exarch-core 0.7.0

//! Security configuration for archive extraction.

use std::marker::PhantomData;
use std::num::NonZeroU64;
use std::ops::Deref;
use std::ops::DerefMut;

use crate::closed_enum::closed_enum;

/// Marker type for a [`SecurityConfig`] whose invariants have not yet been
/// checked.
///
/// This is the default type parameter for [`SecurityConfig`]. The fluent
/// `with_*` builder methods and [`SecurityConfig::validate`] are only
/// available in this state.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct Unvalidated;

/// Marker type for a [`SecurityConfig`] whose invariants have been checked.
///
/// Reachable only through [`SecurityConfig::validate`]. Every entry point
/// that performs security-sensitive work — the
/// [`ArchiveFormat`](crate::formats::traits::ArchiveFormat) trait and
/// everything it calls — requires a `SecurityConfig<Validated>`, so an
/// unvalidated configuration (e.g. one with `max_file_size == 0`) can never
/// reach extraction, listing, or verification. The compiler enforces this;
/// it is not a convention callers must remember to follow.
///
/// Once validated, a config's fields can still be *read* (via [`Deref`]) but
/// no longer *written*: [`DerefMut`] is implemented only for
/// `SecurityConfig<Unvalidated>`, so `cfg.max_compression_ratio = f64::NAN`
/// on a `SecurityConfig<Validated>` is a compile error, not a runtime
/// invariant violation. This is what makes the typestate airtight — without
/// it, a caller could validate a config and then mutate it back into an
/// invalid state before passing it to `ArchiveFormat::extract`.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct Validated;

/// Feature flags controlling what archive features are allowed during
/// extraction.
///
/// All features default to `false` (deny-by-default security policy).
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
#[non_exhaustive]
pub struct AllowedFeatures {
    /// Allow symlinks in extracted archives.
    pub symlinks: bool,

    /// Allow hardlinks in extracted archives.
    pub hardlinks: bool,

    /// Allow absolute paths in archive entries.
    pub absolute_paths: bool,

    /// Allow world-writable files (mode 0o002).
    ///
    /// World-writable files pose security risks in multi-user environments.
    pub world_writable: bool,

    /// Allow Windows reserved device names (`CON`, `NUL`, `COM1`, ...) as path
    /// components.
    ///
    /// Only consulted when extracting on Windows; has no effect elsewhere.
    /// There is no CLI or binding opt-out, and the permissive preset does not
    /// enable it.
    pub windows_reserved_names: bool,
}

closed_enum! {
    /// How ZIP structure that different readers interpret differently is
    /// handled.
    ///
    /// A ZIP archive stores each entry's metadata twice, in a local header and
    /// in the central directory. Random-access readers follow the central
    /// directory and streaming readers follow the local headers, so an
    /// archive whose copies disagree, that hides records, repeats a name or
    /// overlaps entries is a parser differential ("Zip Cloaking").
    ///
    /// `Enforce` (the default, also for [`SecurityConfig::permissive`])
    /// rejects such archives in `extract` and `list` and reports them in
    /// `verify`. `Ignore` keeps the central-directory interpretation and
    /// raises no structural finding; resource limits still apply.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    /// use exarch_core::ZipConsistencyPolicy;
    ///
    /// assert_eq!(
    ///     SecurityConfig::default().zip_consistency,
    ///     ZipConsistencyPolicy::Enforce
    /// );
    /// let relaxed = SecurityConfig::default().with_zip_consistency(ZipConsistencyPolicy::Ignore);
    /// assert_eq!(relaxed.zip_consistency.as_str(), "ignore");
    /// ```
    #[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
    #[non_exhaustive]
    pub enum ZipConsistencyPolicy {
        /// Reject or report structurally ambiguous ZIP archives
        #[default]
        Enforce => "enforce",

        /// Use the central directory interpretation without structural findings
        Ignore => "ignore",
    }
}

/// How much extra memory a 7z block may use to decode LZMA2 runs ahead on
/// worker threads.
///
/// An LZMA2 stream written with multiple threads (7-Zip's default for large
/// inputs) consists of independent runs, so several can be decoded at once.
/// Decoded runs wait in memory until the consumer reaches them, so the
/// lookahead is bounded: `Bounded(n)` lets in-flight runs hold at most `n`
/// bytes on top of the decoder window that
/// [`max_decoder_memory`](SecurityConfigFields::max_decoder_memory) already
/// admits. `Sequential` decodes on the calling thread only.
///
/// Archives written with runs of a few MiB decode within about 10% of an
/// unbounded multi-threaded reader at the default; a stock 7-Zip archive has
/// 64 MiB runs and needs about 100 MiB of lookahead
/// per extra concurrent run.
///
/// A valid archive decodes to the same bytes in either mode, and a corrupt one
/// fails the same file with the same error kind; only how many leading bytes
/// that file received can differ.
///
/// # Concurrency
///
/// The limit applies to one extraction or verification. Each call may start
/// up to 16 worker threads and hold its own lookahead, so concurrent calls
/// (for example from several Python threads or Node promises) multiply both
/// the threads and the memory. Size the setting for the number of calls that
/// can run at once, or use `Sequential`.
///
/// # Examples
///
/// ```
/// use std::num::NonZeroU64;
///
/// use exarch_core::ParallelDecode;
/// use exarch_core::SecurityConfig;
///
/// assert_eq!(
///     SecurityConfig::default().parallel_decode,
///     ParallelDecode::Bounded(NonZeroU64::new(128 * 1024 * 1024).unwrap())
/// );
/// let config = SecurityConfig::default().with_parallel_decode(ParallelDecode::Sequential);
/// assert_eq!(config.parallel_decode, ParallelDecode::Sequential);
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[non_exhaustive]
pub enum ParallelDecode {
    /// Decode on the calling thread only
    Sequential,

    /// Decode runs ahead on worker threads, holding at most this many bytes
    Bounded(NonZeroU64),
}

/// Builds a non-zero constant; a zero literal fails compilation.
const fn non_zero(n: u64) -> NonZeroU64 {
    match NonZeroU64::new(n) {
        Some(n) => n,
        None => panic!("constant must be non-zero"),
    }
}

impl ParallelDecode {
    /// Default lookahead: 128 MiB.
    pub const DEFAULT_BYTES: NonZeroU64 = non_zero(128 * 1024 * 1024);

