Sending transactions

Perhaps the most important feature of the hmy CLI is the ability to create and send signed transactions to the Harmony blockchain.

Overview

Sending a transaction

Using the Binary:

$ ./hmy transfer --node="<endpoint_address>" \
--from <ONE_address> --to <ONE_address> \
--from-shard <shard_#> --to-shard <shard_#> \
--amount <amount> --chain-id <chain-id> --passphrase

Using the Shell Script:

$ ./hmy.sh -- transfer --node="<endpoint_address>" \
--from <ONE_address> --to <ONE_address> \
--from-shard <shard_#> --to-shard <shard_#> \
--amount <amount> --chain-id <chain-id> --passphrase

Example:

$ ./hmy --node="https://api.s0.t.hmny.io" \
transfer --from one1yc06ghr2p8xnl2380kpfayweguuhxdtupkhqzw \
--to one1q6gkzcap0uruuu8r6sldxuu47pd4ww9w9t7tg6 \
--from-shard 0 --to-shard 1 --amount 12.5 --chain-id mainnet --passphrase mypassword

Checking the transaction hash

Check for finality of the transaction by using the transaction hash like so:

Using the Binary:

$ ./hmy blockchain transaction-receipt <transaction_id> --node="<endpoint_address>"

Using the Shell Script:

$ ./hmy.sh -- blockchain transaction-receipt <transaction_id> --node="<node_address>"

Example:

./hmy --node="https://api.s0.t.hmny.io" \
blockchain transaction-receipt \
0x599793f313ee17566f8d09728b9d043b8e26135ddce86beeee13f98767d452f7

Detail

ChainIDs

Let's first check what chain-ids are available for us to use, we can do that easily with:

Using the Binary:

$ ./hmy blockchain known-chains

Using the Shell Script:

$ ./hmy.sh -- blockchain known-chains

Example:

$ ./hmy blockchain known-chains
[
"mainnet",
"testnet",
"devnet"
]

Notice that the output is pretty printed JSON, most outputs of hmy are JSON encoded and hmy defaults to showing it nicely indented. Sometimes though you might want to turn that off, you can do that for any command with the flag --no-pretty.

By default, hmy assumes the testnet chain-id; override that with the --chain-id flag

Our first transaction

We'll use the transfer subcommand of hmy to send a transaction.

$ ./hmy transfer
Error: required flag(s) "amount", "from", "from-shard", "to", "to-shard" not set

Notice that simply invoking the transfer subcommand gave us an error message about certain flags not being set. We'll need to provide legitimate values for these flags for our transaction to proceed successfully. Reading off the flags in the error message from left to right, the semantic meanings are as follows:

  • amount: The quantity of Harmony One token to transfer from the senders to the receiver

  • from: The sender's one address

  • from-shard: Shard from which sender's balance will be drawn from

  • to: Receiver's ONE address

  • to-shard: Shard in which receiver will receive the amount sent by the sender

  • passphrase: your wallet passphrase, which is prompted when you hit enter (or you can use a txt file with password and add it: --passphrase file.txt)

A sharded blockchain is a new kind of blockchain architecture where the network is partitioned into sub-networks called shards. Sharding is one of the distinguishing features of Harmony and it is key to solving the traditional scalability problems encountered in other blockchain protocols.

Note: The same ONE address will have a different balance in each shard. Currently Harmony mainnet has four shards while testnet has three shards. Sending a transaction from one shard to another is called a "cross-shard transaction."

