From 0fce9668ffb5503967e6c7314f1c62856bce81d1 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Sat, 12 Sep 2026 14:52:14 +0200
Subject: [PATCH] test: extend coverage of Lcg and buildTerrain

---
 tests/testNetSession.cpp | 155 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 tests/testNetSession.cpp

diff --git a/tests/testNetSession.cpp b/tests/testNetSession.cpp
new file mode 100644
index 0000000..698f738
--- /dev/null
+++ b/tests/testNetSession.cpp
@@ -0,0 +1,155 @@
+#include "testHarness.h"
+#include "vf/NetSession.h"
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+using namespace vf;
+
+namespace {
+
+struct Lcg {
+    uint64_t state;
+    explicit Lcg(uint64_t seed) : state(seed | 1ull) {}
+    uint32_t next() {
+        state = state * 6364136223846793005ull + 1442695040888963407ull;
+        return static_cast<uint32_t>(state >> 32);
+    }
+    int range(int n) { return static_cast<int>(next() % static_cast<uint32_t>(n)); }
+};
+
+// Deterministic terrain in the chunk plane y = 0, so both ends have something
+// substantial to disagree about if replication is wrong.
+void buildTerrain(World& world, int columnsRadius) {
+    Lcg rng(0x51ed270b);
+    const Block palette[5] = {Block::Stone, Block::Dirt, Block::Grass, Block::Sand, Block::Gravel};
+    for (int cx = -columnsRadius; cx <= columnsRadius; ++cx) {
+        for (int cz = -columnsRadius; cz <= columnsRadius; ++cz) {
+            Chunk& chunk = world.ensureChunk(Vec3i{cx, 0, cz});
+            for (int x = 0; x < chunkSize; ++x) {
+                for (int z = 0; z < chunkSize; ++z) {
+                    int height = 4 + rng.range(9);
+                    for (int y = 0; y < height; ++y)
+                        chunk.set(x, y, z, palette[rng.range(5)]);
+                }
+            }
+        }
+    }
+}
+
+// Canonical over the whole world: chunk coordinates are sorted before hashing,
+// so the digest does not inherit the hash map's iteration order.
+uint64_t worldDigest(const World& world, const std::vector<Vec3i>& coords) {
+    ByteWriter stream;
+    for (const Vec3i& coord : coords) {
+        const Chunk* chunk = world.chunkAt(coord);
+        if (!chunk) continue;
+        stream.putU32(static_cast<uint32_t>(coord.x));
+        stream.putU32(static_cast<uint32_t>(coord.y));
+        stream.putU32(static_cast<uint32_t>(coord.z));
+        for (Block block : chunk->raw()) stream.putU8(static_cast<uint8_t>(block));
+    }
+    return fnv1a64(stream.bytes().data(), stream.bytes().size());
+}
+
+std::vector<Vec3i> sortedCoords(const std::unordered_set<Vec3i, Vec3iHash>& set) {
+    std::vector<Vec3i> coords(set.begin(), set.end());
+    for (std::size_t i = 1; i < coords.size(); ++i) {
+        Vec3i key = coords[i];
+        std::size_t j = i;
+        while (j > 0 && (coords[j - 1].y > key.y ||
+                         (coords[j - 1].y == key.y &&
+                          (coords[j - 1].z > key.z ||
+                           (coords[j - 1].z == key.z && coords[j - 1].x > key.x))))) {
+            coords[j] = coords[j - 1];
+            --j;
+        }
+        coords[j] = key;
+    }
+    return coords;
+}
+
+// Both ends of one connection, wired through a single loopback link.
+struct Pair {
+    LoopbackLink link;
+    Transport serverTransport;
+    Transport clientTransport;
+    NetSession server;
+    NetSession client;
+    World serverWorld;
+    World clientWorld;
+    ServerChunkSync sync;
+
+    Pair(const LinkQuality& quality, const TransportConfig& transportConfig,
+         const SessionConfig& sessionConfig)
+        : link(quality),
+          serverTransport(link, 0, transportConfig),
+          clientTransport(link, 1, transportConfig),
+          server(serverTransport, NetSession::Role::Server, sessionConfig),
+          client(clientTransport, NetSession::Role::Client, sessionConfig) {
+        server.attachWorld(serverWorld);
+        server.attachChunkSync(sync);
+        server.setEntityId(7);
+        client.attachWorld(clientWorld);
+    }
+
+    void step(uint64_t tick) {
+        server.receive(tick);
+        server.send(tick);
+        client.receive(tick);
+        client.send(tick);
+    }
+
+    // Server edit: authoritative world, dirty feed, and this session's own
+    // per-chunk work list all move together.
+    void edit(int gx, int gy, int gz, Block block) {
+        serverWorld.setBlock(gx, gy, gz, block);
+        Vec3i coord{floorDiv(gx, chunkSize), floorDiv(gy, chunkSize), floorDiv(gz, chunkSize)};
+        sync.markDirty(coord, floorMod(gx, chunkSize), floorMod(gy, chunkSize),
+                       floorMod(gz, chunkSize));
+        server.markChunkDirty(coord);
+    }
+
+    void clearDirty() { sync.clearAll(); }
+};
+
+SessionConfig quietConfig() {
+    SessionConfig config;
+    config.viewRadius = 2;
+    config.chunksPerTick = 3;
+    config.keepAliveIntervalTicks = 20;
+    config.keepAliveTimeoutTicks = 1000000;
+    return config;
+}
+
+}  // namespace
+
+VF_TEST(handshakeAndLoginCarryBothEndsOfTheSessionIntoThePlayPhase) {
+    LinkQuality quality;
+    quality.latencyTicks = 1;
+    TransportConfig transportConfig;
+    Pair pair(quality, transportConfig, quietConfig());
+
+    CHECK(pair.server.phase() == SessionPhase::Handshake);
+    CHECK(pair.client.phase() == SessionPhase::Handshake);
+
+    pair.client.beginHandshake("vulp", 0x1111222233334444ull, 0x5555666677778888ull);
+    CHECK(pair.client.phase() == SessionPhase::Login);
+
+    for (uint64_t tick = 0; tick < 12; ++tick) pair.step(tick);
+
+    CHECK(pair.server.phase() == SessionPhase::Play);
+    CHECK(pair.client.phase() == SessionPhase::Play);
+    CHECK(pair.server.playerName() == "vulp");
+    CHECK_EQ(pair.server.uuidHigh(), 0x1111222233334444ull);
+    CHECK_EQ(pair.client.entityId(), 7);
+    CHECK(pair.server.disconnectReason().empty());
+}
+
+VF_TEST(aPlayPacketArrivingBeforeLoginEndsTheSessionWithAReasonInsteadOfCrashing) {
+    LinkQuality quality;
+    quality.latencyTicks = 1;
+    TransportConfig transportConfig;
+    Pair pair(quality, transportConfig, quietConfig());
+