ethapi: implement fillTransaction

internal/ethapi/api.go

@@ -1441,6 +1441,22 @@ func (s *PublicTransactionPoolAPI) SendTransaction(ctx context.Context, args Sen
 	return SubmitTransaction(ctx, s.b, signed)
 }
 
+// FillTransaction fills the defaults (nonce, gas, gasPrice) on a given unsigned transaction,
+// and returns it to the caller for further processing (signing + broadcast)
+func (s *PublicTransactionPoolAPI) FillTransaction(ctx context.Context, args SendTxArgs) (*SignTransactionResult, error) {
+	// Set some sanity defaults and terminate on failure
+	if err := args.setDefaults(ctx, s.b); err != nil {
+		return nil, err
+	}
+	// Assemble the transaction and obtain rlp
+	tx := args.toTransaction()
+	data, err := rlp.EncodeToBytes(tx)
+	if err != nil {
+		return nil, err
+	}
+	return &SignTransactionResult{data, tx}, nil
+}
+
 // SendRawTransaction will add the signed transaction to the transaction pool.
 // The sender is responsible for signing the transaction and using the correct nonce.
 func (s *PublicTransactionPoolAPI) SendRawTransaction(ctx context.Context, encodedTx hexutil.Bytes) (common.Hash, error) {