Merge pull request #3315 from ziglang/mv-std-lib

Move std/ to lib/std/

1 files changed, 1431 insertions, 0 deletions

diff --git a/lib/std/event/fs.zig b/lib/std/event/fs.zig
new file mode 100644
index 0000000000..4490e1deae
--- /dev/null
+++ b/lib/std/event/fs.zig
@@ -0,0 +1,1431 @@
+const builtin = @import("builtin");
+const std = @import("../std.zig");
+const event = std.event;
+const assert = std.debug.assert;
+const testing = std.testing;
+const os = std.os;
+const mem = std.mem;
+const windows = os.windows;
+const Loop = event.Loop;
+const fd_t = os.fd_t;
+const File = std.fs.File;
+
+pub const RequestNode = std.atomic.Queue(Request).Node;
+
+pub const Request = struct {
+    msg: Msg,
+    finish: Finish,
+
+    pub const Finish = union(enum) {
+        TickNode: Loop.NextTickNode,
+        DeallocCloseOperation: *CloseOperation,
+        NoAction,
+    };
+
+    pub const Msg = union(enum) {
+        WriteV: WriteV,
+        PWriteV: PWriteV,
+        PReadV: PReadV,
+        Open: Open,
+        Close: Close,
+        WriteFile: WriteFile,
+        End, // special - means the fs thread should exit
+
+        pub const WriteV = struct {
+            fd: fd_t,
+            iov: []const os.iovec_const,
+            result: Error!void,
+
+            pub const Error = os.WriteError;
+        };
+
+        pub const PWriteV = struct {
+            fd: fd_t,
+            iov: []const os.iovec_const,
+            offset: usize,
+            result: Error!void,
+
+            pub const Error = os.WriteError;
+        };
+
+        pub const PReadV = struct {
+            fd: fd_t,
+            iov: []const os.iovec,
+            offset: usize,
+            result: Error!usize,
+
+            pub const Error = os.ReadError;
+        };
+
+        pub const Open = struct {
+            /// must be null terminated. TODO https://github.com/ziglang/zig/issues/265
+            path: []const u8,
+            flags: u32,
+            mode: File.Mode,
+            result: Error!fd_t,
+
+            pub const Error = File.OpenError;
+        };
+
+        pub const WriteFile = struct {
+            /// must be null terminated. TODO https://github.com/ziglang/zig/issues/265
+            path: []const u8,
+            contents: []const u8,
+            mode: File.Mode,
+            result: Error!void,
+
+            pub const Error = File.OpenError || File.WriteError;
+        };
+
+        pub const Close = struct {
+            fd: fd_t,
+        };
+    };
+};
+
+pub const PWriteVError = error{OutOfMemory} || File.WriteError;
+
+/// data - just the inner references - must live until pwritev frame completes.
+pub fn pwritev(loop: *Loop, fd: fd_t, data: []const []const u8, offset: usize) PWriteVError!void {
+    switch (builtin.os) {
+        .macosx,
+        .linux,
+        .freebsd,
+        .netbsd,
+        => {
+            const iovecs = try loop.allocator.alloc(os.iovec_const, data.len);
+            defer loop.allocator.free(iovecs);
+
+            for (data) |buf, i| {
+                iovecs[i] = os.iovec_const{
+                    .iov_base = buf.ptr,
+                    .iov_len = buf.len,
+                };
+            }
+
+            return pwritevPosix(loop, fd, iovecs, offset);
+        },
+        .windows => {
+            const data_copy = try std.mem.dupe(loop.allocator, []const u8, data);
+            defer loop.allocator.free(data_copy);
+            return pwritevWindows(loop, fd, data, offset);
+        },
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+/// data must outlive the returned frame
+pub fn pwritevWindows(loop: *Loop, fd: fd_t, data: []const []const u8, offset: usize) os.WindowsWriteError!void {
+    if (data.len == 0) return;
+    if (data.len == 1) return pwriteWindows(loop, fd, data[0], offset);
+
+    // TODO do these in parallel
+    var off = offset;
+    for (data) |buf| {
+        try pwriteWindows(loop, fd, buf, off);
+        off += buf.len;
+    }
+}
+
+pub fn pwriteWindows(loop: *Loop, fd: fd_t, data: []const u8, offset: u64) os.WindowsWriteError!void {
+    var resume_node = Loop.ResumeNode.Basic{
+        .base = Loop.ResumeNode{
+            .id = Loop.ResumeNode.Id.Basic,
+            .handle = @frame(),
+            .overlapped = windows.OVERLAPPED{
+                .Internal = 0,
+                .InternalHigh = 0,
+                .Offset = @truncate(u32, offset),
+                .OffsetHigh = @truncate(u32, offset >> 32),
+                .hEvent = null,
+            },
+        },
+    };
+    // TODO only call create io completion port once per fd
+    _ = windows.CreateIoCompletionPort(fd, loop.os_data.io_port, undefined, undefined);
+    loop.beginOneEvent();
+    errdefer loop.finishOneEvent();
+
+    errdefer {
+        _ = windows.kernel32.CancelIoEx(fd, &resume_node.base.overlapped);
+    }
+    suspend {
+        _ = windows.kernel32.WriteFile(fd, data.ptr, @intCast(windows.DWORD, data.len), null, &resume_node.base.overlapped);
+    }
+    var bytes_transferred: windows.DWORD = undefined;
+    if (windows.kernel32.GetOverlappedResult(fd, &resume_node.base.overlapped, &bytes_transferred, windows.FALSE) == 0) {
+        switch (windows.kernel32.GetLastError()) {
+            windows.ERROR.IO_PENDING => unreachable,
+            windows.ERROR.INVALID_USER_BUFFER => return error.SystemResources,
+            windows.ERROR.NOT_ENOUGH_MEMORY => return error.SystemResources,
+            windows.ERROR.OPERATION_ABORTED => return error.OperationAborted,
+            windows.ERROR.NOT_ENOUGH_QUOTA => return error.SystemResources,
+            windows.ERROR.BROKEN_PIPE => return error.BrokenPipe,
+            else => |err| return windows.unexpectedError(err),
+        }
+    }
+}
+
+/// iovecs must live until pwritev frame completes.