    /// The lookahead memory in bytes, or `None` for [`Sequential`].
    ///
    /// [`Sequential`]: ParallelDecode::Sequential
    ///
    /// # Examples
    ///
    /// ```
    /// use std::num::NonZeroU64;
    ///
    /// use exarch_core::ParallelDecode;
    ///
    /// assert_eq!(ParallelDecode::Sequential.lookahead(), None);
    /// let bytes = NonZeroU64::new(1 << 20).unwrap();
    /// assert_eq!(ParallelDecode::Bounded(bytes).lookahead(), Some(bytes));
    /// ```
    #[must_use]
    pub const fn lookahead(self) -> Option<NonZeroU64> {
        match self {
            Self::Sequential => None,
            Self::Bounded(bytes) => Some(bytes),
        }
    }
}

impl From<Option<NonZeroU64>> for ParallelDecode {
    /// `None` is [`ParallelDecode::Sequential`].
    fn from(lookahead: Option<NonZeroU64>) -> Self {
        lookahead.map_or(Self::Sequential, Self::Bounded)
    }
}

impl Default for ParallelDecode {
    fn default() -> Self {
        Self::Bounded(Self::DEFAULT_BYTES)
    }
}

/// The field data of a [`SecurityConfig`], reachable via [`Deref`]/[`DerefMut`]
/// regardless of (or gated by) validation state.
///
/// This type is not itself part of the sealing boundary — it is a plain data
/// bag with `pub` fields, and nothing stops external code from naming it or
/// cloning one out of a `&SecurityConfig`. The boundary is
/// [`SecurityConfig`]'s own private `fields` member: there is no public API
/// that takes a bare `SecurityConfigFields` and wraps it back into a
/// `SecurityConfig<Validated>`, so an externally-forged or externally-mutated
/// `SecurityConfigFields` value can never be smuggled into a `Validated`
/// config. It exists purely so [`SecurityConfig`] can implement `Deref`/
/// `DerefMut` and keep `cfg.max_file_size`-style field access working for
/// every existing caller instead of forcing a getter-method migration.
#[derive(Debug, Clone)]
#[non_exhaustive]
pub struct SecurityConfigFields {
    /// Maximum size for a single file in bytes.
    pub max_file_size: u64,

    /// Maximum total size for all extracted files in bytes.
    pub max_total_size: u64,

    /// Maximum compression ratio allowed (uncompressed / compressed).
    pub max_compression_ratio: f64,

    /// Maximum compression ratio of a whole solid 7z block (summed
    /// uncompressed size of its files / compressed size of its pack streams).
    ///
    /// Solid members share one compressed stream, so no per-file ratio exists;
    /// this limit replaces `max_compression_ratio` for them. It is not exposed
    /// by the CLI or the Python/Node bindings.
    pub max_solid_compression_ratio: f64,

    /// Maximum number of entries that can be extracted.
    ///
    /// The extraction API counts files, symlinks and hardlinks, not
    /// directories. `list` and `verify`, and the CLI's `extract` (which lists
    /// the archive first), count every entry.
    pub max_file_count: usize,

    /// Maximum path depth allowed.
    pub max_path_depth: usize,

    /// Feature flags controlling what archive features are allowed.
    ///
    /// Use this to enable symlinks, hardlinks, absolute paths, etc.
    pub allowed: AllowedFeatures,

    /// Preserve file permissions from archive.
    pub preserve_permissions: bool,

    /// List of allowed file extensions (empty = allow all).
    ///
    /// Extensions are matched case-insensitively (e.g., `"txt"` matches both
    /// `file.txt` and `file.TXT`). The leading dot must be omitted.
    ///
    /// When this list is non-empty, files without a file extension are treated
    /// as not allowed and will be skipped during extraction.
    pub allowed_extensions: Vec<String>,

    /// List of banned path components (e.g., ".git", ".ssh").
    pub banned_path_components: Vec<String>,

    /// Allow extraction from solid 7z archives.
    ///
    /// Solid archives compress multiple files together as a single block.
    /// While this provides better compression ratios, it has security
    /// implications:
    ///
    /// - **Memory exhaustion**: Extracting a single file requires decompressing
    ///   the entire solid block into memory
    /// - **Denial of service**: Malicious archives can create large solid
    ///   blocks that exhaust available memory
    ///
    /// **Security Recommendation**: Only enable for trusted archives.
    ///
    /// Default: `false` (solid archives rejected)
    pub allow_solid_archives: bool,

    /// Maximum memory for solid archive extraction (bytes).
    ///
    /// **7z Solid Archive Memory Model:**
    ///
    /// Solid compression in 7z stores multiple files in a single compressed
    /// block. Extracting ANY file requires decompressing the ENTIRE solid block
    /// into memory, which can cause memory exhaustion attacks.
    ///
    /// **Validation Strategy:**
    /// - Pre-validates total uncompressed size of all files in archive
    /// - This is a conservative heuristic (assumes single solid block)
    /// - Reason: `sevenz-rust2` v0.20 doesn't expose solid block boundaries
    ///
    /// **Security Guarantee:**
    /// - Total uncompressed data cannot exceed this limit
    /// - Combined with `max_file_size`, prevents unbounded memory growth
    /// - Enforced ONLY when `allow_solid_archives` is `true`
    ///
    /// **Note**: Only applies when `allow_solid_archives` is `true`.
    ///
    /// Default: 512 MB (536,870,912 bytes)
    ///
    /// **Recommendation:** Set to 1-2x available RAM for trusted archives only.
    pub max_solid_block_memory: u64,

    /// Maximum bytes the TAR reader may consume for headers and metadata
    /// records in the gap between two consecutive entries.
    ///
    /// **TAR Metadata Buffering Model:**
    ///
    /// GNU long-name (`L`), GNU long-link (`K`), and PAX extended header
    /// (`x`/`g`) records are buffered fully into memory by the underlying
    /// `tar` crate *before* any entry reaches the entry validator or quota
    /// tracker — a crafted record can declare a multi-gigabyte length backed
    /// by a tiny compressed stream, exhausting memory with no quota
    /// enforcement (metadata-entry decompression bomb).
    ///
    /// **Enforcement Strategy:**
    /// - A read-budget wrapper meters bytes the `tar` crate reads while
    ///   searching for the next entry (headers, long-name/long-link/PAX
    ///   records, GNU sparse extension blocks) and returns an error once
    ///   `max_tar_metadata_bytes` is exceeded, before any oversized allocation
    ///   completes
    /// - Applies uniformly to `extract`, `list`, and `verify`
    /// - The window this bounds contains no entry *data* — only metadata — so
    ///   it does not interact with `max_file_size`/`max_total_size`. Draining
    ///   an unread entry before the next header search is a separate concern
    ///   (see `formats::tar_metadata_limit`'s module docs) bounded by
    ///   synthesized-byte accounting, not by this or any other quota value
    /// - Legitimate long-path/xattr metadata records are at most a few
    ///   kilobytes each, and a GNU tar sparse file with heavy fragmentation can
    ///   use up to a few thousand 512-byte extension blocks; either or both
    ///   share this single budget (not "plus" each other), so the default
    ///   leaves headroom for either shape, not necessarily both at their
    ///   extremes simultaneously
    /// - The real peak memory this bounds is roughly 5x the configured value
    ///   (GNU sparse extension blocks expand into multiple `EntryIo` records
    ///   per block before the growth is charged against this budget), not an
    ///   exact multiple — treat it as an order-of-magnitude ceiling, not a
    ///   tight bound
    ///
    /// Default: 4 MiB (4,194,304 bytes)
    pub max_tar_metadata_bytes: u64,

