GetUpdateChain error

[ineiti]

The following else is not optimal:

https://github.com/dedis/cothority/blob/master/skipchain/skipchain.go#L528

Example given: in the current chain, conode.c4dt.org has been removed for some blocks. So it goes through the blocks and finds that the highest link from block 2048 points to a block with a roster where conode.c4dt.org is not in anymore. So it stops searching and returns.

Instead, the node should return as many blocks as he can. At least in this case the clients would receive more blocks like that.

Also the skipchain/Client.GetUpdateChain doesn't recognize the corner case where a node returns a valid block but where the node is not in the roster. This should not happen.

Also the external/js/cothority/src/skipchain/SkipchainRPC.getUpdateChain doesn't work correctly and can fall into an endless loop.