Implements a custom RSA encryption/decryption scheme (with PKCS#1 padding) and a symmetric XOR cipher to encode payloads for the 115.com pro API. It uses big-integer for big number arithmetic and blueimp-md5 for key derivation. The class provides encode/decode methods that wrap the full encryption pipeline: MD5 key generation, symmetric XOR with key-dependent permutation, and asymmetric RSA encryption. This module is self-contained (only depends on two npm packages) and could be extracted for any project needing a similar custom encryption protocol, though the hardcoded keys are specific to 115.

Runs in the main world of the 115.com page (injected via <script> tag). It intercepts the global fetch function to cache file listing responses from the 115 API, enabling quick lookup of file metadata (SHA1, pickcode) without additional network requests. It also listens for contextmenu events to track the hovered file index, and responds to postMessage queries from the extension's content script to return selected/hovered file info. This pattern of monkey-patching fetch and using postMessage for cross-world communication is reusable for any extension that needs to access page-level data without relying on content script injection limitations.

A minimal, clean implementation of the event emitter pattern with on, trigger, and off methods. It is fully self-contained with no dependencies and can be dropped into any JavaScript project to decouple components. While simple, it demonstrates good craftsmanship with clear JSDoc annotations and proper handling of listener arrays.