perf: parallelize pack and unpack with rayon

Pack changes:
- Split into path-collection (sequential) + crypto-processing (parallel)
- Introduce CollectedEntry enum to separate directory walk from file processing
- process_file() now creates thread-local RNG instead of taking &mut Rng
- File entries processed via rayon into_par_iter(), preserving deterministic order

Unpack changes:
- Phase 1: Sequential read of all ciphertexts from archive (single file handle)
- Phase 2: Create all directories sequentially (parent-before-child ordering)
- Phase 3: Parallel verify/decrypt/decompress/write via rayon par_iter
- Phase 4: Sequential result reporting for deterministic output
- Collect results into Vec<UnpackResult> to avoid interleaved stdout/stderr

src/archive.rs

@@ -3,6 +3,7 @@ use std::io::{Read, Seek, SeekFrom, Write};
 use std::path::{Path, PathBuf};
 
 use rand::Rng;
+use rayon::prelude::*;
 use std::os::unix::fs::PermissionsExt;
 
 use crate::compression;
@@ -27,6 +28,22 @@ struct ProcessedFile {
     padding_bytes: Vec<u8>,
 }
 
+/// Collected entry from the directory walk (before crypto processing).
+///
+/// Separates the fast sequential path-collection phase from the
+/// parallelizable crypto-processing phase.
+enum CollectedEntry {
+    Dir {
+        name: String,
+        permissions: u16,
+    },
+    File {
+        path: PathBuf,
+        name: String,
+        permissions: u16,
+    },
+}
+
 /// Read and de-obfuscate archive header and TOC entries.
 ///
 /// Handles XOR header bootstrapping (FORMAT.md Section 10 steps 1-3)
@@ -60,12 +77,13 @@ fn get_permissions(path: &Path) -> anyhow::Result<u16> {
 }
 
 /// Process a single file through the crypto pipeline, returning a ProcessedFile.
+///
+/// Thread-safe: creates a thread-local RNG instead of accepting an external one.
 fn process_file(
     file_path: &Path,
     name: String,
     permissions: u16,
     no_compress: &[String],
-    rng: &mut impl Rng,
 ) -> anyhow::Result<ProcessedFile> {
     let data = fs::read(file_path)?;
 
@@ -103,9 +121,10 @@ fn process_file(
     let hmac = crypto::compute_hmac(&KEY, &iv, &ciphertext);
 
     // Step 6: Generate decoy padding (FORMAT.md Section 9.3)
+    let mut rng = rand::rng();
     let padding_after: u16 = rng.random_range(64..=4096);
     let mut padding_bytes = vec![0u8; padding_after as usize];
-    rand::Fill::fill(&mut padding_bytes[..], rng);
+    rand::Fill::fill(&mut padding_bytes[..], &mut rng);
 
     Ok(ProcessedFile {
         name,
@@ -143,21 +162,22 @@ fn make_directory_entry(name: String, permissions: u16) -> ProcessedFile {
     }
 }
 
-/// Recursively collect all entries (directories and files) from a directory path.
+/// Recursively collect paths from a directory (no crypto processing).
 ///
 /// Entries are emitted in parent-before-child order (DFS preorder).
 /// The base_name is the top-level directory name used as prefix for all relative paths.
-fn collect_directory_entries(
+fn collect_directory_paths(
     dir_path: &Path,
     base_name: &str,
-    no_compress: &[String],
-    rng: &mut impl Rng,
-) -> anyhow::Result<Vec<ProcessedFile>> {
+) -> anyhow::Result<Vec<CollectedEntry>> {
     let mut entries = Vec::new();
 
     // Add the directory itself first (parent-before-child)
     let dir_perms = get_permissions(dir_path)?;
-    entries.push(make_directory_entry(base_name.to_string(), dir_perms));
+    entries.push(CollectedEntry::Dir {
+        name: base_name.to_string(),
+        permissions: dir_perms,
+    });
 
     // Collect children sorted by name for deterministic ordering
     let mut children: Vec<fs::DirEntry> = fs::read_dir(dir_path)?
@@ -173,39 +193,58 @@ fn collect_directory_entries(
                 .ok_or_else(|| anyhow::anyhow!("Non-UTF-8 filename: {}", child_path.display()))?
         );
 
