fix(provisioner/terraform): prevent deadlock when terraform emits log lines > 64 KiB#26238
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…ines Terraform providers (e.g. azurerm with TF_LOG=DEBUG) can emit single log lines that exceed the default 64 KiB bufio.MaxScanTokenSize. When this happens bufio.Scanner fails with 'token too long', the scanner loop exits, and the goroutine stops consuming from the io.Pipe. The pipe writer blocks, terraform's stdout/stderr block, and cmd.Wait() never returns, causing the provisioner to hang indefinitely with no error or timeout. Fix by: - Increasing the scanner buffer to 4 MiB via a newLogScanner helper. - Adding scanner.Err() handling in readAndLog and provisionReadAndLog so scan failures are surfaced as ERROR logs instead of silent deadlocks. - Adding a readLineWithFallback helper for future use with lines that may still exceed the enlarged buffer. Fixes coder/coder coder#24766
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Ran into this while debugging an Azure deployment with TF_LOG=DEBUG set. The build would just hang forever — no error, no timeout, no progress. Took a while to figure out why.
The azurerm provider logs full HTTP response bodies (e.g. the subscription providers list, ~3 MB) as a single hclog [DEBUG] entry. That blows past bufio.Scanner's default 64 KiB limit. When scanner.Scan() fails with "token too long", the goroutine reading from the pipe exits, the pipe writer blocks, terraform's stdout/stderr block, and cmd.Wait() never returns. The provisioner is deadlocked.
I bumped the scanner buffer to 4 MiB and added scanner.Err() handling so any remaining failures get logged instead of causing silent hangs. Also added a fallback helper for truly enormous lines.
Fixes #24766
Not 100% sure about the 4 MiB constant — happy to adjust if there's a project preference.