1
import crypto from 'node:crypto';
2
import { DEFAULT_USER } from '../constants.js';
3
import { getConfigValue } from '../util.js';
4

5
/**
6
 * Sets the Clear-Site-Data header to bust the browser cache.
7
 */
8
class CacheBuster {
9
    /**
10
     * Handles/User-Agents that have already been busted.
11
     * @type {Set<string>}
12
     */
13
    #keys = new Set();
14

15
    /**
16
     * User agent regex to match against requests.
17
     * @type {RegExp | null}
18
     */
19
    #userAgentRegex = null;
20

21
    /**
22
     * Whether the cache buster is enabled.
23
     * @type {boolean | null}
24
     */
25
    #isEnabled = null;
26

27
    constructor() {
28
        this.#isEnabled = !!getConfigValue('cacheBuster.enabled', false, 'boolean');
29
        const userAgentPattern = getConfigValue('cacheBuster.userAgentPattern', '');
30
        if (userAgentPattern) {
31
            try {
32
                this.#userAgentRegex = new RegExp(userAgentPattern, 'i');
33
            } catch {
34
                console.error('[Cache Buster] Invalid user agent pattern:', userAgentPattern);
35
            }
36
        }
37
    }
38

39
    /**
40
     * Check if the cache should be busted for the given request.
41
     * @param {import('express').Request} request Express request object.
42
     * @param {import('express').Response} response Express response object.
43
     * @returns {boolean} Whether the cache should be busted.
44
     */
45
    shouldBust(request, response) {
46
        // If disabled with config, don't do anything
47
        if (!this.#isEnabled) {
48
            return false;
49
        }
50

51
        // If response headers are already sent or response is ended
52
        if (response.headersSent || response.writableEnded) {
53
            console.warn('[Cache Buster] Response ended or headers already sent');
54
            return false;
55
        }
56

57
        // Check if the user agent matches the configured pattern
58
        const userAgent = request.headers['user-agent'] || '';
59

60
        // Bust cache for all requests if no pattern is set
61
        if (!this.#userAgentRegex) {
62
            return true;
63
        }
64

65
        return this.#userAgentRegex.test(userAgent);
66
    }
67

68
    /**
69
     * Middleware to bust the browser cache for the current user.
70
     * @type {import('express').RequestHandler}
71
     */
72
    #middleware(request, response, next) {
73
        const handle = request.user?.profile?.handle || DEFAULT_USER.handle;
74
        const userAgent = request.headers['user-agent'] || '';
75
        const hash = crypto.createHash('sha256').update(userAgent).digest('hex');
76
        const key = `${handle}-${hash}`;
77

78
        if (this.#keys.has(key)) {
79
            return next();
80
        }
81

82
        this.#keys.add(key);
83
        this.bust(request, response);
84
        next();
85
    }
86

87
    /**
88
     * Middleware to bust the browser cache for the current user.
89
     * @returns {import('express').RequestHandler} The middleware function.
90
     */
91
    get middleware() {
92
        return this.#middleware.bind(this);
93
    }
94

95
    /**
96
     * Bust the cache for the given response.
97
     * @param {import('express').Request} request Express request object.
98
     * @param {import('express').Response} response Express response object.
99
     * @returns {void}
100
     */
101
    bust(request, response) {
102
        if (this.shouldBust(request, response)) {
103
            response.setHeader('Clear-Site-Data', '"cache"');
104
        }
105
    }
106
}
107

108
// Export a single instance for the entire application
109
const instance = new CacheBuster();
110
export default instance;