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add l2_blob_tx.md #2

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add l2_blob_tx.md
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43 changes: 43 additions & 0 deletions specs/experimental/l2_blob_tx.md
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# L2 Blob Transaction

<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
**Table of Contents**

- [L2 Blob Transaction](#l2-blob-transaction)
- [Motivation](#motivation)
- [How It Works](#how-it-works)
- [Reference Implementation](#reference-implementation)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->

## Motivation

To make it seamless for dapps that's depending on blob transaction to migrate from L1 to L2, it's important that L2 also supports blob transaction. This will also make L3 more uniform since they can also use blob transaction for batch submitting, just like L2.
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The objective of the proposal is to add BLOB tx support to OP Stack. Describe blob-based txs (examples) that are becoming popular on L1. But L1 is expensive, so it is important to support them in OP Stack to minimize migration cost.

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By default, all BLOB and calldata will use L1 as DA, but we may further explain the proposal can enable hybrid (forget the exact) DA so that

  • High-value applications can use L2 calldata and L1 as DA;
  • Low-value applications can use L2 BLOB and DAC/Plasma as DA.


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Overview of Implementation

Derivation

Depending on L2 BLOB DA configuration:

  • Sequencer-self-hosted: Skip actual L2 BLOB data during derivation
  • DAC: Verify the DAC signatures during derivation
  • L1 DA: Decode and verify L2 BLOB from L1 BLOB during derivation
  • DA challenge (Plasma): Check L1 challenge contract to see if a BLOB is challenged during derivation

BLOB Gas Cost

What is the formula of L2 BLOB gas cost?

BLOB P2P Network

Compared to L1 BLOB processing in P2P network, what we have done?

Other Minor Changes

...

## How It Works

The changes include two parts: optimism and op-geth.
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The changes include two parts: one part in optimism repo and the other part in op-geth repo.


The optimism part mainly includes:
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Suggested change
The optimism part mainly includes:
The `optimism` part mainly includes:

1. Add `L2BlobConfig` field to `rollup.Config` so that if configured, L2 blob tx will be supported and optionally the blob can be stored to a [DA provider](https://github.com/ethstorage/da-server) by sequencer.
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Suggested change
1. Add `L2BlobConfig` field to `rollup.Config` so that if configured, L2 blob tx will be supported and optionally the blob can be stored to a [DA provider](https://github.com/ethstorage/da-server) by sequencer.
1. Add `L2BlobConfig` field to `rollup.Config` so that if configured, L2 blob tx will be supported and optionally the blob can be stored to a [DA provider](https://github.com/ethstorage/da-server) by the sequencer.

1. There're a bunch of workarounds to make L2 blob tx work for op stack:
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Suggested change
1. There're a bunch of workarounds to make L2 blob tx work for op stack:
1. There're a bunch of changes to make L2 blob tx work for OP Stack:

1. [`BuildBlocksValidator`](https://github.com/blockchaindevsh/optimism/blob/106fbfd5d45efa45d6580cf169a5e053e406b933/op-node/p2p/gossip.go#L250) is modified to support non-zero `BlobGasUsed` and `ExcessBlobGas`.
2. [`spanBatchBlobTxData`](https://github.com/blockchaindevsh/optimism/blob/106fbfd5d45efa45d6580cf169a5e053e406b933/op-node/rollup/derive/span_batch_tx.go#L49) is added to support blob tx for span batch.
3. [`CheckBlockHash`](https://github.com/blockchaindevsh/optimism/blob/106fbfd5d45efa45d6580cf169a5e053e406b933/op-service/eth/types.go#L218) is modified to support broadcasting blocks with blob tx.
4. [`SimpleTxManager.craftTx`](https://github.com/blockchaindevsh/optimism/blob/106fbfd5d45efa45d6580cf169a5e053e406b933/op-service/txmgr/txmgr.go#L252) is modified to support blob tx.
5. A `p2p.sync.onlyreqtostatic` flag is [added](https://github.com/ethereum-optimism/optimism/pull/11011) to support fetching blocks from static peers only.
2. For L2 blob tx, only blob hash is submitted to L1 by op-batcher, so a challenge mechanism for blob is planned.


The op-geth part mainly includes:
1. Add `EnableL2Blob` field to `OptimismConfig` so that if configured, L2 blob tx will be supported.
2. Add `blobs` field to `RollupCostData` and update [`newL1CostFuncEcotone`](https://github.com/blockchaindevsh/op-geth/blob/19971ab7ffd0b6879796daf8c05b3206e279f15d/core/types/rollup_cost.go#L191) so that a blob tx will have two extra fees: da fee and da proof fee.
3. Fix [`Transaction.RollupCostData`](https://github.com/blockchaindevsh/op-geth/blob/19971ab7ffd0b6879796daf8c05b3206e279f15d/core/types/transaction.go#L374) so that the result is consistent when called from worker and state processor.
4. [`commitBlobTransaction`](https://github.com/blockchaindevsh/op-geth/blob/19971ab7ffd0b6879796daf8c05b3206e279f15d/miner/worker.go#L806) is modified to support blob tx without blobs when deriving.
5. Port changes from upstream geth to support estimate gas for blob tx.

## Reference Implementation

1. [optimism repo changes](https://github.com/ethstorage/optimism/pull/23)
2. [op-geth repo changes](https://github.com/ethstorage/op-geth/pull/2)