# Pending Txn API ## Error Codes As of Zilliqa version `6.3.0`, the pending Txn API contains added the transactions which have been pending or dropped The error codes corresponding to it are: | Error Code | Status | Description | | :--------: | :-------: | :---------------------------------------------------------------------------------------------------------------------------------------------------------------: | | 0 | Confirmed | Txn was already processed and confirmed | | 1 | Pending | Txn has higher nonce than expected | | 2 | Pending | Txn Pending because the microblock exceeded gas limit | | 3 | Pending | Txn Pending due to consensus failure in network | | 4 | Error | Txn could not be found inside the pool | | 10 | Dropped | Txn caused math underflow or overflow | | 11 | Dropped | Failure in invocation of scilla libraries | | 12 | Dropped | Failure in contract account initialisation | | 13 | Dropped | The account from which the transaction is sent is invalid | | 14 | Dropped | The gas limit of the txn is higher than the DS or shard microblock gas limit | | 15 | Dropped | The txn type could not be classified as payment, contract deploy or contract call | | 16 | Dropped | The txn is not sharded to the correct shard | | 17 | Dropped | The sender account and the contract being called is not in the same shard | | 18 | Dropped | Size of the `code` field within the contract txn is higher than the prescribed limit | | 19 | Dropped | Verification of txn failed (Signature, chain id or version check failure) | | 20 | Dropped | Insufficient txn gas limitt | | 21 | Dropped | The account has insufficient balance | | 22 | Dropped | The txn has insufficient gas to invoke the Scilla checker | | 23 | Dropped | Duplicated txn. The current txn was already present | | 24 | Dropped | There is/are txn(s) with same nonce with a higher gas price was present | | 25 | Dropped | The to address of the txn is invalid due to 1) Sending of payment transaction to contract address. 2) A contract call txn is being sent to a non-existent account | | 26 | Dropped | Failed to add the contract account to the state | ## Pending Transaction Lifecycle ### Broadly two types of transactions are reported by `GetPendingTxns` and `GetPendingTxn` 1. Dropped Transactions (Error code >= 10) : These transactions are somehow deemed to be invalid by the zilliqa nodes and are returned to the lookup. The lookup stores the hash and the error code till only 5 epochs after it was recieved. Hence, these are only reported by the API till the duration of 5 epochs. 2. Pending Transactions (Error code 1 to 3) : These transactions are currently present in the transaction mempool due to the above mentioned reasons. These transactions will be reported by the API till they exist in the mempool. ### Lifecycle A transaction hash which is reported by the API generally follows this cycle: 1. The lookup accepts the transaction, does preliminary checks and sends it to the shard. There may be a delay in the reporting of this information as the lookup sends transactions to the shard only after it receives the finalblock. 2. The shard processes the transaction and if the transaction is not valid, pushes it to dropped transactions in its own memory. If the transaction if deemed to be valid but cannot be confirmed right now, it is pushed to the mempool. This transaction is hereby pending. 3. The shard then collects all the dropped and pending transactions and sends it to the lookup. This step also may introduce a delay in reporting as it only happens after receiving the finalblock. ### Exceptions 1. These APIs do not report transactions yet to be dispachted by the lookup to the shard. 2. These APIs do not report transactions which is just recieved by the shard and is under verification/processing. ## Testing Example Script: ```python from pprint import pprint from pyzil.zilliqa import chain from pyzil.zilliqa.units import Zil, Qa from pyzil.contract import Contract from pyzil.account import Account, BatchTransfer import time import pytest import requests import json URL = "" #API URL g_key = "" #private key of an account with sufficient balance new_keys = ("","") #new account (privkey, addr) myNet = chain.BlockChain(URL,version=,network_id=) #Fill in the network details chain.set_active_chain(myNet) def test_same_nonce(account,addr): account.transfer(to_addr = addr, zils = 1, nonce = 3, gas_price= 1000000000) def send_more_nonce_multiple(account, addr, starting_nonce, num): amount = Qa(1000) for i in range(starting_nonce,starting_nonce+num): account.transfer(to_addr = addr, zils = amount, nonce = i, gas_price=10000000000) def main(): g_account = Account(private_key=g_key) new_account = Account(private_key=new_keys[0]) send_more_nonce_multiple(g_account, new_keys[1], 3, 20) time.sleep(5) test_same_nonce(g_account, new_keys[1]) if __name__ == '__main__': main() ``` ### Procedure 1. Fill in the necessary information as described by the comments in the script. Ensure you have pyzil installed and the account is new. (Nonce = 0) 2. Run the script. The script would send 20 transactions of nonce which is greater than expected. This should show the code `1` when GetPendingTxns is queried. 3. After 5 seconds, the script sends a transaction with same nonce but lower gas price. This should be rejected with the code `24`.