[Bitcoin-development] Multiwallet support

[Eric Lombrozo <elombrozo@gmail.com>]

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I started working on a new feature to allow for watch-only addresses in wallets. https://github.com/bitcoin/bitcoin/pull/2121

In order to integrate this feature nicely into bitcoin / bitcoin, it will be necessary to disable signing and privkey export operations for watch-only addresses. Since disabling these things for only some of the keys in a wallet but not others is an API nightmare and complicates CreateTransaction logic, I propose adding multiple wallet capabilities and specifying upon creation whether a wallet is a:

1)  full signing wallet
	- importaddress is disabled.

2) watch-only wallet
	- signing and privkey export operations are disabled.
	- importprivkey only saves the associated address but not the private key. (behaves like importaddress <address for privkey>)

In order to do the above, it will be necessary to add multiple wallet support. Anyhow, that was my initial motivation for multiple wallets - but obviously, there are a number of other reasons why people might want multiple wallet support.

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Adding the ability to specify multiple wallets with associated names and passphrases in the config file should be fairly straightforward. However, exposing multiple wallets via RPC will be tricky as the existing RPC is not designed to support multiple wallets.

As to not break compatibility with the existing RPC calls, we can have a main wallet which is always used as the default wallet. If the user wants to use a different wallet, the name of the wallet would have to be specified in the call. Unfortunately, it doesn't look like we can use many of the existing RPC calls (sendfrom, sendmany,sendtoaddress, etc...) since they all have optional parameters already and it would be awkward to just tack on the wallet name parameter at the end. Also, walletpassphrase is problematic as it is not stateless. So it looks like we need a whole separate set of calls which require a wallet name and passphrase (if the wallet is encrypted).

For instance,
	walletsendtoaddress <walletname> <passphrase> <bitcoinaddress> <amount> [comment] [comment-to]

I welcome any proposals or suggestions as to how this should be done.



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