Add basic caching layer.

src/main/java/net/fabricmc/meta/FabricMeta.java

@@ -35,6 +35,7 @@
 
 import net.fabricmc.meta.data.VersionDatabase;
 import net.fabricmc.meta.utils.Reference;
+import net.fabricmc.meta.web.CacheHandler;
 import net.fabricmc.meta.web.WebServer;
 
 public class FabricMeta {
@@ -46,6 +47,7 @@ public class FabricMeta {
 	private static final Map<String, String> config = new HashMap<>();
 	private static boolean configInitialized;
 	private static URL heartbeatUrl; // URL pinged with every successful update()
+	private static CacheHandler cacheHandler = new CacheHandler();
 
 	public static void main(String[] args) {
 		Path configFile = Paths.get("config.json");
@@ -79,13 +81,14 @@ public static void main(String[] args) {
 		ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
 		executorService.scheduleAtFixedRate(FabricMeta::update, 1, 1, TimeUnit.MINUTES);
 
-		WebServer webServer = new WebServer(() -> database);
+		WebServer webServer = new WebServer(() -> database, cacheHandler);
 		webServer.createServer().start(5555);
 	}
 
 	private static void update() {
 		try {
 			database = VersionDatabase.generate();
+			cacheHandler.invalidateCache();
 			updateHeartbeat();
 		} catch (Throwable t) {
 			if (database == null) {

src/main/java/net/fabricmc/meta/web/CacheHandler.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2023 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.meta.web;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import io.javalin.http.Handler;
+import io.javalin.http.servlet.JavalinServletContext;
+
+public class CacheHandler {
+	private final Map<String, Response> cache = new ConcurrentHashMap<>();
+
+	public CacheHandler() {
+	}
+
+	public Handler before() {
+		return ctx -> {
+			Response response = cache.get(ctx.path());
+
+			if (response == null) {
+				return;
+			}
+
+			// Replay the response
+			ctx.status(response.status());
+			response.headers().forEach(ctx::header);
+			ctx.contentType(response.contentType());
+			ctx.result(response.body());
+
+			// Replace with ctx.skipRemainingHandlers() in Javalin 6
+			JavalinServletContext jsc = (JavalinServletContext) ctx;
+			jsc.getTasks().clear();
+		};
+	}
+
+	public Handler after() {
+		return ctx -> {
+			if (ctx.statusCode() != 200) {
+				return;
+			}
+
+			if (!ctx.queryParamMap().isEmpty()) {
+				// Don't cache any requests with query params to prevent the cache from growing too big.
+				// Maybe look into something better here
+				return;
+			}
+
+			cache.put(ctx.path(), new Response(
+					ctx.statusCode(),
+					readAllBytes(ctx.resultInputStream()),
+					ctx.headerMap(),
+					ctx.res().getContentType()));
+		};
+	}
+
+	private static byte[] readAllBytes(InputStream is) throws IOException {
+		is.reset();
+		byte[] bytes = is.readAllBytes();
+		is.reset();
+		return bytes;
+	}
+
+	public void invalidateCache() {
+		cache.clear();
+	}
+
+	private record Response(
+			int status,
+			byte[] body,
+			Map<String, String> headers,
+			String contentType) {
+	}
+}

src/main/java/net/fabricmc/meta/web/WebServer.java

@@ -16,6 +16,8 @@
 
 package net.fabricmc.meta.web;
 
+import static io.javalin.apibuilder.ApiBuilder.after;
+import static io.javalin.apibuilder.ApiBuilder.before;
 import static io.javalin.apibuilder.ApiBuilder.path;
 
 import java.util.function.Function;
@@ -39,10 +41,14 @@ public class WebServer {
 	private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
 
 	private final DataProvider dataProvider;
+	private final CacheHandler cacheHandler;
+
 	private final EndpointsV1 endpointsV1;
 
-	public WebServer(DataProvider dataProvider) {
+	public WebServer(DataProvider dataProvider, CacheHandler cacheHandler) {
 		this.dataProvider = dataProvider;
+		this.cacheHandler = cacheHandler;
+
 		endpointsV1 = new EndpointsV1(dataProvider);
 	}
 
