World Downloader Mod

With this mod, you can download parts of a multiplayer world (Earth/Nether) while you are connected to the server.

It adds a button to the multiplayer ESC menu that allows you to dump any incoming world data to disk, effectively creating a singleplayer clone of a remote multiplayer world.
Not a perfect clone as it can only save the "chunks" it receives from the server. To download the whole world you'd have to visit every modified place.
It also saves your inventory, position and health at the time you stopped the download.

The mod will not cause any additional load on the server because it never actively requests anything. It lets Minecraft do all the loading and buffering and then right before MC overwrites a buffered chunk that is no longer needed, it saves this chunk to disk. This will only slow down the client a bit when your HDD is too slow. It also saves the complete chunk buffer when stopping downloading or disconnecting.

If you modify something in singleplayer mode on a downloaded world, the changes are very likely to be overwritten the next time you download a newer version of the world. The local copy of the world will be overwritten chunk by chunk, not as a whole. Once a chunk is saved it will not be deleted again, only updated (overwritten).

All chunks that are to far away from the player while downloading will not be copied. However if you play this world in singleplayer mode these chunks will be generated on the fly based on the world's "seed" value which of course will also be downloaded. The generated scenary will look like the server world looked like before any human modifications.

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Note that in the downloaded world all container blocks (e.g. chest, dispenser, ...) will be empty. Currently I don't know if I can do something about this. Not anymore!
To save the contents of Chests, Dispensers and Furnaces open them while downloading.
To save the pitch of a note block hit it or activate it with redstone while downloadi

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