From e844d303931dde731e52ea437c67d0f0b9f50197 Mon Sep 17 00:00:00 2001
From: Marcin Rataj <lidel@lidel.org>
Date: Wed, 24 Jul 2019 15:41:49 +0200
Subject: [PATCH] fix: limit concurrent HTTP requests (#12)

All HTTP requests made by this module are sent to the same delegate
host. Browsers throttle the number of concurrent requests per hostname,
right now it is 6 per host, which suffocates the use of delegate and
blocking it from being used for preload or delegated content routing.

This introduces a task queue that limits the number of concurrent
requests, making it safe to run in browser context.

See also:
https://github.com/libp2p/js-libp2p-delegated-content-routing/issues/12

License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>
---
 .gitignore         |  3 ++-
 package.json       |  2 ++
 src/index.js       | 22 +++++++++++++++++++---
 test/index.spec.js |  4 ++--
 4 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/.gitignore b/.gitignore
index f86e967..5801c69 100644
--- a/.gitignore
+++ b/.gitignore
@@ -61,4 +61,5 @@ docs
 .env
 
 yarn.lock
-package-lock.json
\ No newline at end of file
+package-lock.json
+dist/
diff --git a/package.json b/package.json
index 664335f..0a68e15 100644
--- a/package.json
+++ b/package.json
@@ -25,7 +25,9 @@
     "ipfsd-ctl": "^0.44.1"
   },
   "dependencies": {
+    "debug": "^4.1.1",
     "ipfs-http-client": "^33.1.0",
+    "p-queue": "^6.1.0",
     "peer-id": "~0.12.2"
   },
   "contributors": [
diff --git a/src/index.js b/src/index.js
index 8446d1c..56f2ce8 100644
--- a/src/index.js
+++ b/src/index.js
@@ -3,18 +3,31 @@
 const PeerId = require('peer-id')
 const dht = require('ipfs-http-client/src/dht')
 const defaultConfig = require('ipfs-http-client/src/utils/default-config')
+const { default: PQueue } = require('p-queue')
+const debug = require('debug')
+
+const log = debug('libp2p-delegated-peer-routing')
+log.error = debug('libp2p-delegated-peer-routing:error')
 
 const DEFAULT_MAX_TIMEOUT = 30e3 // 30 second default
 const DEFAULT_IPFS_API = {
   protocol: 'https',
   port: 443,
-  host: 'ipfs.io'
+  host: 'node0.delegate.ipfs.io'
 }
+const CONCURRENT_HTTP_REQUESTS = 4
 
 class DelegatedPeerRouting {
   constructor (api) {
     this.api = Object.assign({}, defaultConfig(), DEFAULT_IPFS_API, api)
     this.dht = dht(this.api)
+
+    // limit concurrency to avoid request flood in web browser
+    // https://github.com/libp2p/js-libp2p-delegated-content-routing/issues/12
+    this._httpQueue = new PQueue({
+      concurrency: CONCURRENT_HTTP_REQUESTS
+    })
+    log(`enabled DelegatedPeerRouting via ${this.api.protocol}://${this.api.host}:${this.api.port}`)
   }
 
   /**
@@ -29,19 +42,22 @@ class DelegatedPeerRouting {
     if (PeerId.isPeerId(id)) {
       id = id.toB58String()
     }
+    log('findPeer starts: ' + id)
 
     options.maxTimeout = options.maxTimeout || DEFAULT_MAX_TIMEOUT
 
     try {
-      return await this.dht.findPeer(id, {
+      return await this._httpQueue.add(() => this.dht.findPeer(id, {
         timeout: `${options.maxTimeout}ms`// The api requires specification of the time unit (s/ms)
-      })
+      }))
     } catch (err) {
       if (err.message.includes('not found')) {
         return undefined
       }
 
       throw err
+    } finally {
+      log('findPeer finished: ' + id)
     }
   }
 }
diff --git a/test/index.spec.js b/test/index.spec.js
index 59f69a5..b162b25 100644
--- a/test/index.spec.js
+++ b/test/index.spec.js
@@ -64,14 +64,14 @@ describe('DelegatedPeerRouting', function () {
   })
 
   describe('create', () => {
-    it('should default to https://ipfs.io as the delegate', () => {
+    it('should default to https://node0.delegate.ipfs.io as the delegate', () => {
       const router = new DelegatedPeerRouting()
 
       expect(router.api).to.include({
         'api-path': '/api/v0/',
         protocol: 'https',
         port: 443,
-        host: 'ipfs.io'
+        host: 'node0.delegate.ipfs.io'
       })
     })