    /// Maximum memory in bytes an xz decoder may use (dictionary and state).
    ///
    /// The xz block header declares the LZMA2 dictionary size (up to 4 GiB),
    /// so without a limit a tiny archive can drive resident memory far beyond
    /// what the output quotas allow. Archives that need more fail with
    /// `QuotaExceeded { DecoderMemory }`. Applies to `extract`, `list` and
    /// `verify` of `.tar.xz`. Other codecs are bounded by their format
    /// (bzip2 blocks of at most 900 KB; zstd windows above 128 MiB are
    /// rejected) and are not governed by this value. Not exposed through the
    /// CLI or language bindings. Also admits the 7z decoder window; the
    /// lookahead of parallel 7z decoding is budgeted separately by
    /// [`parallel_decode`](Self::parallel_decode).
    ///
    /// Default: 256 MiB (268,435,456 bytes)
    pub max_decoder_memory: u64,

    /// Lookahead memory for decoding independent LZMA2 runs of a 7z block on
    /// worker threads.
    ///
    /// Applies to `extract` and `verify` with integrity checking of 7z
    /// archives. It is separate from `max_decoder_memory`, which keeps
    /// bounding the decoder window. See [`ParallelDecode`].
    ///
    /// Default: `Bounded` at 128 MiB (1 GiB for [`SecurityConfig::permissive`])
    pub parallel_decode: ParallelDecode,

    /// How ZIP archives with ambiguous structure are handled.
    ///
    /// Default: [`ZipConsistencyPolicy::Enforce`], including for
    /// [`SecurityConfig::permissive`]. Pre-ZIP64 archives with more than
    /// 65535 entries (wrapped end-record count) and archives with orphaned
    /// local headers, or with a central directory signature in a gap before an
    /// entry (left by in-place updaters), are rejected under `Enforce`.
    pub zip_consistency: ZipConsistencyPolicy,
}

impl Default for SecurityConfigFields {
    fn default() -> Self {
        Self {
            max_file_size: 50 * 1024 * 1024,   // 50 MB
            max_total_size: 500 * 1024 * 1024, // 500 MB
            max_compression_ratio: 100.0,
            max_solid_compression_ratio: 1000.0,
            max_file_count: 10_000,
            max_path_depth: 32,
            allowed: AllowedFeatures::default(), // All false
            preserve_permissions: false,
            allowed_extensions: Vec::new(),
            banned_path_components: vec![
                ".git".to_string(),
                ".ssh".to_string(),
                ".gnupg".to_string(),
                ".aws".to_string(),
                ".kube".to_string(),
                ".docker".to_string(),
                ".env".to_string(),
            ],
            allow_solid_archives: false,
            max_solid_block_memory: 512 * 1024 * 1024, // 512 MB
            max_tar_metadata_bytes: 4 * 1024 * 1024,   // 4 MiB
            max_decoder_memory: 256 * 1024 * 1024,     // 256 MiB
            parallel_decode: ParallelDecode::Bounded(ParallelDecode::DEFAULT_BYTES),
            zip_consistency: ZipConsistencyPolicy::Enforce,
        }
    }
}

/// Security configuration with default-deny settings.
///
/// This configuration controls various security checks performed during
/// archive extraction to prevent common vulnerabilities.
///
/// # Performance Note
///
/// This struct contains heap-allocated collections (`Vec<String>`). For
/// performance, pass by reference (`&SecurityConfig`) rather than cloning. If
/// shared ownership is needed across threads, consider wrapping in
/// `Arc<SecurityConfig>`.
///
/// # Examples
///
/// ```
/// use exarch_core::SecurityConfig;
///
/// // Use secure defaults
/// let config = SecurityConfig::default();
///
/// // Customize via fluent builder
/// let custom = SecurityConfig::default()
///     .with_max_file_size(100 * 1024 * 1024)
///     .with_max_total_size(1024 * 1024 * 1024)
///     .with_allow_symlinks(true);
/// ```
///
/// # Typestate
///
/// `SecurityConfig` carries a phantom `State` type parameter — [`Unvalidated`]
/// (the default) or [`Validated`] — that tracks whether
/// [`validate`](SecurityConfig::validate) has been called. Builder methods
/// are only available in the `Unvalidated` state; security-sensitive APIs
/// (the [`ArchiveFormat`](crate::formats::traits::ArchiveFormat) trait and
/// everything downstream of it) require `SecurityConfig<Validated>`. This
/// makes skipping validation a compile error instead of a runtime gap.
///
/// # Sealing
///
/// Fields are private and reachable only through
/// <code>[Deref]<Target = [SecurityConfigFields]></code>, so
/// `cfg.max_file_size` continues to work as plain field access for both states.
/// [`DerefMut`] is implemented only for
/// `SecurityConfig<Unvalidated>`, so a `SecurityConfig<Validated>`'s fields
/// cannot be reassigned after the fact — the only way to produce one is
/// [`validate`](SecurityConfig::validate) itself, and it stays that way for
/// its entire lifetime.
#[derive(Debug, Clone)]
pub struct SecurityConfig<State = Unvalidated> {
    fields: SecurityConfigFields,

    /// Typestate marker — see the "Typestate" section on the type-level docs.
    _marker: PhantomData<State>,
}

impl<State> Deref for SecurityConfig<State> {
    type Target = SecurityConfigFields;

    #[inline]
    fn deref(&self) -> &SecurityConfigFields {
        &self.fields
    }
}

