Allow either a valid scope_id or the device name as valid input for the interface

src/mdns.zig

@@ -8,6 +8,7 @@ const MDNSError = error{
     NotResponse,
     NoMatchingAddress,
     AddressBadFormat,
+    SocketBindFail,
 };
 
 pub fn get_mdns(domain: util.Domain, ip_info: util.IPInfo) !util.IP {
@@ -43,6 +44,9 @@ fn get_mdns_socket(ip_info: util.IPInfo) !socket {
     if (std.c.setsockopt(sock, std.c.SOL.SOCKET, std.c.SO.RCVTIMEO, &timeout, @intCast(@sizeOf(std.c.timeval))) == -1) {
         return MDNSError.SocketInitFail;
     }
+    if (std.c.setsockopt(sock, std.c.SOL.SOCKET, std.c.SO.BINDTOIFINDEX, &ip_info.interface, @sizeOf(c_int)) == -1) {
+        return MDNSError.SocketBindFail;
+    }
     return sock;
 }
 
@@ -81,13 +85,7 @@ fn construct_mdns_query(domain: util.Domain, ip_info: util.IPInfo, buff: []u8) !
 fn get_target_address(ip_info: util.IPInfo) !std.net.Address {
     const target_addr: []const u8 = switch (ip_info.version) {
         .IPv4 => "224.0.0.251",
-        .IPv6 => blk: {
-            var buf: [50]u8 = undefined;
-            var byte_buf = std.io.fixedBufferStream(&buf);
-            const writer = byte_buf.writer();
-            try std.fmt.format(writer, "ff02::fb%{d}", .{ip_info.interface});
-            break :blk buf[0..writer.context.pos];
-        },
+        .IPv6 => "ff02::fb",
         else => unreachable,
     };
     return std.net.Address.resolveIp(target_addr, 5353);

src/util.zig

@@ -64,9 +64,15 @@ pub fn get_input() !struct {
     const ip_ver_str = args.next() orelse return ArgError.NotEnoughArgs;
     const ip_ver = std.meta.intToEnum(IP_VER_ENUM, std.fmt.parseInt(u3, ip_ver_str, 10) catch return ArgError.InvalidAddressVer) catch return ArgError.InvalidAddressVer;
 
-    const iface = try std.fmt.parseInt(c_int, args.next() orelse return ArgError.NotEnoughArgs, 10);
-    if (iface < 0) {
-        return ArgError.InvalidInterface;
+    var iface: c_int = undefined;
+    if (args.next()) |iface_str| {
+        iface = std.fmt.parseInt(c_int, iface_str, 10) catch |err| blk: {
+            if (err == std.fmt.ParseIntError.Overflow) return err;
+            break :blk std.c.if_nametoindex(iface_str);
+        };
+        if (iface <= 0) return ArgError.InvalidInterface;
+    } else {
+        return ArgError.NotEnoughArgs;
     }
     return .{ domain, IPInfo{ .version = ip_ver, .interface = iface } };
 }