Libgdx Networking

libGDX Networking

Quick reference for com.badlogic.gdx.Net and com.badlogic.gdx.net.*. Covers HTTP requests, TCP sockets, HttpRequestBuilder, and platform differences.

Net Interface

Access via Gdx.net. Two capabilities: HTTP requests and TCP sockets.

// HTTP
Gdx.net.sendHttpRequest(request, listener);    // async — response via listener
Gdx.net.cancelHttpRequest(request);            // void
Gdx.net.isHttpRequestPending(request);         // boolean

// TCP Sockets
Gdx.net.newServerSocket(Net.Protocol.TCP, port, hints);           // ServerSocket
Gdx.net.newServerSocket(Net.Protocol.TCP, hostname, port, hints); // overload with bind address
Gdx.net.newClientSocket(Net.Protocol.TCP, host, port, hints);     // Socket

// Browser
Gdx.net.openURI("https://example.com");       // opens system browser, returns boolean

Net.Protocol is an enum with only TCP — no UDP support.

HTTP Requests

Net.HttpRequest

Net.HttpRequest request = new Net.HttpRequest(Net.HttpMethods.GET);
request.setUrl("https://api.example.com/data");
request.setHeader("Accept", "application/json");
request.setTimeOut(5000);                      // millis — NOTE: capital O in TimeOut
request.setFollowRedirects(true);              // default: true
request.setIncludeCredentials(false);          // for GWT CORS cookies

// POST with string body
Net.HttpRequest post = new Net.HttpRequest(Net.HttpMethods.POST);
post.setUrl("https://api.example.com/submit");
post.setHeader("Content-Type", "application/json");
post.setContent("{\"key\": \"value\"}");

// POST with stream body
post.setContent(inputStream, contentLength);   // InputStream + long

Gotchas:

• Spelling is setTimeOut (capital O), NOT setTimeout. The getter is getTimeOut().
• There is no setBody() — the method is setContent().
• There is no setMethod() on HttpRequest for changing method after construction — wait, there IS: setMethod(String) exists, but prefer the constructor.
• HttpRequest implements Poolable with a reset() method for object pool reuse.

Net.HttpMethods Constants

Net.HttpMethods is an interface used as a constant holder (not an enum):

Always use these constants. On Desktop/Android/iOS, HttpURLConnection.setRequestMethod() is case-sensitive and requires uppercase. Passing "get" throws ProtocolException.

Sending and Handling Responses

Gdx.net.sendHttpRequest(request, new Net.HttpResponseListener() {
    @Override
    public void handleHttpResponse(Net.HttpResponse httpResponse) {
        int status = httpResponse.getStatus().getStatusCode();
        String body = httpResponse.getResultAsString();

        // CRITICAL: This callback is NOT on the GL thread!
        Gdx.app.postRunnable(() -> {
            label.setText(body);  // safe to touch Scene2D/GL here
        });
    }

    @Override
    public void failed(Throwable t) {
        Gdx.app.postRunnable(() -> {
            Gdx.app.error("Net", "Request failed", t);
        });
    }

    @Override
    public void cancelled() {
        // Request was cancelled via cancelHttpRequest()
    }
});

CRITICAL: Callback Threading

On Desktop, Android, and iOS, response callbacks run on a background thread (the internal NetThread pool), NOT the GL/render thread. Any code that touches OpenGL state, SpriteBatch, Scene2D actors, or game state must be wrapped in Gdx.app.postRunnable().

On GWT, callbacks run on the main JS event loop (which is the render thread), but write code as if they don't — always use postRunnable() for cross-platform safety.

Net.HttpResponse

String body    = response.getResultAsString();  // String
byte[] bytes   = response.getResult();          // byte[] — NOTE: NOT getResultAsBytes()
InputStream is = response.getResultAsStream();  // InputStream

HttpStatus status = response.getStatus();
int code = status.getStatusCode();              // e.g. 200

String header = response.getHeader("Content-Type");            // single header
Map<String, List<String>> all = response.getHeaders();         // all headers

Gotchas:

• The byte[] method is getResult(), NOT getResultAsBytes() — this does not exist.
• getResult() and getResultAsString() may only be called once per response (documented limitation).
• HttpStatus is com.badlogic.gdx.net.HttpStatus (standalone class), not an inner class of Net. It has standard constants like HttpStatus.SC_OK (200), HttpStatus.SC_NOT_FOUND (404), etc.
• The listener parameter on sendHttpRequest is @Null — passing null is allowed (fire-and-forget).

HttpRequestBuilder

Fluent builder for constructing Net.HttpRequest. Located in com.badlogic.gdx.net.

// Static configuration (set once, affects all subsequent builds)
HttpRequestBuilder.baseUrl = "https://api.example.com";  // prepended to all URLs
HttpRequestBuilder.defaultTimeout = 5000;                 // millis, default: 1000

HttpRequestBuilder builder = new HttpRequestBuilder();

// GET request
Net.HttpRequest get = builder.newRequest()
    .method(Net.HttpMethods.GET)
    .url("/users/123")              // becomes "https://api.example.com/users/123"
    .timeout(3000)
    .header("Accept", "application/json")
    .build();

// POST with JSON body
Net.HttpRequest post = builder.newRequest()
    .method(Net.HttpMethods.POST)
    .url("/users")
    .jsonContent(myObject)          // sets Content-Type: application/json, serializes via Json
    .build();

