Hi all!
We'd love feedback on this pitch to introduce a Stat type to the System library. This includes Swift-native APIs for the stat(), lstat(), fstat(), and fstatat() system calls, as well as supporting types for C stat properties and flags. In keeping with the System philosophy, these types would only be available on Unix-like platforms, but future directions could include Windows-specific file metadata APIs. Interested to hear your thoughts!
Proposal link with Markdown: swift-system/NNNN-system-stat.md at stat-proposal ¡ jrflat/swift-system ¡ GitHub
Stat for Swift System
- Proposal: SE-NNNN
- Authors: Jonathan Flat, Michael Ilseman, Rauhul Varma
- Review Manager: TBD
- Status: Awaiting review
- Implementation: apple/swift-system#256
Introduction
This proposal introduces a Swift-native Stat type to the System library, providing comprehensive access to file metadata on Unix-like platforms through type-safe, platform-aware APIs that wrap the C stat types and system calls.
Motivation
Currently, Swift developers who want to work with the file system's lowest level API can only do so through bridged C interfaces. These interfaces lack type safety and require writing non-idiomatic Swift, leading to errors and confusion.
The goal of the Stat type is to provide a faithful and performant Swift wrapper around the underlying C system calls while adding type safety, platform abstraction, and improved discoverability/usability with clear naming. For more on the motivation behind System, see https://www.swift.org/blog/swift-system
Proposed solution
This proposal adds a struct Stat that is available on Unix-like platforms. See discussion on Windows-specific API in Future Directions.
Stat - File Metadata
A Swift wrapper around the C stat struct that provides type-safe access to file metadata:
// Get file status from path String
let stat = try Stat("/path/to/file")
// From FileDescriptor
let stat = try fd.stat()
// From FilePath
let stat = try filePath.stat()
// `followTargetSymlink: true` (default) behaves like `stat()`
// `followTargetSymlink: false` behaves like `lstat()`
let stat = try symlinkPath.stat(followTargetSymlink: false)
// Supply flags and optional file descriptor to use the `fstatat()` variant
let stat = try Stat("path/to/file", relativeTo: fd, flags: .symlinkNoFollow)
print("Size: \(stat.size) bytes")
print("Type: \(stat.type)") // .regular, .directory, .symbolicLink, etc.
print("Permissions: \(stat.permissions)")
print("Modified: \(stat.modificationTime)")
// Platform-specific information when available
#if canImport(Darwin) || os(FreeBSD)
print("Creation time: \(stat.creationTime)")
#endif
Error Handling
All initializers throw the existing Errno type:
do {
let stat = try Stat("/nonexistent/file")
} catch Errno.noSuchFileOrDirectory {
print("File not found")
} catch {
print("Other error: \(error)")
}
These initializers use a typed throws(Errno) and require Swift 6.0 or later.
Detailed design
See the Appendix section at the end of this proposal for a table view of Swift API to C mappings.
All API are marked @_alwaysEmitIntoClient for performance and back-dating of availability.
FileType
This proposal introduces FileType and FileMode types to represent mode_t values from the C stat struct. The type and permissions of a FileMode can be modified for convenience, and FileMode handles the respective bit masking.
/// A file type matching those contained in a C `mode_t`.
///
/// - Note: Only available on Unix-like platforms.
@frozen
public struct FileType: RawRepresentable, Sendable, Hashable, Codable {
/// The raw file-type bits from the C mode.
public var rawValue: CInterop.Mode
/// Creates a strongly-typed file type from the raw C value.
