Blobchan

Blobchan is a fully decentralized image board. You connect with WalletConnect, generate a burner posting key, fund it with testnet ETH, and start posting. Every thread and reply is a 128 KB blob transaction on Sepolia — the on-chain imageboard. Posts are publicly readable by anyone.

Posting (browser → blob)

1. User connects their wallet, generates a dedicated burner posting key, and funds it with ETH. This key is required because no browser wallets support signing EIP-4844 (blob) transactions directly.
2. User writes a post (text + optional WebP image, compressed to ~60 KB)
3. Browser computes a KZG commitment and proof over the 128 KB blob using kzg-wasm (C-KZG compiled to WebAssembly)
4. Viem constructs and signs a Type 3 (EIP-4844) transaction with the blob sidecar using the burner key, then sends it to a fixed marker address (0x...b10b)
5. Post structure: first 2048 bytes = JSON metadata (board, threadId, name, content, timestamp), remaining bytes = hex-encoded image
6. Gas cost: ~0.0001 ETH per post on Sepolia

Reading (blockchain → browser)

1. Etherscan V2 API lists all transactions sent to the marker address
2. For each uncached tx, eth_getBlockByHash retrieves the parentBeaconBlockRoot
3. Beacon API (ethereum-sepolia-beacon-api.publicnode.com) looks up the beacon header by root, gets the slot, fetches blob sidecars
4. Blob hex is decoded: null-terminated JSON header at offset 0, hex image at offset 2048
5. Posts are cached in IndexedDB — cached tx hashes are skipped on subsequent refreshes to save API credits
6. Polls every 30 seconds for new content

Stack

• SvelteKit + static adapter → Cloudflare Pages
• WalletConnect via @reown/appkit + wagmi adapter
• Viem for all chain interactions (send, sign, query)
• kzg-wasm for KZG commitments (required by EIP-4844)
• Public RPC & Beacon API (publicnode.com) — no paid infrastructure
• Etherscan V2 API (free tier) for transaction discovery