Issue Review: cloudflare/workers-sdk#5771

Summary

D1 via Miniflare doesn't accept Buffer type for blob columns - throws assertion error.

Findings

• Created: 2024-05-07
• Updated: 2025-10-30
• Version: wrangler 3.53.1 → 4.61.0
• Component: miniflare, d1
• Labels: bug, miniflare
• Comments: 0

Key Evidence

• Passing Buffer to D1 blob column in local dev throws assertion error in devalue handler
• Passing Uint8Array works fine
• Root cause: Miniflare's devalue.ts has assertion that fails for Buffer (which is a subclass of Uint8Array but has different internal structure)
• Additional issue: Blob data returned as plain JS array instead of ArrayBuffer/Uint8Array
• Repro repo provided: https://github.com/sdarnell/cf-svelte
• Drizzle ORM types require Buffer, causing friction
• Documentation unclear on allowable blob types

Recommendation

Status: KEEP OPEN

Reasoning: Valid bug where Buffer (a common Node.js type) fails but Uint8Array works. Since Buffer extends Uint8Array, this should work. The assertion in devalue.ts needs to handle Buffer correctly. No comments or engagement on this issue despite being over a year old.

Action: Fix miniflare's devalue handler to accept Buffer type. Also investigate the blob return type issue (returning plain array instead of typed array).

Suggested Comment

This issue is still valid. The miniflare devalue handler at src/workers/core/devalue.ts needs to handle Buffer type (which extends Uint8Array).

Workaround: Convert Buffer to Uint8Array before passing to D1:

const data = new Uint8Array(buffer);