net/chain: fetch block from network if not found (for pruned nodes)

FOR EDUCATIONAL PURPOSES ONLY. Do not merge.
pinheadmz · Jun 1, 2020 · ec1f5c9 · ec1f5c9
1 parent 6beb54d
commit ec1f5c9
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Showing 2 changed files with 49 additions and 3 deletions.
diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
@@ -64,6 +64,8 @@ class Chain extends AsyncEmitter {
 
     this.orphanMap = new BufferMap();
     this.orphanPrev = new BufferMap();
+
+    this.getPrunedMap = new BufferMap();
   }
 
   /**
@@ -1371,7 +1373,16 @@ class Chain extends AsyncEmitter {
     }
 
     // Do we already have this block?
-    if (await this.hasEntry(hash)) {
+    const existingEntry = await this.getEntry(hash);
+
+    // FOR EDUCATIONAL PURPOSES ONLY: save block without checking anything
+    if (existingEntry && this.getPrunedMap.has(hash)) {
+      block = block.toBlock();
+      await this.db.save(existingEntry, block, new CoinView());
+      return existingEntry;
+    }
+
+    if (existingEntry) {
       this.logger.debug('Already have block: %h.', block.hash());
       throw new VerifyError(block, 'duplicate', 'duplicate', 0);
     }
@@ -1924,8 +1935,25 @@ class Chain extends AsyncEmitter {
    * @returns {Promise} - Returns {@link Block}.
    */
 
-  getBlock(hash) {
-    return this.db.getBlock(hash);
+  async getBlock(hash) {
+    const block = await this.db.getBlock(hash);
+    if (block) {
+      return block;
+    } else {
+      this.logger.warning('Block not found, attempting to download');
+
+      // Ensure hash not height
+      hash = await this.db.getHash(hash);
+
+      // FOR EDUCATIONAL PURPOSES ONLY: flag block for re-downloading
+      const wait = new Promise((resolve, reject) => {
+        this.getPrunedMap.set(hash, resolve);
+      });
+
+      await this.emitAsync('getprunedblock', hash);
+      await wait;
+      return this.db.getBlock(hash);
+    }
   }
 
   /**

diff --git a/lib/net/pool.js b/lib/net/pool.js
@@ -138,6 +138,16 @@ class Pool extends EventEmitter {
       this.handleBadOrphan('block', err, id);
     });
 
+    this.chain.on('getprunedblock', async (hash) => {
+      // Find the first peer with a completed handshake
+      for (let peer = this.peers.head(); peer; peer = peer.next) {
+        if (!peer.handshake)
+          continue;
+
+        await this.getBlock(peer, [hash]);
+      }
+    });
+
     if (this.mempool) {
       this.mempool.on('tx', (tx) => {
         this.emit('tx', tx);
@@ -2184,6 +2194,14 @@ class Pool extends EventEmitter {
       throw err;
     }
 
+    // Someone was waiting for a pruned block to download
+    const resolve = this.chain.getPrunedMap.get(hash);
+    if (resolve) {
+      this.logger.warning('Received pruned block by special request');
+      this.chain.getPrunedMap.delete(hash);
+      resolve();
+    }
+
     // Block was orphaned.
     if (!entry) {
       if (this.checkpoints) {