Nebulas 101 - 02 Sending Transactions on Nebulas

Youtube Tutorial

For this portion of the tutorial we will pick up where we left off in the Installation tutorial.

Nebulas provides three methods to send transactions:

  1. Sign & Send
  2. Send with Passphrase
  3. Unlock & Send

Here is an introduction to sending a transaction in Nebulas through the three methods above and verifying whether the transaction is successful.

Prepare Accounts

In Nebulas, each address represents an unique account.

Prepare two accounts: an address to send tokens (the sending address, called “from“) and an address to receive the tokens (the receiving address, called “to“).

The Sender

Here we will use the coinbase account in the conf/example/miner.conf, which is n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE as the sender. As the miner‘s coinbase account, it will receive some tokens as the mining reward. Then we could send these tokens to another account later.

The Receiver

Create a new wallet to receive the tokens.

$ ./neb account new
Your new account is locked with a passphrase. Please give a passphrase. Do not forget this passphrase.
Repeat passphrase:
Address: n1SQe5d1NKHYFMKtJ5sNHPsSPVavGzW71Wy
When you run this command you will have a different wallet address with n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE. Please use your generated address as the receiver.

The keystore file of the new wallet will be located in $GOPATH/src/

Start the Nodes

Start Seed Node

Firstly, start a seed node as the first node in local private chain.

./neb -c conf/default/config.conf

Start Miner Node

Secondly, start a miner node connecting to the seed node. This node will generate new blocks in local private chain.

./neb -c conf/example/miner.conf

How long a new block will be minted?

In Nebulas, DPoS is chosen as the temporary consensus algorithm before Proof-of-Devotion(PoD, described in Technical White Paper) is ready. In this consensus algorithm, each miner will mint new block one by one every 15 seconds.

In current context, we have to wait for 315(=15*21) seconds to get a new block because there is only one miner among 21 miners defined in conf/default/genesis.conf working now.

Once a new block minted by the miner, the mining reward will be added to the coinbase wallet address used in conf/example/miner.conf which is n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE.

Interact with Nodes

Nebulas provides developers with HTTP API, gRPC API and CLI to interact with the running nodes. Here, we will share how to send a transaction in three methods with HTTP API (API Module | Admin Module).

The Nebulas HTTP Lisenter is defined in the node configuration. The default port of our seed node is 8685.

At first, check the sender‘s balance before sending a transaction.

Check Account State

Fetch the state of sender‘s account n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE with /v1/user/accountstate in API Module using curl.

> curl -i -H Accept:application/json -X POST http://localhost:8685/v1/user/accountstate -d '{"address":"n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE"}'

    "result": {
        "balance": "5000000000000000000000000",
        "nonce": "0",
        "type": 87,
Note Type is used to check if this account is a smart contract account. 88 represents a smart contract account and 87 a non-contract account. Height is used to indicate the current height of the blockchain when the API is called. Pending is used to show how many pending transactions your address has in the Tx Pool.

As you can see, the receiver has been rewarded with some tokens for mining new blocks.

Then let‘s check the receiver‘s account state.

> curl -i -H Accept:application/json -X POST http://localhost:8685/v1/user/accountstate -d '{"address":"your_address"}'

    "result": {
        "balance": "0",
        "nonce": "0",
        "type": 87,

The new account doesn‘t have tokens as expected.

Send a Transaction

Now let’s send a transaction in three methods to transfer some tokens from the sender to the receiver!

Sign & Send

In this way, we can sign a transaction in an offline environment and then submit it to another online node. This is the safest method for everyone to submit a transaction without exposing your own private key to the Internet.

First, sign the transaction to get raw data.

> curl -i -H 'Content-Type: application/json' -X POST http://localhost:8685/v1/admin/sign -d '{"transaction":{"from":"n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE","to":"n1QZMXSZtW7BUerroSms4axNfyBGyFGkrh5", "value":"1000000000000000000","nonce":1,"gasPrice":"1000000","gasLimit":"2000000"}, "passphrase":"passphrase"}'

Note Nonce is an very important attribute in a transaction. It‘s designed to prevent replay attacks. For a given account, only after its transaction with nonce N is accepted, will its transaction with nonce N+1 be processed. Thus, we have to check the latest nonce of the account on chain before preparing a new transaction.

