Simply return null if no response received instead of crashing

src/mdns.zig

@@ -3,13 +3,11 @@ const util = @import("util.zig");
 
 const MDNSError = error{
     SocketInitFail,
-    UDPConnectFail,
     UDPSendFail,
     UDPRecvFail,
     NotResponse,
     NoMatchingAddress,
     AddressBadFormat,
-    SocketSetTimeoutFail,
 };
 
 pub fn get_mdns(domain: util.Domain, ip_info: util.IPInfo) !util.IP {
@@ -41,9 +39,9 @@ fn get_mdns_socket(ip_info: util.IPInfo) !socket {
     if (sock == -1) {
         return MDNSError.SocketInitFail;
     }
-    const timeout: std.c.timeval = .{ .tv_sec = 1, .tv_usec = 0 };
+    const timeout: std.c.timeval = .{ .tv_sec = 5, .tv_usec = 0 };
     if (std.c.setsockopt(sock, std.c.SOL.SOCKET, std.c.SO.RCVTIMEO, &timeout, @intCast(@sizeOf(std.c.timeval))) == -1) {
-        return MDNSError.SocketSetTimeoutFail;
+        return MDNSError.SocketInitFail;
     }
     return sock;
 }
@@ -87,7 +85,7 @@ fn get_target_address(ip_info: util.IPInfo) !std.net.Address {
             var buf: [50]u8 = undefined;
             var byte_buf = std.io.fixedBufferStream(&buf);
             const writer = byte_buf.writer();
-            try std.fmt.format(writer, "ff02::fb%{s}", .{ip_info.interface.?});
+            try std.fmt.format(writer, "ff02::fb%{d}", .{ip_info.interface});
             break :blk buf[0..writer.context.pos];
         },
         else => unreachable,
@@ -117,7 +115,7 @@ fn receive_response(sock: socket, ip_info: util.IPInfo) !util.IP {
     const n: usize = blk: {
         const ret = std.c.recv(sock, &buff, MSG_BUFF_SIZE, 0);
         if (ret < 0) {
-            return MDNSError.UDPRecvFail;
+            return util.IP{}; // no reply means no matching record on network
         } else {
             break :blk @bitCast(ret);
         }
@@ -181,7 +179,7 @@ fn parse_mdns_response(response: []u8, ip_info: util.IPInfo) !util.IP {
             if (ip_bytes[0] == 0xfd) {
                 var addr_buff: [16]u8 = undefined;
                 @memcpy(&addr_buff, ip_bytes);
-                addr = std.net.Address.initIp6(addr_buff, 0, 0, @intCast(std.c.if_nametoindex(ip_info.interface.?)));
+                addr = std.net.Address.initIp6(addr_buff, 0, 0, @intCast(ip_info.interface));
             }
         }
     }

src/util.zig

@@ -32,7 +32,7 @@ pub fn merge_addrs(v4: IP, v6: IP) IP {
 
 pub const IPInfo = struct {
     version: IP_VER_ENUM,
-    interface: ?[:0]const u8,
+    interface: c_int,
 };
 
 pub const Domain = struct {
@@ -64,14 +64,10 @@ 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;
 
-    var iface: ?[:0]const u8 = null;
+    const iface = try std.fmt.parseInt(c_int, args.next() orelse return ArgError.NotEnoughArgs, 10);
-    if (ip_ver != .IPv4) {
+    if (iface < 0) {
-        iface = args.next() orelse return ArgError.InterfaceRequired;
-        if (std.c.if_nametoindex(iface.?) == 0) {
         return ArgError.InvalidInterface;
     }
-    }
-
     return .{ domain, IPInfo{ .version = ip_ver, .interface = iface } };
 }