Zipkin V1 Receiver + V2 Exporter creates empty annotations

[chris-smith-zocdoc]

In the json zipkin v1 format, the span kind is inferred from the annotations (sr, ss = kind SERVER). The inference is working correctly, but ends up creating empty annotations when used with a v2 Exporter. These annotations contain just a timestamp and no other information. I believe these should be removed.

Example v1 span

[
    {
        "id": "cfa93400b6c64114",
        "name": "GET",
        "annotations": [
            {
                "timestamp": 1589329047638966,
                "value": "sr",
                "endpoint": {
                    "ipv4": "172.29.0.3",
                    "port": 0,
                    "serviceName": "my-service"
                }
            },
            {
                "timestamp": 1589329047643097,
                "value": "ss",
                "endpoint": {
                    "ipv4": "172.29.0.3",
                    "port": 0,
                    "serviceName": "my-service"
                }
            }
        ],
        "binaryAnnotations": [
            {
                "key": "http.host",
                "value": "localhost:5000",
                "endpoint": {
                    "ipv4": "172.29.0.3",
                    "port": 0,
                    "serviceName": "my-service"
                }
            },
            {
                "key": "http.uri",
                "value": "http://localhost:5000/healthcheck",
                "endpoint": {
                    "ipv4": "172.29.0.3",
                    "port": 0,
                    "serviceName": "my-service"
                }
            },
            {
                "key": "http.path",
                "value": "/healthcheck",
                "endpoint": {
                    "ipv4": "172.29.0.3",
                    "port": 0,
                    "serviceName": "my-service"
                }
            }
        ],
        "debug": false,
        "traceId": "778fff36dc3e06cd",
        "timestamp": 1589329047638966,
        "duration": 4130
    }
]

I expect this to produce a span that looks like this

[
    {
        "traceId": "778fff36dc3e06cd",
        "id": "cfa93400b6c64114",
        "kind": "SERVER",
        "name": "get",
        "timestamp": 1589329047638966,
        "duration": 4130,
        "localEndpoint": {
            "serviceName": "my-service",
            "ipv4": "172.29.0.3"
        },
        "tags": {
            "http.host": "localhost:5000",
            "http.path": "/healthcheck",
            "http.uri": "http://localhost:5000/healthcheck"
        }
    }
]

But instead it produces this

[
    {
        "traceId": "690dba9272ff7f43",
        "id": "1691fe50b928203c",
        "kind": "SERVER",
        "name": "get",
        "timestamp": 1589329265584397,
        "duration": 10734,
        "localEndpoint": {
            "serviceName": "my-service",
            "ipv4": "172.29.0.3"
        },
        "annotations": [
            {
                "timestamp": 1589329265584397,
                "value": ""
            },
            {
                "timestamp": 1589329265595132,
                "value": ""
            }
        ],
        "tags": {
            "http.host": "localhost:5000",
            "http.path": "/healthcheck",
            "http.uri": "http://localhost:5000/healthcheck"
        }
    }
]

docker-compose.yml

version: "2"
services:
  otel-collector:
    image: otelcontribcol:latest
    command: ["--config=/etc/otel-collector-config.yaml", "--mem-ballast-size-mib", "4000"]
    volumes:
      - ./otel-collector-config.yaml:/etc/otel-collector-config.yaml
    ports:
      - "8080:9411" # zipkin
    depends_on:
      - zipkin-all-in-one

  zipkin-all-in-one:
    image: openzipkin/zipkin:latest
    ports:
      - "9411:9411"

otel-collector-config.yaml

receivers:
  zipkin:
    endpoint: :9411

exporters:
  zipkin:
    url: "http://zipkin-all-in-one:9411/api/v2/spans"

processors:
  queued_retry:

service:
  pipelines:
    traces:
      receivers: [zipkin]
      processors: [queued_retry]
      exporters: [zipkin]

[chris-smith-zocdoc]

One solution I came up with was to remove these kind annotations during parseZipkinV1Annotations Does this seems like a good solution? Zocdoc@0aa99de

If we agree on an approach I'd be happy to send a pr