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Here's my client-mode implementation so far. Client-only mode only records block headers and doesn't use the tx index. It can't generate, but it can still send and receive transactions. It's not fully finished for use by end-users, but it doesn't matter because it's a complete no-op if fClient is not enabled. It's important to get this in as documentation showing the cut-lines for client-only re-implementers.
If it looks fine to you, go ahead and commit it to SVN. It should be completely innocuous and no-op.
With fClient=true, I've only tested the header-only initial download.
A little background. CBlockIndex contains all the information of the block header, so to operate with headers only, I just maintain the CBlockIndex structure as usual. The nFile/nBlockPos are null, since the full block is not recorded on disk.
The code to gracefully switch between client-mode on/off without deleting blk*.dat in between is not implemented yet. It would mostly be a matter of having non-client LoadBlockIndex ignore block index entries with null block pos. That would make it re-download those as full blocks. Switching back to client-mode is no problem, it doesn't mind if the full blocks are there.
If the initial block download becomes too long, we'll want client mode as an option so new users can get running quickly. With graceful switch-off of client mode, they can later turn off client mode and have it download the full blocks if they want to start generating.
If it looks fine to you, go ahead and commit it to SVN. It should be completely innocuous and no-op.
With fClient=true, I've only tested the header-only initial download.
A little background. CBlockIndex contains all the information of the block header, so to operate with headers only, I just maintain the CBlockIndex structure as usual. The nFile/nBlockPos are null, since the full block is not recorded on disk.
The code to gracefully switch between client-mode on/off without deleting blk*.dat in between is not implemented yet. It would mostly be a matter of having non-client LoadBlockIndex ignore block index entries with null block pos. That would make it re-download those as full blocks. Switching back to client-mode is no problem, it doesn't mind if the full blocks are there.
If the initial block download becomes too long, we'll want client mode as an option so new users can get running quickly. With graceful switch-off of client mode, they can later turn off client mode and have it download the full blocks if they want to start generating.
My plan was to dive into what Satoshi wrote already, understand it, test it in fClient=true mode (sending/receiving/relaying transactions on testnet), fix whatever is broken/unimplemented.
And then write code to switch from fClient=true to fClient=false, downloading full blocks, etc. And then writing code that does the toggle when generation is turned on for the first time or when getwork is called (I think those are the only times you need full blocks).
I haven't looked at or thought about the relaying code. Simply relaying all transactions (without checking to see if they're valid) if fClient=true should work nicely.