Ethereum notes
Basics
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the existence of a Turing-complete programming language means that arbitrary contracts can be created for any transaction type or application.
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a state is made up of objects called "accounts", with each account hacing a 20-byte address and state transitions being direct transfers of value and information between accounts.
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an Ethereum account contains four fields:
- the nounce: a coutner used to make sure each transaction can only be processed once
- the account's current ether balance
- the account's contract code
- the account's storage
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there are two type of accounts: externally owned accounts (controlled by private keys) and contract accounts (controlled by their contract code)
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a transaction refers to the signed data package that stores a message to be sent from an externally owned account. It contains:
- the recipient of the message
- a signature identifying the sender
- the amount of ether to transfer from the sender to the recipient
- an optional data field
- STARTGAS, representing the maxium numner of computation steps the transaction is allowed to take
- GASPRICE, representing the fee the sender pays per computation step
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contracts can send "messages" to other contracts, which are virtual objects that are never serialized and exist only in the Ethereum execution environment. It contains:
- the sender of the message (implicit)
- the recipient of the message
- the amount of ether tot transfer alongside the message
- an optional data field
- STARTGAS
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a message is like a transaction, except it is produced by a contract and not an external actor. A message is produced when a cotnract currently executing code executes the CALL opcode.
Code execution
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the code in Ethereum contracts is written in a low-level, stack-based bytecode language, referred as the EVM.
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The operations have access to three types of space in which to store data:
- the stack, a last-in-first-out container to which values can be pushed and popped
- memory, an infinite expandable byte array
- contract's long-term storage, a key/value store (persist long term)