How does Ethereum Smart Contract work on Mobile Client

Question

I want to deploy a smart contract on server and interact with it using mobile client. I'm not familiar with how does that work but after some research, I found something like below:

If we compare communication through web services in mobile client, then pretty much everything is same expect in Smart contract, is no database or deployment service as the result of decentralized nature of the system. Is that right? We can connect mobile client to smart contract using some library like web3 which would essentially work with Json RPC or websockets.

But what if I don't want to connect each mobile client to smart contract using library like web3? Instead, what if I want to have a HTTP server and then it would connect to smart contract like below?

Is that possible? If yes, then how can I do that?

My second question is regarding deployment. In the centralized server scenario, I would have database deployed on some service like AWS etc. I could estimate the deployment cost. I understood that we have to deploy smart contract on Ethereum mainnet which will cost some x amount of Ether. But then I found out that my users will have to pay for each computation. What if I want to bear all the costs? How can we estimate such costs?

Please guide me on the above questions.Thanks.

Answer 1

Instead, what if I want to have a HTTP server and then it would connect to smart contract like below?

You certainly can do this, some might argue a layer of centralization is added by placing a web server between the DApp and blockchain, but I would disagree. If you want to do this, your DApp would simply call a REST API on your web server which in return would utilize web3.js (node.js), web3j (Java), Nethereum (C#/.NET) or any other flavor of Web3 to interact directly with the blockchain.

What if I want to bear all the costs?

You will only be able to bear the costs of deploying smart contracts which are deployed on your behalf and not on behalf of any potential end-users.

How can we estimate such costs?

You can estimate the gas cost of a contract deployment or contract interaction via web3's estimateGas method. Understand, this cost can be largely effected by how well structured your Solidity smart contract code is written. Note, this is of course also only an estimate as users could always expend more Ether to have their transaction confirmed quicker or the state of the data within the smart contract could change over time requiring higher gas costs (ie iterating a growing array). For more information on gas costs within the Ethereum mainnet, you can take a look at ETH Gas Station .

As a side note, since I do not know your particular use case for blockchain technology, it could be helpful to weigh out whether or not it makes sense to utilize the Ethereum mainnet or to spin up your own private Ethereum blockchain . With the latter you would completely avoid having to spend any Ether to interact with blockchain network, but you would likely have additional overhead.