fix(transport): log directly sent envelopes in DebugTransport

[solnic]

DebugTransport now also logs envelopes passed to send_envelope, such as logs and metrics, not only events. Several processes can write to the log file at once, so each envelope is written in one go and reading skips any unfinished last line.

I stumbled upon this when working on #3057 as SolidQueue workers caused issues with concurrent writing to this debug transport log.

[sentry]

Bug: The logged_envelopes method can crash with an unhandled JSON::ParserError due to concurrent writes to the debug log file corrupting JSON data.
_{Severity: HIGH}

Suggested Fix

Implement file locking using File#flock around the write operation to ensure atomic writes. Additionally, wrap the JSON.parse(line) call within the logged_envelopes method in a begin/rescue JSON::ParserError block to gracefully handle any corrupted lines and prevent crashes.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: sentry-ruby/lib/sentry/transport/debug_transport.rb#L32

Potential issue: The `DebugTransport` writes to a log file using `File.open(log_file,
"a")` without any file locking. In multi-threaded environments, such as with SolidQueue
workers, concurrent writes can corrupt the log file, especially with large payloads. The
`logged_envelopes` method reads these logs and attempts to parse each line with
`JSON.parse` but lacks a `rescue` block. If a line is corrupted due to interleaved
writes, `JSON.parse` will raise an unhandled `JSON::ParserError`, causing the method to
crash. The existing `fully_written?` check is insufficient as it only verifies a
trailing newline and does not prevent JSON corruption from race conditions.

Also affects:

• sentry-ruby/lib/sentry/transport/debug_transport.rb:64~64

_{Did we get this right? 👍 / 👎 to inform future reviews.}