Empty batch sent after oversized message rejection causes retry loop with JSON parse error

[johnnagro]

While working on #81 I noticed some logging and investigated.

When a message exceeds the maximum allowed size (32KB), it is correctly rejected by MessageBatch, but two subsequent issues cause a noisy retry loop.

Issue 1: Empty batch is sent to API

In send_worker.rb, when all messages in a batch are rejected due to size limits, the worker still calls @transport.send with an empty batch:

# send_worker.rb:46
res = @transport.send @api_key, @batch  # @batch may be empty here

The log shows:

[posthog-ruby] a message exceeded the maximum allowed size
[posthog-ruby] Sending request for 0 items

Issue 2: JSON parsing fails on non-JSON response

When the server receives an invalid/empty request, it may return a non-JSON error response. The transport code assumes JSON:

# transport.rb:53
error = JSON.parse(body)['error']

This throws a JSON::ParserError, which triggers the retry logic, resulting in:

[posthog-ruby] Retrying request, 10 retries left
[posthog-ruby] Retrying request, 9 retries left
...
[posthog-ruby] unexpected character: 'request' at line 1 column 1

Suggested fixes

1. Skip sending if batch is empty in send_worker.rb
2. Wrap JSON parsing in a rescue block in transport.rb

Environment

• Ruby 3.4.5
• Rails 8.1.1
• posthog-ruby (local/dev version)