The WebTransportDatagramDuplexStream interface of the WebTransport API represents a duplex stream that can be used for unreliable transport of datagrams between client and server. Provides access to a ReadableStream for reading incoming datagrams, a WritableStream for writing outgoing datagrams, and various settings and statistics related to the stream.

This is accessed via the WebTransport.datagrams property.

"Unreliable" means that transmission of data is not guaranteed, nor is arrival in a specific order. This is fine in some situations and provides very fast delivery. For example, you might want to transmit regular game state updates where each message supersedes the last one that arrives, and order is not important.

incomingHighWaterMark

Gets or sets the high water mark for incoming chunks of data — this is the maximum size, in chunks, that the incoming ReadableStream's internal queue can reach before it is considered full. See Internal queues and queuing strategies for more information.

incomingMaxAge

Gets or sets the maximum age for incoming datagrams, in milliseconds. Returns null if no maximum age has been set.

maxDatagramSize Read only

Returns the maximum allowable size of outgoing datagrams, in bytes, that can be written to writable.

outgoingHighWaterMark

Gets or sets the high water mark for outgoing chunks of data — this is the maximum size, in chunks, that the outgoing WritableStream's internal queue can reach before it is considered full. See Internal queues and queuing strategies for more information.

outgoingMaxAge

Gets or sets the maximum age for outgoing datagrams, in milliseconds. Returns null if no maximum age has been set.

readable Read only

Returns a ReadableStream instance that can be used to read incoming datagrams from the stream.

writable Read only

Returns a WritableStream instance that can be used to write outgoing datagrams to the stream.

The writable property returns a WritableStream object that you can write data to using a writer, for transmission to the server:

const writer = transport.datagrams.writable.getWriter();
const data1 = new Uint8Array([65, 66, 67]);
const data2 = new Uint8Array([68, 69, 70]);
writer.write(data1);
writer.write(data2);

The readable property returns a ReadableStream object that you can use to receive data from the server:

async function readData() {
  const reader = transport.datagrams.readable.getReader();
  while (true) {
    const { value, done } = await reader.read();
    if (done) {
      break;
    }
    // value is a Uint8Array.
    console.log(value);
  }
}

• Using WebTransport
• WebSockets API
• Streams API
• WebTransport over HTTP/3