Can I send files over web-bluetooth?

Question

I am currently developing an embedded system who count the number of cars and saved theirs speed and time. All these data are stored in a simple logs file (thanks to rsyslog). In parallel, I develop an web-API (in Typescript/Angular with Electron for Desktop usage and later Web as well) who allow the user to upload the logs and stored them locally on his laptop.

I setup a GATT server and I'm able to get simple data like battery, and status over Web-Bluetooth, however, can I send/receive over Web-Bluetooth a file ? Or maybe send it in piece by piece ?

I tried the second way, the maximum size is 512 bytes per frame, so I divide my file size by 512 and send X frame(s) to the Web-App but I don't know if it is possible because I can't have something working after a few days ... So then, I found this on Bluetooth's website: https://www.bluetooth.com/specifications/gatt/services/ The 'Object Transfer Service' exist with GATT, but when you click on that we can read: "This service provide management and control features supporting bulk data transfer which occur via a separe L2CAP connection orientel channel". Does that mean we can't send file ?

Should I change my plan and using an protocol ? I also want to send files from laptop to the embedded system, like configuration files and parameters.

Answer 1

I found a solution, I don't know if it is the best one but it is working pretty well! I simply divide my Uint8Array[] in a packet of 512 bytes and send them. Same for writing and reading, below I put my TypeScript code if it can help someone:

async getFile() {
    let file: string = '';
    let value: string = 'begin';
    let returnedValue = null;

    while (value != '') {
      try {
        returnedValue = await this.characteristicScheduling.readValue();
        value = String.fromCharCode.apply(null, new Uint8Array(returnedValue.buffer));
        console.log(value);
        file= file.concat(value);

      } catch(e) {
        console.log(e);
      }
    }

    console.log('file: ' + file);
}

and the write function:

wait(ms: number) {
    var start = new Date().getTime();
    var end = start;
    while(end < start + ms) {
      end = new Date().getTime();
    }
}

pushFile() {
    let file= this.getFileContent();
    let value: string;
    let valueBytes = null;
    console.log(file);

    while (file.length > 0) {
      // Copy the first 512 bytes
      value = file.substr(0, 512);
      // Remove the first 512 bytes
      scheduling = file.substr(512)
      console.log(file);
      valueBytes = new TextEncoder().encode(value);

      console.log(valueBytes);
      const promise = this.characteristic.writeValue(valueBytes);
      promise.then(val => {
        console.log(val);
      });
      // The wait is isn't mandatory .. but just in case my embedded system is very busy
      this.wait(100);
    }

    // Send empty frame to notice the Embedded system than its the end of transmission
    valueBytes = new TextEncoder().encode('');
    const promise = this.characteristic.writeValue(valueBytes);
      promise.then(val => {
        console.log(val);
      });
}

Of course, 'this.characteristic' has been saved in my class before I called these functions. Follow https://googlechrome.github.io/samples/web-bluetooth/get-characteristics.html for more information.

I'm a embedded engineer so be fair with my 'ugly web-code' let me know if you have recommendation to optimism this code. Hope it helps.