/// Only `Unvalidated` configs are mutable — see the "Sealing" section on
/// [`SecurityConfig`]'s type-level docs for why this is the crux of the
/// typestate guarantee.
impl DerefMut for SecurityConfig<Unvalidated> {
    fn deref_mut(&mut self) -> &mut SecurityConfigFields {
        &mut self.fields
    }
}

impl Default for SecurityConfig<Unvalidated> {
    /// Creates a `SecurityConfig` with secure default settings.
    ///
    /// Default values:
    /// - `max_file_size`: 50 MB
    /// - `max_total_size`: 500 MB
    /// - `max_compression_ratio`: 100.0
    /// - `max_solid_compression_ratio`: 1000.0
    /// - `max_file_count`: 10,000
    /// - `max_path_depth`: 32
    /// - `allowed`: All features disabled (deny-by-default)
    /// - `preserve_permissions`: false
    /// - `allowed_extensions`: empty (allow all)
    /// - `banned_path_components`: `[".git", ".ssh", ".gnupg", ".aws", ".kube",
    ///   ".docker", ".env"]`
    /// - `allow_solid_archives`: false (solid archives rejected)
    /// - `max_solid_block_memory`: 512 MB
    /// - `max_tar_metadata_bytes`: 4 MiB
    /// - `max_decoder_memory`: 256 MiB
    /// - `parallel_decode`: `Bounded` at 128 MiB
    /// - `zip_consistency`: `Enforce`
    fn default() -> Self {
        Self {
            fields: SecurityConfigFields::default(),
            _marker: PhantomData,
        }
    }
}

/// Lookahead memory of [`SecurityConfig::permissive`]: 1 GiB.
const PERMISSIVE_PARALLEL_DECODE: NonZeroU64 = non_zero(1024 * 1024 * 1024);

impl SecurityConfig<Unvalidated> {
    /// Creates a permissive configuration for trusted archives.
    ///
    /// This configuration allows symlinks, hardlinks, absolute paths, and
    /// solid archives. Use only when extracting archives from trusted sources.
    #[must_use]
    pub fn permissive() -> Self {
        Self {
            fields: SecurityConfigFields {
                allowed: AllowedFeatures {
                    symlinks: true,
                    hardlinks: true,
                    absolute_paths: true,
                    world_writable: true,
                    windows_reserved_names: false,
                },
                preserve_permissions: true,
                max_compression_ratio: 1000.0,
                max_solid_compression_ratio: 10_000.0,
                banned_path_components: Vec::new(),
                allow_solid_archives: true,
                max_solid_block_memory: 1024 * 1024 * 1024, // 1 GB for permissive
                max_tar_metadata_bytes: 16 * 1024 * 1024,   // 16 MiB for permissive
                max_decoder_memory: 1024 * 1024 * 1024,     // 1 GiB for permissive
                parallel_decode: ParallelDecode::Bounded(PERMISSIVE_PARALLEL_DECODE),
                ..SecurityConfigFields::default()
            },
            _marker: PhantomData,
        }
    }

    /// Validates that the configuration values are logically consistent,
    /// transitioning to the [`Validated`] typestate on success.
    ///
    /// Returns an error if any field has a value that would make security
    /// enforcement impossible (zero limits or non-positive ratio). Consumes
    /// `self`: the only way to obtain a `SecurityConfig<Validated>`, which is
    /// what every security-sensitive API in this crate requires. Once
    /// returned, the `Validated` config's fields can no longer be reassigned
    /// (see the "Sealing" section on the type-level docs), so this check can
    /// never be silently invalidated afterward.
    ///
    /// # Errors
    ///
    /// Returns `ArchiveError::InvalidConfiguration` if:
    /// - `max_compression_ratio` or `max_solid_compression_ratio` is not
    ///   positive and finite
    /// - `max_file_size` is zero
    /// - `max_total_size` is zero
    /// - `max_path_depth` is zero
    /// - `max_file_count` is zero
    /// - `max_solid_block_memory` is zero
    /// - `max_tar_metadata_bytes` is zero
    /// - `max_decoder_memory` is zero
    /// - any entry in `allowed_extensions` or `banned_path_components` is
    ///   empty, contains a null byte, or exceeds
    ///   [`crate::MAX_CONFIG_ENTRY_LENGTH`] bytes
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default();
    /// assert!(config.validate().is_ok());
    ///
    /// let bad = SecurityConfig::default().with_max_file_size(0);
    /// assert!(bad.validate().is_err());
    /// ```
    pub fn validate(self) -> crate::Result<SecurityConfig<Validated>> {
        if !self.max_compression_ratio.is_finite() || self.max_compression_ratio <= 0.0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_compression_ratio must be positive".into(),
            });
        }
        if !self.max_solid_compression_ratio.is_finite() || self.max_solid_compression_ratio <= 0.0
        {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_solid_compression_ratio must be positive".into(),
            });
        }
        if self.max_file_size == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_file_size must not be zero".into(),
            });
        }
        if self.max_total_size == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_total_size must not be zero".into(),
            });
        }
        if self.max_path_depth == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_path_depth must not be zero".into(),
            });
        }
        if self.max_file_count == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_file_count must not be zero".into(),
            });
        }
        if self.max_solid_block_memory == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_solid_block_memory must not be zero".into(),
            });
        }
        if self.max_tar_metadata_bytes == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_tar_metadata_bytes must not be zero".into(),
            });
        }
        if self.max_decoder_memory == 0 {
            return Err(crate::ArchiveError::InvalidConfiguration {
                reason: "max_decoder_memory must not be zero".into(),
            });
        }
        for extension in &self.fields.allowed_extensions {
            crate::security::boundary::validate_config_entry(extension, "allowed extension")?;
        }
        for component in &self.fields.banned_path_components {
            crate::security::boundary::validate_config_entry(component, "banned path component")?;
        }
        Ok(SecurityConfig {
            fields: self.fields,
            _marker: PhantomData,
        })
    }

    /// Sets the maximum size for a single extracted file in bytes.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_file_size(100 * 1024 * 1024);
    /// assert_eq!(config.max_file_size, 100 * 1024 * 1024);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_file_size(mut self, size: u64) -> Self {
        self.fields.max_file_size = size;
        self
    }

    /// Sets the maximum total size for all extracted files in bytes.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_total_size(1024 * 1024 * 1024);
    /// assert_eq!(config.max_total_size, 1024 * 1024 * 1024);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_total_size(mut self, size: u64) -> Self {
        self.fields.max_total_size = size;
        self
    }

    /// Sets the maximum allowed compression ratio (uncompressed / compressed).
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_compression_ratio(50.0);
    /// assert_eq!(config.max_compression_ratio, 50.0);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_compression_ratio(mut self, ratio: f64) -> Self {
        self.fields.max_compression_ratio = ratio;
        self
    }

