allow for progress on write

lib/torrent.js

@@ -114,6 +114,8 @@ class Torrent extends EventEmitter {
     this._servers = []
     this._xsRequests = []
 
+    this._writeCb = opts.writeCb
+
     // TODO: remove this and expose a hook instead
     // optimization: don't recheck every file if it hasn't changed
     this._fileModtimes = opts.fileModtimes
@@ -1597,7 +1599,14 @@ class Torrent extends EventEmitter {
     if (!cb) cb = noop
 
     const readable = new MultiStream(streams)
+    let read = 0
     const writable = new ChunkStoreWriteStream(this.store, this.pieceLength)
+    if (this._writeCb) {
+      writable._blockstream.on('data', data => {
+        read += data.length
+        this._writeCb(this.length, read)
+      })
+    }
 
     pump(readable, writable, err => {
       if (err) return cb(err)