---
 coins/monero/Cargo.toml           |  3 ++-
 coins/monero/src/wallet/decoys.rs | 18 ++++++++++++++----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/coins/monero/Cargo.toml b/coins/monero/Cargo.toml
index cf0549fe..2960fb46 100644
--- a/coins/monero/Cargo.toml
+++ b/coins/monero/Cargo.toml
@@ -91,7 +91,7 @@ std = [
 
   "monero-generators/std",
 
-  "futures/std",
+  "futures?/std",
 
   "hex/std",
   "serde/std",
@@ -100,6 +100,7 @@ std = [
   "base58-monero/std",
 ]
 
+cache-distribution = ["futures"]
 http-rpc = ["digest_auth", "simple-request", "tokio"]
 multisig = ["transcript", "frost", "dleq", "std"]
 binaries = ["tokio/rt-multi-thread", "tokio/macros", "http-rpc"]
diff --git a/coins/monero/src/wallet/decoys.rs b/coins/monero/src/wallet/decoys.rs
index fd1b8bcd..7f1e64af 100644
--- a/coins/monero/src/wallet/decoys.rs
+++ b/coins/monero/src/wallet/decoys.rs
@@ -1,8 +1,11 @@
-use std_shims::{sync::OnceLock, vec::Vec, collections::HashSet};
+use std_shims::{vec::Vec, collections::HashSet};
 
-#[cfg(not(feature = "std"))]
+#[cfg(feature = "cache-distribution")]
+use std_shims::sync::OnceLock;
+
+#[cfg(all(feature = "cache-distribution", not(feature = "std")))]
 use std_shims::sync::Mutex;
-#[cfg(feature = "std")]
+#[cfg(all(feature = "cache-distribution", feature = "std"))]
 use futures::lock::Mutex;
 
 use zeroize::{Zeroize, ZeroizeOnDrop};
@@ -27,9 +30,11 @@ const BLOCK_TIME: usize = 120;
 const BLOCKS_PER_YEAR: usize = 365 * 24 * 60 * 60 / BLOCK_TIME;
 const TIP_APPLICATION: f64 = (LOCK_WINDOW * BLOCK_TIME) as f64;
 
-// TODO: Expose an API to reset this in case a reorg occurs/the RPC fails/returns garbage
+// TODO: Resolve safety of this in case a reorg occurs/the network changes
 // TODO: Update this when scanning a block, as possible
+#[cfg(feature = "cache-distribution")]
 static DISTRIBUTION_CELL: OnceLock<Mutex<Vec<u64>>> = OnceLock::new();
+#[cfg(feature = "cache-distribution")]
 #[allow(non_snake_case)]
 fn DISTRIBUTION() -> &'static Mutex<Vec<u64>> {
   DISTRIBUTION_CELL.get_or_init(|| Mutex::new(Vec::with_capacity(3000000)))
@@ -159,11 +164,16 @@ impl Decoys {
     height: usize,
     inputs: &[SpendableOutput],
   ) -> Result<Vec<Decoys>, RpcError> {
+    #[cfg(feature = "cache-distribution")]
     #[cfg(not(feature = "std"))]
     let mut distribution = DISTRIBUTION().lock();
+    #[cfg(feature = "cache-distribution")]
     #[cfg(feature = "std")]
     let mut distribution = DISTRIBUTION().lock().await;
 
+    #[cfg(not(feature = "cache-distribution"))]
+    let mut distribution = vec![];
+
     let decoy_count = ring_len - 1;
 
     // Convert the inputs in question to the raw output data