    /// Sets the maximum compression ratio of a whole solid 7z block.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_solid_compression_ratio(5000.0);
    /// assert_eq!(config.max_solid_compression_ratio, 5000.0);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_solid_compression_ratio(mut self, ratio: f64) -> Self {
        self.fields.max_solid_compression_ratio = ratio;
        self
    }

    /// Sets the maximum number of files that can be extracted.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_file_count(500);
    /// assert_eq!(config.max_file_count, 500);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_file_count(mut self, count: usize) -> Self {
        self.fields.max_file_count = count;
        self
    }

    /// Sets the maximum path depth allowed.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_path_depth(16);
    /// assert_eq!(config.max_path_depth, 16);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_path_depth(mut self, depth: usize) -> Self {
        self.fields.max_path_depth = depth;
        self
    }

    /// Sets the feature flags controlling allowed archive features.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    /// use exarch_core::config::AllowedFeatures;
    ///
    /// let features = AllowedFeatures::default();
    /// let config = SecurityConfig::default().with_allowed(features);
    /// assert!(!config.allowed.symlinks);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allowed(mut self, allowed: AllowedFeatures) -> Self {
        self.fields.allowed = allowed;
        self
    }

    /// Enables or disables symlinks in extracted archives.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_symlinks(true);
    /// assert!(config.allowed.symlinks);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_symlinks(mut self, allow: bool) -> Self {
        self.fields.allowed.symlinks = allow;
        self
    }

    /// Enables or disables hardlinks in extracted archives.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_hardlinks(true);
    /// assert!(config.allowed.hardlinks);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_hardlinks(mut self, allow: bool) -> Self {
        self.fields.allowed.hardlinks = allow;
        self
    }

    /// Enables or disables absolute paths in archive entries.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_absolute_paths(true);
    /// assert!(config.allowed.absolute_paths);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_absolute_paths(mut self, allow: bool) -> Self {
        self.fields.allowed.absolute_paths = allow;
        self
    }

    /// Enables or disables world-writable files.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_world_writable(true);
    /// assert!(config.allowed.world_writable);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_world_writable(mut self, allow: bool) -> Self {
        self.fields.allowed.world_writable = allow;
        self
    }

    /// Enables or disables Windows reserved device names (`CON`, `NUL`,
    /// `COM1`, ...) as path components. Only consulted on Windows.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_windows_reserved_names(true);
    /// assert!(config.allowed.windows_reserved_names);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_windows_reserved_names(mut self, allow: bool) -> Self {
        self.fields.allowed.windows_reserved_names = allow;
        self
    }

    /// Enables or disables preserving file permissions from the archive.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_preserve_permissions(true);
    /// assert!(config.preserve_permissions);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_preserve_permissions(mut self, preserve: bool) -> Self {
        self.fields.preserve_permissions = preserve;
        self
    }

    /// Sets the list of allowed file extensions.
    ///
    /// An empty list allows all extensions.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default()
    ///     .with_allowed_extensions(vec!["txt".to_string(), "pdf".to_string()]);
    /// assert!(config.is_extension_allowed("txt"));
    /// assert!(!config.is_extension_allowed("exe"));
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allowed_extensions(mut self, extensions: Vec<String>) -> Self {
        self.fields.allowed_extensions = extensions;
        self
    }

    /// Sets the list of banned path components.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_banned_path_components(vec![".git".to_string()]);
    /// assert!(!config.is_path_component_allowed(".git"));
    /// assert!(config.is_path_component_allowed(".ssh"));
    /// ```
    #[must_use]
    #[inline]
    pub fn with_banned_path_components(mut self, components: Vec<String>) -> Self {
        self.fields.banned_path_components = components;
        self
    }

    /// Enables or disables extraction from solid 7z archives.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allow_solid_archives(true);
    /// assert!(config.allow_solid_archives);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_allow_solid_archives(mut self, allow: bool) -> Self {
        self.fields.allow_solid_archives = allow;
        self
    }

    /// Sets the maximum memory for solid archive extraction in bytes.
    ///
    /// Only applies when `allow_solid_archives` is `true`.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default()
    ///     .with_allow_solid_archives(true)
    ///     .with_max_solid_block_memory(1024 * 1024 * 1024);
    /// assert_eq!(config.max_solid_block_memory, 1024 * 1024 * 1024);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_solid_block_memory(mut self, size: u64) -> Self {
        self.fields.max_solid_block_memory = size;
        self
    }

    /// Sets the maximum bytes the TAR reader may consume for headers and
    /// metadata records (GNU long-name/long-link, PAX extended headers, GNU
    /// sparse extension blocks) in the gap between two consecutive entries.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_tar_metadata_bytes(64 * 1024);
    /// assert_eq!(config.max_tar_metadata_bytes, 64 * 1024);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_tar_metadata_bytes(mut self, size: u64) -> Self {
        self.fields.max_tar_metadata_bytes = size;
        self
    }

    /// Sets the maximum memory an xz decoder may use, in bytes.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_max_decoder_memory(64 * 1024 * 1024);
    /// assert_eq!(config.max_decoder_memory, 64 * 1024 * 1024);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_max_decoder_memory(mut self, size: u64) -> Self {
        self.fields.max_decoder_memory = size;
        self
    }

    /// Sets the lookahead memory for parallel 7z LZMA2 decoding.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::ParallelDecode;
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_parallel_decode(ParallelDecode::Sequential);
    /// assert_eq!(config.parallel_decode, ParallelDecode::Sequential);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_parallel_decode(mut self, mode: ParallelDecode) -> Self {
        self.fields.parallel_decode = mode;
        self
    }

    /// Sets how ZIP archives with ambiguous structure are handled.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    /// use exarch_core::ZipConsistencyPolicy;
    ///
    /// let config = SecurityConfig::default().with_zip_consistency(ZipConsistencyPolicy::Ignore);
    /// assert_eq!(config.zip_consistency, ZipConsistencyPolicy::Ignore);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_zip_consistency(mut self, policy: ZipConsistencyPolicy) -> Self {
        self.fields.zip_consistency = policy;
        self
    }
}

/// Read-only queries and crate-internal helpers available regardless of
/// validation state.
impl<State> SecurityConfig<State> {
    /// Validates whether a path component is allowed.
    ///
    /// Comparison is case-insensitive to prevent bypass on case-insensitive
    /// filesystems (Windows, macOS default).
    #[must_use]
    pub fn is_path_component_allowed(&self, component: &str) -> bool {
        !self
            .banned_path_components
            .iter()
            .any(|banned| banned.eq_ignore_ascii_case(component))
    }

