No mutex on Writer

[chrisDeFouRire]

I'm tracking a bug where Graylog says it has received invalid GELF JSON (TCP transport, from docker GELF logger which is using this Writer).

It looks like this mu Mutex is never used...

go-gelf/gelf/writer.go

Line 29 in 7ebf4f5

mu sync.Mutex

Here is the calling code in the Docker logger..

https://github.com/moby/moby/blob/master/daemon/logger/gelf/gelf.go#L184

And here's an extract from my Graylog logs...

2018-03-17 09:27:23,810 ERROR: org.graylog2.inputs.codecs.GelfCodec - Could not parse JSON, first 400 characters: {"version":"1.1","host":"france2.sslping.com","short_message":"2018/03/17 09:27:22 twr1.thewaiting-room.net (80.82.112.63:443): true","timestamp":1521278842.705,"level":3,"_command":"./main","_container_id":"95abe5c05bde85e05a460b4d2a0875d779d23e9469722846430e96bbf8e5afec","_container_name":"nats_cve20162107.3.43d8bhzvc82qkc6ir2lrziyyi","_created":"2018-03-16T17:43:35.735128942Z","_image_id":"sha2...

com.fasterxml.jackson.core.JsonParseException: Unexpected character ('v' (code 118)): was expecting comma to separate Object entries
 at [Source: {"version":"1.1","host":"france2.sslping.com","short_message":"2018/03/17 09:27:22 twr1.thewaiting-room.net (80.82.112.63:443): true","timestamp":1521278842.705,"level":3,"_command":"./main","_container_id":"95abe5c05bde85e05a460b4d2a0875d779d23e9469722846430e96bbf8e5afec","_container_name":"nats_cve20162107.3.43d8bhzvc82qkc6ir2lrziyyi","_created":"2018-03-16T17:43:35.735128942Z","_image_id":"sha256:a70d979f79007e38f57a0b77310145102934eee96c80a4df3f03b642e76aad6e","_image_name":"registry.gitlab.com/chrishartwig/sslping/nats_cve20162107:latest","_tag":"vul{"version":"1.1","host":"france2.sslping.com","short_message":"2018/03/17 09:27:22 pip.lade.io (13.32.214.118:443): false","timestamp":1521278842.831,"level":3,"_command":"./main","_container_id":"8e68654e1ff2ec9838a10362141ac432ca0301dfa246ae52cfa8c81cbe59f9d7","_container_name":"nats_heartbleed.2.fx9blxsrii95z3w7a59t539s1","_created":"2018-03-16T17:42:22.48917432Z","_image_id":"sha256:6d1aed1d88d0b2b38f6f6435396670fa27f060656701efe86e731d3163759624","_image_name":"registry.gitlab.com/chrishartwig/sslping/nats_heartbleed:latest","_tag":"vuln"}; line: 1, column: 565]

It does occur under moderate load (13k messages in 4min) and from the logs, it looks like the 2 mingled messages are always from the same host, possibly from the same container (hard to tell with corrupted JSON)...
I don't know if it's a graylog issue, or a Docker logger issue (maybe the logger should use a mutex)...