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rabbitmqstomp: Opinionated Lua RabbitMQ client library for nginx-module-lua apps based on the cosocket API

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install lua-resty-rabbitmqstomp

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

dnf -y install https://extras.getpagespeed.com/release-latest.rpm
dnf -y install lua5.1-resty-rabbitmqstomp

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-rabbitmqstomp v0.1 released on Jun 01 2013.

lua-resty-rabbitmqstomp - Lua RabbitMQ client library which uses cosocket api for communication over STOMP 1.2 with a RabbitMQ broker which has the STOMP plugin.

Limitations

This library is opinionated and has certain assumptions and limitations which may be addressed in future;

  • RabbitMQ server should have the STOMP adapter enabled that supports STOMP v1.2
  • Assumption that users, vhost, exchanges, queues and bindings are already setup

Status

This library is considered production ready for publishing reliable messages to RabbitMQ.

STOMP v1.2 Client Implementation

This library uses STOMP 1.2 for communication with RabbitMQ broker and implements extensions and restrictions of the RabbitMQ Stomp plugin.

Internally, RabbitMQ uses AMQP to communicate further. This way the library enables implementation of consumers and producers which communicate with the RabbitMQ broker over STOMP, over AMQP. The protocol is frame based and has a command, headers and body terminated by an EOL (^@) which consists of \r (013) and required \n (010) over a TCP stream:

COMMAND
header1:value1
header2: value2

BODY^@

COMMAND is followed by EOL, then EOL separated header in key:value pair format and then a blank line which is where the BODY starts and the frame is terminated by ^@ EOL. COMMAND and headers are UTF-8 encoded.

Connection

To connect we create and send a CONNECT frame over a TCP socket provided by the cosocket api connecting to the broker IP, both IPv4 and IPv6 are supported. In the frame we use login, passcode for authentication, accept-version to enforce client STOMP version support and host to select the VHOST of the broker.

CONNECT
accept-version:1.2
login:guest
passcode:guest
host:/devnode
heart-beat:optional

^@

On error, an ERROR frame is returned for example:

ERROR
message:Bad CONNECT
content-type:text/plain
version:1.0,1.1,1.2
content-length:32

Access refused for user 'admin'^@

On successful connection, we are returned a CONNECTED frame by the broker, for example:

CONNECTED
session:session-sGF0vjCKH1bLhFr6w9QwuQ
heart-beat:0,0
server:RabbitMQ/3.0.4
version:1.2

For creating a connection, username, password, vhost, heartbeat, broker host and port should be provided.

Publishing

We can publish messages to an exchange with a routing key, persistence mode, delivery mode and other header using the SEND command:

SEND
destination:/exchange/exchange_name/routing_key
app-id: luaresty
delivery-mode:2
persistent:true
content-type:json/application
content-length:5

hello^@

Note that content-length includes the message and EOL byte.

Methods

new

syntax: rabbit, err = rabbitmqstomp:new()

Creates a RabbitMQ object. In case of failures, returns nil and a string describing the error.

set_timeout

syntax: rabbit:set_timeout(time)

Sets the timeout (in ms) protection for subsequent operations, including the connect method. Note timeout should be set before calling any other method after creating the object.

connect

syntax: ok, err = red:connect{host=host, port=port, username=username, password=password, vhost=vhost}

Attempts to connect to a stomp broker the RabbitMQ STOMP adapter on a host, port is listening on.

If none of the values are supplied default values are assumed:

  • host: localhost
  • port: 61613
  • username: guest
  • password: guest
  • vhost: /

pool can be given to be used for a custom name for the connection pool being used.

send

syntax: rabbit:send(msg, headers)

Publishers message with a set of headers.

Some header values which can be set:

destination: Destination of the message, for example /exchange/name/bindingpersistent: To delivery a persistent message, value should be "true" if declaredreceipt: Receipt for confirmed deliverycontent-type`: Type of message, for example application/json

For list of supported headers see the STOMP protocol extensions and restriction page: https://www.rabbitmq.com/stomp.html

subscribe

syntax: rabbit:subscribe(headers)

Subscribe to a queue by using headers. It should have a id when persistent is true. On successful subscription MESSAGE frames are sent by the broker.

unsubscribe

syntax: rabbit:unsubscribe(headers)

Unsubscribes from a queue by using headers. On successful unsubscription MESSAGE frames will stop coming from the broker.

receive

syntax: rabbit:receive())

Tries to read any MESSAGE frames received and returns the message. Trying to receive without a valid subscription will lead to errors.

get_reused_times

syntax: times, err = rabbit:get_reused_times()

This method returns the (successfully) reused times for the current connection. In case of error, it returns nil and a string describing the error.

If the current connection does not come from the built-in connection pool, then this method always returns 0, that is, the connection has never been reused (yet). If the connection comes from the connection pool, then the return value is always non-zero. So this method can also be used to determine if the current connection comes from the pool.

set_keepalive

syntax: ok, err = rabbit:set_keepalive(max_idle_timeout, pool_size)

Puts the current RabbitMQ connection immediately into the ngx_lua cosocket connection pool.

You can specify the max idle timeout (in ms) when the connection is in the pool and the maximal size of the pool every nginx worker process.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

Only call this method in the place you would have called the close method instead. Calling this method will immediately turn the current redis object into the closed state. Any subsequent operations other than connect() on the current objet will return the closed error.

close

syntax: ok, err = rabbit:close()

Closes the current RabbitMQ connection gracefully by sending a DISCONNECT to the RabbitMQ STOMP broker and returns the status.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

Example

A simple producer that can send reliable persistent message to an exchange with some binding:

local rabbitmq = require "resty.rabbitmqstomp"
local mq, err = rabbitmq:new()
if not mq then
      return
end

mq:set_timeout(10000)

local ok, err = mq:connect {
                    host = "127.0.0.1",
                    port = 61613,
                    username = "guest",
                    password = "guest",
                    vhost = "/"
                }
if not ok then
    return
end

local strlen =  string.len

local msg = "{'key': 'value'}"
local headers = {}
headers["destination"] = "/exchange/test/binding"
headers["receipt"] = "msg#1"
headers["app-id"] = "luaresty"
headers["persistent"] = "true"
headers["content-type"] = "application/json"

local ok, err = mq:send(msg, headers)
if not ok then
    return
end
ngx.log(ngx.INFO, "Published: " .. msg)

local headers = {}
headers["destination"] = "/amq/queue/queuename"
headers["persistent"] = "true"
headers["id"] = "123"

local ok, err = mq:subscribe(headers)
if not ok then
    return
end

local data, err = mq:receive()
if not ok then
    return
end
ngx.log(ngx.INFO, "Consumed: " .. data)

local headers = {}
headers["persistent"] = "true"
headers["id"] = "123"

local ok, err = mq:unsubscribe(headers)

local ok, err = mq:set_keepalive(10000, 10000)
if not ok then
    return
end

See Also

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-rabbitmqstomp.