fix: serialize BigInt values in social login RPC requests - #5632
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Magic provider uses postMessage to communicate with its iframe, which cannot handle BigInt values via structured cloning. This caused "Do not know how to serialize a BigInt" errors when sending transactions via social login (Google, etc). Added serializeBigInts() helper that recursively converts BigInt values to 0x-prefixed hex strings before passing RPC requests to the iframe. Closes REOWN-4455 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Fixes Magic RPC Error [-32603] Do not know how to serialize a BigInt when sending transactions via social login (REOWN-4455).
Technical Report
Problem
When a user connects via social login (Magic) and sends any transaction, it fails with "Do not know how to serialize a BigInt". Only social login is affected — MetaMask, WalletConnect, and injected wallets work fine.
Root Cause Analysis
W3mFrameProvider.request() passes RPC payloads to the Magic iframe via postMessage(). The browser's structured cloning algorithm (used by postMessage) cannot serialize BigInt values. The wagmi adapter creates transaction params with BigInt values at lines 432-434 of client.ts (BigInt(params.value), BigInt(params.gas), BigInt(params.gasPrice)). These BigInt values flow through to the postMessage call at W3mFrame.ts:242.
Other wallets aren't affected because they use different transport mechanisms that handle BigInt natively (direct provider calls, not iframe postMessage).
Approach & Reasoning
Added serializeBigInts() helper that recursively converts BigInt values to 0x-prefixed hex strings before the payload reaches postMessage. Applied at the single convergence point — W3mFrameProvider.request() — so all RPC methods are covered.
Why 0x hex strings: This is the standard Ethereum JSON-RPC encoding for quantities (gas, value, nonce). The Magic iframe expects this format.
Why recursive: RPC params can be nested objects/arrays (e.g., sendTransaction params contain objects with gas, value fields). The helper traverses the full structure.
Immutability: The helper creates new objects/arrays — the original request is not mutated. This is important because the original request is also passed to rpcSuccessHandler/rpcErrorHandler downstream.
Considered alternatives:
Edge Cases
Verification
Test plan
🤖 Generated with Claude Code