fix: cache preloaded CIDs

We 'preload' most CIDs we interact with on the network. In some cases
this can mean preloading the same CID over and over again which is not
necessary.

This PR adds a LRU cache to the preloader with a default size of 1000.
The cache is used to avoid re-preloading the same CID over and over again
until it drops out of the cache.  We use a cache that will evict CIDs
over time to have some sort of upper bound on memory usage.

Fixes #3307

Author: achingbrain

packages/ipfs-core/src/preload.js

@@ -6,6 +6,9 @@ const CID = require('cids')
 const shuffle = require('array-shuffle')
 const AbortController = require('native-abort-controller')
 const preload = require('./runtime/preload-nodejs')
+/** @type {typeof import('hashlru').default} */
+// @ts-ignore - hashlru has incorrect typedefs
+const hashlru = require('hashlru')
 
 const log = Object.assign(
   debug('ipfs:preload'),
@@ -14,12 +17,14 @@ const log = Object.assign(
 
 /**
  * @param {Object} [options]
- * @param {boolean} [options.enabled]
- * @param {string[]} [options.addresses]
+ * @param {boolean} [options.enabled] - Whether to preload anything
+ * @param {string[]} [options.addresses] - Which preload servers to use
+ * @param {number} [options.cache] - How many CIDs to cache
  */
 const createPreloader = (options = {}) => {
   options.enabled = Boolean(options.enabled)
   options.addresses = options.addresses || []
+  options.cache = options.cache || 1000
 
   if (!options.enabled || !options.addresses.length) {
     log('preload disabled')
@@ -34,6 +39,9 @@ const createPreloader = (options = {}) => {
   let requests = []
   const apiUris = options.addresses.map(toUri)
 
+  // Avoid preloading the same CID over and over again
+  const cache = hashlru(options.cache)
+
   /**
    * @param {string|CID} path
    * @returns {Promise<void>}
@@ -46,6 +54,13 @@ const createPreloader = (options = {}) => {
         path = new CID(path).toString()
       }
 
+      if (cache.has(path)) {
+        return
+      }
+
+      // don't
+      cache.set(path, true)
+
       const fallbackApiUris = shuffle(apiUris)
       let success = false
       const now = Date.now()