1. What hanppened?

We build a cross-platform application with electron. But its auto upgrade feature does not works. In order to explain, we image we have build a desktop application: app.AppImage. When we start the application in terminal and check the latest the version, there are some output information look like below:

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Error: Error: APPIMAGE env is not defined
    at t.newError (/tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:1:12502)
    at Object.task (/tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:142:178326)
    at h.executeDownload (/tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:1:254868)
    at async /tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:315:180714
    at async EventEmitter.Hr (/tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:315:180675)
09:30:53.222 › Cannot dispatch error event: TypeError: Error processing argument at index 1, conversion failure from Error: APPIMAGE env is not defined
    at Object.showErrorBox (/tmp/.mount_no-app2Kmp8v/resources/electron.asar/browser/api/dialog.js:163:24)
    at h.<anonymous> (/tmp/.mount_no-app2Kmp8v/resources/app.asar/dist/main.js:315:179401)

You will more detail inforamtion from output if you start with a debug flag like below

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chmod +x app.AppImage
DEBUG=true ./app.AppImage

You will find the APPIMAGE environment parameter is existing. Yes, it is here, but you program can not find it.

2. Code checking & Research

2.1 from research

According some github issue, we know some pulugin for example: DefinePlugin will reset the environment parameters. Maybe this is the reason.

2.2 from code

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...
const stringified = {
    'process.env': Object.keys(raw).reduce(
      (env, key) => {
        env[key] = JSON.stringify(raw[key]);
        return env;
      }, {}
    ),
  };
new webpack.DefinePlugin(stringified)
...

From the code, we find the we use the DefinePlugin to pass some environment parameter for building. And the important thing is that the whole process.env is rewrited.

3. How to fix?

We have find the reason and there two way to fix the bug:

  • append APPIMAGE to the existing code
  • only rewrite some process.env parameters, look like below:
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const envParames = {};
  Object.keys(raw).forEach(k => {
    envParames[`process.env.${k}`] = JSON.stringify(raw[k])
  });
new webpack.DefinePlugin(envParames)

Because the APPIMAGE is a runtime environment, we can not set the value in building time. So the second it is right way to fix. Build a new application with new code, we test the app.AppImage auto upgrade function, it works now.

4. What have learned?

4.1 there are two kind of environment parameter

  • build time
  • runtime

4.2 never to rewrite whole process.env, only set the what you need

4.3 Summary

if your code running some website, you maybe never to care about runtime environment parameter. But if you code will build to some package application eg: command line tools / desktop application, you should care about the runtime environment.

5. Other useful article