74 lines
2.4 KiB
Plaintext
74 lines
2.4 KiB
Plaintext
/**
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* 协议帧编解码基座（1.4.11）。
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*
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* 帧格式（小端）：
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* [0..3] uint32 整帧长度（含头，6 + payload）
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* [4..5] uint16 序号
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* [6..] bytes 载荷
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*
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* 该格式与 MySQL / MariaDB 的 3 字节长度头不同，是引擎无关的内部封装层：
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* 各引擎协议实现（1.4.3–1.4.10）在载荷里携带自己的报文，本层只负责
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* 传输分帧、粘包拆分与错误长度防御。
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*/
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import { ConnectionError } from '../connection/types';
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/** 一帧数据。 */
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export class Frame {
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readonly seq: number;
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readonly payload: Uint8Array;
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constructor(seq: number, payload: Uint8Array) {
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this.seq = seq;
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this.payload = payload;
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}
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}
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export class FrameCodec {
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/** 头长度：4 字节长度 + 2 字节序号。 */
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static readonly HEADER_BYTES: number = 6;
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/** 单帧载荷上限：16 MB。 */
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static readonly MAX_PAYLOAD_BYTES: number = 16 * 1024 * 1024;
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/** 组帧。载荷超限时抛 ConnectionError。 */
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static encode(seq: number, payload: Uint8Array): Uint8Array {
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if (payload.length > FrameCodec.MAX_PAYLOAD_BYTES) {
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throw new ConnectionError('payload too large: ' + payload.length);
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}
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const total: number = FrameCodec.HEADER_BYTES + payload.length;
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const out: Uint8Array = new Uint8Array(total);
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out[0] = total & 0xFF;
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out[1] = (total >>> 8) & 0xFF;
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out[2] = (total >>> 16) & 0xFF;
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out[3] = (total >>> 24) & 0xFF;
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out[4] = seq & 0xFF;
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out[5] = (seq >>> 8) & 0xFF;
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out.set(payload, FrameCodec.HEADER_BYTES);
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return out;
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}
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/** 读取头部声明的整帧长度；不足 4 字节返回 -1。 */
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static frameLength(header: Uint8Array): number {
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if (header.length < 4) {
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return -1;
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}
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return header[0] | (header[1] << 8) | (header[2] << 16) | (header[3] << 24);
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}
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/** 解出第一帧；数据不足返回 undefined（由调用方继续收）。 */
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static decode(buffer: Uint8Array): Frame | undefined {
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const total: number = FrameCodec.frameLength(buffer);
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if (total < 0) {
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return undefined;
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}
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if (total < FrameCodec.HEADER_BYTES || total > FrameCodec.HEADER_BYTES + FrameCodec.MAX_PAYLOAD_BYTES) {
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throw new ConnectionError('invalid frame length: ' + total);
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}
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if (buffer.length < total) {
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return undefined;
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}
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const seq: number = buffer[4] | (buffer[5] << 8);
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return new Frame(seq, buffer.slice(FrameCodec.HEADER_BYTES, total));
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}
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}
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