### Install Dependencies

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Install project dependencies using npm. This command is typically run after cloning the repository or when setting up the development environment.

```bash
npm install
```

--------------------------------

### Install roslibjs with npm

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Install the roslibjs package using npm or any compatible package manager.

```bash
npm install roslib
```

--------------------------------

### Fibonacci Action Client Example

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/action_client.html

Creates an ActionClient for the Fibonacci action and sends a goal. This snippet requires a running Fibonacci action server and rosbridge_websocket. Ensure the action server name and action message type are correct.

```javascript
// The ActionClient // ---------------- var fibonacciClient = new ROSLIB.ActionClient({
  ros: ros,
  serverName: "/fibonacci",
  actionName: "actionlib_tutorials/FibonacciAction",
}); // Create a goal. var goal = new ROSLIB.Goal({
  actionClient: fibonacciClient,
  goalMessage: {
    order: 7,
  },
}); // Print out their output into the terminal. goal.on("feedback", function (feedback) {
  console.log("Feedback: " + feedback.sequence);
}); goal.on("result", function (result) {
  console.log("Final Result: " + result.sequence);
}); // Send the goal to the action server. goal.send();
```

--------------------------------

### Set and Get a Parameter

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Demonstrates setting a parameter on the ROS Parameter Server and then retrieving its value. A Param object is used for this purpose.

```javascript
// Setting a param value
// ---------------------
// First, we create a Param object with the name of the param.
var maxVelX = new ROSLIB.Param({
  ros: ros,
  name: "max_vel_y",
});

// Then we set the value of the param, which is sent to the ROS Parameter Server.
maxVelX.set(0.8);
maxVelX.get(function (value) {
  console.log("MAX VAL: " + value);
});
```

--------------------------------

### Get All Parameters

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Retrieves all currently set parameters from the ROS Parameter Server. The parameters are returned as a JSON object in the callback.

```javascript
ros.getParams(function (params) {
  console.log(params);
});
```

--------------------------------

### Set and Get Favorite Color Parameter

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Sets a string parameter 'favorite_color' and then retrieves its value. This illustrates parameter manipulation for string types.

```javascript
// Getting a param value
// ---------------------
var favoriteColor = new ROSLIB.Param({
  ros: ros,
  name: "favorite_color",
});

favoriteColor.set("red");
favoriteColor.get(function (value) {
  console.log("My robot's favorite color is " + value);
});
```

--------------------------------

### Get and Set ROS Parameter

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Retrieves the current value of a ROS parameter and then sets a new value. Note that ROS 2 parameters are specified with the format 'node_name:param_name'.

```javascript
var favoriteColor = new ROSLIB.Param({
  ros: ros,
  name: "/add_two_ints_server:use_sim_time",
});

favoriteColor.get(function (value) {
  console.log("The value of use_sim_time before setting is " + value);
});

favoriteColor.set(true);

favoriteColor.get(function (value) {
  console.log("The value of use_sim_time after setting is " + value);
});
```

--------------------------------

### Pose Creation

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/math.html

Demonstrates creating a Pose object using Vector3 for position and Quaternion for orientation. Check the JavaScript console for output.

```javascript
var p = new ROSLIB.Pose({ position: v1, orientation: q1, });
console.log(p);
```

