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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Thu, 7 Aug 2014 23:38:44 -0400
Message-ID: <CAJHLa0Ok6s5xQcMSeLa69adLBXEaicuXqcg45eZrwYtVFbx-dA@mail.gmail.com>
To: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
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Subject: [Bitcoin-development] NODE_EXT_SERVICES and advertising related
	services
Precedence: list

Link: https://github.com/bitcoin/bitcoin/pull/4657

It is not necessary to build all functionality into bitcoind, to form
a decentralized network. BitPay's insight open source block explorer
API project requires, and runs on top of, bitcoind. Therefore, at the
same IP address as bitcoind, other services are made available to the
public (scriptPubkey queries, other added-value queries). This results
in a decentralized network of "anyone running a full node and an
insight server", as a subset of the whole P2P net.  One then does not
need to trust BitPay's insight server, but may query any number of
insight servers from multiple operators, and survey the results.

Obviously, we want to build this in a generic, vendor-neutral way.  As
such, NODE_EXT_SERVICES is advertised via the "addr" P2P message.
Nodes that recognize the NODE_EXT_SERVICES bit may connect to that
node, query a services list via "getextsrv" P2P message, and then take
further action based on the results.  The results are quite
straightforward:

service name, service port (or -1 if undefined), list of string
key/value attribs

Services may only advertise added services if and only if the external
services are at the same IP address that is being advertised.

This is not a fully baked proposal by any means, but more of a trial
balloon to get discussion moving.

There is no need to implement all services inside bitcoind...

-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/