WebTransportDatagramDuplexStream

Instance properties

incomingHighWaterMark

Represents the maximum number of incoming datagrams that can be queued while waiting to be read from the readable stream. Use incomingMaxBufferedDatagrams instead.

incomingMaxAge

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

incomingMaxBufferedDatagrams

Represents the maximum number of incoming datagrams that can be queued while waiting to be read from the readable stream.

maxDatagramSize Read only

Returns the maximum allowable size of outgoing datagrams, in bytes, that can be written to a WebTransportDatagramsWritable obtained via createWritable(), or the deprecated writable property.

outgoingHighWaterMark

Represents the maximum number of outgoing datagrams that can be queued for sending before backpressure is applied. Use outgoingMaxBufferedDatagrams instead.

outgoingMaxAge

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

outgoingMaxBufferedDatagrams

Represents the maximum number of outgoing datagrams that can be queued for sending on each WebTransportDatagramsWritable before backpressure is applied.

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.

Instance methods

createWritable()

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

Examples

Writing outgoing datagrams

This code uses the createWritable() method, if it is supported, to get a WebTransportDatagramsWritable instance that can be used for writing data to the transport. Otherwise, it falls back to the writable property , which returns a WritableStream object that you can write data to using a writer instead:

const writableStream =
  typeof transport.datagrams.createWritable === "function"
    ? transport.datagrams.createWritable()
    : transport.datagrams.writable; // Deprecated and non-standard

const writer = writableStream.getWriter();
const data1 = new Uint8Array([65, 66, 67]);
const data2 = new Uint8Array([68, 69, 70]);
await writer.ready;
writer.write(data1);
await writer.ready;
writer.write(data2);

Reading incoming datagrams

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);
  }
}

Alternatively, to read datagrams into a buffer that you supply, construct the transport with the datagramsReadableType option set to bytes, and read the stream using a ReadableStreamBYOBReader. See the Reading datagrams with a BYOB reader example on the WebTransport() constructor page.

Specifications

Browser compatibility

See also

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