///
/// - Note: `rawValue` should only contain the mode's file-type bits. Otherwise,
/// use `FileMode(rawValue:)` to get a strongly-typed `FileMode`, then
/// call `.type` to get the properly masked `FileType`.
public init(rawValue: CInterop.Mode)
/// Directory
///
/// The corresponding C constant is `S_IFDIR`.
public static var directory: FileType { get }
/// Character special device
///
/// The corresponding C constant is `S_IFCHR`.
public static var characterSpecial: FileType { get }
/// Block special device
///
/// The corresponding C constant is `S_IFBLK`.
public static var blockSpecial: FileType { get }
/// Regular file
///
/// The corresponding C constant is `S_IFREG`.
public static var regular: FileType { get }
/// FIFO (or pipe)
///
/// The corresponding C constant is `S_IFIFO`.
public static var pipe: FileType { get }
/// Symbolic link
///
/// The corresponding C constant is `S_IFLNK`.
public static var symbolicLink: FileType { get }
/// Socket
///
/// The corresponding C constant is `S_IFSOCK`.
public static var socket: FileType { get }
#if SYSTEM_PACKAGE_DARWIN || os(FreeBSD)
/// Whiteout file
///
/// The corresponding C constant is `S_IFWHT`.
public static var whiteout: FileType { get }
#endif
}
FileMode
/// A strongly-typed file mode representing a C `mode_t`.
///
/// - Note: Only available on Unix-like platforms.
@frozen
public struct FileMode: RawRepresentable, Sendable, Hashable, Codable {
/// The raw C mode.
public var rawValue: CInterop.Mode
/// Creates a strongly-typed `FileMode` from the raw C value.
public init(rawValue: CInterop.Mode)
/// Creates a `FileMode` from the given file type and permissions.
///
/// - Note: This initializer masks the inputs with their respective bit masks.
public init(type: FileType, permissions: FilePermissions)
/// The file's type, from the mode's file-type bits.
///
/// Setting this property will mask the `newValue` with the file-type bit mask `S_IFMT`.
public var type: FileType { get set }
/// The file's permissions, from the mode's permission bits.
///
/// Setting this property will mask the `newValue` with the permissions bit mask `0o7777`.
public var permissions: FilePermissions { get set }
}
Supporting ID Types
This proposal also uses new DeviceID, UserID, GroupID, and Inode types to represent the respective C data types found in stat. These are strongly-typed structs instead of CInterop typealiases to prevent ambiguity in future System implementations and to allow for added functionality.
For example, with an implementation of chown, a developer might accidentally misplace user and group parameters with no warning if both were a typealias of the underlying unsigned int. Furthermore, a strongly-typed DeviceID would allow us to add functionality such as a makedev function, or major and minor getters.
For now, we define the following for use in Stat.
@frozen
public struct UserID: RawRepresentable, Sendable, Hashable, Codable {
public var rawValue: CInterop.UserID
public init(rawValue: CInterop.UserID)
}
@frozen
public struct GroupID: RawRepresentable, Sendable, Hashable, Codable {
public var rawValue: CInterop.GroupID
public init(rawValue: CInterop.GroupID)
}
@frozen
public struct DeviceID: RawRepresentable, Sendable, Hashable, Codable {
public var rawValue: CInterop.DeviceID
public init(rawValue: CInterop.DeviceID)
}
@frozen
public struct Inode: RawRepresentable, Sendable, Hashable, Codable {
public var rawValue: CInterop.Inode
public init(rawValue: CInterop.Inode)
}
Each type stores a CInterop typealias to ensure an appropriate rawValue for the current platform. Added functionality is outside the scope of this proposal.
FileFlags
A new FileFlags type represents file-specific flags found in a stat struct on Darwin, FreeBSD, and OpenBSD. These flags are also used in chflags().
/// File-specific flags found in the `st_flags` property of a `stat` struct
/// or used as input to `chflags()`.
///
/// - Note: Only available on Darwin, FreeBSD, and OpenBSD.
@frozen
public struct FileFlags: OptionSet, Sendable, Hashable, Codable {
/// The raw C flags.
public let rawValue: CInterop.FileFlags
/// Creates a strongly-typed `FileFlags` from the raw C value.
public init(rawValue: CInterop.FileFlags)
// MARK: Flags Available on Darwin, FreeBSD, and OpenBSD
/// Do not dump the file during backups.
