fix(dashboard): enforce image proxy limits while streaming

[maskjelly]

Description

The image proxy previously buffered an entire upstream response before applying its 2 MiB limit. This checks size while reading and cancels oversized or rejected responses early.

Slice

• Issue: Closes fix(dashboard): enforce the image proxy size limit while streaming #1115
• Security report: GHSA-5x3c-jc33-g5rw
• Type / area: bug · dashboard image proxy
• Suggested label: bug (author cannot apply upstream labels)
• Base: staging
• Dependencies or overlapping PRs: None; fix(db): erase revenue records with deleted analytics owners #1116 and fix(api): restrict public sharing to unfiltered overview queries #1117 fix separate audit findings.

Changes

• Enforce the 2 MiB limit during streaming even when Content-Length is absent or understated; use one bounded accumulation buffer and a deadline-aware stream pipe.
• Cancel rejected or unread upstream bodies and retain the SSRF guard, redirect restriction, rate limit, response headers, and 10-second deadline.
• Return 504 when the deadline interrupts body reading. The follow-up test holds a read pending and verifies the proxy aborts it without an abort-aware response stub.

Validation

• bun run lint: passed.
• bun run check-types: 37/37 tasks passed.
• bun test app/api/image-proxy/route.test.ts: 11 passed, including oversized streams, exact-limit success, rejected-body cancellation, read failure, SSRF rejection, and a stalled body interrupted by the deadline.
• The timeout regression uses a controlled response stream; a live network stall was not run in this follow-up.

Merge notes

This is an independent change based on current staging. The 2 MiB bound applies to application accumulation; the fetch implementation supplies each incoming chunk. Maintainer review and CI are still required.

Before merge

• Maintainer applies the suggested label and reviews the change.
• Run the fork CI workflow (currently action_required with zero jobs).
• Resolve the Vercel authorization check failures shown on the PR.

AI disclosure: implemented and tested with Codex. Source and local test results were reviewed during implementation; maintainer human review is required.

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[greptile-apps]

Confidence Score: 4/5

[Medium impact] Image proxy streaming and size enforcement logic.

The streaming change appears sound, but the explicit code-rule violations must be resolved before merging.

Findings

1.  Required code rules are broken ▶
2.  Body timeout lacks coverage ▶

Summary

The image proxy now checks each chunk before copying it into a fixed 2 MiB buffer.

• The image proxy stops oversized streams at the 2 MiB limit.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Fetch image with deadline] --> B{Headers accepted?}
  B -->|No| G[Cancel upstream body]
  B -->|Yes| C[Read next chunk]
  C --> D{Exceeds 2 MiB?}
  D -->|Yes| G
  D -->|No| E[Copy into fixed buffer]
  E --> C
  C -->|End of body| F[Return populated bytes]
  C -->|Deadline error| H[Return 504]
  F --> G
  H --> G

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_{Reviews (1) · Last reviewed commit: "fix(dashboard): enforce image proxy limi..." · Reviewed by Greptile}