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## Description - Move subscriptions to tendermint-core section. - Remove unused photot Closes: #XXX
70 lines
2.7 KiB
Markdown
70 lines
2.7 KiB
Markdown
---
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order: 13
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---
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# Light Client
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Light clients are an important part of the complete blockchain system for most
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applications. Tendermint provides unique speed and security properties for
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light client applications.
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See our [light
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package](https://pkg.go.dev/github.com/tendermint/tendermint/light?tab=doc).
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## Overview
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The objective of the light client protocol is to get a commit for a recent
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block hash where the commit includes a majority of signatures from the last
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known validator set. From there, all the application state is verifiable with
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[merkle proofs](https://github.com/tendermint/spec/blob/953523c3cb99fdb8c8f7a2d21e3a99094279e9de/spec/blockchain/encoding.md#iavl-tree).
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## Properties
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- You get the full collateralized security benefits of Tendermint; no
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need to wait for confirmations.
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- You get the full speed benefits of Tendermint; transactions
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commit instantly.
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- You can get the most recent version of the application state
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non-interactively (without committing anything to the blockchain). For
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example, this means that you can get the most recent value of a name from the
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name-registry without worrying about fork censorship attacks, without posting
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a commit and waiting for confirmations. It's fast, secure, and free!
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## Where to obtain trusted height & hash
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[Trust Options](https://pkg.go.dev/github.com/tendermint/tendermint/light?tab=doc#TrustOptions)
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One way to obtain semi-trusted hash & height is to query multiple full nodes
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and compare their hashes:
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```bash
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$ curl -s https://233.123.0.140:26657:26657/commit | jq "{height: .result.signed_header.header.height, hash: .result.signed_header.commit.block_id.hash}"
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{
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"height": "273",
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"hash": "188F4F36CBCD2C91B57509BBF231C777E79B52EE3E0D90D06B1A25EB16E6E23D"
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}
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```
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## Running a light client as an HTTP proxy server
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Tendermint comes with a built-in `tendermint light` command, which can be used
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to run a light client proxy server, verifying Tendermint RPC. All calls that
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can be tracked back to a block header by a proof will be verified before
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passing them back to the caller. Other than that, it will present the same
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interface as a full Tendermint node.
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You can start the light client proxy server by running `tendermint light <chainID>`,
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with a variety of flags to specify the primary node, the witness nodes (which cross-check
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the information provided by the primary), the hash and height of the trusted header,
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and more.
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For example:
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```bash
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$ tendermint light supernova -p tcp://233.123.0.140:26657 \
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-w tcp://179.63.29.15:26657,tcp://144.165.223.135:26657 \
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--height=10 --hash=37E9A6DD3FA25E83B22C18835401E8E56088D0D7ABC6FD99FCDC920DD76C1C57
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```
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For additional options, run `tendermint light --help`.
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