I am using emqtt message broker for mqtt.
I am not a erlang developer and has zero knowledge on that.
I have used this erlang based broker, because after searching many open source broker online and suggestions from people about the advantage of erlang based server.
Now i am kind of stuck with the out put of the emqttd_cli trace command.
Its not json type and if i use a perl parser to convert to json type i am getting delayed output.
I want to know, in which file i could change the trace log output format.
I looked on the trace code of the broker and found a file src/emqttd_protocol.erl. An exported function named trace/3 has the code that you need.
Second argument of this function, named Packet, has the information of receive & send data via broker. You can fetch required data from it and format according to how you want to print.
Edit : Sample modified code added
trace(recv, Packet, ProtoState) ->
PacketHeader = Packet#mqtt_packet.header,
HostInfo = esockd_net:format(ProtoState#proto_state.peername),
%% PacketInfo = {ClientId, Username, ClientIP, ClientPort, Payload, QoS, Retain}
PacketInfo = {ProtoState#proto_state.client_id, ProtoState#proto_state.username, lists:nth(1, HostInfo), lists:nth(3, HostInfo), Packet#mqtt_packet.payload, PacketHeader#mqtt_packet_header.qos, PacketHeader#mqtt_packet_header.retain},
?LOG(info, "Data Received ~s", [PacketInfo], ProtoState);
Related
I did similar with message DLC using predefined function ChkCreate_InconsistentDLC. Looking for options to do the same for message ID.
I have been trying to find some predefined function.
I have a ROS node that allows you to "publish" a data structure to it, to which it responds by publishing an output. The timestamp of what I published and what it publishes is matched.
Is there a mechanism for a blocking function where I send/publish and output, and it waits until I receive an output?
I think you need the ROS_Services (client/server) pattern instead of the publisher/subscriber.
Here is a simple example to do that in Python:
Client code snippet:
import rospy
from test_service.srv import MySrvFile
rospy.wait_for_service('a_topic')
try:
send_hi = rospy.ServiceProxy('a_topic', MySrvFile)
print('Client: Hi, do you hear me?')
resp = send_hi('Hi, do you hear me?')
print("Server: {}".format(resp.response))
except rospy.ServiceException, e:
print("Service call failed: %s"%e)
Server code snippet:
import rospy
from test_service.srv import MySrvFile, MySrvFileResponse
def callback_function(req):
print(req)
return MySrvFileResponse('Hello client, your message received.')
rospy.init_node('server')
rospy.Service('a_topic', MySrvFile, callback_function)
rospy.spin()
MySrvFile.srv
string request
---
string response
Server out:
request: "Hi, do you hear me?"
Client out:
Client: Hi, do you hear me?
Server: Hello client, your message received.
Learn more in ros-wiki
Project repo on GitHub.
[UPDATE]
If you are looking for fast communication, TCP-ROS communication is not your purpose because it is slower than a broker-less communicator like ZeroMQ (it has low latency and high throughput):
ROS-Service pattern equivalent in ZeroMQ is REQ/REP (client/server)
ROS publisher/subscriber pattern equivalent in ZeroMQ is PUB/SUB
ROS publisher/subscriber with waitformessage equivalent in ZeroMQ is PUSH/PULL
ZeroMQ is available in both Python and C++
Also, to transfer huge amounts of data (e.g. pointcloud), there is a mechanism in ROS called nodelet which is supported only in C++. This communication is based on shared memory on a machine instead of TCP-ROS socket.
What exactly is a nodelet?
Since you want to stick with publish/ subscribers, assuming from your comment, that services are to slow I would have a look at waitForMessage (Documentation).
And for an example on how to use it you can have a look at this ros answers question.
All you need to do is to publish your data and immediately call waitForMessage on the output topic and manually pass the received message to your "callback".
I hope this is what you were looking for.
To get this request/reply behaviour ROS has a mechanism called ROS service.
You can specify the input and output of your service in a service file similar to a ROS message definition. You can then call the service of a node with your input and the call will receive an output when the service is finished.
Here is a tutorial how to use this mechanism in python. If you prefer C++ there is also one, you should find it.
I see that gen_udp has support for Unix sockets, and this example shows creating an using one in Erlang.
I want to send messages to an existing Unix socket (to control mpv via its JSON IPC interface). I see there was a self-answered question on the Erlang mailing list about this, but the answer doesn't make sense to me, as Sock2 is used without previous assignment.