// POST with form data
Map<String, String> params = new HashMap<>();
params.put("username", "alice");
params.put("password", "secret");
Net.HttpRequest form = builder.newRequest()
    .method(Net.HttpMethods.POST)
    .url("/login")
    .formEncodedContent(params)     // sets Content-Type: application/x-www-form-urlencoded
    .build();

// Basic authentication
Net.HttpRequest auth = builder.newRequest()
    .method(Net.HttpMethods.GET)
    .url("/protected")
    .basicAuthentication("user", "pass")  // sets Authorization: Basic header
    .build();

Builder Methods

Gotchas:

• url() silently prepends baseUrl. If baseUrl is non-empty and you pass a full URL, you get a mangled URL.
• jsonContent() uses a static Json instance — configure it via HttpRequestBuilder.json if you need custom serialization.
• newRequest() must be called before each request. Calling it twice without build() throws.

TCP Sockets

Socket I/O is blocking — never use on the render thread.

// Server
ServerSocketHints serverHints = new ServerSocketHints();
serverHints.acceptTimeout = 0;   // 0 = block forever; default: 5000ms
ServerSocket server = Gdx.net.newServerSocket(Net.Protocol.TCP, 9090, serverHints);

// Accept clients on a background thread
new Thread(() -> {
    while (running) {
        SocketHints clientHints = new SocketHints();
        Socket client = server.accept(clientHints);  // blocks until connection
        handleClient(client);
    }
}).start();

// Client
SocketHints hints = new SocketHints();
hints.connectTimeout = 5000;     // default: 5000ms
hints.tcpNoDelay = true;         // default: true
hints.keepAlive = true;          // default: true
Socket socket = Gdx.net.newClientSocket(Net.Protocol.TCP, "example.com", 9090, hints);

InputStream in  = socket.getInputStream();
OutputStream out = socket.getOutputStream();
String remote   = socket.getRemoteAddress();
boolean alive   = socket.isConnected();

socket.dispose();   // MUST dispose — Socket extends Disposable
server.dispose();   // ServerSocket also extends Disposable

SocketHints Fields

ServerSocketHints Fields

openURI

boolean opened = Gdx.net.openURI("https://example.com");

Opens the URL in the platform's default browser/handler. Returns false if known to have failed.

Pixmap.downloadFromUrl

Convenience method for downloading images — uses Net internally:

Pixmap.downloadFromUrl("https://example.com/image.png", new Pixmap.DownloadPixmapResponseListener() {
    @Override
    public void downloadComplete(Pixmap pixmap) {
        // Already on GL thread (internally posted via postRunnable) — safe to use directly
        texture = new Texture(pixmap);
    }

    @Override
    public void downloadFailed(Throwable t) {
        // Called on background thread — use postRunnable for GL/UI operations
        Gdx.app.postRunnable(() -> Gdx.app.log("Download", "Failed", t));
    }
});

Platform Differences

Android: Add <uses-permission android:name="android.permission.INTERNET"/> to AndroidManifest.xml.

iOS: App Transport Security (ATS) blocks plain HTTP by default. Use HTTPS or configure ATS exceptions in Info.plist.

GWT: Only getResultAsString() works. getResult() and getResultAsStream() throw GdxRuntimeException. Sockets throw UnsupportedOperationException. Use setIncludeCredentials(true) for cross-origin requests needing cookies.

When to Use libGDX Net vs Third-Party

For JSON parsing of responses, use libGDX's com.badlogic.gdx.utils.Json class. HttpRequestBuilder.jsonContent() already uses it for serialization.

DO NOT use java.net.HttpURLConnection or java.net.URL directly — these are not available on GWT and bypass libGDX's threading model.

Common Mistakes

1. Processing response data off the GL thread — handleHttpResponse runs on a background thread (Desktop/Android/iOS). Touching SpriteBatch, Scene2D, or game state without Gdx.app.postRunnable() causes crashes or silent corruption.
2. Using setTimeout (lowercase o) — The method is setTimeOut (capital O). setTimeout does not exist and will not compile.
3. Calling getResultAsBytes() — This method does not exist. The byte[] method is getResult(). The string method is getResultAsString().
4. Inventing Gdx.net.httpGet(url) or synchronous helpers — No convenience methods exist. You must construct Net.HttpRequest and use an async listener.
5. Using sockets on GWT — newServerSocket and newClientSocket throw UnsupportedOperationException on GWT. Design socket-dependent features with a platform check.
6. Forgetting INTERNET permission on Android — Network calls silently fail or throw without <uses-permission android:name="android.permission.INTERNET"/> in AndroidManifest.xml.
7. Passing lowercase HTTP methods — new Net.HttpRequest("get") throws ProtocolException on Desktop/Android/iOS. Always use Net.HttpMethods.GET etc.
8. Forgetting to dispose sockets — Both Socket and ServerSocket extend Disposable. Leaking them leaks OS file descriptors.
9. Calling getResultAsString() twice on the same response — May only be called once per response. Store the result in a variable.
10. Socket I/O on the render thread — Socket reads/writes are blocking. Use a dedicated thread or the application freezes.
11. Ignoring baseUrl in HttpRequestBuilder — url() prepends HttpRequestBuilder.baseUrl to every URL. Passing a full URL when baseUrl is set produces a mangled URL. Set baseUrl = "" to disable.
12. Using java.net.HttpURLConnection directly — Not cross-platform (fails on GWT), bypasses libGDX's thread pool, and requires manual thread management. Use Gdx.net for portable networking.

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