In this commit, we add the glue infrastructure to make the sub RPC
server system work properly. Our high level goal is the following: using
only the lnrpc package (with no visibility into the sub RPC servers),
the RPC server is able to find, create, run, and manage the entire set
of present and future sub RPC servers. In order to achieve this, we use
the reflect package and build tags heavily to permit a loosely coupled
configuration parsing system for the sub RPC servers.
We start with a new `subRpcServerConfigs` struct which is _always_
present. This struct has its own group, and will house a series of
sub-configs, one for each sub RPC server. Each sub-config is actually
gated behind a build flag, and can be used to allow users on the command
line or in the config to specify arguments related to the sub-server. If
the config isn't present, then we don't attempt to parse it at all, if
it is, then that means the RPC server has been registered, and we should
parse the contents of its config.
The `subRpcServerConfigs` struct has two main methods:
`PopulateDependancies` and `FetchConfig`. The `PopulateDependancies` is
used to dynamically locate and set the config fields for each new
sub-server. As the config may not actually have any fields (if the build
flag is off), we use the reflect pacakge to determine if things are
compiled in or not, then if so, we dynamically set each of the config
parameters. The `PopulateDependancies` method implements the
`lnrpc.SubServerConfigDispatcher` interface. Our goal is to allow sub
servers to look up their actual config in this main config struct. We
achieve this by using reflect to look up the target field _as if it were
a key in a map_. If the field is found, then we check if it has any
actual attributes (it won't if the build flag is off), if it is, then we
return it as we expect it to be populated already.
In this commit, we create a lnrpc.SubServerDriver for signrpc. Note that
this file will only have its init() method executed if the proper build
flag is on. As a result, only if the build flag is set, will the RPC
server be registered, and visible at the packge lnrpc level for the root
server to manipulate.
In this commit, we add a full implementation of the new SignerServer sub
RPC service within the main root RPC service. This service is able to
fully manage its macaroons, and service any connected clients. Atm, this
service only has a single method: SignOutputRaw which mimics the
existing lnwallet.Signer interface within lnd itself. As the API's are
so similar, it will be possible for a client to directly use the
lnwallet.Signer interface, and have a proxy that sends the request over
RPC, and translates the proto layer on both sides. To the client, it
doesn't know that it's using a remote, or local RPC.
In this commit, we add a new proto generation script to match the one in
the main lnrpc package. This script differs, as we don't need to
generate the REST proxy stuff (for now).
In this commit, we introduce a new sub-package within the greater RPC
package. This new sub-package will house a new set of sub-RPC servers
to expose experimental features behind build flags for upstream
consumers. In this commit, we add the first config for the service,
which will simply expose the lnwallet.Signer interface over RPC.
In the default file, we have what the config will be if the build tag
(signerrpc) is off. In this case, the config parser won't detect any
times, and if specified will error out. In the active file, we have the
true config that the server will use. With this new set up, we'll
exploit these build flags heavily in order to create a generalized
framework for adding additional sub RPC servers.
