[fix] #1068 Branch rebasing might fail with already known fork blocks

app/modules/crawler/lib/crawler.ts

@@ -403,6 +403,8 @@ export class BlockCrawler {
                 return block;
               }
               async applyMainBranch(block: BlockDTO): Promise<boolean> {
+                const existing = await server.dal.getAbsoluteBlockByNumberAndHash(block.number, block.hash)
+                if (!existing) {
                   let addedBlock = await server.writeBlock(block, false)
                   if (!this.lastDownloaded) {
                     this.lastDownloaded = await dao.remoteCurrent(node);
@@ -415,6 +417,10 @@ export class BlockCrawler {
                       server.streamPush(addedBlock);
                     }
                   }
+                } else {
+                  this.crawler.logger && this.crawler.logger.info('Downloaded already known block#%s-%s, try to fork...', block.number, block.hash)
+                  await server.BlockchainService.tryToFork()
+                }
                 return true
               }
               async removeForks(): Promise<boolean> {

app/service/BlockchainService.ts

@@ -169,6 +169,13 @@ export class BlockchainService extends FIFOService {
     }
   }
 
+  async tryToFork() {
+    return this.pushFIFO("tryToFork", async () => {
+      const current = await this.mainContext.current()
+      await this.eventuallySwitchOnSideChain(current)
+    })
+  }
+
   private async eventuallySwitchOnSideChain(current:DBBlock) {
     const branches = await this.branches()
     const blocksAdvanceInBlocks = this.conf.switchOnHeadAdvance