Signal Desktop for Windows Update SyntaxError at JSON.parse

[nnpcYvIVl]

• I have searched open and closed issues for duplicates

Bug description

When I run version 1.0.35 on Windows I get a popup with the following:

A JavaScript error occurred in the main process

Uncaught Exception:
SyntaxError: Unexpected end of JSON input
  at JSON.parse (<anonymous>)
  at Z:\Signal Desktop\resources\app.asar\node_modules\electron-updater\src\windowsExecutableCo...:25
  at ChildProcess.exithandler (child_process.js:214:7)
  at emitTwo (events.js:106:13)
  at ChildProcess.emit (events.js:191:7)
  at maybeClose (internal/child_process.js:885:16)
  at Process.ChildProcess._handle.onexit (internal/child_process.js:226:5)

Steps to reproduce

Open a version of Signal Desktop that needs to be updated (such as 1.0.35)
Error pops up in a couple of seconds

Platform info

Operating System: Windows 10
Signal version: 1.0.35

[scottnonnenberg]

That appears to be a problem verifying the signature of the downloaded binary. Can you try something for me?

Open Command Prompt, then navigate to the signal install directory:

cd AppData\Local\Programs\signal-desktop
powershell.exe "Get-AuthenticodeSignature Signal.exe | ConvertTo-Json"

Do you get an error, or does it print out something that includes "StatusMessage": "Signature verified."?

[nnpcYvIVl]

Running that in command prompt works, I see "StatusMessage": "Signature verified."

I don't know if this helps or not but right before the SyntaxError message pops up I do see a powershell window open and close very quickly.

[scottnonnenberg]

Hm. Does it happen consistently every time you restart Signal Desktop? (we check for updates right after startup)

Can you talk any more about your computer's setup? I know for sure that other Windows 10 installs successfully auto-upgrade. What happens when you run this in the command prompt? powershell.exe "$PSVersionTable.PSVersion"

[0xvext]

I also encountered this error two days ago. It happened after my HIPS popped up a warning that a Signal desktop executable was trying to initiate a Powershell command on my system.

This evening I will check verification of files per the above commands, review logs, and I will check to see if I can reproduce the error or provide any other insights.

[scottnonnenberg]

@0xvext Could you talk a little bit more about HIPS? How far from the default setup do you have it? What version of Windows are you on?

And to reiterate, our updater system uses a powershell command to verify the signature of the new application installer.

[0xvext]

It's a third-party HIPS that will fire and warn me when a process spawns another process, particularly for things like Powershell or other built-in executables in Windows System folders. This was on Windows 10.
If I am able to recreate it tonight after work I will provide more details in the hopes of tracking this down. I instructed my HIPS to permit the process execution so it shouldn't have interrupted it. Is it possible it's a time-sensitive function to verify the signature? My setup with the HIPS I use interrupts and waits for human input before allowing the process spawn to proceed, so if there is any time sensitivity/parallel processing that depends on it firing in a timely fashion that could explain why it caused a problem.
Otherwise HIPS shouldn't (in theory) be the cause of the error.

[scottnonnenberg]

@0xvext Looks like the timeout, at least in the very latest electron-updater, is 60s. https://github.com/electron-userland/electron-builder/blob/227d7791aa6fc7a122ef7152e2fe478f46cb64a0/packages/electron-updater/src/windowsExecutableCodeSignatureVerifier.ts#L12

[nnpcYvIVl]

I have figured out what the problem is. There is another file named powershell.exe in my path. Signal executes this file instead of the correct version in the Windows directory.

Can the app be modified to use the full path for powershell.exe instead of assuming it will find the correct one based on a path lookup?

[scottnonnenberg]

@nnpcYvIVl I think on different versions of the OS it's in different places, so that's why the full path isn't used. Why have you made powershell.exe into something else on your system? Is that a common thing for some community of windows users?

[nnpcYvIVl]

@scottnonnenberg I use it as a launcher (from command prompt and explorer) for powershell.

[0xvext]

@scottnonnenberg I was not able to reproduce the javascript error, even when ignoring the HIPS popup regarding powershell on my system. If the error ever occurs again I will provide more information, but so far I can't recreate it on purpose.

[0xvext]

@scottnonnenberg Looks like I spoke too soon. The next time Signal checked for an update, the following sequence of events took place:

1. HIPS popped up, warning me that signal.exe was attempting to run a Powershell script (I confirmed the contents of the script as "Get-AuthenticodeSignature '%Appdata%\Local\Temp\up-EihSwG\Signal-win-1.0.37.exe' | ConvertTo-Json -Compress")
2. I clicked to allow the process to spawn in my HIPS GUI
3. After a few seconds, Signal generated a Javascript error matching the one above, other than the application path reference (error pasted below, for completeness sake).

60 seconds did not elapse between the warning and my clicking to permit it, but I suspect the delay was long enough to be the source of the error, because then I was able to work around the error as follows:

1. Exited Signal Desktop
2. Re-opened Signal Desktop, triggering the update check
3. HIPS popped up the same warning about Powershell
4. I immediately clicked to allow, with no delay
5. Additional HIPS warnings for the update process came up sequentially, with me allowing each of them
6. Signal popped up a message that an update was available and that the application needed to be restarted
7. I clicked to restart Signal Desktop, and it came up successfully with the latest version.

It seems like there is some aspect of the update process that is very delay sensitive to the process being paused by my HIPS implementation.

Regardless, it can be worked around, and doesn't seem to be an issue with Signal itself, per se, just the interaction of it with the HIPS product I use.

Content of the error I received, for completeness:

Uncaught Exception:
SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at %AppData%\Local\Programs\signal-desktop\resources\app.asar\node_modules\electron-updater\src\windowsExecutableCodeSignatureVerifier.ts:36:25
    at ChildProcess.exithandler (child_process.js:214:7)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:191:7)
    at maybeClose (internal/child_process.js:885:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:226:5)