Subject: [bitcoin-dev] Would anyone object to adding a dlopen message hook system?

From: Erik Aronesty <[email-masked]>
Date: Sun, 13 Aug 2017 14:46:37 -0400

I was thinking about something like this that could add the ability for
module extensions in the core client.

When messages are received, modules hooks are called with the message data.

They can then handle, mark the peer invalid, push a message to the peer or
pass through an alternate command.  Also, modules could have their own
private commands prefixed by "x:" or something like that.

The idea is that the base P2P layer is left undisturbed, but there is now a
way to create "enhanced features" that some peers support.

My end goal is to support using lightning network micropayments to allow
people to pay for better node access - creating a market for node services.

But I don't think this should be "baked in" to core.   Nor do I think it
should be a "patch".   It should be a linked-in module, optionally compiled
and added to bitcoin conf, then loaded via dlopen().    Modules should be
slightly robust to Bitcoin versions changing out from under them, but not
if the network layer is changed.   This can be ensured by a) keeping a
module version number, and b) treating module responses as if they were
just received from the network.   Any module incompatibility should throw
an exception...ensuring broken peers don't stay online.

In general I think the core reference would benefit from the ability to
create subnetworks within the Bitcoin ecosystem.   Right now, we have two
choices... full node and get slammed with traffic, or listen-only node, and
do nothing.

Adding a module/hook system would allow a complex ecosystem of
participation - and it would seem to be far more robust in the long term.

Something like this???

class MessageHookIn {
public:
    int hookversion;
    int64_t nodeid;
    int nVersion;
    int64_t serviceflags;
    const char *strCommand;
    const char *nodeaddr;
    const char *vRecv;
    int vRecvLen;
    int64_t nTimeReceived;
};

class MessageHookOut {
public:
    int hookversion;
    int misbehaving;
    const char *logMsg;
    const char *pushCommand;
    const unsigned char *pushData;
    int pushDataLen;
    const char *passCommand;
    CDataStream passStream;
};

class MessageHook {
public:
    int hookversion;
    std::string name;
    typedef bool (*HandlerType)(const MessageHookIn *in, MessageHookOut
*out);
    HandlerType handle;
};