--------------------------------

### ROS2 Action Server Implementation (JavaScript)

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_action_server.html

This snippet sets up a ROS2 connection and defines an Action Server for the Fibonacci action. It includes callbacks for receiving goals, sending feedback, and marking the action as succeeded or failed. Use this to create your own ROS2 action servers in a web environment.

```javascript
import * as ROSLIB from "roslib";

// Connecting to ROS
// -----------------
var ros = new ROSLIB.Ros({
  url: "ws://localhost:9090",
});

// If there is an error on the backend, an 'error' emit will be emitted.
ros.on("error", function (error) {
  console.log(error);
});

// The ActionServer
// ----------------
var fibonacciServer = new ROSLIB.Action({
  ros: ros,
  name: "/fibonacci",
  actionType: "example_interfaces/Fibonacci",
});

var actionCallback = function (goal, id) {
  console.log(
    "Received action goal on " + fibonacciServer.name + ", order: " + goal.order,
  );
  console.log("ID: " + id);
  let fibonacciSequence = [];
  fibonacciSequence.push(0);
  fibonacciSequence.push(1);

  // failure case
  if (goal.order > 47) {
    console.log(
      "Aborting. Value will exceed maximum signed integer value.",
    );
    fibonacciServer.setFailed(id);
    return;
  }

  // publish feedback
  for (var i = 1; i < goal.order; i++) {
    fibonacciSequence.push(
      fibonacciSequence[i] + fibonacciSequence[i - 1],
    );
    console.log("Sending feedback: " + fibonacciSequence);
    fibonacciServer.sendFeedback(id, { sequence: fibonacciSequence });
  }

  // send result
  console.log("Sending result: " + fibonacciSequence);
  fibonacciServer.setSucceeded(id, { sequence: fibonacciSequence });
};

var cancelCallback = function (id) {
  console.log("Canceled action with goal ID " + id);
  fibonacciServer.setCanceled(id, { sequence: [] });
};

fibonacciServer.advertise(actionCallback, cancelCallback);
```

--------------------------------

### Transform Application

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/math.html

Demonstrates creating a Transform object and applying it to a Pose. Check the JavaScript console for output.

```javascript
var tf = new ROSLIB.Transform({ translation: v2, rotation: q2, });
p.applyTransform(tf);
console.log(tf);
```

--------------------------------

### Connect to ROS and Subscribe to TF

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/tf.html

Establishes a connection to the ROS bridge and sets up a TF client to subscribe to TF data for 'turtle1'. Requires a running ROS instance with the turtle_tf_demo launch file and tf2_web_republisher.

```javascript
import * as ROSLIB from "roslib";

// Connecting to ROS
// -----------------
var ros = new ROSLIB.Ros();

// If there is an error on the backend, an 'error' emit will be emitted.
ros.on("error", function (error) {
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("error").style.display = "inline";
  console.log(error);
});

// Find out exactly when we made a connection.
ros.on("connection", function () {
  console.log("Connection made!");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("error").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("connected").style.display = "inline";
});

ros.on("close", function () {
  console.log("Connection closed.");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "inline";
});

// Create a connection to the rosbridge WebSocket server.
ros.connect("ws://localhost:9090");

// TF Client
// ---------
var tfClient = new ROSLIB.TFClient({
  ros: ros,
  fixedFrame: "world",
  angularThres: 0.01,
  transThres: 0.01,
});

// Subscribe to a turtle.
tfClient.subscribe("turtle1", function (tf) {
  console.log(tf);
});
```

--------------------------------

### Build roslibjs

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Build the roslibjs project. This command compiles the source code into distributable files.

```bash
npm run build
```

--------------------------------

### Test roslibjs

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Run the test suite for roslibjs. This command executes all defined tests to ensure the library is functioning correctly.

```bash
npm run test
```

--------------------------------

### Initialize ROS Connection and Load URDF

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/urdf.html

Connects to a ROS instance, retrieves the URDF model from the 'robot_description' parameter, and parses it. Handles connection errors and status updates.

```javascript
function init() {
  // Connect to ROS.
  var ros = new ROSLIB.Ros({
    url: "ws://localhost:9090",
  });

  // Get the URDF value from ROS.
  var param = new ROSLIB.Param({
    ros: ros,
    name: "robot_description",
  });

  param.get(function (param) {
    // Setup the loader for the URDF.
    var urdfModel = new ROSLIB.UrdfModel({
      string: param,
    });
    console.log(urdfModel);
  });

  // If there is an error on the backend, an 'error' emit will be emitted.
  ros.on("error", function (error) {
    document.getElementById("connecting").style.display = "none";
    document.getElementById("connected").style.display = "none";
    document.getElementById("closed").style.display = "none";
    document.getElementById("error").style.display = "inline";
    console.log(error);
  });

  // Find out exactly when we made a connection.
  ros.on("connection", function () {
    console.log("Connection made!");
    document.getElementById("connecting").style.display = "none";
    document.getElementById("error").style.display = "none";
    document.getElementById("closed").style.display = "none";
    document.getElementById("connected").style.display = "inline";
  });

  ros.on("close", function () {
    console.log("Connection closed.");
    document.getElementById("connecting").style.display = "none";
    document.getElementById("connected").style.display = "none";
    document.getElementById("closed").style.display = "inline";
  });
}
```

