bug: syslog error messages run together with the underlying error (missing separator)

[bhuvan-somisetty]

Current Behavior

In apisix/plugins/syslog/init.lua, send_syslog_data builds its two error messages by concatenating the underlying error directly onto the message text, with no separator:

err_msg = "failed when initiating the sys logger processor".. err   -- line 67
...
err_msg = "failed to log message" .. err                            -- line 76

err_msg is returned to the batch processor, which writes it verbatim to error.log (apisix/utils/batch-processor.lua, core.log.error("Batch Processor[", ..., "]: ", err)). The message and the real cause run together into one unreadable token, for example:

failed when initiating the sys logger processorconnection refused
failed to log messagebuffer overflow

Every other error string in the same code base uses a ": " separator (e.g. 'failed to open /dev/urandom: ' .. err, 'failed to loadstring: ' .. err).

Expected Behavior

The underlying error is separated from the message, consistent with the rest of the code base:

failed when initiating the sys logger processor: connection refused
failed to log message: buffer overflow

Error Logs

Not captured from a live run. The strings above are derived from the concatenation at lines 67 and 76 of apisix/plugins/syslog/init.lua on master.

Steps to Reproduce

1. Enable the syslog plugin on a route with host/port pointing at an unreachable syslog server, using sock_type: "tcp".
2. Send a request through the route so the batch processor flushes.
3. Read logs/error.log and look at the Batch Processor[syslog logger] error line: the failure reason is glued to the message text with no separator.

Note: this is separate from #13969 (nil-index crash when logger init fails). It concerns only the formatting of the messages, and applies to the "failed to log message" path too.

Environment

• APISIX version (run apisix version): 3.18.0 (master @ 3234caa)
• Operating system (run uname -a): N/A (found by code inspection)
• OpenResty / Nginx version (run openresty -V or nginx -V): N/A
• etcd version, if relevant: N/A
• APISIX Dashboard version, if relevant: N/A
• Plugin runner version, for issues related to plugin runners: N/A
• LuaRocks version, for installation issues: N/A