tiny.sys.pty

1const std = @import("std");2const builtin = @import("builtin");34const capabilities = @import("capabilities.zig");5const fd = @import("fd.zig");6const linux = std.os.linux;7const native_os = builtin.os.tag;8const posix = std.posix;910extern fn posix_openpt(flags: c_int) c_int;1112pub const required_capabilities = switch (native_os) {13    .linux => capabilities.noLibc(&.{ .descriptors, .terminal }),14    else => capabilities.host(&.{ .descriptors, .terminal }),15};1617pub const Pair = struct {18    master: fd.Descriptor,19    slave: fd.Descriptor,2021    pub fn close(self: Pair) void {22        fd.close(self.slave);23        fd.close(self.master);24    }25};2627pub fn open() !Pair {28    return switch (native_os) {29        .linux => openLinux(),30        .freebsd => openFreeBsd(),31        .ios, .macos, .tvos, .visionos, .watchos => openDarwin(),32        else => error.UnsupportedPlatform,33    };34}3536pub fn isSupported() bool {37    return native_os == .linux or native_os == .freebsd or isDarwin();38}3940fn openLinux() !Pair {41    if (comptime native_os != .linux) return error.UnsupportedPlatform;4243    const master = try openLinuxMaster();44    errdefer fd.close(master);4546    var unlocked: c_int = 0;47    try controlLinux(master, linux.T.IOCSPTLCK, @intFromPtr(&unlocked));4849    const flags: u32 = @bitCast(linux.O{50        .ACCMODE = .RDWR,51        .CLOEXEC = true,52        .NOCTTY = true,53    });54    const slave = while (true) {55        const result = linux.ioctl(master, linux.T.IOCGPTPEER, flags);56        switch (linux.errno(result)) {57            .SUCCESS => break @as(fd.Descriptor, @intCast(result)),58            .INTR => continue,59            .MFILE => return error.ProcessFdQuotaExceeded,60            .NFILE => return error.SystemFdQuotaExceeded,61            .NOMEM => return error.SystemResources,62            .ACCES, .PERM => return error.AccessDenied,63            .INVAL, .IO, .NOTTY => return error.InvalidPseudoTerminal,64            else => return error.OpenSlaveFailed,65        }66    };6768    return .{ .master = master, .slave = slave };69}7071fn openLinuxMaster() !fd.Descriptor {72    if (comptime native_os != .linux) return error.UnsupportedPlatform;7374    while (true) {75        const result = linux.open("/dev/ptmx", .{76            .ACCMODE = .RDWR,77            .CLOEXEC = true,78            .NOCTTY = true,79        }, 0);80        switch (linux.errno(result)) {81            .SUCCESS => return @intCast(result),82            .INTR => continue,83            .ACCES, .PERM => return error.AccessDenied,84            .MFILE => return error.ProcessFdQuotaExceeded,85            .NFILE => return error.SystemFdQuotaExceeded,86            .NOMEM => return error.SystemResources,87            .NOENT => return error.FileNotFound,88            else => return error.OpenMasterFailed,89        }90    }91}9293fn controlLinux(descriptor: fd.Descriptor, request: u32, argument: usize) !void {94    if (comptime native_os != .linux) return error.UnsupportedPlatform;9596    while (true) {97        const result = linux.ioctl(descriptor, request, argument);98        switch (linux.errno(result)) {99            .SUCCESS => return,100            .INTR => continue,101            .ACCES, .PERM => return error.AccessDenied,102            .INVAL, .NOTTY => return error.InvalidPseudoTerminal,103            else => return error.ControlFailed,104        }105    }106}107108fn openDarwin() !Pair {109    if (comptime !isDarwin()) return error.UnsupportedPlatform;110111    const master = try openPosixMaster();112    errdefer fd.close(master);113114    try controlPosix(master, @bitCast(@as(u32, 0x20007454)), 0);115    try controlPosix(master, @bitCast(@as(u32, 0x20007452)), 0);116117    var slave_path: [128]u8 = @splat(0);118    try controlPosix(master, @bitCast(@as(u32, 0x40807453)), @intFromPtr(&slave_path));119    const path_len = std.mem.indexOfScalar(u8, &slave_path, 0) orelse return error.InvalidSlaveName;120    const slave = try openPosixPath(slave_path[0..path_len :0]);121122    return .