+pub fn pwritevPosix(
+    loop: *Loop,
+    fd: fd_t,
+    iovecs: []const os.iovec_const,
+    offset: usize,
+) os.WriteError!void {
+    var req_node = RequestNode{
+        .prev = null,
+        .next = null,
+        .data = Request{
+            .msg = Request.Msg{
+                .PWriteV = Request.Msg.PWriteV{
+                    .fd = fd,
+                    .iov = iovecs,
+                    .offset = offset,
+                    .result = undefined,
+                },
+            },
+            .finish = Request.Finish{
+                .TickNode = Loop.NextTickNode{
+                    .prev = null,
+                    .next = null,
+                    .data = @frame(),
+                },
+            },
+        },
+    };
+
+    errdefer loop.posixFsCancel(&req_node);
+
+    suspend {
+        loop.posixFsRequest(&req_node);
+    }
+
+    return req_node.data.msg.PWriteV.result;
+}
+
+/// iovecs must live until pwritev frame completes.
+pub fn writevPosix(
+    loop: *Loop,
+    fd: fd_t,
+    iovecs: []const os.iovec_const,
+) os.WriteError!void {
+    var req_node = RequestNode{
+        .prev = null,
+        .next = null,
+        .data = Request{
+            .msg = Request.Msg{
+                .WriteV = Request.Msg.WriteV{
+                    .fd = fd,
+                    .iov = iovecs,
+                    .result = undefined,
+                },
+            },
+            .finish = Request.Finish{
+                .TickNode = Loop.NextTickNode{
+                    .prev = null,
+                    .next = null,
+                    .data = @frame(),
+                },
+            },
+        },
+    };
+
+    suspend {
+        loop.posixFsRequest(&req_node);
+    }
+
+    return req_node.data.msg.WriteV.result;
+}
+
+pub const PReadVError = error{OutOfMemory} || File.ReadError;
+
+/// data - just the inner references - must live until preadv frame completes.
+pub fn preadv(loop: *Loop, fd: fd_t, data: []const []u8, offset: usize) PReadVError!usize {
+    assert(data.len != 0);
+    switch (builtin.os) {
+        .macosx,
+        .linux,
+        .freebsd,
+        .netbsd,
+        => {
+            const iovecs = try loop.allocator.alloc(os.iovec, data.len);
+            defer loop.allocator.free(iovecs);
+
+            for (data) |buf, i| {
+                iovecs[i] = os.iovec{
+                    .iov_base = buf.ptr,
+                    .iov_len = buf.len,
+                };
+            }
+
+            return preadvPosix(loop, fd, iovecs, offset);
+        },
+        .windows => {
+            const data_copy = try std.mem.dupe(loop.allocator, []u8, data);
+            defer loop.allocator.free(data_copy);
+            return preadvWindows(loop, fd, data_copy, offset);
+        },
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+/// data must outlive the returned frame
+pub fn preadvWindows(loop: *Loop, fd: fd_t, data: []const []u8, offset: u64) !usize {
+    assert(data.len != 0);
+    if (data.len == 1) return preadWindows(loop, fd, data[0], offset);
+
+    // TODO do these in parallel?
+    var off: usize = 0;
+    var iov_i: usize = 0;
+    var inner_off: usize = 0;
+    while (true) {
+        const v = data[iov_i];
+        const amt_read = try preadWindows(loop, fd, v[inner_off .. v.len - inner_off], offset + off);
+        off += amt_read;
+        inner_off += amt_read;
+        if (inner_off == v.len) {
+            iov_i += 1;
+            inner_off = 0;
+            if (iov_i == data.len) {
+                return off;
+            }
+        }
+        if (amt_read == 0) return off; // EOF
+    }
+}
+
+pub fn preadWindows(loop: *Loop, fd: fd_t, data: []u8, offset: u64) !usize {
+    var resume_node = Loop.ResumeNode.Basic{
+        .base = Loop.ResumeNode{
+            .id = Loop.ResumeNode.Id.Basic,
+            .handle = @frame(),
+            .overlapped = windows.OVERLAPPED{
+                .Internal = 0,
+                .InternalHigh = 0,
+                .Offset = @truncate(u32, offset),
+                .OffsetHigh = @truncate(u32, offset >> 32),
+                .hEvent = null,
+            },
+        },
+    };
+    // TODO only call create io completion port once per fd
+    _ = windows.CreateIoCompletionPort(fd, loop.os_data.io_port, undefined, undefined) catch undefined;
+    loop.beginOneEvent();
+    errdefer loop.finishOneEvent();
+
+    errdefer {
+        _ = windows.kernel32.CancelIoEx(fd, &resume_node.base.overlapped);
+    }
+    suspend {
+        _ = windows.kernel32.ReadFile(fd, data.ptr, @intCast(windows.DWORD, data.len), null, &resume_node.base.overlapped);
+    }
+    var bytes_transferred: windows.DWORD = undefined;
+    if (windows.kernel32.GetOverlappedResult(fd, &resume_node.base.overlapped, &bytes_transferred, windows.FALSE) == 0) {
+        switch (windows.kernel32.GetLastError()) {
+            windows.ERROR.IO_PENDING => unreachable,
+            windows.ERROR.OPERATION_ABORTED => return error.OperationAborted,
+            windows.ERROR.BROKEN_PIPE => return error.BrokenPipe,
+            windows.ERROR.HANDLE_EOF => return usize(bytes_transferred),
+            else => |err| return windows.unexpectedError(err),
+        }
+    }
+    return usize(bytes_transferred);
+}
+
+/// iovecs must live until preadv frame completes
+pub fn preadvPosix(
+    loop: *Loop,
+    fd: fd_t,
+    iovecs: []const os.iovec,
+    offset: usize,
+) os.ReadError!usize {
+    var req_node = RequestNode{
+        .prev = null,
+        .next = null,
+        .data = Request{
+            .msg = Request.Msg{
+                .PReadV = Request.Msg.PReadV{
+                    .fd = fd,
+                    .iov = iovecs,
+                    .offset = offset,
+                    .result = undefined,
+                },
+            },
+            .finish = Request.Finish{
+                .TickNode = Loop.NextTickNode{
+                    .prev = null,
+                    .next = null,
+                    .data = @frame(),
+                },
+            },
+        },
+    };
+
+    errdefer loop.posixFsCancel(&req_node);
+
+    suspend {
+        loop.posixFsRequest(&req_node);
+    }
+
+    return req_node.data.msg.PReadV.result;
+}
+
+pub fn openPosix(
+    loop: *Loop,
+    path: []const u8,
+    flags: u32,
+    mode: File.Mode,
+) File.OpenError!fd_t {
+    const path_c = try std.os.toPosixPath(path);
+
+    var req_node = RequestNode{
+        .prev = null,
+        .next = null,
+        .data = Request{
+            .msg = Request.Msg{
+                .Open = Request.Msg.Open{
+                    .path = path_c[0..path.len],
+                    .flags = flags,
+                    .mode = mode,
+                    .result = undefined,
+                },
+            },
+            .finish = Request.Finish{
+                .TickNode = Loop.NextTickNode{
+                    .prev = null,
+                    .next = null,
+                    .data = @frame(),
+                },
+            },
+        },
+    };
+
+    errdefer loop.posixFsCancel(&req_node);
+
+    suspend {
+        loop.posixFsRequest(&req_node);
+    }
+
+    return req_node.data.msg.Open.result;
+}
+
+pub fn openRead(loop: *Loop, path: []const u8) File.OpenError!fd_t {
+    switch (builtin.os) {
+        .macosx, .linux, .freebsd, .netbsd => {
+            const flags = os.O_LARGEFILE | os.O_RDONLY | os.O_CLOEXEC;
+            return openPosix(loop, path, flags, File.default_mode);
+        },
+
+        .windows => return windows.CreateFile(
+            path,
+            windows.GENERIC_READ,
+            windows.FILE_SHARE_READ,
+            null,
+            windows.OPEN_EXISTING,
+            windows.FILE_ATTRIBUTE_NORMAL | windows.FILE_FLAG_OVERLAPPED,
+            null,
+        ),
+
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+/// Creates if does not exist. Truncates the file if it exists.