    /// Validates whether a file extension is allowed.
    ///
    /// When `allowed_extensions` is empty, all extensions are permitted.
    /// When it is non-empty, only listed extensions are permitted.
    #[must_use]
    pub fn is_extension_allowed(&self, extension: &str) -> bool {
        if self.allowed_extensions.is_empty() {
            return true;
        }
        self.allowed_extensions
            .iter()
            .any(|ext| ext.eq_ignore_ascii_case(extension))
    }

    /// Returns `true` if a file with the given optional extension may be
    /// extracted.
    ///
    /// When `allowed_extensions` is non-empty and `extension` is `None`
    /// (the file has no extension), the file is treated as not allowed.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::SecurityConfig;
    ///
    /// let config = SecurityConfig::default().with_allowed_extensions(vec!["txt".to_string()]);
    ///
    /// assert!(config.is_path_extension_allowed(Some("txt")));
    /// assert!(!config.is_path_extension_allowed(Some("exe")));
    /// // Files without an extension are blocked when the allowlist is non-empty.
    /// assert!(!config.is_path_extension_allowed(None));
    ///
    /// // Empty allowlist permits everything, including extension-less files.
    /// let permissive = SecurityConfig::default();
    /// assert!(permissive.is_path_extension_allowed(None));
    /// ```
    #[must_use]
    pub fn is_path_extension_allowed(&self, extension: Option<&str>) -> bool {
        if self.allowed_extensions.is_empty() {
            return true;
        }
        extension.is_some_and(|ext| self.is_extension_allowed(ext))
    }
}

/// Options controlling extraction behavior (non-security).
///
/// Separate from `SecurityConfig` to keep security settings focused.
/// These options control operational behavior like atomicity.
#[derive(Debug, Clone)]
#[non_exhaustive]
pub struct ExtractionOptions {
    /// Extract atomically: use a temp dir in the same parent as the output
    /// directory, rename on success, and delete on failure.
    ///
    /// When enabled, extraction is all-or-nothing: if extraction fails,
    /// the output directory will not be created. This prevents partial
    /// extraction artifacts from remaining on disk.
    ///
    /// Note: cleanup is best-effort if the process is terminated via SIGKILL.
    pub atomic: bool,

    /// Skip duplicate entries silently instead of aborting.
    ///
    /// When `true` (default), if an archive contains two entries with the same
    /// destination path, the second entry is skipped and a warning is recorded
    /// in `ExtractionReport`. When `false`, duplicate entries cause an error.
    pub skip_duplicates: bool,
}

impl Default for ExtractionOptions {
    fn default() -> Self {
        Self {
            atomic: false,
            skip_duplicates: true,
        }
    }
}

impl ExtractionOptions {
    /// Enables or disables atomic extraction.
    ///
    /// When enabled, extraction is all-or-nothing: the output directory is not
    /// created if extraction fails.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::ExtractionOptions;
    ///
    /// let opts = ExtractionOptions::default().with_atomic(true);
    /// assert!(opts.atomic);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_atomic(mut self, atomic: bool) -> Self {
        self.atomic = atomic;
        self
    }

    /// Enables or disables skipping duplicate entries silently.
    ///
    /// # Examples
    ///
    /// ```
    /// use exarch_core::ExtractionOptions;
    ///
    /// let opts = ExtractionOptions::default().with_skip_duplicates(false);
    /// assert!(!opts.skip_duplicates);
    /// ```
    #[must_use]
    #[inline]
    pub fn with_skip_duplicates(mut self, skip: bool) -> Self {
        self.skip_duplicates = skip;
        self
    }
}

/// Upper bound on the bytes `verify` decodes to check payload integrity.
///
/// The budget bounds the work done **beyond what listing already does**: ZIP
/// entries and 7z blocks are charged their declared uncompressed size before
/// they are decoded, and for compressed TAR it bounds the read from the end
/// marker to decoder EOF. TAR entry content is never charged because listing
/// decodes it anyway. The default is a fixed 500 MiB, equal to the default
/// `max_total_size`; it does not follow a raised `max_total_size`.
///
/// # Examples
///
/// ```
/// use exarch_core::DecompressionBudget;
///
/// assert!(DecompressionBudget::try_from_bytes(0).is_err());
/// let budget = DecompressionBudget::try_from_bytes(1024)?;
/// assert_eq!(budget.get(), 1024);
/// assert_eq!(DecompressionBudget::default(), DecompressionBudget::DEFAULT);
/// # Ok::<(), exarch_core::ArchiveError>(())
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct DecompressionBudget(std::num::NonZeroU64);

impl DecompressionBudget {
    /// The default budget: 500 MiB.
    pub const DEFAULT: Self = match std::num::NonZeroU64::new(500 * 1024 * 1024) {
        Some(bytes) => Self(bytes),
        None => unreachable!(),
    };

    /// Creates a budget from a non-zero byte count.
    #[must_use]
    pub const fn new(bytes: std::num::NonZeroU64) -> Self {
        Self(bytes)
    }

    /// Creates a budget from a byte count.
    ///
    /// # Errors
    ///
    /// Returns [`ArchiveError::InvalidConfiguration`](crate::ArchiveError) when
    /// `bytes` is zero.
    pub fn try_from_bytes(bytes: u64) -> crate::Result<Self> {
        std::num::NonZeroU64::new(bytes).map(Self).ok_or_else(|| {
            crate::ArchiveError::InvalidConfiguration {
                reason: "decompression budget must be greater than zero".into(),
            }
        })
    }

    /// Returns the budget in bytes.
    #[must_use]
    pub const fn get(self) -> u64 {
        self.0.get()
    }
}

impl Default for DecompressionBudget {
    fn default() -> Self {
        Self::DEFAULT
    }
}

/// Whether `verify` checks payload integrity.
///
/// A budget without the check is unrepresentable: the budget lives inside the
/// [`DecodeToEof`](Self::DecodeToEof) variant.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[non_exhaustive]
pub enum IntegrityCheck {
    /// Metadata-only verification (the default).
    #[default]
    Skip,

    /// Decode payload to the decoder's EOF so checksums and codec framing are
    /// verified, spending at most the given budget on extra decoding.
    DecodeToEof(DecompressionBudget),
}

