Issue Review: cloudflare/workers-sdk#7435

Summary

Streaming API responses in wrangler dev are buffered and only returned when complete, rather than streaming sequentially. The root cause has been identified in miniflare's compression handling.

Findings

• Created: December 4, 2024
• Updated: October 30, 2025
• Version: Wrangler 3.92.0 → 4.60.0 (current)
• Component: Miniflare (compression in entry.worker.ts)
• Labels: bug
• Comments: 4 (with valuable investigation)

Key Evidence

• Root cause identified: A commenter (seanparsons) traced the issue to packages/miniflare/src/workers/core/entry.worker.ts#L280 - compression is causing buffering
• Version where it broke: miniflare 3.20240405.1 (April 2024) - introduced in PR #5798 "miniflare: compress responses more like Cloudflare FL"
• Fix in progress: PR #9625 "fix: streamed response bodies in Miniflare should not infer non-streaming compression by default" (opened June 17, 2025, still open)
• PR #9625 explicitly fixes: Issues #8004 and #6577 (duplicates of this issue)
• Workaround exists: Setting Content-Encoding: none header bypasses the buffering
• Duplicate issues: #6577 (Aug 2024), #8004 (Feb 2025) - both still open

Recommendation

Status: CLOSE (as duplicate)

Reasoning: This issue is a duplicate of #8004 and #6577, which are explicitly addressed in PR #9625. The fix is in progress and the open PR clearly states "Fixes #8004" and "Fixes #6577". Issue #7435 describes the same problem and has the same root cause, but is not linked in the PR.

Action: Close this issue as a duplicate of #8004, which has the pending fix in PR #9625.

Suggested Comment

Thank you for reporting this issue and for the detailed reproduction. This has been identified as a duplicate of #8004 and #6577, which are being addressed in PR #9625.

The root cause has been identified: when serving responses without an explicit content-encoding header, Miniflare was inferring a compression algorithm (usually gzip) that does not support streaming, causing the entire response to be buffered.

Workaround: Until the fix is merged, you can work around this by setting a Content-Encoding header explicitly (e.g., Content-Encoding: none or identity).

Closing as duplicate of #8004. Please follow that issue or PR #9625 for updates on the fix.