Server sends cut off UnconnectedPong packets if LANBroadcast=0b in level.dat

In the latest version, if a world is loaded on a dedicated server with its LANBroadcast tag set to 0, the server will send broken pong packets in response to pings.

How to reproduce

• Download the dedicated server files

• Start the server to create the initial world and stop it again

• Change LANBroadcast to 0 in the level.dat using an NBT editor, or use the attached lavel.dat file.

• Start the server again

• Ping the server with a ping utility of your choice (e.g. https://www.npmjs.com/package/craftping)

• See an error message that the response is too short

Issue

Pong packets normally consist of an ID/timestamp echoed from the ping request, a server id, 16 bytes of magic, the length of the body, and the body, which is a string with status information about the server. In the case where LANBroadcast ist 0, it cuts off after the magic.

Correct response:

00000000  1c f5 59 03 f9 c4 95 a9  8e 87 b0 a4 af 9c 2d b6  |..Y...........-.|
00000010  d3 00 ff ff 00 fe fe fe  fe fd fd fd fd 12 34 56  |..............4V|
00000020  78 00 67 4d 43 50 45 3b  44 65 64 69 63 61 74 65  |x.gMCPE;Dedicate|
00000030  64 20 53 65 72 76 65 72  3b 31 30 30 31 3b 31 2e  |d Server;1001;1.|
00000040  32 36 2e 33 30 3b 30 3b  31 30 3b 39 37 37 37 34  |26.30;0;10;97774|
00000050  39 35 38 36 35 31 36 37  38 32 30 34 39 39 3b 42  |95865167820499;B|
00000060  65 64 72 6f 63 6b 20 6c  65 76 65 6c 3b 53 75 72  |edrock level;Sur|
00000070  76 69 76 61 6c 3b 31 3b  33 36 31 32 32 3b 31 39  |vival;1;36122;19|
00000080  31 33 33 3b 30 3b 31 3b  30 3b                    |133;0;1;0;|
0000008a

Incorrect response:

00000000  1c 04 c4 1a 83 e8 48 93  e4 be 09 f8 97 7d b4 fe  |......H......}..|
00000010  ed 00 ff ff 00 fe fe fe  fe fd fd fd fd 12 34 56  |..............4V|
00000020  78                                                |x|
00000021

How exactly worlds with LANBroadcast=0 come to be I don’t know. But users have repeatedly uploaded worlds like this to our platform and reported issues as a result of the bug, so I assume some client/editor option causes the tag to be set to 0. Dedicated servers do not have an option to change/overwrite this back to the correct value. I would say this is a bug, since it makes it impossible to use those worlds correctly on a server for normal users who don’t have access to this information and an NBT editor.

I also don’t see why a field called LANBroadcast would be related to dedicated servers not responding to pings correctly. This is not about the server broadcasting anything, it’s just about responding to network requests.