Use event listener changes for (un)watching downloads.

Author: Frando

README.md

@@ -205,14 +205,6 @@ See the [Hypercore docs](https://github.com/hypercore-protocol/hypercore) for mo
 
 Append a block or array of blocks to the hypercore
 
-#### `await feed.watchDownloads()`
-
-Emit `download` events for all blocks downloaded from now.
-
-#### `await feed.unwatchDownloads()`
-
-Stop emitting `download` events.
-
 #### `feed.peers`
 
 A list of peers this feed is connected to.
@@ -231,7 +223,7 @@ Emitted when the feed is appended to, either locally or remotely.
 
 #### `feed.on('download', seq)`
 
-Emitted when block is downloaded. Has to be enabled with `watchDownloads()` first.
+Emitted when a block is downloaded.
 
 # License
 

index.js

@@ -363,6 +363,21 @@ class RemoteHypercore extends Nanoresource {
     this._extensions = new Map()
     this._onwaits = new FreeMap(1)
 
+    // Track listeners for the download event, and enable/disable download watching.
+    this._downloadListeners = 0
+    this.on('newListener', (event, _listener) => {
+      if (event === 'download') {
+        if (!this._downloadListeners) this._watchDownloads()
+        this._downloadListeners += 1
+      }
+    })
+    this.on('removeListener', (event, _listener) => {
+      if (event === 'download') {
+        this._downloadListeners -= 1
+        if (!this._downloadListeners) this._unwatchDownloads()
+      }
+    })
+
     if (!this.lazy) this.ready(() => {})
   }
 
@@ -579,13 +594,19 @@ class RemoteHypercore extends Nanoresource {
   }
 
   async _watchDownloads () {
-    if (!this.opened) await this.open()
-    if (this.closed) throw new Error('Feed is closed')
-    return this._client.hypercore.watchDownloads({ id: this._id })
+    try {
+      if (!this.opened) await this.open()
+      if (this.closed) return
+      await this._client.hypercore.watchDownloads({ id: this._id })
+    } catch (_) {}
   }
 
   async _unwatchDownloads () {
-    return this._client.hypercore.unwatchDownloads({ id: this._id })
+    try {
+      if (!this.opened) await this.open()
+      if (this.closed) return
+      await this._client.hypercore.unwatchDownloads({ id: this._id })
+    } catch (_) {}
   }
 
   // Public Methods
@@ -710,14 +731,6 @@ class RemoteHypercore extends Nanoresource {
     return prom.then(() => () => this._client.hypercore.releaseLockNoReply({ id: this._id }))
   }
 
-  watchDownloads (cb) {
-    return maybe(cb, this._watchDownloads())
-  }
-
-  unwatchDownloads (cb) {
-    return maybe(cb, this._unwatchDownloads())
-  }
-
   // TODO: Unimplemented methods
 
   registerExtension (name, opts) {