-        if child_path.is_dir() {
-            // Recurse into subdirectory
-            let sub_entries = collect_directory_entries(
+        // Use symlink_metadata to avoid following symlinks.
+        // is_dir()/is_file() follow symlinks, which can cause infinite
+        // recursion or massively inflated entry counts with symlink farms
+        // (e.g., pnpm node_modules with hundreds of directory symlinks).
+        let meta = fs::symlink_metadata(&child_path)?;
+
+        if meta.file_type().is_symlink() {
+            eprintln!(
+                "Warning: skipping symlink: {}",
+                child_path.display()
+            );
+            continue;
+        } else if meta.is_dir() {
+            // Recurse into real subdirectory (not a symlink)
+            let sub_entries = collect_directory_paths(
                 &child_path,
                 &child_name,
-                no_compress,
-                rng,
             )?;
             entries.extend(sub_entries);
         } else {
-            // Process file
-            let file_perms = get_permissions(&child_path)?;
-            let pf = process_file(&child_path, child_name, file_perms, no_compress, rng)?;
-            entries.push(pf);
+            // Collect file path for later parallel processing
+            let file_perms = (meta.permissions().mode() & 0o7777) as u16;
+            entries.push(CollectedEntry::File {
+                path: child_path,
+                name: child_name,
+                permissions: file_perms,
+            });
         }
     }
 
     Ok(entries)
 }
 
-/// Collect all entries from input paths (files and directories).
+/// Collect all entry paths from input paths (files and directories).
 ///
-/// For files: processes through crypto pipeline with filename-only name.
-/// For directories: recursively collects all children with relative paths.
-fn collect_entries(
-    inputs: &[PathBuf],
-    no_compress: &[String],
-    rng: &mut impl Rng,
-) -> anyhow::Result<Vec<ProcessedFile>> {
-    let mut processed = Vec::new();
+/// Returns a list of CollectedEntry items in deterministic order,
+/// ready for parallel processing of file entries.
+fn collect_paths(inputs: &[PathBuf]) -> anyhow::Result<Vec<CollectedEntry>> {
+    let mut collected = Vec::new();
 
     for input_path in inputs {
-        if input_path.is_dir() {
+        // Check for symlinks at top level too
+        let meta = fs::symlink_metadata(input_path)?;
+        if meta.file_type().is_symlink() {
+            eprintln!(
+                "Warning: skipping symlink: {}",
+                input_path.display()
+            );
+            continue;
+        }
+
+        if meta.is_dir() {
             // Get the directory's own name for the archive prefix
             let dir_name = input_path
                 .file_name()
@@ -214,13 +253,8 @@ fn collect_entries(
                 .ok_or_else(|| anyhow::anyhow!("Non-UTF-8 directory name: {}", input_path.display()))?
                 .to_string();
 
-            let dir_entries = collect_directory_entries(
-                input_path,
-                &dir_name,
-                no_compress,
-                rng,
-            )?;
-            processed.extend(dir_entries);
+            let dir_entries = collect_directory_paths(input_path, &dir_name)?;
+            collected.extend(dir_entries);
         } else {
             // Single file: use just the filename
             let name = input_path
@@ -231,29 +265,55 @@ fn collect_entries(
                 .to_string();
 
             let file_perms = get_permissions(input_path)?;
-            let pf = process_file(input_path, name, file_perms, no_compress, rng)?;
-            processed.push(pf);
+            collected.push(CollectedEntry::File {
+                path: input_path.clone(),
+                name,
+                permissions: file_perms,
+            });
         }
     }
 
-    Ok(processed)
+    Ok(collected)
 }
 
 /// Pack files and directories into an encrypted archive.
 ///
-/// Two-pass algorithm with full obfuscation:
-///   Pass 1: Read, hash, compress, encrypt each file; generate decoy padding.
-///           Directories are stored as zero-length entries.
-///   Pass 2: Encrypt TOC, compute offsets, XOR header, write archive.
+/// Two-pass algorithm with full obfuscation and parallel file processing:
+///   Pass 1a: Walk directory tree sequentially, collect paths in deterministic order.
+///   Pass 1b: Process file entries in parallel (read, hash, compress, encrypt, padding).
+///            Directory entries become zero-length entries (no processing needed).
+///   Pass 2:  Encrypt TOC, compute offsets, XOR header, write archive sequentially.
 pub fn pack(files: &[PathBuf], output: &Path, no_compress: &[String]) -> anyhow::Result<()> {
     anyhow::ensure!(!files.is_empty(), "No input files specified");
 