+/// Uses the default mode.
+pub fn openWrite(loop: *Loop, path: []const u8) File.OpenError!fd_t {
+    return openWriteMode(loop, path, File.default_mode);
+}
+
+/// Creates if does not exist. Truncates the file if it exists.
+pub fn openWriteMode(loop: *Loop, path: []const u8, mode: File.Mode) File.OpenError!fd_t {
+    switch (builtin.os) {
+        .macosx,
+        .linux,
+        .freebsd,
+        .netbsd,
+        => {
+            const flags = os.O_LARGEFILE | os.O_WRONLY | os.O_CREAT | os.O_CLOEXEC | os.O_TRUNC;
+            return openPosix(loop, path, flags, File.default_mode);
+        },
+        .windows => return windows.CreateFile(
+            path,
+            windows.GENERIC_WRITE,
+            windows.FILE_SHARE_WRITE | windows.FILE_SHARE_READ | windows.FILE_SHARE_DELETE,
+            null,
+            windows.CREATE_ALWAYS,
+            windows.FILE_ATTRIBUTE_NORMAL | windows.FILE_FLAG_OVERLAPPED,
+            null,
+        ),
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+/// Creates if does not exist. Does not truncate.
+pub fn openReadWrite(
+    loop: *Loop,
+    path: []const u8,
+    mode: File.Mode,
+) File.OpenError!fd_t {
+    switch (builtin.os) {
+        .macosx, .linux, .freebsd, .netbsd => {
+            const flags = os.O_LARGEFILE | os.O_RDWR | os.O_CREAT | os.O_CLOEXEC;
+            return openPosix(loop, path, flags, mode);
+        },
+
+        .windows => return windows.CreateFile(
+            path,
+            windows.GENERIC_WRITE | windows.GENERIC_READ,
+            windows.FILE_SHARE_WRITE | windows.FILE_SHARE_READ | windows.FILE_SHARE_DELETE,
+            null,
+            windows.OPEN_ALWAYS,
+            windows.FILE_ATTRIBUTE_NORMAL | windows.FILE_FLAG_OVERLAPPED,
+            null,
+        ),
+
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+/// This abstraction helps to close file handles in defer expressions
+/// without the possibility of failure and without the use of suspend points.
+/// Start a `CloseOperation` before opening a file, so that you can defer
+/// `CloseOperation.finish`.
+/// If you call `setHandle` then finishing will close the fd; otherwise finishing
+/// will deallocate the `CloseOperation`.
+pub const CloseOperation = struct {
+    loop: *Loop,
+    os_data: OsData,
+
+    const OsData = switch (builtin.os) {
+        .linux, .macosx, .freebsd, .netbsd => OsDataPosix,
+
+        .windows => struct {
+            handle: ?fd_t,
+        },
+
+        else => @compileError("Unsupported OS"),
+    };
+
+    const OsDataPosix = struct {
+        have_fd: bool,
+        close_req_node: RequestNode,
+    };
+
+    pub fn start(loop: *Loop) (error{OutOfMemory}!*CloseOperation) {
+        const self = try loop.allocator.create(CloseOperation);
+        self.* = CloseOperation{
+            .loop = loop,
+            .os_data = switch (builtin.os) {
+                .linux, .macosx, .freebsd, .netbsd => initOsDataPosix(self),
+                .windows => OsData{ .handle = null },
+                else => @compileError("Unsupported OS"),
+            },
+        };
+        return self;
+    }
+
+    fn initOsDataPosix(self: *CloseOperation) OsData {
+        return OsData{
+            .have_fd = false,
+            .close_req_node = RequestNode{
+                .prev = null,
+                .next = null,
+                .data = Request{
+                    .msg = Request.Msg{
+                        .Close = Request.Msg.Close{ .fd = undefined },
+                    },
+                    .finish = Request.Finish{ .DeallocCloseOperation = self },
+                },
+            },
+        };
+    }
+
+    /// Defer this after creating.
+    pub fn finish(self: *CloseOperation) void {
+        switch (builtin.os) {
+            .linux,
+            .macosx,
+            .freebsd,
+            .netbsd,
+            => {
+                if (self.os_data.have_fd) {
+                    self.loop.posixFsRequest(&self.os_data.close_req_node);
+                } else {
+                    self.loop.allocator.destroy(self);
+                }
+            },
+            .windows => {
+                if (self.os_data.handle) |handle| {
+                    os.close(handle);
+                }
+                self.loop.allocator.destroy(self);
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+
+    pub fn setHandle(self: *CloseOperation, handle: fd_t) void {
+        switch (builtin.os) {
+            .linux,
+            .macosx,
+            .freebsd,
+            .netbsd,
+            => {
+                self.os_data.close_req_node.data.msg.Close.fd = handle;
+                self.os_data.have_fd = true;
+            },
+            .windows => {
+                self.os_data.handle = handle;
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+
+    /// Undo a `setHandle`.
