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Change getPublicUrlForMxc function for authmedia

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Cadence Ember 2024-09-12 16:59:48 +12:00
commit decc32f7e6
6 changed files with 39 additions and 14 deletions
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43
m2d/converters/utils.js
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@ -1,8 +1,13 @@
// @ts-check
const assert = require("assert").strict
const passthrough = require("../../passthrough")
const {db} = passthrough
const {reg} = require("../../matrix/read-registration")
const userRegex = reg.namespaces.users.map(u => new RegExp(u.regex))
const assert = require("assert").strict
/** @type {import("xxhash-wasm").XXHashAPI} */ // @ts-ignore
let hasher = null
// @ts-ignore
@ -35,16 +40,6 @@ function eventSenderIsFromDiscord(sender) {
return false
}
/**
* @param {string} mxc
* @returns {string?}
*/
function getPublicUrlForMxc(mxc) {
const avatarURLParts = mxc?.match(/^mxc:\/\/([^/]+)\/(\w+)$/)
if (avatarURLParts) return `${reg.ooye.server_origin}/_matrix/media/r0/download/${avatarURLParts[1]}/${avatarURLParts[2]}`
else return null
}
/**
* Event IDs are really big and have more entropy than we need.
* If we want to store the event ID in the database, we can store a more compact version by hashing it with this.
@ -213,6 +208,32 @@ async function getViaServersQuery(roomID, api) {
return qs
}
/**
* Since the introduction of authenticated media, this can no longer just be the /_matrix/media/r0/download URL
* because Discord and Discord users cannot use those URLs. Media now has to be proxied through the bridge.
* To avoid the bridge acting as a proxy for *any* media, there is a list of permitted media stored in the database.
* (The other approach would be signing the URLs with a MAC (or similar) and adding the signature, but I'm not a
* cryptographer, so I don't want to.) To reduce database disk space usage, instead of storing each permitted URL,
* we just store its xxhash as a signed (as in +/-, not signature) 64-bit integer, which fits in an SQLite integer field.
* @see https://matrix.org/blog/2024/06/26/sunsetting-unauthenticated-media/ background
* @see https://matrix.org/blog/2024/06/20/matrix-v1.11-release/ implementation details
* @see https://www.sqlite.org/fileformat2.html#record_format SQLite integer field size
* @param {string} mxc
* @returns {string?}
*/
function getPublicUrlForMxc(mxc) {
assert(hasher, "xxhash is not ready yet")
const avatarURLParts = mxc?.match(/^mxc:\/\/([^/]+)\/(\w+)$/)
if (!avatarURLParts) return null
const serverAndMediaID = `${avatarURLParts[1]}/${avatarURLParts[2]}`
const unsignedHash = hasher.h64(serverAndMediaID)
const signedHash = unsignedHash - 0x8000000000000000n // shifting down to signed 64-bit range
db.prepare("INSERT OR IGNORE INTO media_proxy (permitted_hash) VALUES (?)").run(signedHash)
return `${reg.ooye.bridge_origin}/download/matrix/${serverAndMediaID}`
}
module.exports.BLOCK_ELEMENTS = BLOCK_ELEMENTS
module.exports.eventSenderIsFromDiscord = eventSenderIsFromDiscord
module.exports.getPublicUrlForMxc = getPublicUrlForMxc