-    let mut rng = rand::rng();
+    // --- Pass 1a: Collect paths sequentially (fast, deterministic) ---
+    let collected = collect_paths(files)?;
 
-    // --- Pass 1: Collect and process all entries ---
-    let processed = collect_entries(files, no_compress, &mut rng)?;
+    anyhow::ensure!(!collected.is_empty(), "No entries to archive");
 
-    anyhow::ensure!(!processed.is_empty(), "No entries to archive");
+    // Guard against u16 overflow: file_count field in header is u16 (max 65535)
+    anyhow::ensure!(
+        collected.len() <= u16::MAX as usize,
+        "Too many entries: {} exceeds maximum of {} (u16 file_count limit)",
+        collected.len(),
+        u16::MAX
+    );
+
+    // --- Pass 1b: Process files in parallel, directories inline ---
+    // We use par_iter on the collected entries while preserving their order.
+    // Each entry is processed independently; file entries go through the full
+    // crypto pipeline in parallel, directory entries are trivially converted.
+    let processed: Vec<ProcessedFile> = collected
+        .into_par_iter()
+        .map(|entry| match entry {
+            CollectedEntry::Dir { name, permissions } => {
+                Ok(make_directory_entry(name, permissions))
+            }
+            CollectedEntry::File { path, name, permissions } => {
+                process_file(&path, name, permissions, no_compress)
+            }
+        })
+        .collect::<anyhow::Result<Vec<_>>>()?;
 
     // Count files and directories
     let file_count = processed.iter().filter(|pf| pf.entry_type == 0).count();
@@ -459,15 +519,42 @@ pub fn inspect(archive: &Path) -> anyhow::Result<()> {
     Ok(())
 }
 
+/// Data read from the archive for a single entry, ready for parallel processing.
+enum ReadEntry {
+    /// Directory entry: just needs creation and permission setting.
+    Dir {
+        name: String,
+        permissions: u16,
+    },
+    /// File entry: ciphertext has been read, ready for verify/decrypt/decompress/write.
+    File {
+        entry: TocEntry,
+        ciphertext: Vec<u8>,
+    },
+    /// Entry with unsafe name that was skipped during reading.
+    Skipped {
+        _name: String,
+    },
+}
+
+/// Result of processing a single file entry during parallel unpack.
+enum UnpackResult {
+    /// File extracted successfully.
+    Ok { name: String, original_size: u32 },
+    /// File had a verification error but was still written (SHA-256 mismatch).
+    Written { name: String, original_size: u32 },
+    /// File processing failed (HMAC, decryption, or decompression error).
+    Error { name: String, message: String },
+}
+
 /// Unpack an encrypted archive, extracting all files and directories with
 /// HMAC and SHA-256 verification, and Unix permission restoration.
 ///
-/// Follows FORMAT.md Section 10 decode order:
-///   1. Read header with XOR bootstrapping
-///   2. Read and decrypt TOC entries
-///   3. For each entry:
-///      - Directory: create directory, set permissions
-///      - File: seek to data_offset, verify HMAC, decrypt, decompress, verify SHA-256, write, set permissions
+/// Uses parallel processing for the verify/decrypt/decompress/write pipeline:
+///   1. Read header and TOC sequentially (single file handle).
+///   2. Create all directories sequentially (ensures parent dirs exist).
+///   3. Read all file ciphertexts sequentially from the archive.
+///   4. Process and write files in parallel (HMAC, decrypt, decompress, SHA-256, write).
 pub fn unpack(archive: &Path, output_dir: &Path) -> anyhow::Result<()> {
     let mut file = fs::File::open(archive)?;
 
@@ -478,60 +565,104 @@ pub fn unpack(archive: &Path, output_dir: &Path) -> anyhow::Result<()> {
     fs::create_dir_all(output_dir)?;
 
     let entry_count = entries.len();
-    let mut error_count: usize = 0;
-    let mut success_count: usize = 0;
 
