# Proofing

Some of the Flex Liquidity Pool [takers](/flex-liquidity-pools/takers.md) rely on Flex Proof protocol. The proof protocol provides a way to verify an event occurrence on other chain.

The fastest way to prove an event for the pool protocol is using *signature* proof variant. This proof can be issued by Flex Node, which is hosted at [`https://node.swaps.io`](https://node.swaps.io/) . It supports the following HTTP API:

* #### Get Chain Proof Info
  * `GET /api/v0/proof/chain/<chain>` , where:
  * `<chain>` *(path param)* - chain ID to get proof info of
* #### Get Event Proof
  * `GET /api/v0/proof?chain=<chain>&hash=<hash>&log=<log>` , where:
  * `<chain>` *(query param)* - chain ID of the event
  * `<hash>` *(query param)* - hash of the event transaction
  * `<log>` *(query param)* - log index in the transaction

Request & response examples:

```bash
# Get proof info for Optimism chain (ID 10):
curl 'https://node.swaps.io/api/v0/proof/chain/10'

# Example of successful chain proof info response:
{
  "chain": 10,
  "latestBlock": 138194551,
  "minConfirmations": 30,
  "provableBlock": 138194521,
  "signer": "0xb0baabc608dd2d1704d190ccdeecca624104c6ac"
}


# Get proof of Arbitrum chain (ID 42161) event occured in transaction with hash
# "0xd97a2a1306bfbdde8c0b929c2aa85fae38699af3d1ec581258bd6a936fe50f46" at index #0:
curl 'https://node.swaps.io/api/v0/proof?chain=42161&hash=0xd97a2a1306bfbdde8c0b929c2aa85fae38699af3d1ec581258bd6a936fe50f46&log=0'

# Example of successful event proof response:
{
  "chain": 42161,
  "hash": "0xd97a2a1306bfbdde8c0b929c2aa85fae38699af3d1ec581258bd6a936fe50f46",
  "log": 0,
  "block": 350395852,
  "confirmations": 5180366,
  "minConfirmations": 240,
  "emitter": "0xfd086bc7cd5c481dcc9c85ebe478a1c0b69fcbb9",
  "topics": [
    "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
    "0x0000000000000000000000009f6d65052ad5818768fcbac3b799a67f2b8e7170",
    "0x000000000000000000000000b58b4060745ec6377ea0b65c9f2eb4e1c4068374"
  ],
  "data": "0x0000000000000000000000000000000000000000000000000000000028351f10",
  "proof": "0x000000000000000000000000000000000000000000000000000000000000012c8ad459dfe203ceeec8eed289d95a9c81dc8c810a74dd647f2b9df98b305900a1356b3ee37ac75b752167cbf41427933bf9be4bd15c67680277ea2ddb9eb43f9f1c",
  "signature": "0x8ad459dfe203ceeec8eed289d95a9c81dc8c810a74dd647f2b9df98b305900a1356b3ee37ac75b752167cbf41427933bf9be4bd15c67680277ea2ddb9eb43f9f1c",
  "signer": "0xb0baabc608dd2d1704d190ccdeecca624104c6ac"
}


# Example of an error response (note "error" field presented):
{
  "error": "Block 355577210 of transaction 42161/0x64d1d125349bf365fb42064763274df23c5f21c40bc09a49868bae5d2ec6a4df has only 69 confirmations - at least 240 required to prove log #1 (wait 171 more blocks)"
}
```

The result `proof` value can then be passed as `bytes` to a taker that requires it - for example, `giveProof` param of [`TransferTaker`](https://github.com/swaps-io/flex-pool-contracts/blob/f01e565a2f2e6f107c20d76cd2644a055ea7acb1/contracts/taker/transfer/TransferTaker.sol#L53).


---

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