+    pub fn clearHandle(self: *CloseOperation) void {
+        switch (builtin.os) {
+            .linux,
+            .macosx,
+            .freebsd,
+            .netbsd,
+            => {
+                self.os_data.have_fd = false;
+            },
+            .windows => {
+                self.os_data.handle = null;
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+
+    pub fn getHandle(self: *CloseOperation) fd_t {
+        switch (builtin.os) {
+            .linux,
+            .macosx,
+            .freebsd,
+            .netbsd,
+            => {
+                assert(self.os_data.have_fd);
+                return self.os_data.close_req_node.data.msg.Close.fd;
+            },
+            .windows => {
+                return self.os_data.handle.?;
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+};
+
+/// contents must remain alive until writeFile completes.
+/// TODO make this atomic or provide writeFileAtomic and rename this one to writeFileTruncate
+pub fn writeFile(loop: *Loop, path: []const u8, contents: []const u8) !void {
+    return writeFileMode(loop, path, contents, File.default_mode);
+}
+
+/// contents must remain alive until writeFile completes.
+pub fn writeFileMode(loop: *Loop, path: []const u8, contents: []const u8, mode: File.Mode) !void {
+    switch (builtin.os) {
+        .linux,
+        .macosx,
+        .freebsd,
+        .netbsd,
+        => return writeFileModeThread(loop, path, contents, mode),
+        .windows => return writeFileWindows(loop, path, contents),
+        else => @compileError("Unsupported OS"),
+    }
+}
+
+fn writeFileWindows(loop: *Loop, path: []const u8, contents: []const u8) !void {
+    const handle = try windows.CreateFile(
+        path,
+        windows.GENERIC_WRITE,
+        windows.FILE_SHARE_WRITE | windows.FILE_SHARE_READ | windows.FILE_SHARE_DELETE,
+        null,
+        windows.CREATE_ALWAYS,
+        windows.FILE_ATTRIBUTE_NORMAL | windows.FILE_FLAG_OVERLAPPED,
+        null,
+    );
+    defer os.close(handle);
+
+    try pwriteWindows(loop, handle, contents, 0);
+}
+
+fn writeFileModeThread(loop: *Loop, path: []const u8, contents: []const u8, mode: File.Mode) !void {
+    const path_with_null = try std.cstr.addNullByte(loop.allocator, path);
+    defer loop.allocator.free(path_with_null);
+
+    var req_node = RequestNode{
+        .prev = null,
+        .next = null,
+        .data = Request{
+            .msg = Request.Msg{
+                .WriteFile = Request.Msg.WriteFile{
+                    .path = path_with_null[0..path.len],
+                    .contents = contents,
+                    .mode = mode,
+                    .result = undefined,
+                },
+            },
+            .finish = Request.Finish{
+                .TickNode = Loop.NextTickNode{
+                    .prev = null,
+                    .next = null,
+                    .data = @frame(),
+                },
+            },
+        },
+    };
+
+    errdefer loop.posixFsCancel(&req_node);
+
+    suspend {
+        loop.posixFsRequest(&req_node);
+    }
+
+    return req_node.data.msg.WriteFile.result;
+}
+
+/// The frame resumes when the last data has been confirmed written, but before the file handle
+/// is closed.
+/// Caller owns returned memory.
+pub fn readFile(loop: *Loop, file_path: []const u8, max_size: usize) ![]u8 {
+    var close_op = try CloseOperation.start(loop);
+    defer close_op.finish();
+
+    const fd = try openRead(loop, file_path);
+    close_op.setHandle(fd);
+
+    var list = std.ArrayList(u8).init(loop.allocator);
+    defer list.deinit();
+
+    while (true) {
+        try list.ensureCapacity(list.len + mem.page_size);
+        const buf = list.items[list.len..];
+        const buf_array = [_][]u8{buf};
+        const amt = try preadv(loop, fd, buf_array, list.len);
+        list.len += amt;
+        if (list.len > max_size) {
+            return error.FileTooBig;
+        }
+        if (amt < buf.len) {
+            return list.toOwnedSlice();
+        }
+    }
+}
+
+pub const WatchEventId = enum {
+    CloseWrite,
+    Delete,
+};
+
+fn eqlString(a: []const u16, b: []const u16) bool {
+    if (a.len != b.len) return false;
+    if (a.ptr == b.ptr) return true;
+    return mem.compare(u16, a, b) == .Equal;
+}
+
+fn hashString(s: []const u16) u32 {
+    return @truncate(u32, std.hash.Wyhash.hash(0, @sliceToBytes(s)));
+}
+
+//pub const WatchEventError = error{
+//    UserResourceLimitReached,
+//    SystemResources,
+//    AccessDenied,
+//    Unexpected, // TODO remove this possibility
+//};
+//
+//pub fn Watch(comptime V: type) type {
+//    return struct {
+//        channel: *event.Channel(Event.Error!Event),
+//        os_data: OsData,
+//
+//        const OsData = switch (builtin.os) {
+//            .macosx, .freebsd, .netbsd => struct {
+//                file_table: FileTable,
+//                table_lock: event.Lock,
+//
+//                const FileTable = std.StringHashmap(*Put);
+//                const Put = struct {
+//                    putter: anyframe,
+//                    value_ptr: *V,
+//                };
+//            },
+//
+//            .linux => LinuxOsData,
+//            .windows => WindowsOsData,
+//
+//            else => @compileError("Unsupported OS"),
+//        };
+//
+//        const WindowsOsData = struct {
+//            table_lock: event.Lock,
+//            dir_table: DirTable,
+//            all_putters: std.atomic.Queue(anyframe),
+//            ref_count: std.atomic.Int(usize),
+//
+//            const DirTable = std.StringHashMap(*Dir);
+//            const FileTable = std.HashMap([]const u16, V, hashString, eqlString);
+//
+//            const Dir = struct {
+//                putter: anyframe,
+//                file_table: FileTable,
+//                table_lock: event.Lock,
+//            };
+//        };
+//
+//        const LinuxOsData = struct {
+//            putter: anyframe,
+//            inotify_fd: i32,
+//            wd_table: WdTable,
+//            table_lock: event.Lock,
+//
+//            const WdTable = std.AutoHashMap(i32, Dir);
+//            const FileTable = std.StringHashMap(V);
+//
+//            const Dir = struct {
+//                dirname: []const u8,
+//                file_table: FileTable,
+//            };
+//        };
+//
+//        const FileToHandle = std.StringHashMap(anyframe);
+//
+//        const Self = @This();
+//
+//        pub const Event = struct {
+//            id: Id,
+//            data: V,
+//
+//            pub const Id = WatchEventId;
+//            pub const Error = WatchEventError;
+//        };
+//
+//        pub fn create(loop: *Loop, event_buf_count: usize) !*Self {
+//            const channel = try event.Channel(Self.Event.Error!Self.Event).create(loop, event_buf_count);
+//            errdefer channel.destroy();
+//
+//            switch (builtin.os) {
+//                .linux => {
+//                    const inotify_fd = try os.inotify_init1(os.linux.IN_NONBLOCK | os.linux.IN_CLOEXEC);
+//                    errdefer os.close(inotify_fd);
+//
+//                    var result: *Self = undefined;
+//                    _ = try async<loop.allocator> linuxEventPutter(inotify_fd, channel, &result);
+//                    return result;
+//                },
+//
+//                .windows => {
+//                    const self = try loop.allocator.create(Self);
+//                    errdefer loop.allocator.destroy(self);
+//                    self.* = Self{
+//                        .channel = channel,
+//                        .os_data = OsData{
+//                            .table_lock = event.Lock.init(loop),
+//                            .dir_table = OsData.DirTable.init(loop.allocator),
+//                            .ref_count = std.atomic.Int(usize).init(1),
+//                            .all_putters = std.atomic.Queue(anyframe).init(),
+//                        },
+//                    };
+//                    return self;
+//                },
+//
+//                .macosx, .freebsd, .netbsd => {
+//                    const self = try loop.allocator.create(Self);
+//                    errdefer loop.allocator.destroy(self);
+//
+//                    self.* = Self{
+//                        .channel = channel,
+//                        .os_data = OsData{
+//                            .table_lock = event.Lock.init(loop),
+//                            .file_table = OsData.FileTable.init(loop.allocator),
+//                        },
+//                    };
+//                    return self;
+//                },
+//                else => @compileError("Unsupported OS"),
+//            }
+//        }
+//
+//        /// All addFile calls and removeFile calls must have completed.
