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* fix whitespace * added zmq stuff for governance objects and votes it seems that zmq is currently not in a working state, need to figure that out. Need to: plug in the new methods added possibly plug in the old methods, as it doesn't look like they are. * formatting fix. Will probably need to revert for this PR * continue linking new zmq messages in * added comment, might need to revert * fixes error of it not knowing about the classes * Actually link in, all new govobjects and govvotes should be broadcast over zmq now. * fix compile error, forgot to change params when copying * fix compile error * add imports to the header files in zmqconfig.h * fixing linking(i think) error * Revert "added comment, might need to revert" This reverts commit 2918ea40fe9a96834c4bd89e13cb458cde6814f2. * Revert "formatting fix. Will probably need to revert for this PR" This reverts commit ca10558866ab61e3dd0c70541fdcfee6f5115157. * fix tabs etc * EOL added * optimization of hash.begin() @nmarley thoughts? * remove formatting changes * iterator i -> it and removal of notifier * typo in df879f57 * use auto for the iterators * introduce hash prefix * implement changes in zmq_sub.py, update the doc, and change argument name to fix typo * deref iterators before calling methods * continued e8a4c505 * missed one... continued e8a4c505 * killing some tabs * fix spacing for setting or comparing iterators * change order of new variables to match current setup * re-add elif's I didn't realize got removed * Revert "fix spacing for setting or comparing iterators" This reverts commit 8ce2068148dcd275ebba7ee6038d0db1c582b9f3. * Revert "use auto for the iterators" This reverts commit cb16cf0760bfaf68c56684877898611802bf2303. * Revert "missed one... continued e8a4c505" This reverts commit 2087cf894f7e9682508b4692b89897b4fa4e4b7a. * Revert "continued e8a4c505" This reverts commit a78c8ad2c9bb1602242a8f040e17ef958982348c. * Revert "deref iterators before calling methods" This reverts commit e8a4c505d1d34360eaf882d92cd8fbc55436cfcc. * Revert "iterator i -> it and removal of notifier" This reverts commit 29574248b1a0d05c18d60454d07c77979aae6fb2. * Revert "fix whitespace" This reverts commit 612be48d963000b4cbc5f64981a88a3225428b37. * Revert "typo in df879f5" * Revert "Optimization of hash.begin()" * fixes problem with revert * Udjin complain's a lot ;) * help text, init.cpp * add signals in validationinterface.cpp * Change location of vote notification call. * remain consistent * remove unneeded include due to change of notification location * implement raw notifications
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Block and Transaction Broadcasting with ZeroMQ
ZeroMQ is a lightweight wrapper around TCP connections, inter-process communication, and shared-memory, providing various message-oriented semantics such as publish/subscribe, request/reply, and push/pull.
The Dash Core daemon can be configured to act as a trusted "border router", implementing the dash wire protocol and relay, making consensus decisions, maintaining the local blockchain database, broadcasting locally generated transactions into the network, and providing a queryable RPC interface to interact on a polled basis for requesting blockchain related data. However, there exists only a limited service to notify external software of events like the arrival of new blocks or transactions.
The ZeroMQ facility implements a notification interface through a set of specific notifiers. Currently there are notifiers that publish blocks and transactions. This read-only facility requires only the connection of a corresponding ZeroMQ subscriber port in receiving software; it is not authenticated nor is there any two-way protocol involvement. Therefore, subscribers should validate the received data since it may be out of date, incomplete or even invalid.
ZeroMQ sockets are self-connecting and self-healing; that is, connections made between two endpoints will be automatically restored after an outage, and either end may be freely started or stopped in any order.
Because ZeroMQ is message oriented, subscribers receive transactions and blocks all-at-once and do not need to implement any sort of buffering or reassembly.
Prerequisites
The ZeroMQ feature in Dash Core requires ZeroMQ API version 4.x or newer. Typically, it is packaged by distributions as something like libzmq3-dev. The C++ wrapper for ZeroMQ is not needed.
In order to run the example Python client scripts in contrib/ one must also install python3-zmq, though this is not necessary for daemon operation.
Enabling
By default, the ZeroMQ feature is automatically compiled in if the necessary prerequisites are found. To disable, use --disable-zmq during the configure step of building bitcoind:
$ ./configure --disable-zmq (other options)
To actually enable operation, one must set the appropriate options on the command line or in the configuration file.
Usage
Currently, the following notifications are supported:
-zmqpubhashtx=address
-zmqpubhashtxlock=address
-zmqpubhashblock=address
-zmqpubrawblock=address
-zmqpubrawtx=address
-zmqpubrawtxlock=address
-zmqpubhashgovernancevote=address
-zmqpubhashgovernanceobject=address
-zmqpubrawgovernancevote=address
-zmqpubhashgovernanceobject=address
The socket type is PUB and the address must be a valid ZeroMQ socket address. The same address can be used in more than one notification.
For instance:
$ dashd -zmqpubhashtx=tcp://127.0.0.1:28332 \
-zmqpubrawtx=ipc:///tmp/dashd.tx.raw
Each PUB notification has a topic and body, where the header
corresponds to the notification type. For instance, for the
notification -zmqpubhashtx the topic is hashtx (no null
terminator) and the body is the hexadecimal transaction hash (32
bytes).
These options can also be provided in dash.conf.
ZeroMQ endpoint specifiers for TCP (and others) are documented in the ZeroMQ API.
Client side, then, the ZeroMQ subscriber socket must have the
ZMQ_SUBSCRIBE option set to one or either of these prefixes (for
instance, just hash); without doing so will result in no messages
arriving. Please see contrib/zmq/zmq_sub.py for a working example.
Remarks
From the perspective of dashd, the ZeroMQ socket is write-only; PUB sockets don't even have a read function. Thus, there is no state introduced into dashd directly. Furthermore, no information is broadcast that wasn't already received from the public P2P network.
No authentication or authorization is done on connecting clients; it is assumed that the ZeroMQ port is exposed only to trusted entities, using other means such as firewalling.
Note that when the block chain tip changes, a reorganisation may occur and just the tip will be notified. It is up to the subscriber to retrieve the chain from the last known block to the new tip.
There are several possibilities that ZMQ notification can get lost during transmission depending on the communication type your are using. Dashd appends an up-counting sequence number to each notification which allows listeners to detect lost notifications.