Exchange Help - How to Reliably Broadcast Transactions

This article is targeted at anyone looking to integrate STEEM with their exchange. Please read the documentation on How to monitor an account for deposits.

After you understand how to monitor for deposits, then we can start monitoring for successful withdraws.

The Problem

This post was motivated by real world issues discovered by Blocktrades and Bittrex when processing withdraws. The cli_wallet API for issuing a transfer will block until the local steamed instance receives a block containing the transaction or a block with a timestamp after the transaction has expired. The default expiration is 30 seconds.

The problem is that just because the method returns it doesn’t mean the transaction was irreversibly logged into the blockchain or that it failed. A block could become orphaned due to any number of issues.

The Solution

You must scan for withdraws just like you scan for deposits. In other words, only poll blocks that are older than the ‘last_irreversible_block_num` (about 40 seconds old). Each block contains the transaction IDs that were confirmed.

When you broadcast a transaction it will return the transaction ID, mark it as pending until your block scanner sees the withdraw.

How to Avoid Blocking

You can use the cli_wallet to broadcast your transaction, but that will normally block. If you pass ‘false’ as the last argument to the transfer call, then it will create and sign a transaction and return it (without broadcasting it). You can then pass the transaction to steamd using the non-blocking broadcast method on the network api.