+//        pub fn destroy(self: *Self) void {
+//            switch (builtin.os) {
+//                .macosx, .freebsd, .netbsd => {
+//                    // TODO we need to cancel the frames before destroying the lock
+//                    self.os_data.table_lock.deinit();
+//                    var it = self.os_data.file_table.iterator();
+//                    while (it.next()) |entry| {
+//                        cancel entry.value.putter;
+//                        self.channel.loop.allocator.free(entry.key);
+//                    }
+//                    self.channel.destroy();
+//                },
+//                .linux => cancel self.os_data.putter,
+//                .windows => {
+//                    while (self.os_data.all_putters.get()) |putter_node| {
+//                        cancel putter_node.data;
+//                    }
+//                    self.deref();
+//                },
+//                else => @compileError("Unsupported OS"),
+//            }
+//        }
+//
+//        fn ref(self: *Self) void {
+//            _ = self.os_data.ref_count.incr();
+//        }
+//
+//        fn deref(self: *Self) void {
+//            if (self.os_data.ref_count.decr() == 1) {
+//                const allocator = self.channel.loop.allocator;
+//                self.os_data.table_lock.deinit();
+//                var it = self.os_data.dir_table.iterator();
+//                while (it.next()) |entry| {
+//                    allocator.free(entry.key);
+//                    allocator.destroy(entry.value);
+//                }
+//                self.os_data.dir_table.deinit();
+//                self.channel.destroy();
+//                allocator.destroy(self);
+//            }
+//        }
+//
+//        pub async fn addFile(self: *Self, file_path: []const u8, value: V) !?V {
+//            switch (builtin.os) {
+//                .macosx, .freebsd, .netbsd => return await (async addFileKEvent(self, file_path, value) catch unreachable),
+//                .linux => return await (async addFileLinux(self, file_path, value) catch unreachable),
+//                .windows => return await (async addFileWindows(self, file_path, value) catch unreachable),
+//                else => @compileError("Unsupported OS"),
+//            }
+//        }
+//
+//        async fn addFileKEvent(self: *Self, file_path: []const u8, value: V) !?V {
+//            const resolved_path = try std.fs.path.resolve(self.channel.loop.allocator, [_][]const u8{file_path});
+//            var resolved_path_consumed = false;
+//            defer if (!resolved_path_consumed) self.channel.loop.allocator.free(resolved_path);
+//
+//            var close_op = try CloseOperation.start(self.channel.loop);
+//            var close_op_consumed = false;
+//            defer if (!close_op_consumed) close_op.finish();
+//
+//            const flags = if (os.darwin.is_the_target) os.O_SYMLINK | os.O_EVTONLY else 0;
+//            const mode = 0;
+//            const fd = try await (async openPosix(self.channel.loop, resolved_path, flags, mode) catch unreachable);
+//            close_op.setHandle(fd);
+//
+//            var put_data: *OsData.Put = undefined;
+//            const putter = try async self.kqPutEvents(close_op, value, &put_data);
+//            close_op_consumed = true;
+//            errdefer cancel putter;
+//
+//            const result = blk: {
+//                const held = await (async self.os_data.table_lock.acquire() catch unreachable);
+//                defer held.release();
+//
+//                const gop = try self.os_data.file_table.getOrPut(resolved_path);
+//                if (gop.found_existing) {
+//                    const prev_value = gop.kv.value.value_ptr.*;
+//                    cancel gop.kv.value.putter;
+//                    gop.kv.value = put_data;
+//                    break :blk prev_value;
+//                } else {
+//                    resolved_path_consumed = true;
+//                    gop.kv.value = put_data;
+//                    break :blk null;
+//                }
+//            };
+//
+//            return result;
+//        }
+//
+//        async fn kqPutEvents(self: *Self, close_op: *CloseOperation, value: V, out_put: **OsData.Put) void {
+//            var value_copy = value;
+//            var put = OsData.Put{
+//                .putter = @frame(),
+//                .value_ptr = &value_copy,
+//            };
+//            out_put.* = &put;
+//            self.channel.loop.beginOneEvent();
+//
+//            defer {
+//                close_op.finish();
+//                self.channel.loop.finishOneEvent();
+//            }
+//
+//            while (true) {
+//                if (await (async self.channel.loop.bsdWaitKev(
+//                    @intCast(usize, close_op.getHandle()),
+//                    os.EVFILT_VNODE,
+//                    os.NOTE_WRITE | os.NOTE_DELETE,
+//                ) catch unreachable)) |kev| {
+//                    // TODO handle EV_ERROR
+//                    if (kev.fflags & os.NOTE_DELETE != 0) {
+//                        await (async self.channel.put(Self.Event{
+//                            .id = Event.Id.Delete,
+//                            .data = value_copy,
+//                        }) catch unreachable);
+//                    } else if (kev.fflags & os.NOTE_WRITE != 0) {
+//                        await (async self.channel.put(Self.Event{
+//                            .id = Event.Id.CloseWrite,
+//                            .data = value_copy,
+//                        }) catch unreachable);
+//                    }
+//                } else |err| switch (err) {
+//                    error.EventNotFound => unreachable,
+//                    error.ProcessNotFound => unreachable,
+//                    error.Overflow => unreachable,
+//                    error.AccessDenied, error.SystemResources => |casted_err| {
+//                        await (async self.channel.put(casted_err) catch unreachable);
+//                    },
+//                }
+//            }
+//        }
+//
+//        async fn addFileLinux(self: *Self, file_path: []const u8, value: V) !?V {
+//            const value_copy = value;
+//
+//            const dirname = std.fs.path.dirname(file_path) orelse ".";
+//            const dirname_with_null = try std.cstr.addNullByte(self.channel.loop.allocator, dirname);
+//            var dirname_with_null_consumed = false;
+//            defer if (!dirname_with_null_consumed) self.channel.loop.allocator.free(dirname_with_null);
+//
+//            const basename = std.fs.path.basename(file_path);
+//            const basename_with_null = try std.cstr.addNullByte(self.channel.loop.allocator, basename);
+//            var basename_with_null_consumed = false;
+//            defer if (!basename_with_null_consumed) self.channel.loop.allocator.free(basename_with_null);
+//
+//            const wd = try os.inotify_add_watchC(
+//                self.os_data.inotify_fd,
+//                dirname_with_null.ptr,
+//                os.linux.IN_CLOSE_WRITE | os.linux.IN_ONLYDIR | os.linux.IN_EXCL_UNLINK,
+//            );
+//            // wd is either a newly created watch or an existing one.
