From d540058ebd7f32e613d26c33e8a99b16d39a13d8 Mon Sep 17 00:00:00 2001
From: John Hiesey <john@hiesey.com>
Date: Wed, 30 Jun 2021 13:19:18 -0700
Subject: [PATCH] feat: Use a cache on the chunk store (#2095)

---
 docs/api.md    |  3 ++-
 lib/torrent.js | 21 +++++++++++++++++++--
 package.json   |  1 +
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/docs/api.md b/docs/api.md
index f64d2bef89..5302f9519a 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -94,6 +94,7 @@ If `opts` is specified, then the default options (shown below) will be overridde
   private: Boolean,          // If true, client will not share the hash with the DHT nor with PEX (default is the privacy of the parsed torrent)
   store: Function            // Custom chunk store (must follow [abstract-chunk-store](https://www.npmjs.com/package/abstract-chunk-store) API)
   destroyStoreOnDestroy: Boolean // If truthy, client will delete the torrent's chunk store (e.g. files on disk) when the torrent is destroyed
+  storeCacheSlots: Number    // Number of chunk store entries (torrent pieces) to cache in memory [default=20]; 0 to disable caching
 }
 ```
 
@@ -110,7 +111,7 @@ If you provide `opts.store`, it will be called as
 
 * `storeOpts.length` - size of all the files in the torrent
 * `storeOpts.files` - an array of torrent file objects
-* `storeOpts.torrent` - the torrent instance being stored
+* `storeOpts.name` - the info hash of the torrent instance being stored
 
 **Note:** Downloading a torrent automatically seeds it, making it available for download by other peers.
 
diff --git a/lib/torrent.js b/lib/torrent.js
index 1f0be5b6ff..b46cde3b01 100644
--- a/lib/torrent.js
+++ b/lib/torrent.js
@@ -2,6 +2,7 @@
 
 const addrToIPPort = require('addr-to-ip-port')
 const BitField = require('bitfield').default
+const CacheChunkStore = require('cache-chunk-store')
 const ChunkStoreWriteStream = require('chunk-store-stream/write')
 const cpus = require('cpus')
 const debug = require('debug')('webtorrent:torrent')
@@ -12,6 +13,7 @@ const FSChunkStore = require('fs-chunk-store') // browser: `memory-chunk-store`
 const get = require('simple-get')
 const ImmediateChunkStore = require('immediate-chunk-store')
 const ltDontHave = require('lt_donthave')
+const MemoryChunkStore = require('memory-chunk-store')
 const MultiStream = require('multistream')
 const net = require('net') // browser exclude
 const os = require('os') // browser exclude
@@ -75,6 +77,7 @@ class Torrent extends EventEmitter {
     this.skipVerify = !!opts.skipVerify
     this._store = opts.store || FSChunkStore
     this._preloadedStore = opts.preloadedStore || null
+    this._storeCacheSlots = opts.storeCacheSlots !== undefined ? opts.storeCacheSlots : 20
     this._destroyStoreOnDestroy = opts.destroyStoreOnDestroy || false
     this._getAnnounceOpts = opts.getAnnounceOpts
 
@@ -470,8 +473,11 @@ class Torrent extends EventEmitter {
 
     this._rarityMap = new RarityMap(this)
 
-    this.store = new ImmediateChunkStore(
-      this._preloadedStore || new this._store(this.pieceLength, {
+    let rawStore = this._preloadedStore
+    if (!rawStore) {
+      rawStore = new this._store(this.pieceLength, {
+        // opts.torrent is deprecated (replaced by the name property).
+        // it doesn't appear to be used by current versions of any stores on npm.
         torrent: {
           infoHash: this.infoHash
         },
@@ -483,6 +489,17 @@ class Torrent extends EventEmitter {
         length: this.length,
         name: this.infoHash
       })
+    }
+
+    // don't use the cache if the store is already in memory
+    if (this._storeCacheSlots > 0 && !(rawStore instanceof MemoryChunkStore)) {
+      rawStore = new CacheChunkStore(rawStore, {
+        max: this._storeCacheSlots
+      })
+    }
+
+    this.store = new ImmediateChunkStore(
+      rawStore
     )
 
     this.files = this.files.map(file => new File(this, file))
diff --git a/package.json b/package.json
index 0a1cb43f5e..b0994e90f9 100644
--- a/package.json
+++ b/package.json
@@ -40,6 +40,7 @@
     "bitfield": "^4.0.0",
     "bittorrent-dht": "^10.0.0",
     "bittorrent-protocol": "^3.3.1",
+    "cache-chunk-store": "^3.2.2",
     "chrome-net": "^3.3.4",
     "chunk-store-stream": "^4.3.0",
     "cpus": "^1.0.3",