From 9b4f850fe5d618548683f2782c66365f58cfd81a Mon Sep 17 00:00:00 2001
From: Muaz Ahmad <mahmad2000@protonmail.com>
Date: Sat, 11 May 2024 16:12:19 +0500
Subject: [PATCH] Add mDNS query construction

---
 src/mdns.zig | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/mdns.zig b/src/mdns.zig
index 107a8ea..76fbf60 100644
--- a/src/mdns.zig
+++ b/src/mdns.zig
@@ -41,11 +41,33 @@ fn get_mdns_socket(ip_info: util.IPInfo) !socket {
 }
 
 fn construct_mdns_query(domain: util.Domain, ip_info: util.IPInfo, buff: []u8) !usize {
-    _ = domain;
-    _ = ip_info;
     var n: usize = 0;
     var buff_writer = std.io.fixedBufferStream(buff);
-    n += try buff_writer.write("test");
+
+    const header =
+        [_]u8{0x00} ** 2 ++ // transaction ID
+        [_]u8{ 0x00, 0x00 } ++ // Standard Query flags
+        [_]u8{ 0x00, 0x01 } ++ // 1 question
+        [_]u8{0x00} ** 6 // Response only
+    ;
+    n += try buff_writer.write(&header);
+
+    for (domain.labels) |label| {
+        if (label.len == 0) break;
+        n += try buff_writer.write(&[_]u8{@truncate(label.len)});
+        n += try buff_writer.write(label);
+    }
+    n += try buff_writer.write(&[_]u8{0x00}); // End null byte
+
+    const question_footer =
+        [_]u8{ 0x00, switch (ip_info.version) {
+        util.IP_VER_ENUM.IPv4 => 0x01,
+        util.IP_VER_ENUM.IPv6 => 0x1c,
+    } } ++ // A or AAAA record
+        [_]u8{ 0x00, 0x01 } // IN query
+    ;
+    n += try buff_writer.write(&question_footer);
+
     return n;
 }