-    for entry in &entries {
+    // --- Phase 1: Sequential read of all entry data ---
+    // Separate directories from files, read ciphertexts for files.
+    let mut read_entries: Vec<ReadEntry> = Vec::with_capacity(entry_count);
+
+    for entry in entries {
         // Sanitize filename: reject directory traversal
         if entry.name.starts_with('/') || entry.name.contains("..") {
             eprintln!(
                 "Skipping entry with unsafe name: {} (directory traversal attempt)",
                 entry.name
             );
-            error_count += 1;
+            read_entries.push(ReadEntry::Skipped { _name: entry.name.clone() });
             continue;
         }
 
-        let output_path = output_dir.join(&entry.name);
-
         if entry.entry_type == 1 {
-            // Directory entry: create and set permissions
-            fs::create_dir_all(&output_path)?;
-            fs::set_permissions(
-                &output_path,
-                fs::Permissions::from_mode(entry.permissions as u32),
-            )?;
-            println!("Created directory: {}", entry.name);
-            success_count += 1;
-            continue;
-        }
-
-        // File entry: extract with full verification pipeline
-
-        // Create parent directories if name contains path separators
-        if let Some(parent) = output_path.parent() {
-            fs::create_dir_all(parent)?;
-        }
-
-        // Seek to data_offset and read ciphertext
+            read_entries.push(ReadEntry::Dir {
+                name: entry.name.clone(),
+                permissions: entry.permissions,
+            });
+        } else {
+            // Seek to data_offset and read ciphertext into memory
             file.seek(SeekFrom::Start(entry.data_offset as u64))?;
             let mut ciphertext = vec![0u8; entry.encrypted_size as usize];
             file.read_exact(&mut ciphertext)?;
 
+            read_entries.push(ReadEntry::File {
+                entry,
+                ciphertext,
+            });
+        }
+    }
+
+    // --- Phase 2: Create directories sequentially (parent-before-child order) ---
+    let mut dir_count: usize = 0;
+    for re in &read_entries {
+        if let ReadEntry::Dir { name, permissions } = re {
+            let output_path = output_dir.join(name);
+            fs::create_dir_all(&output_path)?;
+            fs::set_permissions(
+                &output_path,
+                fs::Permissions::from_mode(*permissions as u32),
+            )?;
+            println!("Created directory: {}", name);
+            dir_count += 1;
+        }
+    }
+
+    // --- Phase 3: Process and write files in parallel ---
+    // Count skipped entries from phase 1
+    let skipped_count = read_entries.iter()
+        .filter(|re| matches!(re, ReadEntry::Skipped { .. }))
+        .count();
+
+    // Collect only file entries for parallel processing
+    let file_entries: Vec<(&TocEntry, &Vec<u8>)> = read_entries.iter()
+        .filter_map(|re| {
+            if let ReadEntry::File { entry, ciphertext } = re {
+                Some((entry, ciphertext))
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    // Process all files in parallel: HMAC verify, decrypt, decompress, SHA-256, write
+    let results: Vec<UnpackResult> = file_entries
+        .par_iter()
+        .map(|(entry, ciphertext)| {
+            let output_path = output_dir.join(&entry.name);
+
+            // Create parent directories if name contains path separators
+            if let Some(parent) = output_path.parent() {
+                if let Err(e) = fs::create_dir_all(parent) {
+                    return UnpackResult::Error {
+                        name: entry.name.clone(),
+                        message: format!("Failed to create parent directory: {}", e),
+                    };
+                }
+            }
+
             // Step 1: Verify HMAC FIRST (encrypt-then-MAC)
-        if !crypto::verify_hmac(&KEY, &entry.iv, &ciphertext, &entry.hmac) {
-            eprintln!("HMAC verification failed for {}, skipping", entry.name);
-            error_count += 1;
-            continue;
+            if !crypto::verify_hmac(&KEY, &entry.iv, ciphertext, &entry.hmac) {
+                return UnpackResult::Error {
+                    name: entry.name.clone(),
+                    message: "HMAC verification failed".to_string(),
+                };
             }
 
