Sending a file descriptor through a UNIX socket.
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4fac81b143
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const std = @import("std");
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/// TODO: move this to std
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/// This definition enables the use of Zig types with a cmsghdr structure.
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/// The oddity of this layout is that the data must be aligned to @sizeOf(usize)
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/// rather than its natural alignment.
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pub fn Cmsghdr(comptime T: type) type {
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const Header = extern struct {
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len: usize,
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level: c_int,
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@"type": c_int,
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};
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const data_align = @sizeOf(usize);
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const data_offset = std.mem.alignForward(@sizeOf(Header), data_align);
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return extern struct {
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const Self = @This();
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bytes: [data_offset + @sizeOf(T)]u8 align(@alignOf(Header)),
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pub fn init(args: struct {
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level: c_int,
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@"type": c_int,
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data: T,
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}) Self {
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var self: Self = undefined;
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self.headerPtr().* = .{
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.len = data_offset + @sizeOf(T),
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.level = args.level,
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.@"type" = args.@"type",
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};
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self.dataPtr().* = args.data;
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return self;
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}
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// TODO: include this version if we submit a PR to add this to std
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pub fn initNoData(args: struct {
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level: c_int,
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@"type": c_int,
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}) Self {
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var self: Self = undefined;
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self.headerPtr().* = .{
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.len = data_offset + @sizeOf(T),
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.level = args.level,
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.@"type" = args.@"type",
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};
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return self;
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}
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pub fn headerPtr(self: *Self) *Header {
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return @ptrCast(*Header, self);
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}
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pub fn dataPtr(self: *Self) *align(data_align) T {
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return @ptrCast(*T, self.bytes[data_offset..]);
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}
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};
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}
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test {
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std.testing.refAllDecls(Cmsghdr([3]std.os.fd_t));
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}
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const std = @import("std");
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const testing = std.testing;
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const net = std.net;
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const fmt = std.fmt;
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const mem = std.mem;
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const os = std.os;
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const print = std.debug.print;
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const Cmsghdr = @import("./cmsghdr.zig").Cmsghdr;
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fn disconnect(stream: net.Stream) void { stream.close(); }
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fn connect(path: []const u8) !net.Stream {
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return try net.connectUnixSocket(path);
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}
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const SCM_RIGHTS: c_int = 1;
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fn send_msg(sock: os.socket_t, msg: []const u8, fd: os.fd_t) void {
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var iov = [_]os.iovec_const{
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.{
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.iov_base = msg.ptr,
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.iov_len = msg.len,
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},
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};
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var cmsg = Cmsghdr(os.fd_t).init(.{
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.level = os.SOL.SOCKET,
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.@"type" = SCM_RIGHTS,
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.data = fd,
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});
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const len = os.sendmsg(sock, .{
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.name = undefined,
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.namelen = 0,
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.iov = &iov,
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.iovlen = iov.len,
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.control = &cmsg,
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.controllen = @sizeOf(@TypeOf(cmsg)),
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.flags = 0,
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}, 0) catch |err| {
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print("error sendmsg failed with {s}", .{@errorName(err)});
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return;
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};
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if (len != msg.len) {
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// we don't have much choice but to exit here
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// log.err(@src(), "expected sendmsg to return {} but got {}", .{msg.len, len});
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print("expected sendmsg to return {} but got {}", .{msg.len, len});
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os.exit(0xff);
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}
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}
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// const buffer_size = 10000;
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// var buffer: [buffer_size]u8 = undefined;
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// var fba = std.heap.fixedBufferAllocator(&buffer);
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fn add_line_in_file() !void {
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var cwd = std.fs.cwd();
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var f = try cwd.createFile("some-file.log", .{.read = true});
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defer f.close();
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var writer = f.writer();
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try writer.print("hello\n", .{});
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}
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pub fn main() !u8 {
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var path = "/tmp/.TEST_USOCK";
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print("Connection to {s}...\n", .{path});
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var stream = try connect(path);
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print("Connected! Opening a file...\n", .{});
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var file = try std.fs.cwd().createFile("some-file.log", .{.read = true});
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defer file.close();
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print("File opened! Writing some data into it...\n", .{});
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var writer = file.writer();
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try writer.print("hello this is the first process\n", .{});
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print("Data written! Sending its fd...\n", .{});
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send_msg(stream.handle, "hello", file.handle);
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print("Sent fd! Disconnection...\n", .{});
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disconnect(stream);
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print("Disconnected!\n", .{});
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return 0;
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}
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