/// Options controlling `verify` behavior.
///
/// # Examples
///
/// ```
/// use exarch_core::DecompressionBudget;
/// use exarch_core::IntegrityCheck;
/// use exarch_core::VerificationOptions;
///
/// let options = VerificationOptions::default();
/// assert_eq!(options.integrity, IntegrityCheck::Skip);
///
/// let options = options.with_integrity(IntegrityCheck::DecodeToEof(DecompressionBudget::DEFAULT));
/// assert_ne!(options.integrity, IntegrityCheck::Skip);
/// ```
#[derive(Debug, Clone, Copy, Default)]
#[non_exhaustive]
pub struct VerificationOptions {
    /// Payload integrity check mode.
    pub integrity: IntegrityCheck,
}

impl VerificationOptions {
    /// Sets the payload integrity check mode.
    #[must_use]
    pub fn with_integrity(mut self, integrity: IntegrityCheck) -> Self {
        self.integrity = integrity;
        self
    }
}

/// Whether listing reads the symlink targets a format keeps in compressed
/// entry data.
///
/// 7z keeps link targets in compressed entry data, so reading them decodes
/// part of the archive, which in a solid block can be most of it. Listing
/// therefore skips them by default. Other formats always report their targets:
/// TAR keeps them in headers, and ZIP reads them from a small local entry. This
/// is a Rust API option only; the Python and Node `list_archive` skip 7z
/// targets.
///
/// # Examples
///
/// ```
/// use exarch_core::StoredTargets;
///
/// assert_eq!(StoredTargets::default(), StoredTargets::Skip);
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[non_exhaustive]
pub enum StoredTargets {
    /// Leave 7z link targets unread, so listing decodes no entry data (the
    /// default).
    #[default]
    Skip,

    /// Read the targets, decoding the blocks that hold them.
    Read,
}

/// Options controlling `list` behavior.
///
/// # Examples
///
/// ```
/// use exarch_core::ListOptions;
/// use exarch_core::StoredTargets;
///
/// let options = ListOptions::default();
/// assert_eq!(options.stored_targets, StoredTargets::Skip);
///
/// let options = options.with_stored_targets(StoredTargets::Read);
/// assert_eq!(options.stored_targets, StoredTargets::Read);
/// ```
#[derive(Debug, Clone, Copy, Default)]
#[non_exhaustive]
pub struct ListOptions {
    /// Whether to read the link targets a format keeps in entry data.
    pub stored_targets: StoredTargets,
}

impl ListOptions {
    /// Sets whether link targets kept in entry data are read.
    #[must_use]
    pub fn with_stored_targets(mut self, stored_targets: StoredTargets) -> Self {
        self.stored_targets = stored_targets;
        self
    }
}

#[cfg(test)]
#[allow(
    clippy::unwrap_used,
    clippy::expect_used,
    clippy::field_reassign_with_default
)]
mod tests {
    use super::*;

    #[test]
    fn test_default_config() {
        let config = SecurityConfig::default();
        assert!(!config.allowed.symlinks);
        assert!(!config.allowed.hardlinks);
        assert!(!config.allowed.absolute_paths);
        assert_eq!(config.max_file_size, 50 * 1024 * 1024);
    }

    #[test]
    fn test_permissive_config() {
        let config = SecurityConfig::permissive();
        assert!(config.allowed.symlinks);
        assert!(config.allowed.hardlinks);
        assert!(config.allowed.absolute_paths);
    }

    #[test]
    fn test_extension_allowed_empty_list() {
        let config = SecurityConfig::default();
        assert!(config.is_extension_allowed("txt"));
        assert!(config.is_extension_allowed("pdf"));
    }

    #[test]
    fn test_extension_allowed_with_list() {
        let mut config = SecurityConfig::default();
        config.allowed_extensions = vec!["txt".to_string(), "pdf".to_string()];
        assert!(config.is_extension_allowed("txt"));
        assert!(config.is_extension_allowed("TXT"));
        assert!(!config.is_extension_allowed("exe"));
    }

    #[test]
    fn test_path_component_allowed() {
        let config = SecurityConfig::default();
        assert!(config.is_path_component_allowed("src"));
        assert!(!config.is_path_component_allowed(".git"));
        assert!(!config.is_path_component_allowed(".ssh"));

        // Case-insensitive matching prevents bypass
        assert!(!config.is_path_component_allowed(".Git"));
        assert!(!config.is_path_component_allowed(".GIT"));
        assert!(!config.is_path_component_allowed(".SSH"));
        assert!(!config.is_path_component_allowed(".Gnupg"));
    }

    // M-TEST-3: Config field validation
    #[test]
    fn test_config_default_security_flags() {
        let config = SecurityConfig::default();

        // All security-sensitive flags should be false by default
        // (deny-by-default)
        assert!(
            !config.allowed.symlinks,
            "symlinks should be denied by default"
        );
        assert!(
            !config.allowed.hardlinks,
            "hardlinks should be denied by default"
        );
        assert!(
            !config.allowed.absolute_paths,
            "absolute paths should be denied by default"
        );
        assert!(
            !config.preserve_permissions,
            "permissions should not be preserved by default"
        );
        assert!(
            !config.allowed.world_writable,
            "world-writable should be denied by default"
        );
    }

    #[test]
    fn test_config_permissive_security_flags() {
        let config = SecurityConfig::permissive();

        // Permissive config should allow all features
        assert!(config.allowed.symlinks, "permissive allows symlinks");
        assert!(config.allowed.hardlinks, "permissive allows hardlinks");
        assert!(
            config.allowed.absolute_paths,
            "permissive allows absolute paths"
        );
        assert!(
            config.preserve_permissions,
            "permissive preserves permissions"
        );
        assert!(
            config.allowed.world_writable,
            "permissive allows world-writable"
        );
    }

    #[test]
    fn test_config_quota_limits() {
        let config = SecurityConfig::default();

        // Verify default quota values are sensible
        assert_eq!(config.max_file_size, 50 * 1024 * 1024, "50 MB file limit");
        assert_eq!(
            config.max_total_size,
            500 * 1024 * 1024,
            "500 MB total limit"
        );
        assert_eq!(config.max_file_count, 10_000, "10k file count limit");
        assert_eq!(config.max_path_depth, 32, "32 level depth limit");
        #[allow(clippy::float_cmp)]
        {
            assert_eq!(
                config.max_compression_ratio, 100.0,
                "100x compression ratio limit"
            );
        }
    }

    #[test]
    fn test_config_banned_components_not_empty() {
        let config = SecurityConfig::default();

