CPFP support (#395)

* CPFP support.

fixes #5
fixes #353
fixes #360

* Use effectiveFeePerVsize for mempool statistics.

* Renaming endpoint cpfp-info to just cpfp.

* Renaming decended to BestDescendant.

* Updating language file with new strings.

backend/src/routes.ts

@@ -94,6 +94,30 @@ class Routes {
     res.json(times);
   }
 
+  public getCpfpInfo(req: Request, res: Response) {
+    if (!/^[a-fA-F0-9]{64}$/.test(req.params.txId)) {
+      res.status(501).send(`Invalid transaction ID.`);
+      return;
+    }
+
+    const tx = mempool.getMempool()[req.params.txId];
+    if (!tx) {
+      res.status(404).send(`Transaction doesn't exist in the mempool.`);
+      return;
+    }
+
+    if (tx.cpfpChecked) {
+      res.json({
+        ancestors: tx.ancestors,
+        bestDescendant: tx.bestDescendant || null,
+      });
+    }
+
+    const cpfpInfo = Common.setRelativesAndGetCpfpInfo(tx, mempool.getMempool());
+
+    res.json(cpfpInfo);
+  }
+
   public getBackendInfo(req: Request, res: Response) {
     res.json(backendInfo.getBackendInfo());
   }