🐛 Multi ReadCharacteristic Value Race Condition on iOS

[andrewcharnley]

Prerequisites

• I checked the documentation and FAQ without finding a solution
• I checked to make sure that this issue has not already been filed

Expected Behavior

On iOS with 3.50 calls to readcharacteristic sometimes return the value for a different characteristic. While I haven't looked at the Java I suspect it's returning the Promise early and the next iteration is then conflicting. If readCharacteristic should support parallel async calls then the internal code must have an issue, but here I am sequencing them.

It's only occurring on iOS and only sometimes but this will be down to timing/race. I've also tried the Promise patch file from the other PR. I didn't see this or have it reported by users on 3.2.* and will roll back.

Here's the code I have which will occasionally return the value for a different characteristic. I've verified with a user when it occurs the value returned for one characteristic is actually the value for another.

      for (const { name, uuid } of service.characteristics
         .filter(({ read }) => read)) {
              const {value} = await device.readCharacteristicForService(service.uuid, uuid);
              const output = ret.characteristics[name];
              const buffer = decodeBase64(value);
              output.bufferLength = buffer.length;
              addDebug(`Read ${name} of length ${buffer.length}`);
        
...

Current Behavior

It's unreliable.

Library version

3.5.0

Device

iOS

Environment info

N/A

Steps to reproduce

N/A

Formatted code sample or link to a repository

No

Relevant log output

N/A

Additional information

No response

[andrewcharnley]

Reverted back to 3.2.1 and users report all is well again. Something between then and 3.5.0 changed things.