Adds a Producer Interceptor example

a consumer interceptor should be similar

examples/README.md

@@ -8,3 +8,6 @@ In these examples, we use `github.com/Shopify/sarama` as import path. We do this
 
 [http_server](./http_server) is a simple HTTP server uses both the sync producer to produce data as part of the request handling cycle, as well as the async producer to maintain an access log. It also uses the [mocks subpackage](https://godoc.org/github.com/Shopify/sarama/mocks) to test both.
 
+#### Interceptors
+
+Basic example to use a producer interceptor that produces oTel spans and add some headers for each intercepted message.

examples/consumergroup/go.mod

@@ -1,5 +1,7 @@
 module github.com/Shopify/sarama/examples/consumer
 
+go 1.14
+
 replace github.com/Shopify/sarama => ../../
 
-require github.com/Shopify/sarama v1.22.0
+require github.com/Shopify/sarama v1.27.0

examples/consumergroup/go.sum

@@ -1,34 +1,77 @@
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examples/interceptors/README.md

@@ -0,0 +1,116 @@
+# Interceptors Example
+
+It creates a *Producer* interceptor to produce some oTel spans and also modifies
+the intercepted message to include some headers.
+
+``` go
+conf.Producer.Interceptors = []sarama.ProducerInterceptor{xxx}
+```
+
+## Run the example
+- `go run main.go trace_interceptor.go`.
+- or `go build and pass different parameters.
+``` sh
+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 oTel 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":"b3922fbbaab23b16401c353b0ff9ce6b","SpanID":"269f5133c0d0116e","TraceFlags":1},"ParentSpanID":"0000000000000000","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":"269f5133c0d0116e"}}],"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
+```

examples/interceptors/go.mod

@@ -0,0 +1,13 @@
+module github.com/Shopify/sarama/examples/interceptors
+
+go 1.14
+
+replace github.com/Shopify/sarama => ../../
+
+require (
+	github.com/Shopify/sarama v1.27.0
+	github.com/sirupsen/logrus v1.6.0
+	go.opentelemetry.io/otel v0.10.0
+	go.opentelemetry.io/otel/exporters/stdout v0.10.0
+	google.golang.org/genproto v0.0.0-20200331122359-1ee6d9798940 // indirect
+)