--------------------------------

### ROS Connection and Event Handling

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/action_client.html

Establishes a WebSocket connection to a ROS instance and handles connection, error, and close events. Ensure the ROS instance is running and accessible.

```javascript
import * as ROSLIB from "roslib"; // Connecting to ROS // ----------------- var ros = new ROSLIB.Ros({ url: "ws://localhost:9090", }); // If there is an error on the backend, an 'error' emit will be emitted. ros.on("error", function (error) {
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("error").style.display = "inline";
  console.log(error);
}); // Find out exactly when we made a connection. ros.on("connection", function () {
  console.log("Connection made!");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("error").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("connected").style.display = "inline";
}); ros.on("close", function () {
  console.log("Connection closed.");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "inline";
});
```

--------------------------------

### Vector3 Operations

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/math.html

Demonstrates creating, cloning, and adding Vector3 objects. Check the JavaScript console for output.

```javascript
import * as ROSLIB from "roslib";

var v1 = new ROSLIB.Vector3({ x: 1, y: 2, z: 3, });
var v2 = v1.clone();
v1.add(v2);
console.log(v1);
```

--------------------------------

### ROS Action Server Implementation (JavaScript)

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/action_server.html

This snippet shows the server-side logic for a Fibonacci action. It handles incoming goals, calculates the sequence, sends feedback, and sets the final result or preempts the action if canceled.

```javascript
import * as ROSLIB from "roslib"; // Connecting to ROS // ----------------- var ros = new ROSLIB.Ros({ url: "ws://localhost:9090", }); // If there is an error on the backend, an 'error' emit will be emitted. ros.on("error", function (error) { console.log(error); }); // The ActionServer // ---------------- const fibonacciServer = new ROSLIB.SimpleActionServer({ ros: ros, serverName: "/fibonacci", actionName: "actionlib_tutorials/FibonacciAction", }); var canceled = false; //handle fibonacci action request. fibonacciServer.on("goal", function (goalMessage) { console.log(goalMessage); var fibonacciSequence = []; fibonacciSequence.push(0); fibonacciSequence.push(1); for (var i = 1; i < goalMessage.order; i++) { fibonacciSequence.push( fibonacciSequence[i] + fibonacciSequence[i - 1], ); if (canceled === true) { console.log("Action server preempted"); fibonacciServer.setPreempted(); } console.log(fibonacciSequence); //send feedback var feedback = { sequence: fibonacciSequence }; fibonacciServer.sendFeedback(fibonacciSequence); } //send result var result = { sequence: fibonacciSequence }; fibonacciServer.setSucceeded(result); }); fibonacciServer.on("cancel", function (goalMessage) { canceled = true; });
```

--------------------------------

### Quaternion Operations

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/math.html

Demonstrates creating, cloning, multiplying, and inverting Quaternion objects. Check the JavaScript console for output.

```javascript
var q1 = new ROSLIB.Quaternion({ x: 0.1, y: 0.2, z: 0.3, w: 0.4, });
var q2 = q1.clone();
q1.multiply(q2);
q1.invert();
console.log(q1);
```

--------------------------------

### Connect to Rosbridge WebSocket

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Establishes a connection to the rosbridge WebSocket server. Handles connection, error, and close events.

```javascript
import * as ROSLIB from "roslib";

var ros = new ROSLIB.Ros();

ros.on("error", function (error) {
  console.log(error);
});

ros.on("connection", function () {
  console.log("Connection made!");
});

ros.on("close", function () {
  console.log("Connection closed.");
});

ros.connect("ws://localhost:9090");
```

