test: Support configurable base port for concurrent test processes

Read LDK_NODE_TEST_BASE_PORT env var to offset the listening port range,
avoiding collisions when multiple test processes run simultaneously.
Assign base ports 20000, 21000, 22000 to the three concurrent processes
in the stress-test CI job.

AI tools were used in preparing this commit.

Author: joostjager

.github/workflows/rust.yml

@@ -128,7 +128,7 @@ jobs:
           for i in $(seq 1 5); do
             echo "=== Iteration $i (shard ${{ matrix.shard }}) ==="
             for j in 1 2 3; do
-              RUSTFLAGS="--cfg no_download --cfg cycle_tests" cargo test --test integration_tests_rust -- --nocapture > /tmp/stress-${j}.log 2>&1 &
+              LDK_NODE_TEST_BASE_PORT=$((20000 + (j - 1) * 1000)) RUSTFLAGS="--cfg no_download --cfg cycle_tests" cargo test --test integration_tests_rust -- --nocapture > /tmp/stress-${j}.log 2>&1 &
               pids[${j}]=$!
             done
             for j in 1 2 3; do

tests/common/mod.rs

@@ -15,7 +15,7 @@ use std::env;
 use std::future::Future;
 use std::path::PathBuf;
 use std::sync::atomic::{AtomicU16, Ordering};
-use std::sync::{Arc, RwLock};
+use std::sync::{Arc, LazyLock, RwLock};
 use std::time::Duration;
 
 use bitcoin::hashes::hex::FromHex;
@@ -274,7 +274,10 @@ pub(crate) fn random_storage_path() -> PathBuf {
 	temp_path
 }
 
-static NEXT_PORT: AtomicU16 = AtomicU16::new(20000);
+static BASE_PORT: LazyLock<u16> = LazyLock::new(|| {
+	env::var("LDK_NODE_TEST_BASE_PORT").ok().and_then(|v| v.parse().ok()).unwrap_or(20000)
+});
+static NEXT_PORT: LazyLock<AtomicU16> = LazyLock::new(|| AtomicU16::new(*BASE_PORT));
 
 pub(crate) fn generate_listening_addresses() -> Vec<SocketAddress> {
 	let port = NEXT_PORT.fetch_add(2, Ordering::Relaxed);