### What does this PR do?
Fixes#23314 where `zlib.zstdCompress()` created data that caused an
out-of-memory error when decompressed with `Bun.zstdDecompressSync()`.
#### 1. `zlib.zstdCompress()` now sets `pledgedSrcSize`
The async convenience method now automatically sets the `pledgedSrcSize`
option to the input buffer size. This ensures the compressed frame
includes the content size in the header, making sync and async
compression produce identical output.
**Node.js compatibility**: `pledgedSrcSize` is a documented Node.js
option:
-
[`vendor/node/doc/api/zlib.md:754-758`](https://github.com/oven-sh/bun/blob/main/vendor/node/doc/api/zlib.md#L754-L758)
-
[`vendor/node/lib/zlib.js:893`](https://github.com/oven-sh/bun/blob/main/vendor/node/lib/zlib.js#L893)
-
[`vendor/node/src/node_zlib.cc:890-904`](https://github.com/oven-sh/bun/blob/main/vendor/node/src/node_zlib.cc#L890-L904)
#### 2. Added `bun.zstd.decompressAlloc()` - centralized safe
decompression
Created a new function in `src/deps/zstd.zig` that handles decompression
in one place with automatic safety features:
- **Handles unknown content sizes**: Automatically switches to streaming
decompression when the zstd frame doesn't include content size (e.g.,
from streams without `pledgedSrcSize`)
- **16MB safety limit**: For security, if the reported decompressed size
exceeds 16MB, streaming decompression is used instead of blindly
trusting the header
- **Fast path for small files**: Still uses efficient pre-allocation for
files < 16MB with known sizes
This centralized fix automatically protects:
- `Bun.zstdDecompressSync()` / `Bun.zstdDecompress()`
- `StandaloneModuleGraph` source map decompression
- Any other code using `bun.zstd` decompression
### How did you verify your code works?
**Before:**
```typescript
const input = "hello world";
// Async compression
const compressed = await new Promise((resolve, reject) => {
zlib.zstdCompress(input, (err, result) => {
if (err) reject(err);
else resolve(result);
});
});
// This would fail with "Out of memory"
const decompressed = Bun.zstdDecompressSync(compressed);
```
**Error**: `RangeError: Out of memory` (tried to allocate UINT64_MAX
bytes)
**After:**
```typescript
const input = "hello world";
// Async compression (now includes content size)
const compressed = await new Promise((resolve, reject) => {
zlib.zstdCompress(input, (err, result) => {
if (err) reject(err);
else resolve(result);
});
});
// ✅ Works! Falls back to streaming decompression if needed
const decompressed = Bun.zstdDecompressSync(compressed);
console.log(decompressed.toString()); // "hello world"
```
**Tests:**
- ✅ All existing tests pass
- ✅ New regression tests for async/sync compression compatibility
(`test/regression/issue/23314/zstd-async-compress.test.ts`)
- ✅ Test for large (>16MB) decompression using streaming
(`test/regression/issue/23314/zstd-large-decompression.test.ts`)
- ✅ Test for various input sizes and types
(`test/regression/issue/23314/zstd-large-input.test.ts`)
**Security:**
The 16MB safety limit protects against malicious zstd frames that claim
huge decompressed sizes in the header, preventing potential OOM attacks.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