             // Step 2: Decrypt
-        let decrypted = match crypto::decrypt_data(&ciphertext, &KEY, &entry.iv) {
+            let decrypted = match crypto::decrypt_data(ciphertext, &KEY, &entry.iv) {
                 Ok(data) => data,
                 Err(e) => {
-                eprintln!("Decryption failed for {}: {}", entry.name, e);
-                error_count += 1;
-                continue;
+                    return UnpackResult::Error {
+                        name: entry.name.clone(),
+                        message: format!("Decryption failed: {}", e),
+                    };
                 }
             };
 
@@ -540,9 +671,10 @@ pub fn unpack(archive: &Path, output_dir: &Path) -> anyhow::Result<()> {
                 match compression::decompress(&decrypted) {
                     Ok(data) => data,
                     Err(e) => {
-                    eprintln!("Decompression failed for {}: {}", entry.name, e);
-                    error_count += 1;
-                    continue;
+                        return UnpackResult::Error {
+                            name: entry.name.clone(),
+                            message: format!("Decompression failed: {}", e),
+                        };
                     }
                 }
             } else {
@@ -551,35 +683,73 @@ pub fn unpack(archive: &Path, output_dir: &Path) -> anyhow::Result<()> {
 
             // Step 4: Verify SHA-256
             let computed_sha256 = crypto::sha256_hash(&decompressed);
-        if computed_sha256 != entry.sha256 {
-            eprintln!(
-                "SHA-256 mismatch for {} (data may be corrupted)",
-                entry.name
-            );
-            error_count += 1;
-            // Still write the file per spec
+            let sha256_ok = computed_sha256 == entry.sha256;
+
+            // Step 5: Write file (even if SHA-256 mismatch, per spec)
+            if let Err(e) = fs::write(&output_path, &decompressed) {
+                return UnpackResult::Error {
+                    name: entry.name.clone(),
+                    message: format!("Write failed: {}", e),
+                };
             }
 
-        // Step 5: Write file
-        fs::write(&output_path, &decompressed)?;
-
             // Step 6: Set file permissions
-        fs::set_permissions(
+            if let Err(e) = fs::set_permissions(
                 &output_path,
                 fs::Permissions::from_mode(entry.permissions as u32),
-        )?;
+            ) {
+                return UnpackResult::Error {
+                    name: entry.name.clone(),
+                    message: format!("Failed to set permissions: {}", e),
+                };
+            }
 
-        println!("Extracted: {} ({} bytes)", entry.name, entry.original_size);
-        success_count += 1;
+            if sha256_ok {
+                UnpackResult::Ok {
+                    name: entry.name.clone(),
+                    original_size: entry.original_size,
+                }
+            } else {
+                UnpackResult::Written {
+                    name: entry.name.clone(),
+                    original_size: entry.original_size,
+                }
+            }
+        })
+        .collect();
+
+    // --- Phase 4: Report results (sequential for deterministic output) ---
+    let mut final_error_count = skipped_count;
+    let mut final_success_count = dir_count;
+
+    for result in &results {
+        match result {
+            UnpackResult::Ok { name, original_size } => {
+                println!("Extracted: {} ({} bytes)", name, original_size);
+                final_success_count += 1;
+            }
+            UnpackResult::Written { name, original_size } => {
+                eprintln!("SHA-256 mismatch for {} (data may be corrupted)", name);
+                println!("Extracted: {} ({} bytes)", name, original_size);
+                final_error_count += 1;
+                // Original code increments both error_count AND success_count for
+                // SHA-256 mismatch (file is still written and counted as extracted).
+                final_success_count += 1;
+            }
+            UnpackResult::Error { name, message } => {
+                eprintln!("{} for {}, skipping", message, name);
+                final_error_count += 1;
+            }
+        }
     }
 
     println!(
         "Extracted {}/{} entries",
-        success_count, entry_count
+        final_success_count, entry_count
     );
 
-    if error_count > 0 {
-        anyhow::bail!("{} entry(ies) had verification errors", error_count);
+    if final_error_count > 0 {
+        anyhow::bail!("{} entry(ies) had verification errors", final_error_count);
     }
 
     Ok(())