Bun Filesystem Helpers

Pure Bun-native filesystem utilities from @side-quest/core/fs - zero node:fs dependencies, command-injection safe.

When to Use

• Writing new code - Always prefer these over node:fs
• Command injection concerns - All shell commands use array args (safe)
• Token efficiency - Smaller imports, faster operations
• Bun-first projects - Leverages Bun's native APIs

Available Functions

File Existence

import { pathExists, pathExistsSync } from "@side-quest/core/fs";

// Async
if (await pathExists("/path/to/file")) { }

// Sync
if (pathExistsSync("/path/to/file")) { }

Implementation: Uses Bun.file().exists() (async) or test -e command (sync)

Reading Files

import { readTextFile, readTextFileSync, readJsonFile, readJsonFileSync } from "@side-quest/core/fs";

// Async text
const content = await readTextFile("/path/to/file.txt");

// Sync text
const content = readTextFileSync("/path/to/file.txt");

// Async JSON
const data = await readJsonFile<MyType>("/path/to/data.json");

// Sync JSON
const data = readJsonFileSync<MyType>("/path/to/data.json");

Implementation: Uses Bun.file().text() (async) or cat command (sync)

Writing Files

import { writeTextFile, writeTextFileSync, writeJsonFile, writeJsonFileSync } from "@side-quest/core/fs";

// Async text
await writeTextFile("/path/to/file.txt", "content");

// Sync text
writeTextFileSync("/path/to/file.txt", "content");

// Async JSON
await writeJsonFile("/path/to/data.json", { foo: "bar" }, 2);

// Sync JSON
writeJsonFileSync("/path/to/data.json", { foo: "bar" }, 2);

Implementation: Uses Bun.write() (async) or printf via shell (sync)

Directory Operations

import { ensureDir, ensureDirSync, readDir, readDirAsync } from "@side-quest/core/fs";

// Create directory (recursive)
await ensureDir("/path/to/nested/dir");
ensureDirSync("/path/to/nested/dir");

// List directory contents
const files = readDir("/path/to/dir");  // Sync
const files = await readDirAsync("/path/to/dir");  // Async

Implementation: Uses mkdir -p command, ls -1 command

File Operations

import { copyFile, moveFile, rename, unlink, unlinkSync } from "@side-quest/core/fs";

// Copy file
await copyFile("/source.txt", "/dest.txt");

// Move file (copy + delete)
await moveFile("/source.txt", "/dest.txt");

// Rename/move atomically
await rename("/old-path.txt", "/new-path.txt");

// Delete file
await unlink("/path/to/file.txt");
unlinkSync("/path/to/file.txt");

Implementation: Uses Bun.write() for copy, mv command for rename, rm command for delete

File Stats

import { stat } from "@side-quest/core/fs";

const stats = await stat("/path/to/file.txt");
console.log(stats.size);      // File size in bytes
console.log(stats.mtimeMs);   // Last modified timestamp

Implementation: Uses Bun.file().size and Bun.file().lastModified

Use case: TOCTOU protection - check file before AND after operations

Hashing

import { sha256, sha256File, fastHash } from "@side-quest/core/fs";

// Hash string
const hash = sha256("content");  // Hex string (64 chars)

// Hash file
const hash = await sha256File("/path/to/file.pdf");

// Fast non-cryptographic hash (cache keys)
const hash = fastHash("content");  // bigint or number

Implementation: Uses Bun.CryptoHasher (SHA256) or Bun.hash (xxHash64)

Deep Equality

import { deepEquals } from "@side-quest/core/fs";

const equal = deepEquals(obj1, obj2);           // Loose mode
const equal = deepEquals(obj1, obj2, true);     // Strict mode

Implementation: Uses Bun.deepEquals()

Security Guarantees

✅ Command injection safe - All shell commands use array arguments:

// Safe - array args prevent injection
Bun.spawnSync(["mkdir", "-p", userInput]);

// Never - string interpolation allows injection
Bun.spawnSync(`mkdir -p ${userInput}`);  // ❌ DON'T DO THIS

✅ TOCTOU protection - Use stat() before AND after file operations to detect tampering

Migration from node:fs

// Before (node:fs)
import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";

existsSync("/path");
mkdirSync("/path", { recursive: true });
readFileSync("/path", "utf8");
writeFileSync("/path", "content", "utf8");

// After (@side-quest/core/fs)
import { pathExistsSync, ensureDirSync, readTextFileSync, writeTextFileSync } from "@side-quest/core/fs";

pathExistsSync("/path");
ensureDirSync("/path");
readTextFileSync("/path");
writeTextFileSync("/path", "content");

Performance Characteristics

Operation	Speed	Notes
pathExists	~1ms	Bun.file().exists()
pathExistsSync	~2ms	test -e command
readTextFile	~5-50ms	Depends on file size
writeTextFile	~5-20ms	Bun.write() is fast
ensureDir	~10ms	mkdir -p command
readDir	~5-15ms	ls -1 command
sha256File	~50-500ms	Depends on file size
fastHash	<1ms	xxHash64 is very fast

Common Patterns

Atomic File Updates

import { pathExistsSync, writeTextFileSync, rename } from "@side-quest/core/fs";

// Write to temp file, then atomically rename
const tempPath = `${targetPath}.tmp`;
writeTextFileSync(tempPath, newContent);
await rename(tempPath, targetPath);  // POSIX guarantees atomicity

Safe File Modification with TOCTOU Protection

import { stat, readTextFileSync, writeTextFileSync } from "@side-quest/core/fs";

// Get pre-modification stats
const preStat = await stat(filePath);

// Read and modify
const content = readTextFileSync(filePath);
const modified = transform(content);

// Verify file unchanged before writing
const postStat = await stat(filePath);
if (postStat.mtimeMs !== preStat.mtimeMs) {
  throw new Error("File was modified during read (TOCTOU attack detected)");
}

writeTextFileSync(filePath, modified);

Idempotent Processing with Content Hashing

import { sha256File, pathExistsSync } from "@side-quest/core/fs";

const hash = await sha256File(sourceFile);
const processedMarker = `.processed/${hash}`;

if (pathExistsSync(processedMarker)) {
  console.log("Already processed - skipping");
  return;
}

// Process file...
writeTextFileSync(processedMarker, new Date().toISOString());

Implementation Details

All functions are exported from core/src/fs/index.ts and use:

• Bun.file() - File existence, reading, size, timestamps
• Bun.write() - Writing files
• Bun.spawn() / Bun.spawnSync() - Shell commands with array args
• Bun.CryptoHasher - SHA256 hashing
• Bun.hash - Fast non-cryptographic hashing (xxHash64)
• Bun.deepEquals() - Deep equality checks
• Bun.Glob - Recursive file scanning (used elsewhere, not exported from fs)

Zero node:fs dependencies in production code.

References

• Core package source: core/src/fs/index.ts
• Test coverage: 423 tests passing
• Used by: para-obsidian inbox processing, registry, PDF processor