///
/// The corresponding C constant is `UF_NODUMP`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var noDump: FileFlags { get }
/// File may not be changed.
///
/// The corresponding C constant is `UF_IMMUTABLE`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var userImmutable: FileFlags { get }
/// Writes to the file may only append.
///
/// The corresponding C constant is `UF_APPEND`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var userAppend: FileFlags { get }
/// File has been archived.
///
/// The corresponding C constant is `SF_ARCHIVED`.
/// - Note: This flag may only be changed by the superuser.
public static var archived: FileFlags { get }
/// File may not be changed.
///
/// The corresponding C constant is `SF_IMMUTABLE`.
/// - Note: This flag may only be changed by the superuser.
public static var systemImmutable: FileFlags { get }
/// Writes to the file may only append.
///
/// The corresponding C constant is `SF_APPEND`.
/// - Note: This flag may only be changed by the superuser.
public static var systemAppend: FileFlags { get }
// MARK: Flags Available on Darwin and FreeBSD
#if SYSTEM_PACKAGE_DARWIN || os(FreeBSD)
/// Directory is opaque when viewed through a union mount.
///
/// The corresponding C constant is `UF_OPAQUE`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var opaque: FileFlags { get }
/// File is compressed at the file system level.
///
/// The corresponding C constant is `UF_COMPRESSED`.
/// - Note: This flag is read-only. Attempting to change it will result in undefined behavior.
public static var compressed: FileFlags { get }
/// File is tracked for the purpose of document IDs.
///
/// The corresponding C constant is `UF_TRACKED`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var tracked: FileFlags { get }
/// File should not be displayed in a GUI.
///
/// The corresponding C constant is `UF_HIDDEN`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var hidden: FileFlags { get }
/// File requires an entitlement for writing.
///
/// The corresponding C constant is `SF_RESTRICTED`.
/// - Note: This flag may only be changed by the superuser.
public static var restricted: FileFlags { get }
/// File may not be removed or renamed.
///
/// The corresponding C constant is `SF_NOUNLINK`.
/// - Note: This flag may only be changed by the superuser.
public static var systemNoUnlink: FileFlags { get }
#endif
// MARK: Flags Available on Darwin only
#if SYSTEM_PACKAGE_DARWIN
/// File requires an entitlement for reading and writing.
///
/// The corresponding C constant is `UF_DATAVAULT`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var dataVault: FileFlags { get }
/// File is a firmlink.
///
/// Firmlinks are used by macOS to create transparent links between
/// the read-only system volume and writable data volume. For example,
/// the `/Applications` folder on the system volume is a firmlink to
/// the `/Applications` folder on the data volume, allowing the user
/// to see both system- and user-installed applications in a single folder.
///
/// The corresponding C constant is `SF_FIRMLINK`.
/// - Note: This flag may only be changed by the superuser.
public static var firmlink: FileFlags { get }
/// File is a dataless placeholder (content is stored remotely).
///
/// The system will attempt to materialize the file when accessed according to
/// the dataless file materialization policy of the accessing thread or process.
/// See `getiopolicy_np(3)`.
///
/// The corresponding C constant is `SF_DATALESS`.
/// - Note: This flag is read-only. Attempting to change it will result in undefined behavior.
public static var dataless: FileFlags { get }
#endif
// MARK: Flags Available on FreeBSD Only
#if os(FreeBSD)
/// File may not be removed or renamed.
///
/// The corresponding C constant is `UF_NOUNLINK`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var userNoUnlink: FileFlags { get }
/// File has the Windows offline attribute.
///
/// File systems may use this flag for compatibility with the Windows `FILE_ATTRIBUTE_OFFLINE` attribute,
/// but otherwise provide no special handling when it's set.
///
/// The corresponding C constant is `UF_OFFLINE`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var offline: FileFlags { get }
/// File is read-only.
///
/// File systems may use this flag for compatibility with the Windows `FILE_ATTRIBUTE_READONLY` attribute.
