1 files changed, 65 insertions, 0 deletions
diff --git a/src/ancillary-data.zig b/src/ancillary-data.zig
new file mode 100644
index 0000000..0754720
--- /dev/null
+++ b/src/ancillary-data.zig
@@ -0,0 +1,65 @@
+const std = @import("std");
+
+const ControlMessage = extern struct {
+    const Level = enum(u32) {
+        socket = std.posix.SOL.SOCKET,
+    };
+
+    // WARNING: this kind enum might be wrong for non-linux posix systems.
+    const Kind = enum(u32) {
+        rights = 1,
+        credentials = 2,
+    };
+
+    const Header = extern struct {
+        length: usize,
+        level: Level,
+        kind: Kind,
+    };
+
+    header: Header,
+    payload: union {
+        fd: [255]std.posix.fd_t,
+    },
+
+    pub fn alignment(length: usize) usize {
+        return (length + @sizeOf(usize) - 1) & ~(@sizeOf(usize) - 1);
+    }
+
+    pub fn space(self: @This()) usize {
+        return self.alignment(self.length) + self.alignment(@sizeOf(Header));
+    }
+
+    pub fn from_fds(fds: []std.posix.fd_t) @This() {
+        var self: @This() = .{
+        };
+
+        self.level = .socket;
+        self.kind = .rights;
+        self.length = self.alignment(@sizeOf(Header)) + (fds.len * @sizeOf(std.posix.fd_t));
+
+        @memcpy(self.payload, fds);
+    }
+};
+
+pub fn send_fds(socket: std.posix.socket_t, fds: []std.posix.fd_t) !void {
+    var iobuf: [1]u8 = std.mem.zeroes([1]u8);
+
+    const io = std.posix.iovec {
+        .base = &iobuf,
+        .len = iobuf.len,
+    };
+
+    var cmsg: ControlMessage = .from_fds(fds);
+
+    const msghdr = std.posix.msghdr_const {
+        .name = null,
+        .namelen = 0,
+        .iov = &io,
+        .iolen = 1,
+        .control = &cmsg,
+        .controllen = cmsg.control_length(),
+    };
+
+    _ = try std.posix.sendmsg(socket, &msghdr, 0);
+}