[fix] #1325 Do not always select the same nodes for P2P downloading

app/modules/crawler/lib/sync/P2PSyncDownloader.ts

@@ -68,10 +68,7 @@ export class P2PSyncDownloader extends ASyncDownloader implements ISyncDownloade
       nodesAvailable = nodesAvailable.concat(readyNodes)
       i++
     }
-    return nodesAvailable.slice(0, needed).map(n => {
-      n.reserve()
-      return n
-    })
+    return nodesAvailable
   }
 
   /**
@@ -81,12 +78,17 @@ export class P2PSyncDownloader extends ASyncDownloader implements ISyncDownloade
    */
   private async getP2Pcandidates(chunkIndex: number): Promise<P2pCandidate[]> {
     return this.fifoPromise.pushFIFOPromise('getP2Pcandidates_' + getNanosecondsTime(), async () => {
+      const needed = 1
       // We wait a bit to have some available nodes
       const readyNodes = await this.waitForAvailableNodesAndReserve()
       // We remove the nodes impossible to reach (timeout)
       let byAvgAnswerTime = Underscore.sortBy(readyNodes, p => p.avgResponseTime())
       const parallelMax = Math.min(this.PARALLEL_PER_CHUNK, byAvgAnswerTime.length)
       byAvgAnswerTime = byAvgAnswerTime.slice(0, parallelMax)
+      this.watcher.reserveNodes(byAvgAnswerTime)
+      byAvgAnswerTime.slice(0, needed).forEach(n => {
+        n.reserve()
+      })
       if (byAvgAnswerTime.length === 0) {
         this.logger.warn('No node found to download chunk #%s.', chunkIndex)
         this.watcher.unableToDownloadChunk(chunkIndex)

app/modules/crawler/lib/sync/p2p/p2p-candidate.ts

@@ -43,6 +43,7 @@ export class P2pCandidate {
     return Promise.race([
       // Wait for availablity
       (async () => !this.isExcluded
+        && !this.reserved
         && (this.apiPromise.isRejected() ? await newResolveTimeoutPromise(maxWait, false) : !!(await this.apiPromise))
         && (this.dlPromise.isRejected() ? await newResolveTimeoutPromise(maxWait, false) : !!(await this.dlPromise)))(),
       // Maximum wait trigger
@@ -55,6 +56,9 @@ export class P2pCandidate {
   }
 
   avgResponseTime() {
+    if (!this.responseTimes.length) {
+      return 0
+    }
     return this.responseTimes.reduce((sum, rt) => sum + rt, 0) / this.responseTimes.length
   }