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What exactly is an Ethereum client? Is it a full network node that can post transactions to the blockchain (if that is the correct lingo?) or could it also be a light JS client that connects from a browser to a full node?
Could someone please shed some light on what clients there currently are and what roles they fulfill?
An 'Ethereum client' is just a term. It refers to any node able to parse and verify the blockchain, its smart contracts and everything related. It also allows you/provides interfaces to create transactions and mine blocks which is the key for any blockchain interaction.
There are currently three reference implementations available, as you already highlighted:
Aleth - C++ client: https://github.com/ethereum/aleth. (It was formerly known as cpp-ethereum: https://github.com/ethereum/webthree-umbrella)Geth - Golang client of the go-ethereum project: https://github.com/ethereum/go-ethereumTrinity - Python client: https://github.com/ethereum/trinityAll clients should work the same, from the user's perspective. They provide the same interfaces and so on. For example, if you launch a DApp or the Ethereum Wallet or a DApp browser instance, it should not note any difference in communicating with the client.
Non-official clients implementing the yellow paper specification are:
Besu - (ex-Pantheon) Java client by PegaSys: https://github.com/hyperledger/besuEthereumJ - Java client by the ether.camp team: https://github.com/ethereum/ethereumjEthereumJS VM - Javascript Ethereum Virtual Machine: https://github.com/ethereumjs/ethereumjs-vmMana - Elixir by POA Network - https://github.com/mana-ethereum/manaMinimal - Go client by umbracle - https://github.com/umbracle/minimalNethermind - C# / .NET by NethermindParity Ethereum - Rust client by Parity Technologies : https://www.parity.io/ethereum/Non-official clients with a graphical user interface are:
Etherwall, a Qt client like the good ol' bitcoin clients: https://github.com/almindor/etherwall Official reference implementations (CLI):
Pyethapp - (pyethapp has been deprecated) Python client of the pyethereum project: https://github.com/ethereum/pyethappGraphical clients:
AlethZero (Alethzero has been deprecated): https://github.com/ethereum/alethzeroMist Browser (Mist and Ethereum Wallet have been deprecated): https://github.com/ethereum/mistThird Party clients:
ethereumH - Haskell client from consensys, but it's not developed anymore: https://github.com/jamshidh/ethereum-client-haskell
(project has not been updated in a long time)node-blockchain-server - simple Javascript server: https://github.com/ethereumjs/node-blockchain-server
(project has not been updated in a long time)ruby-ethereum - Ruby client: https://github.com/janx/ruby-ethereum (project has not been updated in a long time)NOTE: all clients are listed in alphabetical order.
There are a couple of "reference implementations" that the Ethereum foundation is supporting.
There are a couple of reasons for doing this.
Bitcoin was created in an isolated environment, because of this some bugs crept in that are hard to fix because they break the consensus and would require a fork. Because of this anybody wanting to build a app to support the Bitcoin protocol need to add these bugs in or they won't be able to get consensus.
By supporting multiple clients from the start you have multiple people interpreting the white and yellow paper so any consensus issues will pop-up much faster, and they did. Luckily this is happening less and less as the technology matures.
If there is an attack vector or bug in any of the Ethereum implementations it means the network is usually fine as there is a bigger diversity of clients available. As I'm writing this this is sadly not 100% true yet because Geth has a majority of the network but we hope that the other clients will grow in usage in the coming months.
Not all languages are good in the same thing (some opinions in the next bit)
Hope this helps understand it.
As you mentioned there are 3 official clients mentioned in the wiki
by the way, a github search resulted in a lot more list..
This could do with an update:
https://github.com/ethereum/wiki/wiki/Clients,-tools,-dapp-browsers,-wallets-and-other-projects
I'm still not sure which can run a full client/node. The only ones on Ethstats are Geth, Parity and C++, plus a few unspecified nodes:
On Ethernodes, Geth has about two thirds, and Parity has most of the other third. I haven't seen the names for the other clients before. I looked up a couple of the tiny ones. Moac just provides an interface for Geth, Parity and Eth. Simillarly, Pirl (349) uses Geth. Eth (C++) has 9 nodes, ethereumJS has 27. Alot of the other clients start with g, indicating that they may be a custom/forked Geth client. Here's an archived snapshot of these stats.
To put it briefly , an Ethereum client is simply a piece of software that provide an application a gateway to interact with the ethereum blockchain .
Full nodes running on ethereum clients validate transactions in ethereum . There are remote clients as well like metamask that depend on full clients for access of the blockchain . Remote clients cannot perform validations on the blokchain,they provide a functionality of a wallet i.e they only create/braodcast transactions.
Clients can be written in many languages , parity (written in Rust ) and Geth(written in golang) are the most famous ones ...
Whereas Parity supports all of the ethereum-based blockchains , for different blockchains you require different versions of Geth.
These clients provide an API (JSON-RPC API) through which you can send/recieve JSON requests.