@@ -52,6 +58,8 @@ public Javalin createServer() {
 			config.showJavalinBanner = false;
 			config.plugins.enableCors(cors -> cors.add(CorsPluginConfig::anyHost));
 		}).routes(() -> {
+			before(cacheHandler.before());
+			after(cacheHandler.after());
 			path("v1", endpointsV1.routes());
 		});
 

src/main/java/net/fabricmc/meta/web/v1/ModelsV1.java

@@ -31,13 +31,14 @@
 import net.fabricmc.meta.web.JsonModel;
 
 /**
- * Strongly defined records of the public API. Take extra care to record to method return types here.
+ * Strongly defined records of the public API. Take extra care when changing method return types and record components.
  */
 public sealed interface ModelsV1 extends JsonModel permits ModelsV1.GameVersion, ModelsV1.MappingVersion, ModelsV1.LoaderVersion, ModelsV1.LoaderInfo, ModelsV1.LoaderLauncherInfo {
 	/**
-	 * /v2/versions/game
+	 * /v1/versions/game
 	 */
 	static List<GameVersion> gameVersions(DataProvider dataProvider) {
+		System.out.println("ohno");
 		LinkedList<GameVersion> versions = new LinkedList<>();
 
 		for (BaseVersion version : dataProvider.getGameVersions()) {
@@ -48,7 +49,7 @@ static List<GameVersion> gameVersions(DataProvider dataProvider) {
 	}
 
 	/**
-	 * /v2/game/{game_version}
+	 * /v1/game/{game_version}
 	 */
 	static List<GameVersion> gameVersions(DataProvider dataProvider, String gameVersion) {
 		for (BaseVersion version : dataProvider.getGameVersions()) {
@@ -61,7 +62,7 @@ static List<GameVersion> gameVersions(DataProvider dataProvider, String gameVers
 	}
 
 	/**
-	 * /v2/versions/mappings
+	 * /v1/versions/mappings
 	 */
 	static List<MappingVersion> mappingVersions(DataProvider dataProvider) {
 		LinkedList<MappingVersion> versions = new LinkedList<>();
@@ -74,7 +75,7 @@ static List<MappingVersion> mappingVersions(DataProvider dataProvider) {
 	}
 
 	/**
-	 * /v2/mappings/{game_version}
+	 * /v1/mappings/{game_version}
 	 */
 	static List<MappingVersion> mappingVersions(DataProvider dataProvider, String gameVersion) {
 		LinkedList<MappingVersion> versions = new LinkedList<>();
@@ -89,7 +90,7 @@ static List<MappingVersion> mappingVersions(DataProvider dataProvider, String ga
 	}
 
 	/**
-	 * /v2/versions/loader
+	 * /v1/versions/loader
 	 */
 	static List<LoaderVersion> loaderVersions(DataProvider dataProvider) {
 		LinkedList<LoaderVersion> versions = new LinkedList<>();
@@ -102,7 +103,7 @@ static List<LoaderVersion> loaderVersions(DataProvider dataProvider) {
 	}
 
 	/**
-	 * /v2/versions/loader/{game_version}/{loader_version}
+	 * /v1/versions/loader/{game_version}/{loader_version}
 	 */
 	static List<LoaderInfo> loaderInfo(DataProvider dataProvider, String gameVersion) {
 		MavenBuildGameVersion mappings = null;
@@ -128,7 +129,7 @@ static List<LoaderInfo> loaderInfo(DataProvider dataProvider, String gameVersion
 	}
 
 	/**
-	 * /v2/versions/loader/{game_version}/{loader_version}
+	 * /v1/versions/loader/{game_version}/{loader_version}
 	 */
 	static LoaderLauncherInfo loaderLauncherInfo(DataProvider dataProvider, String gameVersion, String loaderVersion) {
 		MavenBuildVersion loader = null;

src/test/java/net/fabricmc/meta/test/TestUtils.java

@@ -19,10 +19,12 @@
 import io.javalin.Javalin;
 
 import net.fabricmc.meta.FabricMeta;
+import net.fabricmc.meta.web.CacheHandler;
 import net.fabricmc.meta.web.WebServer;
 
 public class TestUtils {
 	public static Javalin createServer() {
-		return new WebServer(() -> FabricMeta.database).createServer();
+		CacheHandler cacheHandler = new CacheHandler();
+		return new WebServer(() -> FabricMeta.database, cacheHandler).createServer();
 	}
 }