Comments (16)
qiuzhong
commented on August 17, 2024
1
We should figure out why before a publisher node sending this JointState type message, the JSON.stringify works:
{"header":{
"stamp":{
"sec":123456,
"nanosec":789},
"frame_id":"main frame"},
"name":["Tom","Jerry"],
"position":[1,2],
"velocity":[2,3],
"effort":[4,5,6]}
While a subscription node received this message, then the JSON.stringify didn't work:
{ "header":{
"stamp":{
"sec":123456,
"nanosec":789},
"frame_id":"main frame"},
"name":["Tom","Jerry"],
"position":{"0":1,"1":2},
"velocity":{"0":2,"1":3},
"effort":{"0":4,"1":5,"2":6}}
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minggangw
commented on August 17, 2024
Do you mean if we create a object below
let obj = { op: 'publish', id: 'publish_setup_jointstate', topic: 'subscribe_jointstate_topic',
msg: {
header: {
stamp: {
sec: 123456, nanosec: 789
},
frame_id: 'main frame'},
name: ['Tom', 'Jerry'], position: [1, 2], velocity: [2, 3], effort: [4, 5, 6]}}then invoke:
let str = JSON.stringify(obj);
let obj = JSON.parse(str); Finally, the structure changed?
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qiuzhong
commented on August 17, 2024
Yes. This should be not a problem if users only use rclnodejs since there is no need to make JSON conversion. But for the bridge server, this could be a issue.
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minggangw
commented on August 17, 2024
Yes, indeed.
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minggangw
commented on August 17, 2024
I made a quick test and found that if you print the result of str = JSON.stringify(obj), the string returned is right:
{"op":"publish","id":"publish_setup_jointstate","topic":"subscribe_jointstate_topic","msg":{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":[1,2],"velocity":[2,3],"effort":[4,5,6]}}
you can get the value of key nanosec and sec after executing JSON.parse(str). Would you help me to check this @qiuzhong? thanks!
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qiuzhong
commented on August 17, 2024
@minggangw , you're right. Simply making JSON conversion will not raise this.
But this issue is found when I got the data from web socket transferring of the bridge server. What I means is that when web socket clients receive the serialized message, it can be re-construct the original object any more.
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qiuzhong
commented on August 17, 2024
Here is the bridge log:
node bin/rosbridge.js
ros2-web-bridge:index The ros2-web-bridge has started. +0ms
The web socket server started on ws://localhost:9090
ros2-web-bridge:Bridge Web bridge 8581766c-47e6-4966-add6-c47f22dd1595 is created +0ms
ros2-web-bridge:Bridge JSON command received: {"op":"subscribe","id":"subscribe_jointstate","topic":"subscribe_jointstate_topic","type":"sensor_msgs/JointState"} +2ms
ros2-web-bridge:Bridge subscribe a topic named subscribe_jointstate_topic +1ms
rclnodejs:node Finish creating subscription, topic = subscribe_jointstate_topic. +0ms
ros2-web-bridge:SubscriptionManager Subscription has been created, and the topic name is subscribe_jointstate_topic. +0ms
ros2-web-bridge:Bridge Response: {"op":"set_level","level":"none"} +17ms
ros2-web-bridge:Bridge JSON command received: {"op":"advertise","id":"advertise_setup_jointstate","topic":"subscribe_jointstate_topic","type":"sensor_msgs/JointState"} +1ms
ros2-web-bridge:Bridge advertise a topic: subscribe_jointstate_topic +1ms
rclnodejs:node Finish creating publisher, topic = subscribe_jointstate_topic. +3ms
ros2-web-bridge:ResourceProvider Publisher has been created, and the topic name is subscribe_jointstate_topic. +0ms
ros2-web-bridge:Bridge Response: {"op":"set_level","level":"none"} +0ms
ros2-web-bridge:Bridge JSON command received: {"op":"publish","id":"publish_setup_jointstate","topic":"subscribe_jointstate_topic","msg":{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":[1,2],"velocity":[2,3],"effort":[4,5,6]}} +1ms
ros2-web-bridge:Bridge Publish a topic named subscribe_jointstate_topic with {"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":[1,2],"velocity":[2,3],"effort":[4,5,6]} +0ms
rclnodejs:publisher Message of topic subscribe_jointstate_topic has been published. +2ms
ros2-web-bridge:Bridge Response: {"op":"set_level","level":"none"} +1ms
rclnodejs:subscription Message of topic subscribe_jointstate_topic received. +1ms
ros2-web-bridge:Bridge Send message to subscription. +2ms
ros2-web-bridge:RefCountingHandle Handle is destroyed. +0ms
rclnodejs:node subscription destroyed. +5ms
ros2-web-bridge:RefCountingHandle Handle is destroyed. +0ms
ros2-web-bridge:Bridge Web bridge 8581766c-47e6-4966-add6-c47f22dd1595 is closed +4ms
...
