Added pass through endpoint to API (#255)

Author: devgianlu

api/README.md

@@ -57,9 +57,15 @@ The currently available events are:
 - `connectionEstablished` Successfully reconnected
 - `panic` Entered the panic state, playback is stopped. This is usually recoverable.
 
+### Web API pass through
+Use any endpoint from the [public Web API](https://developer.spotify.com/documentation/web-api/reference/) by appending it to `/web-api/`, the request will be made to the API with the correct `Authorization` header and the result will be returned.
+The method, body, and content type headers will pass through. Additionally, you can specify an `X-Spotify-Scope` header to override the requested scope, by default all will be requested.
+
 ## Examples
 `curl -X POST -d "uri=spotify:track:xxxxxxxxxxxxxxxxxxxxxx&play=true" http://localhost:24879/player/load`
 
 `curl -X POST http://localhost:24879/metadata/track/spotify:track:xxxxxxxxxxxxxxxxxxxxxx`
 
 `curl -X POST http://localhost:24879/metadata/spotify:track:xxxxxxxxxxxxxxxxxxxxxx`
+
+`curl -X GET http://localhost:24879/web-api/v1/me/top/artists`

api/src/main/java/xyz/gianlu/librespot/api/ApiServer.java

@@ -2,6 +2,8 @@
 
 import io.undertow.Undertow;
 import io.undertow.server.RoutingHandler;
+import io.undertow.server.handlers.PathHandler;
+import io.undertow.server.handlers.ResponseCodeHandler;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.jetbrains.annotations.NotNull;
@@ -24,7 +26,10 @@ public ApiServer(int port, @NotNull String host, @NotNull SessionWrapper wrapper
                 .post("/search/{query}", new SearchHandler(wrapper))
                 .post("/token/{scope}", new TokensHandler(wrapper))
                 .post("/profile/{user_id}/{action}", new ProfileHandler(wrapper))
-                .get("/events", events);
+                .post("/web-api/{endpoint}", new WebApiHandler(wrapper))
+                .get("/events", events)
+                .setFallbackHandler(new PathHandler(ResponseCodeHandler.HANDLE_404)
+                        .addPrefixPath("/web-api", new WebApiHandler(wrapper)));
 
         wrapper.setListener(events);
     }

api/src/main/java/xyz/gianlu/librespot/api/handlers/WebApiHandler.java

@@ -0,0 +1,64 @@
+package xyz.gianlu.librespot.api.handlers;
+
+import io.undertow.server.HttpServerExchange;
+import io.undertow.util.FileUtils;
+import io.undertow.util.HeaderValues;
+import io.undertow.util.Headers;
+import io.undertow.util.HttpString;
+import okhttp3.*;
+import org.jetbrains.annotations.NotNull;
+import xyz.gianlu.librespot.api.SessionWrapper;
+import xyz.gianlu.librespot.core.Session;
+import xyz.gianlu.librespot.core.TokenProvider;
+
+public final class WebApiHandler extends AbsSessionHandler {
+    private static final String[] API_TOKENS_ALL = new String[]{"ugc-image-upload", "playlist-read-collaborative", "playlist-modify-private", "playlist-modify-public", "playlist-read-private", "user-read-playback-position", "user-read-recently-played", "user-top-read", "user-modify-playback-state", "user-read-currently-playing", "user-read-playback-state", "user-read-private", "user-read-email", "user-library-modify", "user-library-read", "user-follow-modify", "user-follow-read", "streaming", "app-remote-control"};
+    private static final HttpUrl BASE_API_URL = HttpUrl.get("https://api.spotify.com");
+    private static final HttpString HEADER_X_SCOPE = HttpString.tryFromString("X-Spotify-Scope");
+
+    public WebApiHandler(@NotNull SessionWrapper wrapper) {
+        super(wrapper);
+    }
+
+    @Override
+    protected void handleRequest(@NotNull HttpServerExchange exchange, @NotNull Session session) throws Exception {
+        exchange.startBlocking();
+        if (exchange.isInIoThread()) {
+            exchange.dispatch(this);
+            return;
+        }
+
+        String body = FileUtils.readFile(exchange.getInputStream());
+        HeaderValues contentType = exchange.getRequestHeaders().get(Headers.CONTENT_TYPE);
+
+        String[] scopes = API_TOKENS_ALL;
+        if (exchange.getRequestHeaders().contains(HEADER_X_SCOPE))
+            scopes = exchange.getRequestHeaders().get(HEADER_X_SCOPE).toArray(new String[0]);
+
+        TokenProvider.StoredToken token = session.tokens().getToken(scopes);
+
+        HttpUrl.Builder url = BASE_API_URL.newBuilder()
+                .addPathSegments(exchange.getRelativePath().substring(1))
+                .query(exchange.getQueryString());
+
+        Request.Builder req = new Request.Builder()
+                .url(url.build())
+                .addHeader("Authorization", "Bearer " + token.accessToken);
+
+        String method = exchange.getRequestMethod().toString();
+        if (!body.isEmpty() && contentType != null)
+            req.method(method, RequestBody.create(body, MediaType.get(contentType.getFirst())));
+        else
+            req.method(method, null);
+
+        try (Response resp = session.client().newCall(req.build()).execute()) {
+            exchange.setStatusCode(resp.code());
+
+            String respContentType = resp.header("Content-Type");
+            if (respContentType != null) exchange.getResponseHeaders().add(Headers.CONTENT_TYPE, respContentType);
+
+            ResponseBody respBody = resp.body();
+            if (respBody != null) exchange.getOutputStream().write(respBody.bytes());
+        }
+    }
+}