REST Api CORS Blocked

Blue Robotics Software
1

Hey. We have got the REST API working and displaying/updating information. We would like to integrate parts of the data to a web-application we are building, but trying to send a GET request only results in:

“Access to fetch at ‘http://192.168.2.2:4777/mavlink’ from origin ‘http://localhost:4200’ has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.”

Seems like this is something that must be allowed server-side.
linkhttps://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

Is this something you are planning to allow? Can’t see any security issues as the web-application we are building must run on the laptop driving the ROV to work anyway.

It is the mavlink2rest executable that hosts the web-server for the api. How can I go about configuring this for a local test here?

Regards,
Mads
JM Robotics

2

Hi @maphstra,

You are right, I opened a PR doing that in Companion side:
You can do that (or something similar) for now.
It will expose the mavlink api at http://192.168.2.2:2770/mavlink

I also opened an issue in Mavlink2Rest project to discuss getting it done there.

3

Hi @maphstra,

I have update mavlink2rest to allow cors.
It’s necessary to replace mavlink2rest to test it:
1- Access the ROV terminal, check our documentation for more information.
2- Run this command:
screen -X -S mavlink2rest quit | sudo pkill -9 -f mavlink2rest | wget https://github.com/patrickelectric/mavlink2rest/releases/download/0.7.2/mavlink2rest-armv7-unknown-linux-musleabihf -O ~/companion/tools/mavlink2rest | chmod +x ~/companion/tools/mavlink2rest

These commands will update mavlink2rest to the last version 0.7.2, that has CORS enabled.
After finished, remember to restart companion via the web interface.

4

It works! That’s great guys, thanks!

Mads

5

Follow-up question: Using mavlink-inspector i can see SERVO_OUTPUT_RAW.servo9_raw. This value (and the higher ones) are missing from the REST-api. Anything I can do to remedy this?

We are interested in reading the camera tilt angle.

6

Hi Mands,

You should be able to see the lights and all the servo outputs, I just did a quick test here and it’s working:
chan9_raw and and chan10_raw are light1 and light2 with max bright.

Json 
{
  "chan10_raw": 1900,
  "chan11_raw": 1100,
  "chan12_raw": 0,
  "chan13_raw": 0,
  "chan14_raw": 0,
  "chan15_raw": 0,
  "chan16_raw": 0,
  "chan17_raw": 0,
  "chan18_raw": 0,
  "chan1_raw": 1500,
  "chan2_raw": 1500,
  "chan3_raw": 1500,
  "chan4_raw": 1500,
  "chan5_raw": 1500,
  "chan6_raw": 1500,
  "chan7_raw": 1500,
  "chan8_raw": 1500,
  "chan9_raw": 1900,
  "chancount": 0,
  "message_information": {
    "counter": 543702,
    "frequency": 9.99305248260498,
    "time": {
      "first_message": "2020-06-18T22:18:36.856449734+00:00",
      "last_message": "2020-06-19T13:25:25.479091361+00:00"
    }
  },
  "rssi": 0,
  "time_boot_ms": 54414402,
  "type": "RC_CHANNELS"
}

For the camera position appears in SERVO_OUTPUT_RAW, but there is a bug in mavlink2rest where only the first 8 channels appears, you can check the status of the issue here:

It’s also possible to fetch position information from MOUNT_STATUS, but there is a problem related to the library used:

7

Can you try this binary to fix the SERVO_OUTPUT_RAW message (and others) ?
The command:
$(screen -X -S mavlink2rest quit | sudo pkill -9 -f mavlink2rest) || wget https://github.com/patrickelectric/mavlink2rest/releases/download/continuous/mavlink2rest-armv7-unknown-linux-musleabihf -O ~/companion/tools/mavlink2rest && chmod +x ~/companion/tools/mavlink2rest
Remember to restart the ROV.