[0.15.10] Pump and backwards chem plant causes desync

[mingo888]

A small multiplayer world that myself and some friends played on has become unusable in multiplayer. This is a vanilla 0.15.10 world, and no mods whatsoever are installed.

Recently, we saved the game and stopped the server (there were only about 3 people on at the time). But when the server was hosted again with that save, any user that tried to connect immediately entered a desync loop, constantly redownloading the world each time. This happens only with the world, but affects all players that try to connect. Other worlds do not pose a desync issue. We have tried using a different host and this does not resolve the issue, suggesting that the problem is with the world itself.

In singleplayer, or in multiplayer before someone connects, the world works fine with no issues noticed. I can't tell what could have caused this; of the three players, two were standing still on solid ground and one was in a car. We have hosted this world numerous times with no issues before, so this is unusual.

Below are the log and report files. To reproduce the issue, simply go to Multiplayer -> Load World and select the world file below. Anybody that connects, new or old, should immediately desync and enter a loop.

Log File: https://1drv.ms/u/s!As5e88NCWzT60CmjJYLtt8_FDa11
Desync Report #1: https://1drv.ms/u/s!As5e88NCWzT60Ct2aAoRe4mCFN94
Desync Report #2: https://1drv.ms/u/s!As5e88NCWzT60ConxihvzyrY1BiO
World File: https://1drv.ms/u/s!As5e88NCWzT60CwczosCskOvnJo2

[mingo888]

Through thorough testing and map editing, we have narrowed down the issue to one specific source.

It seems that at some point before the map was saved, a pump was placed at the end of a petroleum pipeline facing the output of a chemical plant. That is, the pump (which was powered fully) was trying to pump petroleum into the output of an empty chemical plant, rather than the input. No recipe had been assigned to the chemical plant. Upon rotating this chemical plant or pump, either with the map editor, in singleplayer, or in multiplayer before others joined, the desync issue would disappear and others would be able to join fine.

I would like to stress that simply arranging the pump and chemical plant in this way does not cause players to desync, but rather prevents players from joining the server. Those already connected have no problem, which is why the problem wasn't realized until some time later when we reloaded the world.

Coordinates of the offending pump in the above save file (from top left vertices): (362, -125), (363, -125)

The thread title has been modified accordingly.

[Nexela]

Nice find. Confirmed on a test map

Pushing fluids through a pump directly into the chem plant output causes destinks

[Rseding91]

Thanks for the detailed investigation and steps to reproduce

It's now fixed for the next version of 0.15.