Detect RBF-transactions and offer to track them.

fixes #78

backend/src/api/common.ts

@@ -25,4 +25,26 @@ export class Common {
     arr.push(transactions[lastindex].feePerVsize);
     return arr;
   }
+
+  static findRbfTransactions(added: TransactionExtended[], deleted: TransactionExtended[]): { [txid: string]: TransactionExtended } {
+    const matches: { [txid: string]: TransactionExtended } = {};
+    deleted
+      // The replaced tx must have at least one input with nSequence < maxint-1 (That’s the opt-in)
+      .filter((tx) => tx.vin.some((vin) => vin.sequence < 0xfffffffe))
+      .forEach((deletedTx) => {
+        const foundMatches = added.find((addedTx) => {
+          // The new tx must, absolutely speaking, pay at least as much fee as the replaced tx.
+          return addedTx.fee > deletedTx.fee
+            // The new transaction must pay more fee per kB than the replaced tx.
+            && addedTx.feePerVsize > deletedTx.feePerVsize
+            // Spends one or more of the same inputs
+            && deletedTx.vin.some((deletedVin) =>
+              addedTx.vin.some((vin) => vin.txid === deletedVin.txid));
+            });
+        if (foundMatches) {
+          matches[deletedTx.txid] = foundMatches;
+        }
+      });
+    return matches;
+  }
 }