///
/// The corresponding C constant is `UF_READONLY`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var readOnly: FileFlags { get }
/// File contains a Windows reparse point.
///
/// File systems may use this flag for compatibility with the Windows `FILE_ATTRIBUTE_REPARSE_POINT` attribute.
///
/// The corresponding C constant is `UF_REPARSE`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var reparse: FileFlags { get }
/// File is sparse.
///
/// File systems may use this flag for compatibility with the Windows `FILE_ATTRIBUTE_SPARSE_FILE` attribute,
/// or to indicate a sparse file.
///
/// The corresponding C constant is `UF_SPARSE`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var sparse: FileFlags { get }
/// File has the Windows system attribute.
///
/// File systems may use this flag for compatibility with the Windows `FILE_ATTRIBUTE_SYSTEM` attribute,
/// but otherwise provide no special handling when it's set.
///
/// The corresponding C constant is `UF_SYSTEM`.
/// - Note: This flag may be changed by the file owner or superuser.
public static var system: FileFlags { get }
/// File is a snapshot.
///
/// The corresponding C constant is `SF_SNAPSHOT`.
/// - Note: This flag may only be changed by the superuser.
public static var snapshot: FileFlags { get }
#endif
}
Stat
Stat can be initialized from a FilePath, UnsafePointer<CChar>, or FileDescriptor. This proposal also includes functions on FileDescriptor and FilePath for creating a Stat object, seen in the section below.
The initializer that takes a FileDescriptor corresponds to fstat(). If the file descriptor points to a symlink, this will return information about the symlink itself.
In the non-FileDescriptor case, one form of the initializer takes a followTargetSymlink: Bool = true parameter. The default true corresponds to stat() and will follow a symlink at the end of the path. Setting followTargetSymlink: false corresponds to lstat() and will return information about the symlink itself.
The last form of the initializer receives a path, which can be resolved against a given file descriptor, and a set of Stat.Flags. These APIs correspond to the fstatat() system call and use a default file descriptor of AT_FDCWD if one isn't supplied.
/// A Swift wrapper of the C `stat` struct.
///
/// - Note: Only available on Unix-like platforms.
@frozen
public struct Stat: RawRepresentable, Sendable {
/// The raw C `stat` struct.
public var rawValue: CInterop.Stat
/// Creates a Swift `Stat` from the raw C struct.
public init(rawValue: CInterop.Stat)
// MARK: Stat.Flags
/// Flags representing those passed to `fstatat()`.
@frozen
public struct Flags: OptionSet, Sendable, Hashable, Codable {
/// The raw C flags.
public let rawValue: CInt
/// Creates a strongly-typed `Stat.Flags` from raw C flags.
public init(rawValue: CInt)
/// If the path ends with a symbolic link, return information about the link itself.
///
/// The corresponding C constant is `AT_SYMLINK_NOFOLLOW`.
public static var symlinkNoFollow: Flags { get }
#if SYSTEM_PACKAGE_DARWIN
/// If the path ends with a symbolic link, return information about the link itself.
/// If _any_ symbolic link is encountered during path resolution, return an error.
///
/// The corresponding C constant is `AT_SYMLINK_NOFOLLOW_ANY`.
/// - Note: Only available on Darwin.
public static var symlinkNoFollowAny: Flags { get }
#endif
#if SYSTEM_PACKAGE_DARWIN || os(FreeBSD)
/// If the path does not reside in the hierarchy beneath the starting directory, return an error.
///
/// The corresponding C constant is `AT_RESOLVE_BENEATH`.
/// - Note: Only available on Darwin and FreeBSD.
public static var resolveBeneath: Flags { get }
#endif
#if os(FreeBSD) || os(Linux) || os(Android)
/// If the path is an empty string (or `NULL` since Linux 6.11),
/// return information about the given file descriptor.
///
/// The corresponding C constant is `AT_EMPTY_PATH`.
