feat(lib): cache blockhash in redis (5s TTL)

[raushan728]

Adds a 5-second Redis cache for getLatestBlockhash to reduce RPC load on high-traffic endpoints.

• Changes: get_blockhash and transfer_transaction now use cached blockhash.
• Safety: Gracefully falls back to direct RPC call on Redis miss or error.
• Tests: Added unit tests verifying fallback behavior when cache is disabled.

[greptile-apps]

Greptile Summary

Adds Redis caching for getLatestBlockhash with a 5-second TTL to reduce RPC load on high-traffic endpoints. The implementation follows the existing cache patterns in the codebase with graceful fallback to direct RPC calls when cache is unavailable or errors occur.

Key Changes:

• CacheUtil::get_or_fetch_latest_blockhash() provides cached blockhash with automatic fallback
• get_blockhash and transfer_transaction endpoints now use the cached implementation
• Cache failures are logged but don't fail requests
• Unit tests verify fallback behavior when cache is disabled

Notes:

• Other blockhash-fetching code paths (e.g., bundle operations in bundle/helper.rs:224, transaction utilities in transaction/versioned_transaction.rs:299) continue to call RPC directly
• Under very high concurrency, multiple simultaneous requests during cache expiration may create a brief burst of RPC calls

Confidence Score: 4/5

• Safe to merge with solid implementation and proper fallback handling
• Well-structured caching implementation following existing patterns with graceful error handling. One minor performance consideration around cache stampede under very high concurrency, but this is a common tradeoff in caching systems and doesn't affect correctness.
• No files require special attention

Important Files Changed

Filename	Overview
crates/lib/src/cache.rs	Added blockhash caching with 5s TTL, graceful fallback to RPC on cache errors
crates/lib/src/rpc_server/method/get_blockhash.rs	Replaced direct RPC call with cached blockhash lookup
crates/lib/src/rpc_server/method/transfer_transaction.rs	Updated deprecated endpoint to use cached blockhash

Sequence Diagram

sequenceDiagram
    participant Client
    participant GetBlockhash as get_blockhash endpoint
    participant CacheUtil
    participant Redis
    participant RPC as Solana RPC

    Client->>GetBlockhash: Request blockhash
    GetBlockhash->>CacheUtil: get_or_fetch_latest_blockhash()
    
    alt Cache enabled
        CacheUtil->>Redis: GET kora:blockhash
        alt Cache hit
            Redis-->>CacheUtil: Return cached hash
            CacheUtil-->>GetBlockhash: Return hash
        else Cache miss
            Redis-->>CacheUtil: None
            CacheUtil->>RPC: get_latest_blockhash_with_commitment(confirmed)
            RPC-->>CacheUtil: Fresh blockhash
            CacheUtil->>Redis: SET kora:blockhash (TTL: 5s)
            CacheUtil-->>GetBlockhash: Return hash
        end
    else Cache disabled/error
        CacheUtil->>RPC: get_latest_blockhash_with_commitment(confirmed)
        RPC-->>CacheUtil: Fresh blockhash
        CacheUtil-->>GetBlockhash: Return hash
    end
    
    GetBlockhash-->>Client: Return blockhash

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_{Last reviewed commit: f0e8939}

[greptile-apps]

_{3 files reviewed, 1 comment}

_{Edit Code Review Agent Settings | Greptile}

[dev-jodee]

@raushan728 if you can fix the ci issue, rest looks good

[dev-jodee]

lgtm

[raushan728]

hi @dev-jodee is current soluntion is good or should i use #[allow(clippy::needless_borrow)] ?

[dev-jodee]

@raushan728 the fix is to get a reference of get_config like so

let config = &get_config()?;

[raushan728]

@dev-jodee done

[github-actions]

✅ Fork external live tests passed.

fork-external-live-pass:bd04aad5bed631fa1d127eb6dbd93e64bcc2aa70
run: https://github.com/solana-foundation/kora/actions/runs/22633482663