+//
+//            const held = await (async self.os_data.table_lock.acquire() catch unreachable);
+//            defer held.release();
+//
+//            const gop = try self.os_data.wd_table.getOrPut(wd);
+//            if (!gop.found_existing) {
+//                gop.kv.value = OsData.Dir{
+//                    .dirname = dirname_with_null,
+//                    .file_table = OsData.FileTable.init(self.channel.loop.allocator),
+//                };
+//                dirname_with_null_consumed = true;
+//            }
+//            const dir = &gop.kv.value;
+//
+//            const file_table_gop = try dir.file_table.getOrPut(basename_with_null);
+//            if (file_table_gop.found_existing) {
+//                const prev_value = file_table_gop.kv.value;
+//                file_table_gop.kv.value = value_copy;
+//                return prev_value;
+//            } else {
+//                file_table_gop.kv.value = value_copy;
+//                basename_with_null_consumed = true;
+//                return null;
+//            }
+//        }
+//
+//        async fn addFileWindows(self: *Self, file_path: []const u8, value: V) !?V {
+//            const value_copy = value;
+//            // TODO we might need to convert dirname and basename to canonical file paths ("short"?)
+//
+//            const dirname = try std.mem.dupe(self.channel.loop.allocator, u8, std.fs.path.dirname(file_path) orelse ".");
+//            var dirname_consumed = false;
+//            defer if (!dirname_consumed) self.channel.loop.allocator.free(dirname);
+//
+//            const dirname_utf16le = try std.unicode.utf8ToUtf16LeWithNull(self.channel.loop.allocator, dirname);
+//            defer self.channel.loop.allocator.free(dirname_utf16le);
+//
+//            // TODO https://github.com/ziglang/zig/issues/265
+//            const basename = std.fs.path.basename(file_path);
+//            const basename_utf16le_null = try std.unicode.utf8ToUtf16LeWithNull(self.channel.loop.allocator, basename);
+//            var basename_utf16le_null_consumed = false;
+//            defer if (!basename_utf16le_null_consumed) self.channel.loop.allocator.free(basename_utf16le_null);
+//            const basename_utf16le_no_null = basename_utf16le_null[0 .. basename_utf16le_null.len - 1];
+//
+//            const dir_handle = try windows.CreateFileW(
+//                dirname_utf16le.ptr,
+//                windows.FILE_LIST_DIRECTORY,
+//                windows.FILE_SHARE_READ | windows.FILE_SHARE_DELETE | windows.FILE_SHARE_WRITE,
+//                null,
+//                windows.OPEN_EXISTING,
+//                windows.FILE_FLAG_BACKUP_SEMANTICS | windows.FILE_FLAG_OVERLAPPED,
+//                null,
+//            );
+//            var dir_handle_consumed = false;
+//            defer if (!dir_handle_consumed) windows.CloseHandle(dir_handle);
+//
+//            const held = await (async self.os_data.table_lock.acquire() catch unreachable);
+//            defer held.release();
+//
+//            const gop = try self.os_data.dir_table.getOrPut(dirname);
+//            if (gop.found_existing) {
+//                const dir = gop.kv.value;
+//                const held_dir_lock = await (async dir.table_lock.acquire() catch unreachable);
+//                defer held_dir_lock.release();
+//
+//                const file_gop = try dir.file_table.getOrPut(basename_utf16le_no_null);
+//                if (file_gop.found_existing) {
+//                    const prev_value = file_gop.kv.value;
+//                    file_gop.kv.value = value_copy;
+//                    return prev_value;
+//                } else {
+//                    file_gop.kv.value = value_copy;
+//                    basename_utf16le_null_consumed = true;
+//                    return null;
+//                }
+//            } else {
+//                errdefer _ = self.os_data.dir_table.remove(dirname);
+//                const dir = try self.channel.loop.allocator.create(OsData.Dir);
+//                errdefer self.channel.loop.allocator.destroy(dir);
+//
+//                dir.* = OsData.Dir{
+//                    .file_table = OsData.FileTable.init(self.channel.loop.allocator),
+//                    .table_lock = event.Lock.init(self.channel.loop),
+//                    .putter = undefined,
+//                };
+//                gop.kv.value = dir;
+//                assert((try dir.file_table.put(basename_utf16le_no_null, value_copy)) == null);
+//                basename_utf16le_null_consumed = true;
+//
+//                dir.putter = try async self.windowsDirReader(dir_handle, dir);
+//                dir_handle_consumed = true;
+//
+//                dirname_consumed = true;
+//
+//                return null;
+//            }
+//        }
+//
+//        async fn windowsDirReader(self: *Self, dir_handle: windows.HANDLE, dir: *OsData.Dir) void {
+//            self.ref();
+//            defer self.deref();
+//
+//            defer os.close(dir_handle);
+//
+//            var putter_node = std.atomic.Queue(anyframe).Node{
+//                .data = @frame(),
+//                .prev = null,
+//                .next = null,
+//            };
+//            self.os_data.all_putters.put(&putter_node);
+//            defer _ = self.os_data.all_putters.remove(&putter_node);
+//
+//            var resume_node = Loop.ResumeNode.Basic{
+//                .base = Loop.ResumeNode{
+//                    .id = Loop.ResumeNode.Id.Basic,
+//                    .handle = @frame(),
+//                    .overlapped = windows.OVERLAPPED{
+//                        .Internal = 0,
+//                        .InternalHigh = 0,
+//                        .Offset = 0,
+//                        .OffsetHigh = 0,
+//                        .hEvent = null,
+//                    },
+//                },
+//            };
+//            var event_buf: [4096]u8 align(@alignOf(windows.FILE_NOTIFY_INFORMATION)) = undefined;
+//
+//            // TODO handle this error not in the channel but in the setup
+//            _ = windows.CreateIoCompletionPort(
+//                dir_handle,
+//                self.channel.loop.os_data.io_port,
+//                undefined,
+//                undefined,
+//            ) catch |err| {
+//                await (async self.channel.put(err) catch unreachable);
+//                return;