Thus, a correct usage of transfer looks like:

Using the Binary:

$ ./hmy transfer --node="<node_address>" \
--from <ONE_address> --to <ONE_address> \
--from-shard <shard_#> --to-shard <shard_#> \
--amount <amount> --chain-id <chain-id> --passphrase

Using the Shell Wrapper:

$ ./hmy.sh -- transfer --node="<node_address>" \
--from <ONE_address> --to <ONE_address> \
--from-shard <shard_#> --to-shard <shard_#> \
--amount <amount> --chain-id <chain-id> --passphrase

Example:

$ ./hmy transfer --node="https://api.s0.t.hmny.io" \
--from one1yc06ghr2p8xnl2380kpfayweguuhxdtupkhqzw \
--to one1q6gkzcap0uruuu8r6sldxuu47pd4ww9w9t7tg6 \
--from-shard 0 --to-shard 1 --amount 10 --chain-id mainnet
{"transaction-receipt":"0x455f98a3aa11ef50ee5cc5ac8bbd79e04f2fe353180bb7e25fc6c921fc8fdc83"}

hmy assumes that the private keys needed for signing the transaction on behalf of the sender (one1yc06ghr2p8xnl2380kpfayweguuhxdtupkhqzw in this example) exist in the local keystore or in the hardware wallet if the --ledger flag was used.

The sender's account must have enough of a balance on the from-shard to send a transaction. In our example,one1yc06ghr2p8xnl2380kpfayweguuhxdtupkhqzw must have an amount balance of at least 10 in shard 0.

Try out your transaction with the flag --dry-run, this flag tells hmy to create, cryptographically sign the transaction but not actually send it off. Sender's balances are checked and the output is a JSON dump of the signed transaction.

Signing and sending a transaction is very quick, about 2 seconds maximum. The actual sending of the transaction is done via an RPC (Remote Procedure Call), you'll notice that we did not explicitly say where to send the transaction to. This is because the default destination of the RPC call goes to http://localhost:9500, the default HTTP RPC server running when you start a local harmony blockchain. For real world usage though, you'll want a different location. You can control that with the --node flag (see the top of this page for an example).

Result of the transaction

Once an RPC machine receives a transaction, it sends you back a transaction hash. This transaction hash is the key identifier used when querying the blockchain for transactions.

Simply having a transaction hash does NOT imply that the transaction was successfully accepted by the blockchain. A transaction is successfully accepted once it has been added to the blockchain. In the case of cross-shard transactions (when the from-shard, to-shard values are different), this means each shard has added the transaction to their blockchain.

We can pull down details of the finalized transaction with ./hmy blockchain transaction-receipt as well:

Using the Binary:

$ ./hmy blockchain transaction-receipt --node="<endpoint-address>" <transaction-hash>

Using the Shell Wrapper:

$ ./hmy.sh -- blockchain transaction-receipt --node="<endpoint-address>" <transaction-hash>

Example:

$ ./hmy blockchain transaction-receipt \
--node="https://api.s0.t.hmny.io" \
0x25dd32397b5a69146b2dc3bbdc8ef8aae271e9b12a36c6dff1eb8995cac9dcba
{
"id": "0",
"jsonrpc": "2.0",
"result": {
"blockHash": "0x67eb5d671af76814d9ab326f9ec36c5b889b872e0c34e8cbe484aea20f0611ea",
"blockNumber": "0x21017f",
"contractAddress": null,
"cumulativeGasUsed": "0x5208",
"from": "one1sp4q22r7cc78742mzrufu6xwcekqxjgq78jk3m",
"gasUsed": "0x5208",
"logs": [],
"logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
"shardID": 0,
"status": "0x1",
"to": "one129r9pj3sk0re76f7zs3qz92rggmdgjhtwge62k",
"transactionHash": "0x25dd32397b5a69146b2dc3bbdc8ef8aae271e9b12a36c6dff1eb8995cac9dcba",
"transactionIndex": "0x0"
}
}

If the transaction has not finalized then the "result" key in the JSON output will have value of null.

You should set the value of --node to the same shard that sent the transaction, notice that the URL we used, https://api.s0.t.hmny.io contained s0, this means that this URL is targeting shard 0. For further information, see Querying the Blockchain.

You can tell hmy to wait until transaction confirmation by providing a positive integer value to flag --wait-for-confirm. For example, --wait-for-confirm=10 will try checking the receipt of the transaction for 10 seconds.