Add ERC: Solana Storage Router

ERCS/erc-7694.md

@@ -0,0 +1,110 @@
+---
+eip: 7694
+title: Solana storage handler for CCIP-Write
+description: Cross-chain write deferral protocol incorporating storage handler for Solana
+author: Avneet Singh (@sshmatrix), 0xc0de4c0ffee (@0xc0de4c0ffee)
+discussions-to: https://ethereum-magicians.org/t/eip-7694-solana-storage-handler-for-ccip-write/19706
+status: Draft
+type: Standards Track
+category: ERC
+created: 2024-04-18
+---
+
+## Abstract
+The following standard is an extension to the cross-chain write deferral protocol introducing storage handler for Solana.
+
+## Motivation
+[EIP-5559](./eip-5559) introduces two external handlers for deferring write operations to L2s and databases. This document extends that specification by introducing a third storage handler targeting Solana as the storage provider. 
+
+L2s and databases both have centralising catalysts in their stack. For L2s, this centralising agent is the shared security with Ethereum mainnet. In case of databases, the centralising agent is trivial; it is the physical server hosting the database. In light of this, a storage provider that relies on its own independent consensus mechanism is preferred. This specification instructs how the clients should treat write deferrals made to the Solana handler.
+
+Solana is a cheap L1 solution that is fairly popular among Ethereum community and is widely supported alongside Ethereum by almost all wallet providers. There are several chain-agnostic protocols on Ethereum which could benefit from direct access to Solana blockspace; ENS is one such example where it can serve users of Solana via its chain-agnostic properties while also using Solana's own native storage. This development will encourage more cross-chain functionalities between Ethereum and Solana at core. 
+
+## Specification
+A Solana storage handler `StorageHandledBySolana()` requires the hex-encoded `programId` and the manager `account` on the Solana blockchain. `programId` is equivalent to a contract address on Solana while `account` is the manager wallet on Solana handling write operations on behalf of `msg.sender`.
+
+```solidity
+// Revert handling Solana storage handler
+error StorageHandledBySolana(
+    bytes32 programId,
+    bytes32 account
+);
+
+// Generic function in a contract
+function setValue(
+    bytes32 node,
+    bytes32 key,
+    bytes32 value
+) external {
+    // Get metadata from on-chain sources
+    (
+        bytes32 programId, // Program (= contract) address on Solana; hex-encoded
+        bytes32 account // Manager account on Solana; hex-encoded
+    ) = getMetadata(node); // Arbitrary code
+    // programId = 0x37868885bbaf236c5d2e7a38952f709e796a1c99d6c9d142a1a41755d7660de3
+    // account = 0xe853e0dcc1e57656bd760325679ea960d958a0a704274a5a12330208ba0f428f
+    // Defer write call to Solana handler
+    revert StorageHandledBySolana( 
+        programId,
+        account
+    );
+};
+```
+
+Since Solana natively uses `base58` encoding in its virtual machine setup, `programId` values that are hex-encoded on EVM must be `base58`-decoded for usage on SVM. Clients implementing the Solana handler must call the Solana `programId` using a Solana wallet that is connected to `account` using the `base58`-decoded (and casted to appropriate datatype) calldata that it originally received. 
+
+```js
+/* Pseudo-code to write to Solana program (= contract) */
+// Decode all 'bytes32' types in EVM to 'PubKey' type in SVM
+const [programId, account, node, key, value] = svmPubkey([programId, account, node, key, value])
+// Instantiate program interface on Solana
+const program = new program(programId, rpcProvider);
+// Connect to Solana wallet
+const wallet = useWallet();
+// Call the Solana program using connected wallet with initial calldata
+// [!] Only approved manager in the Solana program should call
+if (wallet.publicKey === account) {
+    await program(wallet).setValue(node, key, value);
+}
+```
+
+In the above example, EVM-specific `bytes32`-type variables `programId`, `account`, `node`, `key` and `value` must all be converted to SVM-specific `PubKey` type. The equivalent `setValue()` function in the Solana program is of the form
+
+```rust 
+// Example function in Solana program
+pub fn setValue(
+    ctx: Context,
+    node: PubKey,
+    key: PubKey,
+    value: PubKey
+) -> ProgramResult {
+    // Code to verify PROGRAM_ID and rent exemption status
+    ...
+    // Code for de-serialising, updating and re-serialising the data
+    ...
+    // Write serialised data to account
+    // [!] Stored data must be mapped by node & account
+    ...
+}
+```
+
+Since EVM and SVM have differing architectures, it is important to define precise datatype castings from EVM to SVM. Some pre-existing custom but popular datatypes in SVM that equate to common EVM datatypes are:
+
+| EVM             | SVM          |
+|:---------------:|:------------:|
+| `bytes32`       | `PubKey`     |
+| `string`        | `String`     |
+
+For other encoding-specific datatypes such as `bytesN` (`N < 32`) and `address` (`N = 20`), this specification requires that all such variables must be padded up to `bytes32`. Using this strategy, most current use-cases of `StorageHandledBySolana()` are accounted for.
+
+## Rationale
+`StorageHandledBySolana()` works in a similar fashion to `StorageHandledByL2()` in [EIP-5559](./eip-5559) in the sense that the client needs to be pointed to a certain contract on another chain by the revert event. Other than that, the only technical difference is casting between EVM and SVM datatypes.
+
+## Backwards Compatibility
+None.
+
+## Security Considerations
+None.
+
+## Copyright
+Copyright and related rights waived via [`CC0`](../LICENSE.md).