Sending Messages

1. Sending Text Messages

Method	Accepts
`ws.send(string)`	UTF-8 text frame (opcode 0x1)
`ws.send(ArrayBuffer)`	Binary frame (0x2)
`ws.send(TypedArray)`	Binary frame
`ws.send(Blob)`	Binary frame

Example: Text send

ws.send("hello server");

Warning: Calling send() when readyState !== OPEN throws InvalidStateError.

2. Sending JSON Data

Example: Typed message envelope

function emit(type, payload) {
  ws.send(JSON.stringify({ "type": type, "id": crypto.randomUUID(), "ts": Date.now(), "payload": payload }));
}
emit("chat.message", { "room": "general", "text": "hi" });

Field	Purpose
`type`	Dispatch key
`id`	Correlation / dedup
`ts`	Client timestamp
`payload`	Type-specific data

3. Checking Buffer Amount

Example: Backpressure-aware send

const MAX_BUFFER = 1 * 1024 * 1024; // 1 MB
function safeSend(data) {
  if (ws.bufferedAmount > MAX_BUFFER) return false;
  ws.send(data);
  return true;
}

Property	Detail
`bufferedAmount`	Bytes queued in user agent, not yet on wire
Updated	After each `send()`
Reaches 0	When fully flushed to network

4. Queuing Messages

Example: Pre-open queue

const queue = [];
function send(msg) {
  if (ws.readyState === WebSocket.OPEN) ws.send(msg);
  else queue.push(msg);
}
ws.addEventListener("open", () => { while (queue.length) ws.send(queue.shift()); });

Strategy	When
FIFO queue	Order matters
Coalesce	Latest-state wins (e.g. cursor)
Drop oldest	Bounded memory

5. Validating Message Size

Limit	Typical
Browser per-frame	Unlimited (memory-bound)
ws library default (Node)	100 MB (`maxPayload`)
Nginx `client_max_body_size`	N/A (different mechanism)
Recommended	≤ 64 KB / msg

6. Handling Send Errors

Example: Guarded send

try { ws.send(data); }
catch (err) {
  if (err.name === "InvalidStateError") queue.push(data);
  else throw err;
}

Error	Meaning
`InvalidStateError`	Socket not OPEN
`SyntaxError`	Invalid UTF-8 in string

7. Sending Binary Data

Example: Send ArrayBuffer

const buf = new ArrayBuffer(4);
new DataView(buf).setUint32(0, 0xDEADBEEF);
ws.send(buf);

Type	Frame
`ArrayBuffer`	Binary (0x2)
`Blob`	Binary
`Uint8Array` etc.	Binary

8. Sending Typed Arrays

Typed Array	Bytes / Element
`Uint8Array`	1
`Int16Array`	2
`Float32Array`	4
`BigInt64Array`	8

Note: Endianness is little-endian on most platforms; encode explicitly with DataView for cross-platform protocols.

9. Implementing Message Batching

Example: Time-window batcher

let pending = [], timer = null;
function batchSend(msg) {
  pending.push(msg);
  timer ??= setTimeout(() => {
    ws.send(JSON.stringify({ "type": "batch", "items": pending }));
    pending = []; timer = null;
  }, 20);
}

Trigger	Use
Time window	Even update rate
Count threshold	Bounded latency
Size threshold	Bandwidth efficient

10. Compressing Messages

Approach	Trade-off
permessage-deflate (auto)	Negotiated extension; CPU cost
App-level gzip/brotli	Manual; better control
Binary format (MessagePack/Protobuf)	Smaller than JSON+deflate often

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