From e2c42668ae1297fd4bdda960a7daf73c50db4db7 Mon Sep 17 00:00:00 2001 From: Javier Vargas Date: Fri, 26 Jun 2020 17:05:47 +0200 Subject: [PATCH] Create 15_3_Receiving_Bitcoind_Notifications_with_C.md --- ...Receiving_Bitcoind_Notifications_with_C.md | 196 ++++++++++++++++++ 1 file changed, 196 insertions(+) create mode 100644 15_3_Receiving_Bitcoind_Notifications_with_C.md diff --git a/15_3_Receiving_Bitcoind_Notifications_with_C.md b/15_3_Receiving_Bitcoind_Notifications_with_C.md new file mode 100644 index 0000000..4db5ec8 --- /dev/null +++ b/15_3_Receiving_Bitcoind_Notifications_with_C.md @@ -0,0 +1,196 @@ +# 15.3 Receiving Bitcoind Notifications with C + +> **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning. + +[ยง15.3](15_3_Receiving_Bitcoind_Notifications_with_C.md) In this chapter we will show how to create a simple listener for bitcoin blockchain to receive notifications using ZMQ-based (http://zeromq.org/) notification interface, which is a highly scalable networking library written in C that acts like a concurrency framework. Bitcoin allows connection points where clients can subscribe to get notified about blockchain events like raw transactions or raw blocks. + +## Install ZMQ + +To create a blockchain listener in C you need to install ZMQ following this steps. + + 1. Install ZMQ + 2. Create C program. + 3. Compile C program. + 4. Configure bitcoind to allow ZMQ notifications + 5. Execute listener. + +### 1. Install ZMQ + +``` +sudo apt-get install libzmq3-dev +``` +Output + +``` +Reading package lists... Done +Building dependency tree +Reading state information... Done +The following NEW packages will be installed: + libzmq3-dev +0 upgraded, 1 newly installed, 0 to remove and 18 not upgraded. +Need to get 400 kB of archives. +After this operation, 2.227 kB of additional disk space will be used. +Get:1 http://es.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 libzmq3-dev amd64 4.2.5-1ubuntu0.2 [400 kB] +Fetched 400 kB in 0s (1.114 kB/s) +Selecting previously unselected package libzmq3-dev:amd64. +(Reading database ... 313982 files and directories currently installed.) +Preparing to unpack .../libzmq3-dev_4.2.5-1ubuntu0.2_amd64.deb ... +Unpacking libzmq3-dev:amd64 (4.2.5-1ubuntu0.2) ... +Setting up libzmq3-dev:amd64 (4.2.5-1ubuntu0.2) ... +Processing triggers for man-db (2.8.3-2ubuntu0.1) ... +``` +Then + +``` +sudo apt-get install libczmq-dev +``` +Output: + +``` +Reading package lists... Done +Building dependency tree +Reading state information... Done +The following additional packages will be installed: + libczmq4 +The following NEW packages will be installed: + libczmq-dev libczmq4 +0 upgraded, 2 newly installed, 0 to remove and 18 not upgraded. +Need to get 496 kB of archives. +After this operation, 2.148 kB of additional disk space will be used. +Do you want to continue? [Y/n] y +Get:1 http://es.archive.ubuntu.com/ubuntu bionic/universe amd64 libczmq4 amd64 4.1.0-2 [145 kB] +Get:2 http://es.archive.ubuntu.com/ubuntu bionic/universe amd64 libczmq-dev amd64 4.1.0-2 [351 kB] +Fetched 496 kB in 0s (1.287 kB/s) +Selecting previously unselected package libczmq4:amd64. +(Reading database ... 314055 files and directories currently installed.) +Preparing to unpack .../libczmq4_4.1.0-2_amd64.deb ... +Unpacking libczmq4:amd64 (4.1.0-2) ... +Selecting previously unselected package libczmq-dev:amd64. +Preparing to unpack .../libczmq-dev_4.1.0-2_amd64.deb ... +Unpacking libczmq-dev:amd64 (4.1.0-2) ... +Setting up libczmq4:amd64 (4.1.0-2) ... +Setting up libczmq-dev:amd64 (4.1.0-2) ... +Processing triggers for man-db (2.8.3-2ubuntu0.1) ... +Processing triggers for libc-bin (2.27-3ubuntu1) ... +``` + +### 2. Create C Program + +Now we've installed ZMQ and we can compile our C program using it's notifications. +The program use czmq.h library and receives two parameters as follows, first param is the point exposed by bitcoind and second the topic about we'll listen. + +``` c +#include +int main(int argc, char ** argv) { + + char *zmqserver; + char *topic; + + if (argc < 3) { + printf("\nUSAGE:\nchainlistener \n\n"); + return 0; + } else { + zmqserver = argv[1]; + topic = argv[2]; + } + + zsock_t *socket = zsock_new_sub(zmqserver, topic); + assert(socket); + + while(1) { + zmsg_t *msg; + int rc = zsock_recv(socket, "m", &msg); + assert(rc == 0); + + char *header = zmsg_popstr(msg); + zframe_t *zdata = zmsg_pop(msg); + unsigned int *no = (unsigned int*)zmsg_popstr(msg); + + char *data = zframe_strhex(zdata); + int len = zframe_size(zdata); + printf("Size: %d\n", len); + printf("Data: %s", data); + printf("\nNo: %d\n", *no); + + free(header); + free(data); + free(no); + free(zdata); + zmsg_destroy(&msg); + sleep(1); + } + zsock_destroy(&socket); + return 0; +} +``` + +### 3. Compile C program + +To compile this C program you have to do it with clang or gcc compiler and test zmq and czmq libraries. + +``` +gcc -o chainlistener chainlistener.c -I/usr/local/include -L/usr/local/lib -lzmq -lczmq +``` + +### 4. Configure ZMQ on bitcoind + +Add this lines to bitcoin.conf file and restart daemon. + +``` +zmqpubrawblock=tcp://127.0.0.1:28332 +zmqpubrawtx=tcp://127.0.0.1:28333 +``` +Then test it's working using this command + +``` +$ bitcoin-cli --testnet getzmqnotifications +``` +Output: +``` +[ + { + "type": "pubrawblock", + "address": "tcp://127.0.0.1:28332", + "hwm": 1000 + }, + { + "type": "pubrawtx", + "address": "tcp://127.0.0.1:28333", + "hwm": 1000 + } +] +``` +### 5. Execute listener: + +``` +$ ./chainlistener tcp://127.0.0.1:28333 rawtx +Size: 250 +Data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o: 67 +Size: 249 +Data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o: 68 +Size: 250 +Data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o: 69 +Size: 250 +Data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o: 70 +....... +``` + + +### For More Information + +In this repository you can browse find more details about ZMQ notifications and others kind of messages. (https://github.com/Actinium-project/ChainTools/blob/master/docs/chainlistener.md) + +### Summary Receiving Bitcoind Notifications with C.md + +By using ZMQ framework, you can easily receive notifications by subscribing to a connection point exposed by bitcoind changing configuration file. + + + + + + +