Fixed: Remove UB-prone uninit slice cast in blocking webfetch

[Sewer56]

Summary

• Replace unsafe MaybeUninit slice casting in the blocking webfetch read loop with a safe initialized [0u8; 8192] buffer.
• Keep chunked read/append behavior and response size checks unchanged.
• Remove undefined behavior risk from creating &mut [u8] over uninitialized memory.

Basically, the old behaviour was technically correct.
But the slice constructor assumes that the data is 'initialized'.
I don't want to risk it with future compiler changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 348806a and 272e0db.

📒 Files selected for processing (1)

• src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs

📜 Recent review details

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (5)

• GitHub Check: Build and Test (Blocking) (windows-latest, x86_64-pc-windows-msvc, false)
• GitHub Check: Build and Test (Async/Tokio) (ubuntu-latest, x86_64-unknown-linux-gnu, false)
• GitHub Check: Build and Test (Async/Tokio) (windows-latest, x86_64-pc-windows-msvc, false)
• GitHub Check: Build and Test (Blocking) (macos-latest, aarch64-apple-darwin, false)
• GitHub Check: Build and Test (Async/Tokio) (macos-latest, aarch64-apple-darwin, false)

🧰 Additional context used

📓 Path-based instructions (1)

src/**/*.rs

📄 CodeRabbit inference engine (src/AGENTS.md)

src/**/*.rs: Preallocate collections when size is known or estimable using String::with_capacity(estimated_len), Vec::with_capacity(count), or BufReader::with_capacity(size, reader)
Prefer &str / &[T] returns over owned types when lifetime allows
Use Cow<'_, str> for conditional ownership (e.g., String::from_utf8_lossy)
Use &'static str for compile-time constant strings
Reuse buffers by calling .clear() and reusing Vec/String instead of reallocating
Use const generics for compile-time branching (e.g., <const LINE_NUMBERS: bool>)
Use #[inline] on small, hot-path functions
Prefer core over std where possible (e.g., core::mem over std::mem)
Use memchr crate for fast byte searching over manual iteration
Keep modules under 500 lines (excluding tests); split if larger
Place use statements inside functions only for #[cfg] conditional compilation
Document public items with /// and add examples in docs where helpful
Use //! for module-level documentation
Use [TypeName] rustdoc links instead of backticks in documentation

Files:

• src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs

🧠 Learnings (3)

📓 Common learnings

Learnt from: CR
Repo: Sewer56/llm-coding-tools PR: 0
File: src/AGENTS.md:0-0
Timestamp: 2026-02-07T22:53:26.067Z
Learning: Applies to src/**/*.rs : Reuse buffers by calling `.clear()` and reusing `Vec`/`String` instead of reallocating

📚 Learning: 2026-02-07T22:53:26.067Z

Learnt from: CR
Repo: Sewer56/llm-coding-tools PR: 0
File: src/AGENTS.md:0-0
Timestamp: 2026-02-07T22:53:26.067Z
Learning: Applies to src/**/*.rs : Reuse buffers by calling `.clear()` and reusing `Vec`/`String` instead of reallocating

Applied to files:

• src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs

📚 Learning: 2026-02-07T22:53:26.067Z

Learnt from: CR
Repo: Sewer56/llm-coding-tools PR: 0
File: src/AGENTS.md:0-0
Timestamp: 2026-02-07T22:53:26.067Z
Learning: Applies to src/**/*.rs : Preallocate collections when size is known or estimable using `String::with_capacity(estimated_len)`, `Vec::with_capacity(count)`, or `BufReader::with_capacity(size, reader)`

Applied to files:

• src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs

🧬 Code graph analysis (1)

src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs (1)

src/llm-coding-tools-core/src/tools/webfetch/mod.rs (1)

• check_size (46-54)

🔇 Additional comments (2)

src/llm-coding-tools-core/src/tools/webfetch/blocking_impl.rs (2)

55-60: Safe read buffer change is correct and removes UB risk.

This replacement with a fully initialized [0u8; 8192] buffer and direct read(&mut buffer) is a solid safety improvement with equivalent behavior.

---

66-66: Chunk append remains correct and bounds-safe.

Using &buffer[..n] correctly appends only the bytes actually read.

---

Walkthrough

This change modifies the web fetch blocking implementation by replacing an unsafe MaybeUninit-based buffer with a direct [u8; 8192] stack-allocated byte array. The unsafe pointer arithmetic and raw pointer slice construction are removed in favor of directly calling read(&mut buffer). Data extraction adjusts to use &buffer[..n] instead. The refactoring preserves byte accumulation logic, content length validation, streaming until EOF, and error handling via ToolError::Http. No public API signatures are affected. The change results in a net reduction of 7 lines of code.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and specifically describes the main change: removing undefined behavior from unsafe MaybeUninit casting in the blocking webfetch implementation.
Description check	✅ Passed	The PR description covers the key changes and safety improvements, though it lacks detailed context about why this fix was necessary beyond UB elimination.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

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• Commit unit tests in branch fix/blocking-webfetch-init-buffer

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.84%. Comparing base (348806a) to head (272e0db).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   74.91%   74.84%   -0.07%     
==========================================
  Files          67       67              
  Lines        1985     1980       -5     
==========================================
- Hits         1487     1482       -5     
  Misses        498      498              

Flag	Coverage Δ
unittests	74.84% <100.00%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ing-tools-core/src/tools/webfetch/blocking_impl.rs	91.89% <100.00%> (-0.97%)	⬇️

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