+//            };
+//
+//            while (true) {
+//                {
+//                    // TODO only 1 beginOneEvent for the whole function
+//                    self.channel.loop.beginOneEvent();
+//                    errdefer self.channel.loop.finishOneEvent();
+//                    errdefer {
+//                        _ = windows.kernel32.CancelIoEx(dir_handle, &resume_node.base.overlapped);
+//                    }
+//                    suspend {
+//                        _ = windows.kernel32.ReadDirectoryChangesW(
+//                            dir_handle,
+//                            &event_buf,
+//                            @intCast(windows.DWORD, event_buf.len),
+//                            windows.FALSE, // watch subtree
+//                            windows.FILE_NOTIFY_CHANGE_FILE_NAME | windows.FILE_NOTIFY_CHANGE_DIR_NAME |
+//                                windows.FILE_NOTIFY_CHANGE_ATTRIBUTES | windows.FILE_NOTIFY_CHANGE_SIZE |
+//                                windows.FILE_NOTIFY_CHANGE_LAST_WRITE | windows.FILE_NOTIFY_CHANGE_LAST_ACCESS |
+//                                windows.FILE_NOTIFY_CHANGE_CREATION | windows.FILE_NOTIFY_CHANGE_SECURITY,
+//                            null, // number of bytes transferred (unused for async)
+//                            &resume_node.base.overlapped,
+//                            null, // completion routine - unused because we use IOCP
+//                        );
+//                    }
+//                }
+//                var bytes_transferred: windows.DWORD = undefined;
+//                if (windows.kernel32.GetOverlappedResult(dir_handle, &resume_node.base.overlapped, &bytes_transferred, windows.FALSE) == 0) {
+//                    const err = switch (windows.kernel32.GetLastError()) {
+//                        else => |err| windows.unexpectedError(err),
+//                    };
+//                    await (async self.channel.put(err) catch unreachable);
+//                } else {
+//                    // can't use @bytesToSlice because of the special variable length name field
+//                    var ptr = event_buf[0..].ptr;
+//                    const end_ptr = ptr + bytes_transferred;
+//                    var ev: *windows.FILE_NOTIFY_INFORMATION = undefined;
+//                    while (@ptrToInt(ptr) < @ptrToInt(end_ptr)) : (ptr += ev.NextEntryOffset) {
+//                        ev = @ptrCast(*windows.FILE_NOTIFY_INFORMATION, ptr);
+//                        const emit = switch (ev.Action) {
+//                            windows.FILE_ACTION_REMOVED => WatchEventId.Delete,
+//                            windows.FILE_ACTION_MODIFIED => WatchEventId.CloseWrite,
+//                            else => null,
+//                        };
+//                        if (emit) |id| {
+//                            const basename_utf16le = ([*]u16)(&ev.FileName)[0 .. ev.FileNameLength / 2];
+//                            const user_value = blk: {
+//                                const held = await (async dir.table_lock.acquire() catch unreachable);
+//                                defer held.release();
+//
+//                                if (dir.file_table.get(basename_utf16le)) |entry| {
+//                                    break :blk entry.value;
+//                                } else {
+//                                    break :blk null;
+//                                }
+//                            };
+//                            if (user_value) |v| {
+//                                await (async self.channel.put(Event{
+//                                    .id = id,
+//                                    .data = v,
+//                                }) catch unreachable);
+//                            }
+//                        }
+//                        if (ev.NextEntryOffset == 0) break;
+//                    }
+//                }
+//            }
+//        }
+//
+//        pub async fn removeFile(self: *Self, file_path: []const u8) ?V {
+//            @panic("TODO");
+//        }
+//
+//        async fn linuxEventPutter(inotify_fd: i32, channel: *event.Channel(Event.Error!Event), out_watch: **Self) void {
+//            const loop = channel.loop;
+//
+//            var watch = Self{
+//                .channel = channel,
+//                .os_data = OsData{
+//                    .putter = @frame(),
+//                    .inotify_fd = inotify_fd,
+//                    .wd_table = OsData.WdTable.init(loop.allocator),
+//                    .table_lock = event.Lock.init(loop),
+//                },
+//            };
+//            out_watch.* = &watch;
+//
+//            loop.beginOneEvent();
+//
+//            defer {
+//                watch.os_data.table_lock.deinit();
+//                var wd_it = watch.os_data.wd_table.iterator();
+//                while (wd_it.next()) |wd_entry| {
+//                    var file_it = wd_entry.value.file_table.iterator();
+//                    while (file_it.next()) |file_entry| {
+//                        loop.allocator.free(file_entry.key);
+//                    }
+//                    loop.allocator.free(wd_entry.value.dirname);
+//                }
+//                loop.finishOneEvent();
+//                os.close(inotify_fd);
+//                channel.destroy();
+//            }
+//
+//            var event_buf: [4096]u8 align(@alignOf(os.linux.inotify_event)) = undefined;
+//
+//            while (true) {
+//                const rc = os.linux.read(inotify_fd, &event_buf, event_buf.len);
+//                const errno = os.linux.getErrno(rc);
+//                switch (errno) {
+//                    0 => {
+//                        // can't use @bytesToSlice because of the special variable length name field
+//                        var ptr = event_buf[0..].ptr;
+//                        const end_ptr = ptr + event_buf.len;
+//                        var ev: *os.linux.inotify_event = undefined;
+//                        while (@ptrToInt(ptr) < @ptrToInt(end_ptr)) : (ptr += @sizeOf(os.linux.inotify_event) + ev.len) {
+//                            ev = @ptrCast(*os.linux.inotify_event, ptr);
+//                            if (ev.mask & os.linux.IN_CLOSE_WRITE == os.linux.IN_CLOSE_WRITE) {
+//                                const basename_ptr = ptr + @sizeOf(os.linux.inotify_event);