--------------------------------

### Fibonacci Action Client with RoslibJS

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_action_client.html

Implements an action client for the Fibonacci action. Sends a goal with a specified order and logs the resulting sequence and any feedback received.

```javascript
// The ActionClient
// ----------------
var fibonacciClient = new ROSLIB.Action({
  ros: ros,
  name: "/fibonacci",
  actionType: "example_interfaces/Fibonacci",
});

// Send an action goal
var goal = {
  order: 5
};

var goal_id = fibonacciClient.sendGoal(
  goal,
  function (result) {
    console.log(
      "Result for action goal on " + fibonacciClient.name + ": " + result.sequence,
    );
  },
  function (feedback) {
    console.log("Feedback for action on " + fibonacciClient.name + ": " + feedback.sequence);
  }
);
```

--------------------------------

### Connect to Rosbridge

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Establishes a WebSocket connection to the rosbridge server. It includes event listeners for connection status (error, connection, close) and updates the UI accordingly.

```javascript
import * as ROSLIB from "roslib";

// Connecting to ROS
// -----------------
var ros = new ROSLIB.Ros();

// If there is an error on the backend, an 'error' emit will be emitted.
ros.on("error", function (error) {
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("error").style.display = "inline";
  console.log(error);
});

// Find out exactly when we made a connection.
ros.on("connection", function () {
  console.log("Connection made!");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("error").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("connected").style.display = "inline";
});

ros.on("close", function () {
  console.log("Connection closed.");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "inline";
});

// Create a connection to the rosbridge WebSocket server.
ros.connect("ws://localhost:9090");
```

--------------------------------

### ROS 2 Connection and Event Handling with RoslibJS

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_action_client.html

Establishes a WebSocket connection to a ROS 2 instance via rosbridge. Handles connection, error, and close events to manage the connection status.

```javascript
import * as ROSLIB from "roslib";

// Connecting to ROS
// -----------------
var ros = new ROSLIB.Ros({
  url: "ws://localhost:9090",
});

// If there is an error on the backend, an 'error' emit will be emitted.
ros.on("error", function (error) {
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("error").style.display = "inline";
  console.log(error);
});

// Find out exactly when we made a connection.
ros.on("connection", function () {
  console.log("Connection made!");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("error").style.display = "none";
  document.getElementById("closed").style.display = "none";
  document.getElementById("connected").style.display = "inline";
});

ros.on("close", function () {
  console.log("Connection closed.");
  document.getElementById("connecting").style.display = "none";
  document.getElementById("connected").style.display = "none";
  document.getElementById("closed").style.display = "inline";
});
```

--------------------------------

### Call a Service

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Calls a ROS service with a given request and handles the response in a callback function. Requires creating a Service client object.

```javascript
// Calling a service
// -----------------
// First, we create a Service client with details of the service's name and service type.
var addTwoIntsClient = new ROSLIB.Service({
  ros: ros,
  name: "/add_two_ints",
  serviceType: "rospy_tutorials/AddTwoInts",
});

// Then we create a Service Request. The object we pass in to ROSLIB.ServiceRequest matches the
// fields defined in the rospy_tutorials AddTwoInts.srv file.
var request = {
  a: 1,
  b: 2,
};

// Finally, we call the /add_two_ints service and get back the results in the callback. The result
// is a ROSLIB.ServiceResponse object.
addTwoIntsClient.callService(request, function (result) {
  console.log(
    "Result for service call on " + addTwoIntsClient.name + ": " + result.sum,
  );
});
```

--------------------------------

### Lint roslibjs

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Run the linter to check for code style and potential errors in the roslibjs codebase. This helps maintain code quality and consistency.

```bash
npm run lint
```

--------------------------------

### Advertise a ROS Service

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Advertises a ROS service, providing a callback function to handle incoming requests and return a response. The callback should return true if the service was handled successfully.

```javascript
var setBoolServer = new ROSLIB.Service({
  ros: ros,
  name: "/set_bool",
  serviceType: "std_srvs/SetBool",
});

setBoolServer.advertise(function (request, response) {
  console.log(
    "Received service request on " + setBoolServer.name + ": " + request.data,
  );
  response["success"] = true;
  response["message"] = "Set successfully";
  return true;
});
```

--------------------------------

### Listen to ROS Connection Events

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Listen for 'error' and 'connection' events on the ROS object to monitor the connection status. This is useful for debugging and providing user feedback.

```javascript
ros.on("error", function (error) {
  console.log(error);
});
ros.on("connection", function () {
  console.log("Connection made!");
});
```