/// - Note: Only available on FreeBSD, Linux, and Android.
public static var emptyPath: Flags { get }
#endif
}
// MARK: Initializers
/// Creates a `Stat` struct from a `FilePath`.
///
/// `followTargetSymlink` determines the behavior if `path` ends with a symbolic link.
/// By default, `followTargetSymlink` is `true` and this initializer behaves like `stat()`.
/// If `followTargetSymlink` is set to `false`, this initializer behaves like `lstat()` and
/// returns information about the symlink itself.
///
/// The corresponding C function is `stat()` or `lstat()` as described above.
public init(
_ path: FilePath,
followTargetSymlink: Bool = true,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from an`UnsafePointer<CChar>` path.
///
/// `followTargetSymlink` determines the behavior if `path` ends with a symbolic link.
/// By default, `followTargetSymlink` is `true` and this initializer behaves like `stat()`.
/// If `followTargetSymlink` is set to `false`, this initializer behaves like `lstat()` and
/// returns information about the symlink itself.
///
/// The corresponding C function is `stat()` or `lstat()` as described above.
public init(
_ path: UnsafePointer<CChar>,
followTargetSymlink: Bool = true,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from a `FileDescriptor`.
///
/// The corresponding C function is `fstat()`.
public init(
_ fd: FileDescriptor,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from a `FilePath` and `Flags`.
///
/// If `path` is relative, it is resolved against the current working directory.
///
/// The corresponding C function is `fstatat()`.
public init(
_ path: FilePath,
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from a `FilePath` and `Flags`,
/// including a `FileDescriptor` to resolve a relative path.
///
/// If `path` is absolute (starts with a forward slash), then `fd` is ignored.
/// If `path` is relative, it is resolved against the directory given by `fd`.
///
/// The corresponding C function is `fstatat()`.
public init(
_ path: FilePath,
relativeTo fd: FileDescriptor,
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from an `UnsafePointer<CChar>` path and `Flags`.
///
/// If `path` is relative, it is resolved against the current working directory.
///
/// The corresponding C function is `fstatat()`.
public init(
_ path: UnsafePointer<CChar>,
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno)
/// Creates a `Stat` struct from an `UnsafePointer<CChar>` path and `Flags`,
/// including a `FileDescriptor` to resolve a relative path.
///
/// If `path` is absolute (starts with a forward slash), then `fd` is ignored.
/// If `path` is relative, it is resolved against the directory given by `fd`.
///
/// The corresponding C function is `fstatat()`.
public init(
_ path: UnsafePointer<CChar>,
relativeTo fd: FileDescriptor,
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno)
// MARK: Properties
/// ID of device containing file
///
/// The corresponding C property is `st_dev`.
public var deviceID: DeviceID { get set }
/// Inode number
///
/// The corresponding C property is `st_ino`.
public var inode: Inode { get set }
/// File mode
///
/// The corresponding C property is `st_mode`.
public var mode: FileMode { get set }
/// File type for the given mode
public var type: FileType { get set }
/// File permissions for the given mode
public var permissions: FilePermissions { get set }
/// Number of hard links
///
/// The corresponding C property is `st_nlink`.
public var linkCount: Int { get set }
/// User ID of owner
///
/// The corresponding C property is `st_uid`.
public var userID: UserID { get set }
/// Group ID of owner
///
/// The corresponding C property is `st_gid`.
public var groupID: GroupID { get set }
/// Device ID (if special file)
///
/// For character or block special files, the returned `DeviceID` may have
/// meaningful `.major` and `.minor` values. For non-special files, this
/// property is usually meaningless and often set to 0.
