[lizthegrey]

Fixes #1206.

Decoder.Reset decodes a Bytes()/Len() source shorter than WithDecodeBuffersBelow in one go through DecodeAll, where WithDecoderMaxMemory caps the total decoded size. A Reader is documented with the streaming contract, where the option caps the window, so the same Reader followed one rule or the other depending on input length.

Change: when the shortcut's DecodeAll reports ErrDecoderSizeExceeded, fall through to the normal streaming decode of the same reader (the shortcut has not consumed its bytes). Memory stays bounded as documented: the in-memory attempt stops at the cap, its buffer is dropped rather than kept for reuse, and streaming holds a window.

Test: TestDecoderBufferShortcutFallsBackToStreaming encodes 4 MiB with a 64 KiB window (a few hundred compressed bytes), sets a 1 MiB limit, asserts DecodeAll still fails as documented, and asserts a Reader over a bytes.Buffer and over a plain io.Reader both produce the full output. It fails on master with decompressed size exceeds configured limit on the buffer case. The original 1740-byte fuzz reproducer from #1206 also passes the differential harness with this change.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Decoding now automatically falls back to streaming when an optimized in-memory decode exceeds the configured maximum memory limit.
  • Readers backed by in-memory byte sources now behave consistently with standard readers, allowing oversized compressed data to decode successfully without exceeding the configured memory cap.
  • Added coverage to verify successful decoding and output integrity across both decoding paths.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Team

Run ID: c5be7302-d988-46ac-9fe5-17a46653ffa2

📥 Commits

Reviewing files that changed from the base of the PR and between 75489f9 and 92f1ca8.

📒 Files selected for processing (2)

• zstd/decoder.go
• zstd/decoder_test.go

Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review.

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📝 Walkthrough

Walkthrough

The decoder now falls back from DecodeAll to streaming when the configured decoded-size limit is exceeded. The change discards the oversized buffer and adds coverage for byte-backed and plain reader sources.

Changes

Decoder shortcut fallback

Layer / File(s)	Summary
Synchronous decode fallback and regression coverage zstd/decoder.go, zstd/decoder_test.go	Decoder.Reset detects ErrDecoderSizeExceeded, drops the shortcut buffer, and continues through streaming decode. The test verifies equivalent output for bytes.Buffer and plain io.Reader sources under WithDecoderMaxMemory.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 92f1c

Small buffered zstd Reader inputs that exceed the in-memory decode limit now continue with bounded streaming decode, matching plain-reader behavior. The targeted regression coverage supports merge readiness with no remaining actionable risk.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.	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 clearly summarizes the main change: streaming fallback when in-memory decoding exceeds the configured size limit.
Linked Issues check	✅ Passed	The changes satisfy issue #1206. Decoder.Reset falls back to streaming after DecodeAll returns ErrDecoderSizeExceeded, preserves the unconsumed input, releases the oversized buffer, and adds cov…
Out of Scope Changes check	✅ Passed	The changes are limited to the decoder fallback logic and targeted regression tests. They directly support the linked issue and stated objectives.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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