[exporter-zipkin 1.1.0] otel.dropped_attributes_count - 400: json: cannot unmarshal number into Go struct field .tags of type string

[tomasjanda]

Hello, i am using zipkin exporter in version 1.1.0 and opentelemetry-collector with zipkin receiver and i got 400 - Bad request when tags cointains otel.dropped_attributes_count attribute formattes as number, not string.

Here is correct comment in source code:

// Zipkin tags must be strings, but opentelemetry
// accepts strings, booleans, numbers, and lists of each.

but when library sets custom tag otel.dropped_attributes_count, there is not casting to string

Collector settings

receivers:
  zipkin:
    endpoint: 0.0.0.0:9411

processors:
  batch:
    send_batch_max_size: 10485760
    send_batch_size: 1048576
    timeout: 5s

exporters:
  otlphttp:
    endpoint: ${env:OTELCOL_EXPORTER}
    tls:
      insecure: true

service:
  pipelines:
    traces:
      receivers: [zipkin]
      processors: [batch]
      exporters: [otlphttp]

Generated payload

[
    {
        "id": "5a19611a37ba40c4",
        "traceId": "03f6f604f59e0ec4cf39931e87e0db2e",
        "localEndpoint": {
            "serviceName": "api.cv1-core"
        },
        "name": "mdw PERMISSIONS",
        "timestamp": 1729012528523110,
        "duration": 257155,
        "tags": {
            "otel.status_code": "Ok",
            "permission.context": "ADMINISTRATOR",
            "permission.ignoreBlockedService": "false",
            "user.clientId": "test_client",
            "user.clientRole": "ADMINISTRATOR",
            "user.clientScopes": "administrator",
            "service.name": "api.cv1-core",
            "service.version": "unknown",
            "deployment.environment.name": "develop",
            "service.instance.id": "local",
            "otel.dropped_attributes_count": 1
        },
        "parentId": "e2d7b2cdac905f5f",
        "otel.scope.name": "api.cv1-core",
        "annotations": [
            {
                "timestamp": 1729012528523121,
                "value": "\"Call user-management to resolve admin role\""
            },
            {
                "timestamp": 1729012528780249,
                "value": "\"User management response\""
            }
        ]
    }
]

Response

400 Bad Request
json: cannot unmarshal number into Go struct field .tags of type string↵