--------------------------------

### Publish to a Topic

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Publishes messages to a specified ROS topic. Requires creating a Topic object and then calling the publish method with a message payload.

```javascript
// Publishing a Topic
// ------------------
// First, we create a Topic object with details of the topic's name and message type.
var cmdVel = new ROSLIB.Topic({
  ros: ros,
  name: "/cmd_vel",
  messageType: "geometry_msgs/Twist",
});

// Then we create the payload to be published. The object we pass in to ros.Message matches the
// fields defined in the geometry_msgs/Twist.msg definition.
var twist = {
  linear: {
    x: 0.1,
    y: 0.2,
    z: 0.3,
  },
  angular: {
    x: -0.1,
    y: -0.2,
    z: -0.3,
  },
};

// And finally, publish.
cmdVel.publish(twist);
```

--------------------------------

### Advertise a Service

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Advertises a ROS service, making it available for other nodes to call. It requires a callback function that processes incoming requests and returns a response.

```javascript
// Advertising a Service
// ---------------------
// The Service object does double duty for both calling and advertising services
var setBoolServer = new ROSLIB.Service({
  ros: ros,
  name: "/set_bool",
  serviceType: "std_srvs/SetBool",
});

// Use the advertise() method to indicate that we want to provide this service
setBoolServer.advertise(function (request, response) {
  console.log(
    "Received service request on " + setBoolServer.name + ": " + request.data,
  );
  response["success"] = true;
  response["message"] = "Set successfully";
  return true;
});
```

--------------------------------

### Subscribe to a Topic

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/simple.html

Subscribes to messages from a ROS topic and registers a callback function to process incoming messages. The subscription can be unsubscribed from within the callback.

```javascript
// Subscribing to a Topic
// ----------------------
// Like when publishing a topic, we first create a Topic object with details of the topic's name
// and message type. Note that we can call publish or subscribe on the same topic object.
var listener = new ROSLIB.Topic({
  ros: ros,
  name: "/listener",
  messageType: "std_msgs/String",
});

// Then we add a callback to be called every time a message is published on this topic.
listener.subscribe(function (message) {
  console.log(
    "Received message on " + listener.name + ": " + message.data,
  );

  // If desired, we can unsubscribe from the topic as well.
  listener.unsubscribe();
});
```

--------------------------------

### Call a ROS Service

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Calls a ROS service with a request object and handles the response in a callback function. Ensure the service name and type are correct.

```javascript
var addTwoIntsClient = new ROSLIB.Service({
  ros: ros,
  name: "/add_two_ints",
  serviceType: "example_interfaces/AddTwoInts",
});

var request = {
  a: 1,
  b: 2,
};

addTwoIntsClient.callService(request, function (result) {
  console.log(
    "Result for service call on " + addTwoIntsClient.name + ": " + result.sum,
  );
});
```

--------------------------------

### Publish to a ROS Topic

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Publishes messages to a specified ROS topic. Ensure the topic and message type are correctly defined.

```javascript
var cmdVel = new ROSLIB.Topic({
  ros: ros,
  name: "/cmd_vel",
  messageType: "geometry_msgs/Twist",
});

var twist = {
  linear: {
    x: 0.1,
    y: 0.2,
    z: 0.3,
  },
  angular: {
    x: -0.1,
    y: -0.2,
    z: -0.3,
  },
};

cmdVel.publish(twist);
```

--------------------------------

### Subscribe to a ROS Topic

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib-examples/src/ros2_simple.html

Subscribes to messages on a ROS topic and defines a callback function to process received messages. Can unsubscribe within the callback.

```javascript
var listener = new ROSLIB.Topic({
  ros: ros,
  name: "/listener",
  messageType: "std_msgs/String",
});

listener.subscribe(function (message) {
  console.log(
    "Received message on " + listener.name + ": " + message.data,
  );
  listener.unsubscribe();
});
```

--------------------------------

### Check for WebSocket Server

Source: https://github.com/robotwebtools/roslibjs/blob/develop/packages/roslib/README.md

Verify if a WebSocket server is running on port 9090 using netstat. This is a common requirement for roslibjs to establish a connection.

```bash
netstat -a | grep 9090
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.