fix: reuse stream scanner buffer in channel handlers

[xujiantop-crypto]

Summary

• add a shared helper.NewStreamScanner that applies the existing stream scanner buffer limit
• update channel-specific stream scanners to use the shared buffered scanner
• log scanner errors in zhipu/cohere paths instead of silently ending on scanner failures

Fixes #5213

Tests

• go test ./relay/helper -run TestNewStreamScanner_AllowsLargeStreamLine -count=1
• go test ./relay/channel/cohere ./relay/channel/zhipu ./relay/channel/cloudflare ./relay/channel/coze ./relay/channel/ollama ./relay/channel/tencent

Note: full go test ./relay/helper still fails on existing TestStreamScannerHandler_StreamStatus_PreInitialized; the focused new scanner test passes.

Summary by CodeRabbit

• Refactor

  • Unified stream scanning across channels with centralized buffer configuration for more reliable, consistent streaming.
  • Stream scanner initialization standardized to prevent truncated/failed reads.

• Bug Fixes

  • Improved detection and logging of stream read errors in streaming handlers.

• Tests

  • Added test validating the scanner handles very large streaming lines without failing.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 99cbe733-4dae-42dd-95c0-8c48dbedcf62

📥 Commits

Reviewing files that changed from the base of the PR and between 25871fe and b9a8b42.

📒 Files selected for processing (9)

• relay/channel/cloudflare/relay_cloudflare.go
• relay/channel/cohere/relay-cohere.go
• relay/channel/coze/relay-coze.go
• relay/channel/ollama/relay-ollama.go
• relay/channel/ollama/stream.go
• relay/channel/tencent/relay-tencent.go
• relay/channel/zhipu/relay-zhipu.go
• relay/helper/stream_scanner.go
• relay/helper/stream_scanner_test.go

✅ Files skipped from review due to trivial changes (1)

• relay/channel/ollama/stream.go

🚧 Files skipped from review as they are similar to previous changes (8)

• relay/channel/coze/relay-coze.go
• relay/channel/zhipu/relay-zhipu.go
• relay/channel/tencent/relay-tencent.go
• relay/channel/ollama/relay-ollama.go
• relay/helper/stream_scanner.go
• relay/channel/cloudflare/relay_cloudflare.go
• relay/helper/stream_scanner_test.go
• relay/channel/cohere/relay-cohere.go

---

Walkthrough

Adds a NewStreamScanner factory that centralizes bufio.Scanner buffer sizing and migrates channel stream handlers to use it; several handlers also add scanner error checks and remove now-unnecessary bufio imports.

Changes

Stream Scanner Consolidation

Layer / File(s)	Summary
Stream scanner helper factory and tests relay/helper/stream_scanner.go, relay/helper/stream_scanner_test.go	Adds NewStreamScanner(reader io.Reader) that wraps bufio.NewScanner and applies configurable buffer sizing; refactors StreamScannerHandler to use it and adds TestNewStreamScanner_AllowsLargeStreamLine.
Simple channel scanner migrations relay/channel/cloudflare/relay_cloudflare.go, relay/channel/coze/relay-coze.go, relay/channel/tencent/relay-tencent.go	Cloudflare, Coze, and Tencent stream handlers now call helper.NewStreamScanner(resp.Body) instead of bufio.NewScanner(resp.Body).
Ollama scanner migrations and import updates relay/channel/ollama/relay-ollama.go, relay/channel/ollama/stream.go	Ollama relay files migrate to helper.NewStreamScanner(resp.Body) and remove bufio imports; both model-pull and main stream handlers updated.
Advanced migrations with error handling relay/channel/cohere/relay-cohere.go, relay/channel/zhipu/relay-zhipu.go	Cohere and Zhipu adopt helper.NewStreamScanner and add post-scan scanner.Err() checks; Cohere also removes the bufio import.

Possibly related PRs

• QuantumNous/new-api#2335: Introduced constant.StreamScannerMaxBufferMB that this PR leverages for scanner buffer sizing.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰
Streams once trimmed by a tiny line cap,
Now buffered wide — no more sudden gap.
NewScanner hums, each long line it will meet,
Carrots and bytes flow steady and sweet.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 13.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: reuse stream scanner buffer in channel handlers' accurately summarizes the main change: refactoring multiple channel handlers to use a centralized stream scanner helper.
Linked Issues check	✅ Passed	All coding objectives from issue #5213 are met: channel handlers now use the shared helper.NewStreamScanner, scanner errors are logged in zhipu and cohere paths, and buffer limits are consistently applied across all affected channels.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to addressing issue #5213: creating the helper function, updating channel handlers to use it, and adding error checking.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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