///
/// The corresponding C property is `st_rdev`.
public var specialDeviceID: DeviceID { get set }
/// Total size, in bytes
///
/// The corresponding C property is `st_size`.
public var size: Int64 { get set }
/// Block size for filesystem I/O, in bytes
///
/// The corresponding C property is `st_blksize`.
public var preferredIOBlockSize: Int { get set }
/// Number of 512-byte blocks allocated
///
/// The corresponding C property is `st_blocks`.
public var blocksAllocated: Int64 { get set }
/// Total size allocated, in bytes
///
/// - Note: Calculated as `512 * blocksAllocated`.
public var sizeAllocated: Int64 { get }
/// Time of last access, given as a `UTCClock.Instant`
///
/// The corresponding C property is `st_atim` (or `st_atimespec` on Darwin).
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public var accessTime: UTCClock.Instant { get set }
/// Time of last modification, given as a `UTCClock.Instant`
///
/// The corresponding C property is `st_mtim` (or `st_mtimespec` on Darwin).
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public var modificationTime: UTCClock.Instant { get set }
/// Time of last status (inode) change, given as a `UTCClock.Instant`
///
/// The corresponding C property is `st_ctim` (or `st_ctimespec` on Darwin).
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public var changeTime: UTCClock.Instant { get set }
#if SYSTEM_PACKAGE_DARWIN || os(FreeBSD)
/// Time of file creation, given as a `UTCClock.Instant`
///
/// The corresponding C property is `st_birthtim` (or `st_birthtimespec` on Darwin).
/// - Note: Only available on Darwin and FreeBSD.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public var creationTime: UTCClock.Instant { get set }
#endif
#if SYSTEM_PACKAGE_DARWIN || os(FreeBSD) || os(OpenBSD)
/// File flags
///
/// The corresponding C property is `st_flags`.
/// - Note: Only available on Darwin, FreeBSD, and OpenBSD.
public var flags: FileFlags { get set }
/// File generation number
///
/// The file generation number is used to distinguish between different files
/// that have used the same inode over time.
///
/// The corresponding C property is `st_gen`.
/// - Note: Only available on Darwin, FreeBSD, and OpenBSD.
public var generationNumber: Int { get set }
#endif
}
// MARK: - Equatable and Hashable
extension Stat: Equatable {
/// Compares the raw bytes of two `Stat` structs for equality.
public static func == (lhs: Self, rhs: Self) -> Bool
}
extension Stat: Hashable {
/// Hashes the raw bytes of this `Stat` struct.
public func hash(into hasher: inout Hasher)
}
FileDescriptor and FilePath Extensions
extension FileDescriptor {
/// Creates a `Stat` struct for the file referenced by this `FileDescriptor`.
///
/// The corresponding C function is `fstat()`.
public func stat(
retryOnInterrupt: Bool = true
) throws(Errno) -> Stat
}
extension FilePath {
/// Creates a `Stat` struct for the file referenced by this `FilePath`.
///
/// `followTargetSymlink` determines the behavior if `path` ends with a symbolic link.
/// By default, `followTargetSymlink` is `true` and this initializer behaves like `stat()`.
/// If `followTargetSymlink` is set to `false`, this initializer behaves like `lstat()` and
/// returns information about the symlink itself.
///
/// The corresponding C function is `stat()` or `lstat()` as described above.
public func stat(
followTargetSymlink: Bool = true,
retryOnInterrupt: Bool = true
) throws(Errno) -> Stat
/// Creates a `Stat` struct for the file referenced by this`FilePath` using the given `Flags`.
///
/// If `path` is relative, it is resolved against the current working directory.
///
/// The corresponding C function is `fstatat()`.
public func stat(
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno) -> Stat
/// Creates a `Stat` struct for the file referenced by this`FilePath` using the given `Flags`,
/// including a `FileDescriptor` to resolve a relative path.
///
/// If `path` is absolute (starts with a forward slash), then `fd` is ignored.
/// If `path` is relative, it is resolved against the directory given by `fd`.