I see in the gen_udp docs this option:
{fd, integer() >= 0}
If a socket has somehow been opened without using gen_udp,
use this option to pass the file descriptor for it.
But when I try to open the socket as a file with file:open/2, I get {error,eopnotsupp}.
How can I send messages to an existing Unix socket?
Answer for my case
This will not be a canonical and thorough answer, because I'm not super familiar with sockets. However, I emailed Joe from the mailing list link above, and he said:
As far as I understand, the unix socket type to erlang module mapping
is as follows:
SOCK_STREAM -> gen_tcp
SOCK_DGRAM -> gen_udp
SOCK_SEQPACKET -> gen_sctp
He suggested using gen_tcp:connect in my case, and it worked! Apparently, mpv created a SOCK_STREAM socket.
So, having started mpv like:
mpv /Users/me/playlist.m3u --input-ipc-server=/tmp/mpv.sock --idle yes --no-audio-display
... so that it expects commands on the socket /tmp/mpv.sock, I could send it a "play a different playlist" command like this in erl:
{ok, Port} = gen_tcp:connect({local, "/tmp/mpv.sock"}, 0, [local]).
Msg = "{ \"command\": [\"loadlist\", \"/Users/me/playlist2.m3u\", \"replace\"] }\n".
gen_tcp:send(Port, Msg).
I am new to message broker development. I tried to convert source SOAP over xml file to target SOAP over xml file.On my message flow source message discarded to catch terminal.I am not able to find out the problem
my flow : MQINPUT NODE ---> COMPUTE NODE --> MQOUTPUT NODE
If any provide solution on this that may me helpful for me.
DECLARE soapenv CHARACTER 'SOAP-ENV';
SET OutputRoot.XMNLSC.soapenv:Envelope.soapenv:Body.params.ORIGIN_TYPE_CD = InputRoot.XMNLSC.soapenv:Envelope.soapenv:Body.params.originType;
**
Your first line is definitely wrong, but you should be able to see that from the exceptions you are getting.
The first line should be:
DECLARE soapenv NAMESPACE 'http://schemas.xmlsoap.org/soap/envelope/';
An in the further lines the domain should be XMLNSC not XMNLSC.
I have Ejabberd up and running with test users, and its working fine. I want to write a module that can intercept messages and modify them, as follows :
intercept "messages"
send them to a php file
get the result from the same php file (immediate)
Modify the message stanza and send it down the wire to the recipient
The ejabberd documentation is weak and tutorials are non-existent. Can you give me some sample code that does this. I can then figure how to configure it for my needs.
Thanks a bundle!
Adil
Here's the basic example of such module:
-module(packet_interceptor).
-behaviour(gen_mod).
-export([start/2,
stop/1]).
-export([on_filter_packet/1]).
start(Host, _Opts) ->
ejabberd_hooks:add(filter_packet, global, ?MODULE, on_filter_packet, 0).
on_filter_packet({From, To, XML} = Packet) ->
%% does something with a packet
%% should return modified Packet or atom `drop` to drop the packet
Packet.
And make sure to add this module into ejabberd's configuration into module section:
{modules,
[...
...
...
{packet_interceptor, []}
]}.
Just extend on_filter_packet/1 the way you want and return appropriately modified packet.
gleber's example is excellent. I also wrote a more complex example of packet manipulation that I built for Chesspark called
mod_sunshine.
How can send this XML data to php (via ?xml=) and retrieve the resulting XML and then pass it to the recipient?
If you have a recent version of ejabberd that uses exmpp, you can use exmpp_xml:node_to_binary/1 or exmpp_xml:node_to_list/1 to turn the internal representation of the XML to a binary or a string respectively.
There were similarly named functions in the older ejabberd, but within the xml module.
It seems that what you want to do there is to create an XMPP server component. Lots of things has already been said on that post Which XMPP server to experiment developing a server component.
I can link you some useful links:
Jabber Component Protocol
An Echo-Bot in Python from metajack.im, a very nice blog from an XMPP guru. This bot listen for any message stanzas and reply to some of them.
Gleber's solution is really "ejabberd" oriented (certainly the easiest one in your case), whereas this one can scale with other XMPP servers.
There is the interface:
ejabberd_router:register_route(MyHost)
which I have used in the past and works well. Once the MyHost is registered with ejabberd, the module will receive the communications intended to MyHost through info messages (assuming gen_server).
As noted by #gleber, don't forget to add your module to the configuration file.