chore(repo): initialize WebDrop monorepo

Signed-off-by: JustMe <mr.toing@outlook.com>

packages/core/src/log.ts

@@ -0,0 +1,86 @@
+import { HEADER_SIZE, ID_SIZE } from './constants.js';
+import { readU32, readU64, toBase64Url, type Bytes } from './bytes.js';
+import { IntegrityError } from './errors.js';
+
+/** 墓碑原因(protocol §8)。 */
+export type RemovedReason = 'deleted' | 'expired' | 'evicted' | 'download_limit' | 'superseded';
+
+const REASONS: readonly RemovedReason[] = ['deleted', 'expired', 'evicted', 'download_limit', 'superseded'];
+
+export type LogRecord =
+  | { kind: 'frame'; seq: number; envelope: Bytes }
+  | { kind: 'tombstone'; seq: number; itemId: string; reason: RemovedReason }
+  | { kind: 'announce'; seq: number; itemId: string; flags: number; createdAt: number };
+
+const KIND_FRAME = 1;
+const KIND_TOMBSTONE = 2;
+const KIND_ANNOUNCE = 3;
+
+/** body 的字节数,不够返回 null。 */
+function bodyLength(kind: number, buf: Uint8Array, bodyStart: number): number | null {
+  switch (kind) {
+    case KIND_FRAME: {
+      // 封装自带 payload_len:body 长度 = 26 + payload_len
+      if (buf.length < bodyStart + HEADER_SIZE) return null;
+      return HEADER_SIZE + readU32(buf, bodyStart + 22);
+    }
+    case KIND_TOMBSTONE:
+      return ID_SIZE + 1;
+    case KIND_ANNOUNCE:
+      return ID_SIZE + 1 + 8;
+    default:
+      throw new IntegrityError('bad_envelope');
+  }
+}
+
+function parseOne(buf: Uint8Array, offset: number): { record: LogRecord; next: number } {
+  if (buf.length < offset + 9) throw new IntegrityError('bad_envelope');
+  const seq = readU64(buf, offset);
+  const kind = buf[offset + 8] as number;
+  const bodyStart = offset + 9;
+
+  const len = bodyLength(kind, buf, bodyStart);
+  if (len === null || buf.length < bodyStart + len) throw new IntegrityError('bad_envelope');
+  const body = buf.subarray(bodyStart, bodyStart + len);
+  const next = bodyStart + len;
+
+  switch (kind) {
+    case KIND_FRAME:
+      return { record: { kind: 'frame', seq, envelope: body.slice() }, next };
+    case KIND_TOMBSTONE: {
+      const reason = REASONS[body[ID_SIZE] as number];
+      if (!reason) throw new IntegrityError('bad_envelope');
+      return { record: { kind: 'tombstone', seq, itemId: toBase64Url(body.subarray(0, ID_SIZE)), reason }, next };
+    }
+    default:
+      return {
+        record: {
+          kind: 'announce',
+          seq,
+          itemId: toBase64Url(body.subarray(0, ID_SIZE)),
+          flags: body[ID_SIZE] as number,
+          createdAt: readU64(body, ID_SIZE + 1),
+        },
+        next,
+      };
+  }
+}
+
+/** 解析 log 接口返回的记录拼接(长轮询的响应体)。 */
+export function parseLogRecords(data: Uint8Array): LogRecord[] {
+  const out: LogRecord[] = [];
+  let offset = 0;
+  while (offset < data.length) {
+    const { record, next } = parseOne(data, offset);
+    out.push(record);
+    offset = next;
+  }
+  return out;
+}
+
+/** 解析恰好一条记录(WebSocket 的一条二进制消息)。多余或缺少字节都视为非法。 */
+export function parseLogRecord(data: Uint8Array): LogRecord {
+  const { record, next } = parseOne(data, 0);
+  if (next !== data.length) throw new IntegrityError('bad_envelope');
+  return record;
+}