///
/// The corresponding C function is `fstatat()`.
public func stat(
relativeTo fd: FileDescriptor,
flags: Stat.Flags,
retryOnInterrupt: Bool = true
) throws(Errno) -> Stat
}
CInterop Extensions
This proposal extends the existing CInterop namespace with platform-appropriate typealiases for the underlying C types. These typealiases are used as the rawValue for their strongly-typed representations.
extension CInterop {
public typealias Stat
public typealias Inode
public typealias UserID
public typealias GroupID
public typealias DeviceID
public typealias FileFlags
}
Source compatibility
This proposal is additive and source-compatible with existing code.
ABI compatibility
This proposal is additive and ABI-compatible with existing code.
Implications on adoption
This feature can be freely adopted and un-adopted in source code with no deployment constraints and without affecting source or ABI compatibility.
Future directions
To remain faithful to the underlying system calls, we don't anticipate extending Stat. However, the types introduced in this proposal could serve as the foundation of broader file system APIs in Swift.
While this proposal does not include Stat on Windows, a separate proposal should provide Swift-native wrappers of idiomatic GetFileInformation functions with their associated types.
A more general FileInfo API could then build on these OS-specific types to provide an ergonomic, cross-platform abstraction for file metadata. These future cross-platform APIs might be better implemented outside of System, such as in Foundation, the standard library, or somewhere in between. They could provide additional information or conveniences, such as reading and modifying extended attributes or setting file timestamps.
In the future, more functionality could be added to types such as DeviceID.
Alternatives considered
FileInfo as the lowest-level type
An alternative approach could be to have a more general FileInfo type be the lowest level of abstraction provided by the System library. This type would then handle all the stat or Windows-specific struct storage and accessors. However, this alternative:
- Is inconsistent with System's philosophy of providing low-level system abstractions.
- Introduces an even larger number of system-specific APIs on each type.
- Misses out on the familiarity of the
statname. Developers know what to look for and what to expect from this type.
Single combined type for both file and file system metadata
Combining Stat and StatFS (separate proposal) into a single type was considered but rejected because file and file system information serve different purposes and are typically needed in different contexts. Storing and/or initializing both stat and statfs structs unnecessarily reduces performance when one isn't needed.
Making Stat available on Windows
It's possible to make Stat available on Windows and use either the non-native _stat functions from CRT or populate the information via a separate GetFileInformation call. However, many of the stat fields are not- or less-applicable on Windows and are treated as such by _stat. For instance, st_uid is always zero on Windows, st_ino has no meaning in FAT, HPFS, or NTFS file systems, and st_mode can only specify a regular file, directory, or character special, with the executable bit depending entirely on the file's path extension.
Rather than forcing Windows file metadata semantics into a cross-platform Stat type, we should instead create Windows-specific types that give developers full access to platform-native file metadata. Combined with a higher-level FileInfo type that is cross-platform, this gives the best of both low-level and platform-agnostic APIs.
Only have FilePath and FileDescriptor extensions rather than initializers that accept these types
While having .stat() functions on FilePath and FileDescriptor is preferred for ergonomics and function chaining, this technique might lack the discoverability of having an initializer on Stat directly. This proposal therefore includes both the initializers and extensions.
Types for time properties
UTCClock.Instant was chosen over alternatives such as Duration or a new Timespec type to provide a comparable instant in time rather than a duration since the Epoch. This would depend on lowering UTCClock to System or the standard library, which could be discussed in a separate pitch.
Type names
Stat was chosen over alternatives like FileStat or FileStatus for its brevity and likeness to the "stat" system call. Unlike generic names such as FileInfo or FileMetadata, Stat emphasizes the platform-specific nature of this type.
Inode was similarly chosen over alternatives like FileIndex or FileID to emphasize the platform-specific nature. IndexNode is a bit verbose, and despite its etymology, "inode" is now ubiquitous and understood as a single word, making the capitalization Inode preferable to INode.
Acknowledgments
These new APIs build on excellent types currently available in the System library.
Appendix
Swift API to C Mappings
See swift-system/NNNN-system-stat.md at stat-proposal ¡ jrflat/swift-system ¡ GitHub