{ .master = master, .slave = slave };123}124125fn openFreeBsd() !Pair {126    if (comptime native_os != .freebsd) return error.UnsupportedPlatform;127128    const flags: u32 = @bitCast(posix.O{129        .ACCMODE = .RDWR,130        .CLOEXEC = true,131        .NOCTTY = true,132    });133    const master = while (true) {134        const result = posix_openpt(@bitCast(flags));135        switch (posix.errno(result)) {136            .SUCCESS => break @as(fd.Descriptor, @intCast(result)),137            .INTR => continue,138            .ACCES, .PERM => return error.AccessDenied,139            .MFILE => return error.ProcessFdQuotaExceeded,140            .NFILE => return error.SystemFdQuotaExceeded,141            .NOMEM => return error.SystemResources,142            else => return error.OpenMasterFailed,143        }144    };145    errdefer fd.close(master);146147    var number: c_int = undefined;148    try controlPosix(master, @bitCast(@as(u32, 0x4004740f)), @intFromPtr(&number));149150    var path_buffer: [64]u8 = undefined;151    const slave_path = std.fmt.bufPrintSentinel(&path_buffer, "/dev/pts/{d}", .{number}, 0) catch return error.InvalidSlaveName;152    const slave = try openPosixPath(slave_path);153154    return .{ .master = master, .slave = slave };155}156157fn openPosixMaster() !fd.Descriptor {158    return openPosixPath("/dev/ptmx");159}160161fn openPosixPath(path: [:0]const u8) !fd.Descriptor {162    return posix.openat(posix.AT.FDCWD, path, .{163        .ACCMODE = .RDWR,164        .CLOEXEC = true,165        .NOCTTY = true,166    }, 0) catch |err| switch (err) {167        error.PermissionDenied => error.AccessDenied,168        else => err,169    };170}171172fn controlPosix(descriptor: fd.Descriptor, request: c_int, argument: usize) !void {173    while (true) {174        const result = posix.system.ioctl(descriptor, request, argument);175        switch (posix.errno(result)) {176            .SUCCESS => return,177            .INTR => continue,178            .ACCES, .PERM => return error.AccessDenied,179            .INVAL, .NOTTY => return error.InvalidPseudoTerminal,180            else => return error.ControlFailed,181        }182    }183}184185fn isDarwin() bool {186    return switch (native_os) {187        .ios, .macos, .tvos, .visionos, .watchos => true,188        else => false,189    };190}191192test "pseudo-terminal pair opens" {193    if (comptime !isSupported()) return error.SkipZigTest;194195    const pair = open() catch |err| switch (err) {196        error.FileNotFound, error.AccessDenied => return error.SkipZigTest,197        else => return err,198    };199    defer pair.close();200201    try std.testing.expect(pair.master >= 0);202    try std.testing.expect(pair.slave >= 0);203204    if (comptime native_os == .linux) {205        try expectCloseOnExec(pair.master);206        try expectCloseOnExec(pair.slave);207    }208}209210test "pseudo-terminal capability follows platform ABI" {211    const expected: capabilities.CapabilityTier = if (native_os == .linux) .no_libc else .host;212    try std.testing.expectEqual(expected, required_capabilities.tier);213}214215fn expectCloseOnExec(descriptor: fd.Descriptor) !void {216    if (comptime native_os != .linux) return error.UnsupportedPlatform;217218    const result = linux.fcntl(descriptor, linux.F.GETFD, 0);219    switch (linux.errno(result)) {220        .SUCCESS => try std.testing.expect(result & linux.FD_CLOEXEC != 0),221        else => return error.FlagQueryFailed,222    }223}

1pub const pty = @import("pty.zig");