import type net from 'node:net';
/**
* Write a length-prefixed JSON frame to a socket.
* Format: 4-byte big-endian length + JSON payload
*/
export function writeFrame(socket: net.Socket, obj: unknown): void {
const json = Buffer.from(JSON.stringify(obj), 'utf8');
const header = Buffer.alloc(4);
header.writeUInt32BE(json.length, 0);
socket.write(Buffer.concat([header, json]));
}
/**
* Create a frame reader that buffers incoming data and emits complete messages.
* Returns a function to be used as the 'data' event handler.
*/
export function createFrameReader(
onMessage: (msg: unknown) => void,
onError?: (err: Error) => void,
): (chunk: Buffer) => void {
let buffer = Buffer.alloc(0);
return (chunk: Buffer) => {
buffer = Buffer.concat([buffer, chunk]);
while (buffer.length >= 4) {
const len = buffer.readUInt32BE(0);
// Sanity check: reject messages larger than 100MB
if (len > 100 * 1024 * 1024) {
const err = new Error(`Message too large: ${len} bytes`);
if (onError) {
onError(err);
}
buffer = Buffer.alloc(0);
return;
}
if (buffer.length < 4 + len) {
// Not enough data yet, wait for more
return;
}
const payload = buffer.subarray(4, 4 + len);
buffer = buffer.subarray(4 + len);
try {
const msg = JSON.parse(payload.toString('utf8')) as unknown;
onMessage(msg);
} catch (err) {
if (onError) {
onError(err instanceof Error ? err : new Error(String(err)));
}
}
}
};
}
