These notifications were added to support real time updates for
btcgui. As the btcgui project is no longer being developed, there are
no more consumers of this API, and it makes sense to remove them given
their various issues (the largest being that notifiations are sent
unsubscribed to clients that may never be interrested in them).
A new notification server has already been added to the wallet package
to handle notifications in a RPC-server agnostic way. This server is
the means by which the wallet notifies changes for gRPC clients. If
per-client registered notifications are to be re-added for the
JSON-RPC server, they should be integrated with the new notification
server rather than using this legacy code.
This is a rather monolithic commit that moves the old RPC server to
its own package (rpc/legacyrpc), introduces a new RPC server using
gRPC (rpc/rpcserver), and provides the ability to defer wallet loading
until request at a later time by an RPC (--noinitialload).
The legacy RPC server remains the default for now while the new gRPC
server is not enabled by default. Enabling the new server requires
setting a listen address (--experimenalrpclisten). This experimental
flag is used to effectively feature gate the server until it is ready
to use as a default. Both RPC servers can be run at the same time,
but require binding to different listen addresses.
In theory, with the legacy RPC server now living in its own package it
should become much easier to unit test the handlers. This will be
useful for any future changes to the package, as compatibility with
Core's wallet is still desired.
Type safety has also been improved in the legacy RPC server. Multiple
handler types are now used for methods that do and do not require the
RPC client as a dependency. This can statically help prevent nil
pointer dereferences, and was very useful for catching bugs during
refactoring.
To synchronize the wallet loading process between the main package
(the default) and through the gRPC WalletLoader service (with the
--noinitialload option), as well as increasing the loose coupling of
packages, a new wallet.Loader type has been added. All creating and
loading of existing wallets is done through a single Loader instance,
and callbacks can be attached to the instance to run after the wallet
has been opened. This is how the legacy RPC server is associated with
a loaded wallet, even after the wallet is loaded by a gRPC method in a
completely unrelated package.
Documentation for the new RPC server has been added to the
rpc/documentation directory. The documentation includes a
specification for the new RPC API, addresses how to make changes to
the server implementation, and provides short example clients in
several different languages.
Some of the new RPC methods are not implementated exactly as described
by the specification. These are considered bugs with the
implementation, not the spec. Known bugs are commented as such.
