Telegraf 1.3 dev socket_writer Plugin (built from master) seg faults with value format

[RandyAbernethy]

Bug report

Telegraf socket_writer Plugin (built from commit 426182b) seg faults with value format when messages are received. Using the below config with with json format works fine (from 1 up to a max of about 36k mps on the test system). Switching to value causes a crash on the first message (see below scenario and output). There is no value OUTPUT FORMAT documented but log WARN or ERR message would be preferable.

Relevant telegraf.conf:

user@ubuntu:~/monitoring/msg-agg/telegraf$ cat local.conf 
[agent]
  interval = "15ms"
  flush_interval = "50ms"
  omit_hostname = true

[[inputs.socket_listener]]
  service_address = "tcp://:8094"
  name_override = "a"
  data_format = "value"
  data_type = "string"

[[outputs.socket_writer]]
  address = "tcp://192.168.131.133:9911"
  data_format = "value"
  
user@ubuntu:~/monitoring/msg-agg/telegraf$ 

System info:

user@ubuntu:~/monitoring/msg-agg/telegraf$ cat dockerfile 
FROM golang:1.8.0-alpine

RUN apk update
RUN apk add --no-cache iputils ca-certificates && \
    update-ca-certificates

RUN apk add git make
RUN go get github.com/influxdata/telegraf
WORKDIR $GOPATH/src/github.com/influxdata/telegraf
RUN make

EXPOSE 8094

CMD ["telegraf"]

Steps to reproduce:

user@ubuntu:~/monitoring/msg-agg/telegraf$ docker run -p 8094:8094 -v $PWD/local.conf:/etc/telegraf/telegraf.conf:ro msg-agg-tg
2017/03/17 00:33:37 I! Using config file: /etc/telegraf/telegraf.conf
2017-03-17T00:33:37Z I! Starting Telegraf (version dev-86-g426182b8)
2017-03-17T00:33:37Z I! Loaded outputs: socket_writer
2017-03-17T00:33:37Z I! Loaded inputs: inputs.socket_listener
2017-03-17T00:33:37Z I! Tags enabled: 
2017-03-17T00:33:37Z I! Agent Config: Interval:15ms, Quiet:false, Hostname:"", Flush Interval:50ms 
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0xf247f0]

goroutine 740 [running]:
github.com/influxdata/telegraf/plugins/outputs/socket_writer.(*SocketWriter).Write(0xc4201f9dd0, 0xc420010700, 0x1, 0x1, 0xc42030ae78, 0x64acd6)
	/go/src/github.com/influxdata/telegraf/plugins/outputs/socket_writer/socket_writer.go:78 +0x60
github.com/influxdata/telegraf/internal/models.(*RunningOutput).write(0xc4201ba460, 0xc420010700, 0x1, 0x1, 0x1, 0x0)
	/go/src/github.com/influxdata/telegraf/internal/models/running_output.go:173 +0xa1
github.com/influxdata/telegraf/internal/models.(*RunningOutput).Write(0xc4201ba460, 0x128ff80, 0xc4200105d0)
	/go/src/github.com/influxdata/telegraf/internal/models/running_output.go:157 +0x497
github.com/influxdata/telegraf/agent.(*Agent).flush.func1(0xc4200105d0, 0xc4201ba460)
	/go/src/github.com/influxdata/telegraf/agent/agent.go:238 +0x59
created by github.com/influxdata/telegraf/agent.(*Agent).flush
	/go/src/github.com/influxdata/telegraf/agent/agent.go:243 +0xa5

Expected behavior:

should work

Actual behavior:

blows up

Additional info:

When the conf format is changed to json all is well

Use case: [Why is this important (helps with prioritizing requests)]

Would be nice to be able to opt out of the JSON stuff like you can on the input side with the "value" format, or better yet a raw format.

[danielnelson]

Thanks for opening this issue. I'm not sure a value output format would make much sense because the value format doesn't have a time or measurement name.

[RandyAbernethy]

We could use it in cases where telegraf is aggregating and we want raw unformatted data passed through. Not a deal killer though. On the other hand I think a segfault is a little user hostile even if it is not something the community wants to add support for.