Какие особенности протокола DDP?

DDP (Distributed Data Protocol) is a protocol used in Meteor (a framework for web and mobile development) for communication between the client and server.

Main features:

• Publication/Subscription: The server "publishes" data (collections of documents), and clients "subscribe" to the publications they are interested in. When data on the server changes, it is automatically sent to all subscribed clients.
• Real-time: Data changes are transmitted instantly, ensuring the information on the client is up-to-date.
• Remote Procedure Calls (RPC): Clients can invoke methods on the server to perform specific actions.
• Idempotency of calls: Repeating a method call with the same arguments does not lead to unwanted side effects (for most standard methods).
• Transport: Usually WebSocket is used for a persistent bidirectional connection, but it can fallback to HTTP.
• Data: Data transfer occurs in JSON format.
• Send data only when necessary: The server sends to the client only the data it is subscribed to, and only when it changes.
• Offline support: Meteor allows clients to temporarily store data changes locally and synchronize them with the server when the connection is restored.

// Example of publishing on the server (Node.js)
Meteor.publish('myCollection', function() {
  return MyCollection.find({}); // Publish all documents from the collection
});

// Example of subscribing on the client (JavaScript)
Meteor.subscribe('myCollection');

// Example of calling a method on the client (JavaScript)
Meteor.call('addDocument', { name: 'New Document' }, function(error, result) {
  if (error) {
    console.error("Error adding document:", error);
  } else {
    console.log("Document successfully added:", result);
  }
});

// Example of implementing a method on the server (Node.js)
Meteor.methods({
  addDocument: function(doc) {
    // Validate and insert the document
    return MyCollection.insert(doc);
  }
});