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minggangw
commented on August 17, 2024
I tested with rclnodejs alone and got below with console.log(JSON.stringify(state)); in example subscription-message-example.js
{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":{"0":1,"1":2},"velocity":{"0":2,"1":3},"effort":{"0":4,"1":5,"2":6}}
So I think the rclnodejs works fine, I will check the bridge later, thanks!
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minggangw
commented on August 17, 2024
The literal string received by websockets is
{"op":"publish","topic":"JointState","msg":{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":{"0":1,"1":2},"velocity":{"0":2,"1":3},"effort":{"0":4,"1":5,"2":6}}}
are you printing the result of JSON.parse to get the output below?
{ op: 'publish',
topic: 'JointState',
msg:
{ header: { stamp: [Object], frame_id: 'main frame' },
name: [ 'Tom', 'Jerry' ],
position: { '0': 1, '1': 2 },
velocity: { '0': 2, '1': 3 },
effort: { '0': 4, '1': 5, '2': 6 } } }from ros2-web-bridge.
qiuzhong
commented on August 17, 2024
Right. That's exact what JSON.parse() got:
node
> var s = '{"op":"publish","topic":"JointState","msg":{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":{"0":1,"1":2},"velocity":{"0":2,"1":3},"effort":{"0":4,"1":5,"2":6}}}';
undefined
> s
'{"op":"publish","topic":"JointState","msg":{"header":{"stamp":{"sec":123456,"nanosec":789},"frame_id":"main frame"},"name":["Tom","Jerry"],"position":{"0":1,"1":2},"velocity":{"0":2,"1":3},"effort":{"0":4,"1":5,"2":6}}}'
> JSON.parse(s);
{ op: 'publish',
topic: 'JointState',
msg:
{ header: { stamp: [Object], frame_id: 'main frame' },
name: [ 'Tom', 'Jerry' ],
position: { '0': 1, '1': 2 },
velocity: { '0': 2, '1': 3 },
effort: { '0': 4, '1': 5, '2': 6 } } }
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minggangw
commented on August 17, 2024
So it's clear now. The thing is that when using console.log to print an object of complex message, the stamp key of Header displays as [Object]. I thinks the output is a kind of behaviour of the console.log function which will not change the object itself, and it's all right here.
You can do a test to print the object defined below
let obj = { op: 'publish', id: 'publish_setup_jointstate', topic: 'subscribe_jointstate_topic',
msg: {
header: {
stamp: {
sec: 123456, nanosec: 789
},
frame_id: 'main frame'},
name: ['Tom', 'Jerry'], position: [1, 2], velocity: [2, 3], effort: [4, 5, 6]}}
console.log(obj);and you get
{ op: 'publish',
id: 'publish_setup_jointstate',
topic: 'subscribe_jointstate_topic',
msg:
{ header: { stamp: [Object], frame_id: 'main frame' },
name: [ 'Tom', 'Jerry' ],
position: [ 1, 2 ],
velocity: [ 2, 3 ],
effort: [ 4, 5, 6 ] } }
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qiuzhong
commented on August 17, 2024
Please note:
After web socket clients received the complex object, stamp changed from object to array, position from array to object.
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minggangw
commented on August 17, 2024
Sorry, I did not notice the position as an array, I did a quick check and found a possible cause here
https://github.com/RobotWebTools/rclnodejs/blob/develop/lib/message_translator.js#L143.
Thanks for finding this undetectable problem.
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minggangw
commented on August 17, 2024
I found the reason why we got, something like "position":{"0":1,"1":2} here. That is because if the type of an array is primitive which may be any of 'int8', 'uint8', 'int16', 'uint16', 'int32', 'uint32', 'float64', 'float32', 'char' and 'byte', rclnodejs will use TypedArray to represent them. Please try the example below:
const typedArray1 = new Int8Array(8);
typedArray1[0] = 32;
let str = JSON.stringify(typedArray1);
console.log(str);
console.log(JSON.parse(str));and you will get the out put:
> "{"0":32,"1":0,"2":0,"3":0,"4":0,"5":0,"6":0,"7":0}"
> Object { 0: 32, 1: 0, 2: 0, 3: 0, 4: 0, 5: 0, 6: 0, 7: 0 }
We use TypedArray to improve the performance, so it's a necessary implementation here.
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qiuzhong
commented on August 17, 2024
This sounds reasonable. As when an array is converted to an object when the indexes become the keys automatically. The object can still behaves like the array. This is not perfect but it can work.
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minggangw
commented on August 17, 2024
So let's close this issue.
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