glog: check that stderr is valid before using it by default #72
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Windows Services are [spawned without `stdout` and `stderr`](https://learn.microsoft.com/en-us/windows/console/getstdhandle#return-value:~:text=If%20an%20application%20does%20not%20have%20associated%20standard%20handles%2C%20such%20as%20a%20service%20running%20on%20an%20interactive%20desktop%2C%20and%20has%20not%20redirected%20them%2C%20the%20return%20value%20is%20NULL.), so any attempt to use them equates to referencing an invalid file `Handle`. `stderrSink` returns the error, which makes `logsink` trigger the termination of the process. The result is that any call to `log.Error` (or `log.Fatal`) from a Windows Service will always crash the program. This approach checks that `os.Stderr`'s embedded file descriptor (`Handle`, for Windows) is non-NULL once during `init` to determine its validity and if it fails, then never registers `stderrSink` as a logsink. Disabling based upon whether `os.Stderr` is NULL was chosen because it's precise, doesn't actually influence the result of any output and doesn't require any syscalls, but still detects the case in which `stderr` is unavailable on Windows. A rejected approach here would've been to swallow the errors from `stderrSink.Emit`, thus sparing us program termination at the hands of `logsink`. I rejected this approach because it felt like it could result in some subtle behavioral changes. For example, invoking `log.Error` after `os.Stderr.Close()` would no longer exit the program and that felt like a non-trivial change (although I can think of no reason why one would desire this behavior). cl/680817112 (google-internal)
stapelberg
approved these changes
Nov 4, 2024
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Windows Services are spawned without
stdoutandstderr, so any attempt to use them equates to referencing an invalid fileHandle.stderrSinkreturns the error, which makeslogsinktrigger the termination of the process. The result is that any call tolog.Error(orlog.Fatal) from a Windows Service will always crash the program.This approach checks that
os.Stderr's embedded file descriptor (Handle, for Windows) is non-NULL once duringinitto determine its validity and if it fails, then never registersstderrSinkas a logsink.Disabling based upon whether
os.Stderris NULL was chosen because it's precise, doesn't actually influence the result of any output and doesn't require any syscalls, but still detects the case in whichstderris unavailable on Windows.A rejected approach here would've been to swallow the errors from
stderrSink.Emit, thus sparing us program termination at the hands oflogsink. I rejected this approach because it felt like it could result in some subtle behavioral changes. For example, invokinglog.Errorafteros.Stderr.Close()would no longer exit the program and that felt like a non-trivial change (although I can think of no reason why one would desire this behavior).cl/680817112 (google-internal)