Adding custom report filter (#163)

README.md

@@ -32,6 +32,22 @@ if err != nil {
 }
 defer r.Close()
 tracer, err := go2sky.NewTracer("example", go2sky.WithReporter(r))
+```
+In some scenarios, we may need a filter to filter segments that do not need to be submitted, for example, to reduce the load of gRPC reporting, or only track the request of error.
+
+```go
+r, err := reporter.NewGRPCReporter("oap-skywalking:11800", reporter.WithReportStrategy(func(s *v3.SegmentObject) bool {
+	var isReport bool
+	for _, span := s.GetSpans() {
+		if span.GetIsError() {
+			isReport = true
+			break
+		}
+	}
+
+	return isReport
+}))
+
 ```
 
 You can also create tracer with sampling rate. It supports decimals between **0-1** (two decimal places), representing the sampling percentage of trace.
@@ -292,4 +308,4 @@ Also, when the go2sky keep alive with backend, modify and open time of the metad
 Please read the [official documentation of rover](https://skywalking.apache.org/docs/skywalking-rover/latest/en/setup/configuration/process_discovery/scanner/#agent-sensor-mode) to get more information.
 
 # License
-Apache License 2.0. See [LICENSE](LICENSE) file for details.
+Apache License 2.0. See [LICENSE](LICENSE) file for details.

reporter/grpc.go

@@ -108,6 +108,9 @@ type gRPCReporter struct {
 	cdsService       *go2sky.ConfigDiscoveryService
 	cdsClient        configuration.ConfigurationDiscoveryServiceClient
 
+	// set report strategy
+	rs ReportStrategy
+
 	md    metadata.MD
 	creds credentials.TransportCredentials
 
@@ -232,6 +235,9 @@ func (r *gRPCReporter) initSendPipeline() {
 				continue StreamLoop
 			}
 			for s := range r.sendCh {
+				if r.rs != nil && !r.rs(s) {
+					continue
+				} 
 				err = stream.Send(s)
 				if err != nil {
 					r.logger.Errorf("send segment error %v", err)

reporter/grpc_opts.go

@@ -27,6 +27,10 @@ import (
 	agentv3 "skywalking.apache.org/repo/goapi/collect/language/agent/v3"
 )
 
+// ReportStrategy allowed to set a custom filter
+// to filter the reported segment
+type ReportStrategy func(s *agentv3.SegmentObject) bool
+
 // GRPCReporterOption allows for functional options to adjust behaviour
 // of a gRPC reporter to be created by NewGRPCReporter
 type GRPCReporterOption func(r *gRPCReporter)
@@ -119,3 +123,10 @@ func WithProcessStatusHook(enable bool) GRPCReporterOption {
 		r.processStatusHookEnable = enable
 	}
 }
+
+// WithReportStrategy set report strategy
+func WithReportStrategy(rs ReportStrategy) GRPCReporterOption {
+	return func(r *gRPCReporter) {
+		r.rs = rs
+	}
+}