From c4d9d65a7bfb0e675ff9b43c50332032bcec6b25 Mon Sep 17 00:00:00 2001
From: hemisputnik <hemisputnik@proton.me>
Date: Wed, 22 Jul 2026 11:28:31 +0300
Subject: [PATCH] std.Io.net: send control data with .net_write

Add a new parameter to .net_write - control.
---
 lib/std/Io.zig          |  1 +
 lib/std/Io/Threaded.zig | 15 ++++++++++-----
 lib/std/Io/net.zig      |  4 ++++
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/lib/std/Io.zig b/lib/std/Io.zig
index e7bef51fce5b8160af6b5d1deef4869edd6e594a..ab0f8514b407cb567c048db502eb3b52d4a27fd4 100644
--- a/lib/std/Io.zig
+++ b/lib/std/Io.zig
@@ -453,6 +453,7 @@ pub const Operation = union(enum) {
         header: []const u8 = &.{},
         data: []const []const u8,
         splat: usize = 1,
+        control: []const u8 = &.{},
 
         pub const Error = error{
             /// Another TCP Fast Open is already in progress.
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 4ae0a35668728c0a17b1708d6cba113dfe843e60..77f14f6f991faa3ec821c8ad784445f1c2dd8d09 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -2590,9 +2590,9 @@ fn operate(userdata: ?*anyopaque, operation: Io.Operation) Io.Cancelable!Io.Oper
         },
         .net_write => |o| return .{
             .net_write = (if (is_windows)
-                netWriteWindows(o.socket_handle, o.header, o.data, o.splat)
+                netWriteWindows(o.socket_handle, o.header, o.data, o.splat, o.control)
             else
-                netWritePosix(o.socket_handle, o.header, o.data, o.splat)) catch |err| switch (err) {
+                netWritePosix(o.socket_handle, o.header, o.data, o.splat, o.control)) catch |err| switch (err) {
                 error.Canceled => |e| return e,
                 else => |e| e,
             },
@@ -3306,7 +3306,7 @@ fn batchDrainSubmittedWindows(t: *Threaded, b: *Io.Batch, concurrency: bool) (Io
                 // TODO integrate with overlapped I/O or equivalent to avoid this error
                 if (concurrency) return error.ConcurrencyUnavailable;
                 batchCompleteBlockingWindows(b, operation_userdata, .{
-                    .net_write = netWriteWindows(o.socket_handle, o.header, o.data, o.splat) catch |err| switch (err) {
+                    .net_write = netWriteWindows(o.socket_handle, o.header, o.data, o.splat, o.control) catch |err| switch (err) {
                         error.Canceled => |e| return e,
                         else => |e| e,
                     },
@@ -13389,6 +13389,7 @@ fn netWritePosix(
     header: []const u8,
     data: []const []const u8,
     splat: usize,
+    control: []const u8,
 ) net.Stream.Writer.Error!usize {
     if (!have_networking) return error.NetworkDown;
 
@@ -13398,8 +13399,8 @@ fn netWritePosix(
         .namelen = 0,
         .iov = &iovecs,
         .iovlen = 0,
-        .control = null,
-        .controllen = 0,
+        .control = if (control.len == 0) null else @constCast(control.ptr),
+        .controllen = @intCast(control.len),
         .flags = 0,
     };
     addBuf(&iovecs, &msg.iovlen, header);
@@ -13481,9 +13482,13 @@ fn netWriteWindows(
     header: []const u8,
     data: []const []const u8,
     splat: usize,
+    control: []const u8,
 ) net.Stream.Writer.Error!usize {
     if (!have_networking) return error.NetworkDown;
 
+    // Windows doesn't have the concept of control/ancillary data.
+    _ = control;
+
     var iovecs: [max_iovecs_len]windows.AFD.WSABUF(.@"const") = undefined;
     var len: u32 = 0;
     addAfdBuf(.@"const", &iovecs, &len, header);
diff --git a/lib/std/Io/net.zig b/lib/std/Io/net.zig
index 82bbcc0e707836d807cc5f7dea739f0668a583b5..01547a1a9df1c53ffdac6a370f2108136d6b6af2 100644
--- a/lib/std/Io/net.zig
+++ b/lib/std/Io/net.zig
@@ -1457,6 +1457,8 @@ pub const Stream = struct {
     pub const Writer = struct {
         io: Io,
         interface: Io.Writer,
+        /// Will be sent on next drain, then set back to an empty slice.
+        control: []const u8 = &.{},
         stream: Stream,
         err: ?Error = null,
         write_file_err: ?WriteFileError = null,
@@ -1499,6 +1501,7 @@ pub const Stream = struct {
                 .header = buffered,
                 .data = data,
                 .splat = splat,
+                .control = w.control,
             } }) catch |err| {
                 w.err = err;
                 return error.WriteFailed;
@@ -1507,6 +1510,7 @@ pub const Stream = struct {
                 w.err = err;
                 return error.WriteFailed;
             };
+            w.control = &.{};
             return io_w.consume(n);
         }
 
-- 
2.54.0