Interceptors Example

It creates a Producer interceptor to produce some OpenTelemetry spans and also modifies the intercepted message to include some headers.

conf.Producer.Interceptors = []sarama.ProducerInterceptor{xxx}

Run the example

go run main.go trace_interceptor.go.

or `go build and pass different parameters.

go build && ./interceptors --h
Usage of ./interceptors:
-brokers string
    The Kafka brokers to connect to, as a comma separated list (default "localhost:9092")
-topic string
    The Kafka topic to use (default "default_topic")

App will output OpenTelemetry spans for every intercepted message, i.e:

```

go run main.go trace_interceptor.go [Sarama] 2020/08/11 11:35:56 Initializing new client [Sarama] 2020/08/11 11:35:56 ClientID is the default of 'sarama', you should consider setting it to something application-specific. [Sarama] 2020/08/11 11:35:56 ClientID is the default of 'sarama', you should consider setting it to something application-specific. [Sarama] 2020/08/11 11:35:56 client/metadata fetching metadata for all topics from broker localhost:9092 [Sarama] 2020/08/11 11:35:56 Connected to broker at localhost:9092 (unregistered) [Sarama] 2020/08/11 11:35:56 client/brokers registered new broker #1 at localhost:9092 [Sarama] 2020/08/11 11:35:56 Successfully initialized new client INFO[0000] Starting to produce 2 messages every 5s INFO[0005] producing 2 messages at 2020-08-11T11:36:01-07:00 topic=default_topic [ {

"SpanContext": {
  "TraceID": "2c4210c1d6c2ebe758eb41cbc95a0478",
  "SpanID": "046bfc6d6db17ed7",
  "TraceFlags": 1
},
"ParentSpanID": "0000000000000000",
"SpanKind": 1,
"Name": "default_topic",
"StartTime": "2020-08-11T11:36:01.57487-07:00",
"EndTime": "2020-08-11T11:36:01.574891849-07:00",
"Attributes": [
  {
    "Key": "messaging.destination_kind",
    "Value": { "Type": "STRING", "Value": "topic" }
  },
  {
    "Key": "span.otel.kind",
    "Value": { "Type": "STRING", "Value": "PRODUCER" }
  },
  {
    "Key": "messaging.system",
    "Value": { "Type": "STRING", "Value": "kafka" }
  },
  {
    "Key": "net.transport",
    "Value": { "Type": "STRING", "Value": "IP.TCP" }
  },
  {
    "Key": "messaging.url",
    "Value": { "Type": "STRING", "Value": "localhost:9092" }
  },
  {
    "Key": "messaging.destination",
    "Value": { "Type": "STRING", "Value": "default_topic" }
  },
  {
    "Key": "messaging.message_id",
    "Value": { "Type": "STRING", "Value": "046bfc6d6db17ed7" }
  }
],
"MessageEvents": null,
"Links": null,
"StatusCode": 0,
"StatusMessage": "",
"HasRemoteParent": false,
"DroppedAttributeCount": 0,
"DroppedMessageEventCount": 0,
"DroppedLinkCount": 0,
"ChildSpanCount": 0,
"Resource": null,
"InstrumentationLibrary": {
  "Name": "shopify.com/sarama/examples/interceptors",
  "Version": ""
}

} ] [{"SpanContext":{"TraceID":"b3922fbbaa","SpanID":"269f5133c0","TraceFlags":1},"ParentSpanID":"0000000000","SpanKind":1,"Name":"default_topic","StartTime":"2020-08-11T11:36:01.575388-07:00","EndTime":"2020-08-11T11:36:01.575399065-07:00","Attributes":[{"Key":"messaging.destination_kind","Value":{"Type":"STRING","Value":"topic"}},{"Key":"span.otel.kind","Value":{"Type":"STRING","Value":"PRODUCER"}},{"Key":"messaging.system","Value":{"Type":"STRING","Value":"kafka"}},{"Key":"net.transport","Value":{"Type":"STRING","Value":"IP.TCP"}},{"Key":"messaging.url","Value":{"Type":"STRING","Value":"localhost:9092"}},{"Key":"messaging.destination","Value":{"Type":"STRING","Value":"default_topic"}},{"Key":"messaging.message_id","Value":{"Type":"STRING","Value":"269f5133c0"}}],"MessageEvents":null,"Links":null,"StatusCode":0,"StatusMessage":"","HasRemoteParent":false,"DroppedAttributeCount":0,"DroppedMessageEventCount":0,"DroppedLinkCount":0,"ChildSpanCount":0,"Resource":null,"InstrumentationLibrary":{"Name":"shopify.com/sarama/examples/interceptors","Version":""}}] [Sarama] 2020/08/11 11:36:01 ClientID is the default of 'sarama', you should consider setting it to something application-specific. [Sarama] 2020/08/11 11:36:01 producer/broker/1 starting up [Sarama] 2020/08/11 11:36:01 producer/broker/1 state change to [open] on default_topic/0 [Sarama] 2020/08/11 11:36:01 Connected to broker at localhost:9092 (registered as #1) ^CINFO[0005] terminating the program INFO[0005] Bye :) [Sarama] 2020/08/11 11:36:02 Producer shutting down.


## Check the produced intercepted messages

Check that messages have some headers added by the interceptor:
``` sh
kafkacat -Cb localhost:9092 -t default_topic -f '\n- %s\nheaders: %h'

headers: trace_id=235b3424775d8b2f9bf21e458496f447,span_id=50da1552c105e712,message_id=50da1552c105e712
- test message 1/2 from kafka-client-go-test at 2020-08-11T11:36:01-07:00
headers: trace_id=2c4210c1d6c2ebe758eb41cbc95a0478,span_id=046bfc6d6db17ed7,message_id=046bfc6d6db17ed7
- test message 2/2 from kafka-client-go-test at 2020-08-11T11:36:01-07:00
% Reached end of topic default_topic [0] at offset 444

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Interceptors Example

Run the example

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