Runtime.callFunctionOn returns an empty value on debugging

[RedMickey]

Hello, we are the development team of VS Code extension for debugging React Native apps (vscode-react-native). Now we are working on React Native Hermes debugger and we've faced the problem related to usage of Chrome DevTools Protocol method callFunctionOn. We use vscode-chrome-debug-core library to communicate with Hermes debugger. Some functions of the library (e.g. getNumPropsByEval) use Chrome DevTools Protocol method Runtime.callFunctionOn. But each call of this method returns the following response "{"result":{},"id":someId}" - an empty result object. We tried to call Runtime.callFunctionOn function with different parameters, but the result remained the same.
Below is the list of the function calls with different arguments that we tried:

1. For example in case of usage of getNumPropsByEval method, the Runtime.callFunctionOn function is used to evaluate the length of the watched array. Below there is an example of the function call:

        this.chrome.Runtime.callFunctionOn({
            objectId,    // 121 
            functionDeclaration: " function() { return [this.length, Object.keys(this).length - this.length + 2]; }",
            silent: true,
            returnByValue: true
        })

2. The function should only return a static array. Without silent mode.

        this.chrome.Runtime.callFunctionOn({
            objectId,    // 121 
            functionDeclaration: "function() { return [0, 2]; }",
            silent: false,
            returnByValue: true
        })

3. The function should return process variable. Doesn't provide objectId prop and without silent mode.

        this.chrome.Runtime.callFunctionOn({
            functionDeclaration: "function() { return process; }",
            silent: false,
            returnByValue: true
        })

For all cases that are described above the callFunctionOn method returns empty result object.
Runtime.callFunctionOn method also doesn't return any error messages.

Could you please tell us if Runtime.callFunctionOn method is implemented in Hermes debugger and if it is, how can we use it?

For reference: the list of known issues with Hermes debugging for React Native Tools extension.

react-native info command output:

System:
    OS: macOS 10.15.2
    CPU: (6) x64 Intel(R) Core(TM) i5-8500B CPU @ 3.00GHz
    Memory: 33.88 MB / 32.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 10.16.3 - /usr/local/bin/node
    Yarn: 1.17.3 - /usr/local/bin/yarn
    npm: 6.9.0 - /usr/local/bin/npm
    Watchman: 4.9.0 - /usr/local/bin/watchman
  SDKs:
    iOS SDK:
      Platforms: iOS 13.2, DriverKit 19.0, macOS 10.15, tvOS 13.2, watchOS 6.1
    Android SDK:
      API Levels: 23, 25, 27, 28, 29
      Build Tools: 23.0.1, 25.0.1, 25.0.2, 27.0.3, 28.0.3, 29.0.0, 29.0.1
      System Images: android-28 | Google APIs Intel x86 Atom, android-29 | Google APIs Intel x86 Atom
  IDEs:
    Android Studio: 3.4 AI-183.6156.11.34.5692245
    Xcode: 11.3/11C29 - /usr/bin/xcodebuild
  npmPackages:
    react: 16.9.0 => 16.9.0 
    react-native: 0.61.5 => 0.61.5 
  npmGlobalPackages:
    react-native-cli: 2.0.1

[tmikov]

Thanks for bringing this up! We will look into it.

[willholen]

You can find a list of implemented messages here: https://github.com/facebook/react-native/blob/master/ReactCommon/hermes/inspector/tools/message_types.txt

Runtime.callFunctionOn is not currently one of them, and the empty response you're getting is a default response for unsupported messages.

[willholen]

@RedMickey Can you help us prioritize this issue relative to the messages in #209?

[RedMickey]

@willholen, During the migration of React Native Tools extension on js-debug, we faced the similar problem as described in this issue. After the refactoring the requests that the debugger sends to the target have changed a bit. The debugger uses Runtime.callFunctionOn method, when it's trying to retrieve arrays content. Now it sends the following messages to the target:

{
  "id": 66,
  "method": "Runtime.callFunctionOn",
  "params": {
    "functionDeclaration": "function(){const e={__proto__:this.__proto__},t=Object.getOwnPropertyNames(this);for(let r=0;r<t.length;++r){const n=t[r],i=n>>>0;if(String(i>>>0)===n&&i>>>0!=4294967295)continue;const a=Object.getOwnPropertyDescriptor(this,n);a&&Object.defineProperty(e,n,a)}return e}",
    "arguments": [],
    "objectId": "389",
    "generatePreview": true
  }
}

{
  "id": 68,
  "method": "Runtime.callFunctionOn",
  "params": {
    "functionDeclaration": "function(e,t){const r={},n=-1===e?0:e,i=-1===t?this.length:e+t;for(let e=n;e<i&&e<this.length;++e){const t=Object.getOwnPropertyDescriptor(this,e);t&&Object.defineProperty(r,e,t)}return r}",
    "arguments": [
      {
        "value": -1
      },
      {
        "value": -1
      }
    ],
    "generatePreview": false,
    "objectId": "389"
  }
}

The target sends such a response:

[Reply From Target To Debugger] {
  "result": {},
  "id": 66
}

We currently process these requests in a special way, since Hermes engine returns an empty result object, and we cannot get specific remote objects, containing an array's ObjectId. We tried to add returnByValue: true field, but this didn't help. I think this method is important for debugging Hermes apps. It will be awesome if we can retrieve arrays data without special handlers.

[mattbfb]

Hello @RedMickey,

We are revisiting and address outstanding CDP issues in Hermes, and I believe this one has been fixed in the current version of Hermes. Do you still experience this issue?

Trying the call that was previously shown to be empty:

{
   "id": 1236,
   "method": "Runtime.callFunctionOn",
   "params": {
     "functionDeclaration": "function(){const e={__proto__:this.__proto__},t=Object.getOwnPropertyNames(this);for(let r=0;r<t.length;++r){const n=t[r],i=n>>>0;if(String(i>>>0)===n&&i>>>0!=4294967295)continue;const a=Object.getOwnPropertyDescriptor(this,n);a&&Object.defineProperty(e,n,a)}return e}",
     "arguments": [],
     "objectId": "12",
     "generatePreview": true
   }
 }

{"result":{"result":{"type":"object","description":"Object","className":"Object","objectId":"13"}},"id":1236}

[tmikov]

Closing since no activity and appears fixed on our side