Integrate ZAP with SettableLoggerV2.

The settable_test.go is a good example of integration of
testing harness with grpclogging using zaptest,
that is canonical usecase for this infrastructure.

logging/zap/doc.go

@@ -70,5 +70,6 @@ Note - due to implementation ZAP differs from Logrus in the "grpc.request.conten
 
 
 Please see examples and tests for examples of use.
+Please see settable_test.go for canonical integration through "zaptest" with golang testing infrastructure.
 */
 package grpc_zap

logging/zap/grpclogger.go

@@ -6,6 +6,7 @@ package grpc_zap
 import (
 	"fmt"
 
+	grpc_logsettable "github.com/grpc-ecosystem/go-grpc-middleware/logging/settable"
 	"go.uber.org/zap"
 	"google.golang.org/grpc/grpclog"
 )
@@ -47,11 +48,13 @@ func (l *zapGrpcLogger) Println(args ...interface{}) {
 }
 
 // ReplaceGrpcLoggerV2 replaces the grpc_log.LoggerV2 with the provided logger.
+// It should be called before any gRPC functions.
 func ReplaceGrpcLoggerV2(logger *zap.Logger) {
 	ReplaceGrpcLoggerV2WithVerbosity(logger, 0)
 }
 
 // ReplaceGrpcLoggerV2WithVerbosity replaces the grpc_.LoggerV2 with the provided logger and verbosity.
+// It should be called before any gRPC functions.
 func ReplaceGrpcLoggerV2WithVerbosity(logger *zap.Logger, verbosity int) {
 	zgl := &zapGrpcLoggerV2{
 		logger:    logger.With(SystemField, zap.Bool("grpc_log", true)),
@@ -60,6 +63,22 @@ func ReplaceGrpcLoggerV2WithVerbosity(logger *zap.Logger, verbosity int) {
 	grpclog.SetLoggerV2(zgl)
 }
 
+// SetGrpcLoggerV2 replaces the grpc_log.LoggerV2 with the provided logger.
+// It can be used even when grpc infrastructure was initialized.
+func SetGrpcLoggerV2(settable grpc_logsettable.SettableLoggerV2, logger *zap.Logger) {
+	SetGrpcLoggerV2WithVerbosity(settable, logger, 0)
+}
+
+// SetGrpcLoggerV2WithVerbosity replaces the grpc_.LoggerV2 with the provided logger and verbosity.
+// It can be used even when grpc infrastructure was initialized.
+func SetGrpcLoggerV2WithVerbosity(settable grpc_logsettable.SettableLoggerV2, logger *zap.Logger, verbosity int) {
+	zgl := &zapGrpcLoggerV2{
+		logger:    logger.With(SystemField, zap.Bool("grpc_log", true)),
+		verbosity: verbosity,
+	}
+	settable.Set(zgl)
+}
+
 type zapGrpcLoggerV2 struct {
 	logger    *zap.Logger
 	verbosity int

logging/zap/settable_test.go

@@ -0,0 +1,31 @@
+package grpc_zap_test
+
+import (
+	"testing"
+
+	grpc_logsettable "github.com/grpc-ecosystem/go-grpc-middleware/logging/settable"
+	grpc_zap "github.com/grpc-ecosystem/go-grpc-middleware/logging/zap"
+	"go.uber.org/zap/zaptest"
+)
+
+var grpc_logger grpc_logsettable.SettableLoggerV2
+
+func init() {
+	grpc_logger = grpc_logsettable.ReplaceGrpcLoggerV2()
+}
+
+func beforeTest(t testing.TB) {
+	grpc_zap.SetGrpcLoggerV2(grpc_logger, zaptest.NewLogger(t))
+	t.Cleanup(func() {
+		grpc_logger.Reset()
+	})
+}
+
+// This test illustrates setting up a testing harness that attributes
+// all grpc logs emitted during the test to the test-specific log.
+//
+// In case of test failure, only logs emitted by this testcase will be printed.
+func TestSpecificLogging(t *testing.T) {
+	beforeTest(t)
+	grpc_logger.Info("Test specific log-line")
+}