        // Default should ban common sensitive directories
        assert!(
            !config.banned_path_components.is_empty(),
            "should have banned components by default"
        );
        assert!(
            config.banned_path_components.contains(&".git".to_string()),
            "should ban .git"
        );
        assert!(
            config.banned_path_components.contains(&".ssh".to_string()),
            "should ban .ssh"
        );
    }

    #[test]
    fn test_config_solid_archives_default() {
        let config = SecurityConfig::default();

        // Solid archives should be denied by default (security)
        assert!(
            !config.allow_solid_archives,
            "solid archives should be denied by default"
        );
        assert_eq!(
            config.max_solid_block_memory,
            512 * 1024 * 1024,
            "max solid block memory should be 512 MB"
        );
    }

    #[test]
    fn test_config_permissive_solid_archives() {
        let config = SecurityConfig::permissive();

        // Permissive config should allow solid archives
        assert!(
            config.allow_solid_archives,
            "permissive config should allow solid archives"
        );
        assert_eq!(
            config.max_solid_block_memory,
            1024 * 1024 * 1024,
            "permissive should have 1 GB solid block limit"
        );
    }

    #[test]
    fn test_config_tar_metadata_bytes_default() {
        let config = SecurityConfig::default();
        assert_eq!(
            config.max_tar_metadata_bytes,
            4 * 1024 * 1024,
            "max TAR metadata bytes should be 4 MiB by default"
        );
    }

    #[test]
    fn test_config_permissive_tar_metadata_bytes() {
        let config = SecurityConfig::permissive();
        assert_eq!(
            config.max_tar_metadata_bytes,
            16 * 1024 * 1024,
            "permissive should have 16 MiB TAR metadata budget"
        );
    }

    #[test]
    fn test_with_max_tar_metadata_bytes_builder() {
        let config = SecurityConfig::default().with_max_tar_metadata_bytes(2048);
        assert_eq!(config.max_tar_metadata_bytes, 2048);
    }

    // Regression tests for #172: SecurityConfig::validate() must reject configs
    // that would make security enforcement impossible.

    #[test]
    fn test_validate_default_is_ok() {
        assert!(SecurityConfig::default().validate().is_ok());
    }

    #[test]
    fn test_validate_rejects_negative_compression_ratio() {
        let mut cfg = SecurityConfig::default();
        cfg.max_compression_ratio = -1.0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_compression_ratio() {
        let mut cfg = SecurityConfig::default();
        cfg.max_compression_ratio = 0.0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_invalid_solid_compression_ratio() {
        for ratio in [0.0, -1.0, f64::NAN, f64::INFINITY] {
            let mut cfg = SecurityConfig::default();
            cfg.max_solid_compression_ratio = ratio;
            assert!(cfg.validate().is_err(), "{ratio} must be rejected");
        }
    }

    #[test]
    fn test_solid_compression_ratio_defaults() {
        assert_eq!(
            SecurityConfig::default().max_solid_compression_ratio,
            1000.0
        );
        assert_eq!(
            SecurityConfig::permissive().max_solid_compression_ratio,
            10_000.0
        );
    }

    #[test]
    fn test_validate_rejects_zero_max_file_size() {
        let mut cfg = SecurityConfig::default();
        cfg.max_file_size = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_total_size() {
        let mut cfg = SecurityConfig::default();
        cfg.max_total_size = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_path_depth() {
        let mut cfg = SecurityConfig::default();
        cfg.max_path_depth = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_nan_compression_ratio() {
        let mut cfg = SecurityConfig::default();
        cfg.max_compression_ratio = f64::NAN;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_infinite_compression_ratio() {
        let mut cfg = SecurityConfig::default();
        cfg.max_compression_ratio = f64::INFINITY;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_file_count() {
        let mut cfg = SecurityConfig::default();
        cfg.max_file_count = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_solid_block_memory() {
        let mut cfg = SecurityConfig::default();
        cfg.max_solid_block_memory = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_tar_metadata_bytes() {
        let mut cfg = SecurityConfig::default();
        cfg.max_tar_metadata_bytes = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_zero_max_decoder_memory() {
        let mut cfg = SecurityConfig::default();
        cfg.max_decoder_memory = 0;
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_parallel_decode_defaults() {
        let bytes = |config: SecurityConfig| match config.parallel_decode {
            ParallelDecode::Bounded(n) => n.get(),
            ParallelDecode::Sequential => 0,
        };
        assert_eq!(bytes(SecurityConfig::default()), 128 * 1024 * 1024);
        assert_eq!(bytes(SecurityConfig::permissive()), 1024 * 1024 * 1024);
    }

    #[test]
    fn test_max_decoder_memory_defaults() {
        assert_eq!(
            SecurityConfig::default().max_decoder_memory,
            256 * 1024 * 1024
        );
        assert_eq!(
            SecurityConfig::permissive().max_decoder_memory,
            1024 * 1024 * 1024
        );
    }

    // Regression tests for #449: SecurityConfig::validate() must reject
    // malformed allowed_extensions/banned_path_components entries.

    #[test]
    fn test_validate_permissive_is_ok() {
        assert!(SecurityConfig::permissive().validate().is_ok());
    }

    #[test]
    fn test_validate_accepts_empty_allowed_extensions_vec() {
        let cfg = SecurityConfig::default().with_allowed_extensions(Vec::new());
        assert!(cfg.validate().is_ok());
    }

    #[test]
    fn test_validate_rejects_empty_allowed_extension_entry() {
        let cfg = SecurityConfig::default().with_allowed_extensions(vec![String::new()]);
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_empty_banned_path_component_entry() {
        let cfg = SecurityConfig::default().with_banned_path_components(vec![String::new()]);
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_null_byte_in_allowed_extension() {
        let cfg = SecurityConfig::default().with_allowed_extensions(vec!["bad\0ext".to_string()]);
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn test_validate_rejects_overlong_banned_path_component() {
        let long_component = "x".repeat(256);
        let cfg = SecurityConfig::default().with_banned_path_components(vec![long_component]);
        assert!(cfg.validate().is_err());
    }

    // Regression test for the C1 finding on #433/#434/#435: a
    // `SecurityConfig<Validated>` must not be mutable. `DerefMut` is only
    // implemented for `SecurityConfig<Unvalidated>`, so this is enforced at
    // compile time — see `tests/ui/validated_config_field_mutation.rs` for
    // the corresponding compile-fail fixture. This test only pins the
    // read-side behavior: fields remain readable after validation.
    #[test]
    fn test_validated_config_fields_remain_readable() {
        let validated = SecurityConfig::default()
            .with_max_file_size(123)
            .validate()
            .expect("valid config");
        assert_eq!(validated.max_file_size, 123);
    }
}