Smart contract on a private Ethereum Blockchain - Workflow & questions
I am trying to build a small app that would rely on a private Ethereum Blockchain. I am relatively new to this and am still having a few questions about the whole process. I will try to be as clear as I can explaining the difficulties I am facing. What I have A running private blockchain, installed on a specific server (that I manage) A working synchronisation between multiple nodes A smart contra
How could msg.sender != tx.origin AND extcodesize(caller) == 0 be true?
I'm working on a puzzle where msg.sender != tx.origin, so the implication is that the caller needs to be a contract or at least something in between the calling account. But extcodesize(caller) == 0 also needs to be true. So the caller needs to be an address or externally owned account. How can both of these be true? Can the caller's codesize ever be 0 if not an address/EOA?
How to store IPFS hash using bytes32?
Your example shows storing an IPFS identity using it's alphanumeric encoding (Qm...), which is the same Base58 encoding that Bitcoin uses. However, what it's representing at its core is a number (the hash). Storing the identifier in the Base58 format needs to be a String because it includes letters (and what actually gets saved is the ASCII code for each alphanumeric character in the identifier).
How do I determine the constructor ABI for Etherscan contract verification?
I am facing issues trying to verify a contract that I deployed on Rinkeby. My contract constructor has 3 parameters, how do I pass values of these parameters in the contract verification form? How do I determine the constructor ABI for my contract. Btw, I am using compiler version 4.11 and the contract was built using truffle framework. Any help would be truly appreciated.
`external` vs `public` best practices
Apart from the public modifier Ethereum introduces the external one. Both may be called outside of the contract and inside (the later one by this.f() pattern). Moreover, according to the docs: External functions are sometimes more efficient when they receive large arrays of data. but there is no further information what does actually sometimes mean and if this efficiency gain is held also for inte
Query multiple smart contracts' public data
I have a smart contract that holds the details of a person. Each new person gets a new smart contract that they 'own'. I have a regulator/ admin who wants to see the number of such smart contracts existing on the system and see the person who owns it. He will not be able to view any of the private data stored on them (data will be encrypted). Only the owner name (public variable) will be in unencr
What's the difference between 'msg.sender' and 'tx.origin'?
If either are used in the body of a Solidity function that may change the state of a contract (write call), what's the primary difference and/or benefit of using one over the other. For example: function setOwner() { owner = msg.sender; } vs. function setOwner() { owner = tx.origin; } What's the difference?
Difference between require and assert and the difference between revert and throw
I was looking at the docs and I'm looking for clarification on the difference between require and assert and throw and revert. assert(bool condition): abort execution and revert state changes if condition is false (use for internal error) require(bool condition): abort execution and revert state changes if condition is false (use for malformed input) Specifically with respect to assert and require
What are the best practices to allow user signup and login for a dapp?
From what I have researched, it seems that all of the methods for allowing a user to signup and login for an Ethereum dapp are very cumbersome for the user to use. What are the best practices to allow signup and login that match the following criteria: The method for signup and login should not be cumbersome; ie: simple as normal methods of username/password or facebook and google oauth. The metho
Upgradeable smart contracts
If the contract issuer wants to have a way to upgrade the contract code, so that account data and other things carry over, can Ethereum provide this? Also can this be done without changing the contract address or does one always need to deploy a new contract? Do "annex" mechanisms exist to add some new functionality to a contract without a total rewrite?
Are there well-solved and simple storage patterns for Solidity?
Here are some simple and useful patterns in increasing order of utility. Event logs are omitted for brevity. In practice, it's desirable to emit events for every important state change. Simple List Using Array Strengths Reliably chronological order Provides a count Random access by Row Number (not Id) Weaknesses No random access by Id No assurance of uniqueness No check for duplicates Uncontrolled
How can we retrieve the evolution of the state of an smart contract variable?
I have a simple smart contract with a variable color which stores a string. If I unterstand correctly, each transaction can change the state of this variable and is stored permanently into the blockchain. Let's say tx#1 changes it to red, tx#1 changes it to blue, and tx#2 to red, tx#3 to green. I want to have red, blue and green, and not just the last state of this variable color. How can I achiev
Unable to define greeterContract in the Greeter tutorial. Breaking change in Solidity 0.4.9!
I was following the Greeter tutorial on Go Ethereum wiki and got stuck on the "var greeterContract = web3.eth.contract(greeterCompiled.greeter.info.abiDefinition)" phase returning TypeError: Cannot access member 'info' of undefined. I have solC installed and linked - (eth.getCompilers() returns ["Solidity"]) and source code compiled. The only difference I spotted against the tutorial and other pos
Can I send ethereum to a contract outside of its constructor?
How do I fund Solidity contracts with Ether? The example in the Solidity FAQ, http://solidity.readthedocs.io/en/develop/frequently-asked-questions.html#store-ether-in-a-contract, funds a contract via the contract's constructor. Can you do the same outside of the constructor? Some background; I want a contract to be able to send Ether to someone's address via something like recipient.send(169000000
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