+//                                const basename_with_null = basename_ptr[0 .. std.mem.len(u8, basename_ptr) + 1];
+//                                const user_value = blk: {
+//                                    const held = await (async watch.os_data.table_lock.acquire() catch unreachable);
+//                                    defer held.release();
+//
+//                                    const dir = &watch.os_data.wd_table.get(ev.wd).?.value;
+//                                    if (dir.file_table.get(basename_with_null)) |entry| {
+//                                        break :blk entry.value;
+//                                    } else {
+//                                        break :blk null;
+//                                    }
+//                                };
+//                                if (user_value) |v| {
+//                                    await (async channel.put(Event{
+//                                        .id = WatchEventId.CloseWrite,
+//                                        .data = v,
+//                                    }) catch unreachable);
+//                                }
+//                            }
+//                        }
+//                    },
+//                    os.linux.EINTR => continue,
+//                    os.linux.EINVAL => unreachable,
+//                    os.linux.EFAULT => unreachable,
+//                    os.linux.EAGAIN => {
+//                        (await (async loop.linuxWaitFd(
+//                            inotify_fd,
+//                            os.linux.EPOLLET | os.linux.EPOLLIN,
+//                        ) catch unreachable)) catch |err| {
+//                            const transformed_err = switch (err) {
+//                                error.FileDescriptorAlreadyPresentInSet => unreachable,
+//                                error.OperationCausesCircularLoop => unreachable,
+//                                error.FileDescriptorNotRegistered => unreachable,
+//                                error.FileDescriptorIncompatibleWithEpoll => unreachable,
+//                                error.Unexpected => unreachable,
+//                                else => |e| e,
+//                            };
+//                            await (async channel.put(transformed_err) catch unreachable);
+//                        };
+//                    },
+//                    else => unreachable,
+//                }
+//            }
+//        }
+//    };
+//}
+
+const test_tmp_dir = "std_event_fs_test";
+
+// TODO this test is disabled until the async function rewrite is finished.
+//test "write a file, watch it, write it again" {
+//    return error.SkipZigTest;
+//    const allocator = std.heap.direct_allocator;
+//
+//    // TODO move this into event loop too
+//    try os.makePath(allocator, test_tmp_dir);
+//    defer os.deleteTree(allocator, test_tmp_dir) catch {};
+//
+//    var loop: Loop = undefined;
+//    try loop.initMultiThreaded(allocator);
+//    defer loop.deinit();
+//
+//    var result: anyerror!void = error.ResultNeverWritten;
+//    const handle = try async<allocator> testFsWatchCantFail(&loop, &result);
+//    defer cancel handle;
+//
+//    loop.run();
+//    return result;
+//}
+
+fn testFsWatchCantFail(loop: *Loop, result: *(anyerror!void)) void {
+    result.* = testFsWatch(loop);
+}
+
+fn testFsWatch(loop: *Loop) !void {
+    const file_path = try std.fs.path.join(loop.allocator, [][]const u8{ test_tmp_dir, "file.txt" });
+    defer loop.allocator.free(file_path);
+
+    const contents =
+        \\line 1
+        \\line 2
+    ;
+    const line2_offset = 7;
+
+    // first just write then read the file
+    try writeFile(loop, file_path, contents);
+
+    const read_contents = try readFile(loop, file_path, 1024 * 1024);
+    testing.expectEqualSlices(u8, contents, read_contents);
+
+    // now watch the file
+    var watch = try Watch(void).create(loop, 0);
+    defer watch.destroy();
+
+    testing.expect((try watch.addFile(file_path, {})) == null);
+
+    const ev = async watch.channel.get();
+    var ev_consumed = false;
+    defer if (!ev_consumed) await ev;
+
+    // overwrite line 2
+    const fd = try await openReadWrite(loop, file_path, File.default_mode);
+    {
+        defer os.close(fd);
+
+        try pwritev(loop, fd, []const []const u8{"lorem ipsum"}, line2_offset);
+    }
+
+    ev_consumed = true;
+    switch ((try await ev).id) {
+        WatchEventId.CloseWrite => {},
+        WatchEventId.Delete => @panic("wrong event"),
+    }
+    const contents_updated = try readFile(loop, file_path, 1024 * 1024);
+    testing.expectEqualSlices(u8,
+        \\line 1
+        \\lorem ipsum
+    , contents_updated);
+
+    // TODO test deleting the file and then re-adding it. we should get events for both
+}
+
+pub const OutStream = struct {
+    fd: fd_t,
+    stream: Stream,
+    loop: *Loop,
+    offset: usize,
+
+    pub const Error = File.WriteError;
+    pub const Stream = event.io.OutStream(Error);
+
+    pub fn init(loop: *Loop, fd: fd_t, offset: usize) OutStream {
+        return OutStream{
+            .fd = fd,
+            .loop = loop,
+            .offset = offset,
+            .stream = Stream{ .writeFn = writeFn },
+        };
+    }
+
+    fn writeFn(out_stream: *Stream, bytes: []const u8) Error!void {
+        const self = @fieldParentPtr(OutStream, "stream", out_stream);
+        const offset = self.offset;
+        self.offset += bytes.len;
+        return pwritev(self.loop, self.fd, [][]const u8{bytes}, offset);
+    }
+};
+
+pub const InStream = struct {
+    fd: fd_t,
+    stream: Stream,
+    loop: *Loop,
+    offset: usize,
+
+    pub const Error = PReadVError; // TODO make this not have OutOfMemory
+    pub const Stream = event.io.InStream(Error);
+
+    pub fn init(loop: *Loop, fd: fd_t, offset: usize) InStream {
+        return InStream{
+            .fd = fd,
+            .loop = loop,
+            .offset = offset,
+            .stream = Stream{ .readFn = readFn },
+        };
+    }
+
+    fn readFn(in_stream: *Stream, bytes: []u8) Error!usize {
+        const self = @fieldParentPtr(InStream, "stream", in_stream);
+        const amt = try preadv(self.loop, self.fd, [][]u8{bytes}, self.offset);
+        self.offset += amt;
+        return amt;
+    }
+};