Then, send the raw data to an online Nebulas node.

> curl -i -H 'Content-Type: application/json' -X POST http://localhost:8685/v1/user/rawtransaction -d '{"data":"CiAbjMP5dyVsTWILfXL1MbwZ8Q6xOgX/JKinks1dpToSdxIaGVcH+WT/SVMkY18ix7SG4F1+Z8evXJoA35caGhlXbip8PupTNxwV4SRM87r798jXWADXpWngIhAAAAAAAAAAAA3gtrOnZAAAKAEwuKuC1wU6CAoGYmluYXJ5QGRKEAAAAAAAAAAAAAAAAAAPQkBSEAAAAAAAAAAAAAAAAAAehIBYAWJBVVuRHWSNY1e3bigbVKd9i6ci4f1LruDC7AUtXDLirHlsmTDZXqjSMGLio1ziTmxYJiLj+Jht5RoZxFKqFncOIQA="}'


Send with Passphrase

If you trust a Nebulas node so much that you can delegate your keystore files to it, the second method is a good fit for you.

First, upload your keystore files to the keydir folders in the trusted Nebulas node.

Then, send the transaction with your passphrase.

> curl -i -H 'Content-Type: application/json' -X POST http://localhost:8685/v1/admin/transactionWithPassphrase -d '{"transaction":{"from":"n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE","to":"n1QZMXSZtW7BUerroSms4axNfyBGyFGkrh5", "value":"1000000000000000000","nonce":2,"gasPrice":"1000000","gasLimit":"2000000"},"passphrase":"passphrase"}'

Note Because we have sent a transaction with nonce 1 from the account n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE, new transaction with same from should be increased by 1, namely 2.

Unlock & Send

This is the most dangerous method. You probably shouldn’t use it unless you have complete trust in the receiving Nebulas node.

First, upload your keystore files to the keydir folders in the trusted Nebulas node.

Then unlock your accounts with your passphrase for a given duration in the node. The unit of the duration is nano seconds (300000000000=300s).

> curl -i -H 'Content-Type: application/json' -X POST http://localhost:8685/v1/admin/account/unlock -d '{"address":"n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE","passphrase":"passphrase","duration":"300000000000"}'


After unlocking the account, everyone is able to send any transaction directly within the duration in that node without your authorization.

> curl -i -H 'Content-Type: application/json' -X POST http://localhost:8685/v1/admin/transaction -d '{"from":"n1FF1nz6tarkDVwWQkMnnwFPuPKUaQTdptE","to":"n1QZMXSZtW7BUerroSms4axNfyBGyFGkrh5", "value":"1000000000000000000","nonce":3,"gasPrice":"1000000","gasLimit":"2000000"}'


Transaction Receipt

We‘ll get a txhash in three methods after sending a transaction successfully. The txhash value can be used to query the transaction status.

> curl -i -H Accept:application/json -X POST http://localhost:8685/v1/user/getTransactionReceipt -d '{"hash":"8d69dea784f0edfb2ee678c464d99e155bca04b3d7e6cdba6c5c189f731110cf"}'


The status fields may be 0, 1 or 2.

  • 0: Failed. It means the transaction has been submitted on chain but its execution failed.
  • 1: Successful. It means the transaction has been submitted on chain and its execution successeed.
  • 2: Pending. It means the transaction hasn‘t been packed into a block.

Double Check

Let‘s double check the receiver‘s balance.

> curl -i -H Accept:application/json -X POST http://localhost:8685/v1/user/accountstate -d '{"address":"n1QZMXSZtW7BUerroSms4axNfyBGyFGkrh5"}'


Here you should see a balance that is the total of all the successful transfers that you executed.