Ethereum API – Calling from Software Application without Running Node

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I was wondering if it's possible to make a call to Ethereum blockchain from a software application on my computer without having to run an ethereum node ?

for example, I want to make calls from a normal software application such as a java program to send messages/transactions to a smart contract on the ethereum blockchain which returns something. Is that possible ?

or do I have to run an ethereum node through geth or mist to be able to make those calls?

Best Answer

Etherscan provides an API to send raw transactions as documented in https://etherscan.io/apis#proxy .

Etherchain provides API services as well but does not provide the ability to send transactions - see https://etherchain.org/documentation/api/ .

You would not want to send transactions using eth_sendTransaction as documented in https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sendtransaction as the API server would need your private key to sign the transaction data.

The Etherscan service has an important note on the top of the API documentation page. I would not rely on these external services and would just run a geth node and have a reliable tap into the Ethereum blockchain.

Related Solutions

[Ethereum] Deploying and calling a contract works only with Ganache (not with Geth)

TLDR, but here is a fundamental difference between Ganache and Geth:

When Ganache starts, it automatically unlocks the accounts specified in the command-line.

For example:

ganache-cli
    --port=8545
    --gasPrice=20000000000
    --gasLimit=8000000
    --account=0x0000000000000000000000000000000000000000000000000000000000000001,1000000
    --account=0x0000000000000000000000000000000000000000000000000000000000000002,1000000

Will unlock the accounts with private keys 0x0...1 and 0x0...2 (2 accounts).

The default (if you don't specify anything) is 0x0...1 thru 0x0...a (10 accounts).

Geth doesn't do that, so you must unlock the accounts yourself prior to running any of your Truffle tests, by sending to Geth an "unlock account" command for each one of the accounts used in these tests.

Alternatively, you can sign each transaction with your private key before sending it to your Geth node. Other than for testing, this approach is actually the recommended one, because if somebody hacks your node then they can obtain your account credentials.

[Ethereum] Empty value (0x) returned from contract web3j

use the load(...) method from SampleContract Wrapper and then call getSample()

I can't test it now but it should look something like this

// your code for deploy and wait until it deployed
SampleContract myContract = SampleContract.load(<your-contract-address>, web3j, credentails, ......etc);
BigInteger sNumber = myContract.getSample().send();   
//or BigInteger sNumber = myContract.getSample().sendAsync().get();

Best Answer

Related Solutions

[Ethereum] Deploying and calling a contract works only with Ganache (not with Geth)

[Ethereum] Empty value (0x) returned from contract web3j

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