enhancement: Ability to set gRPC stats handler

Otel library has finally moved to using `stats.Handler` to record gRPC
traces and metrics. This means that we need a way for users to set a
`stats.Handler` on the connection established by the Cerbos client.

Signed-off-by: Charith Ellawala <charith@cerbos.dev>

cerbos/grpc.go

@@ -12,15 +12,17 @@ import (
  "os"
  "time"
 
- effectv1 "github.com/cerbos/cerbos/api/genpb/cerbos/effect/v1"
- enginev1 "github.com/cerbos/cerbos/api/genpb/cerbos/engine/v1"
- requestv1 "github.com/cerbos/cerbos/api/genpb/cerbos/request/v1"
- svcv1 "github.com/cerbos/cerbos/api/genpb/cerbos/svc/v1"
  grpc_retry "github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/retry"
  "github.com/rs/xid"
  "google.golang.org/grpc"
  "google.golang.org/grpc/credentials"
  "google.golang.org/grpc/credentials/insecure"
+ "google.golang.org/grpc/stats"
+
+ effectv1 "github.com/cerbos/cerbos/api/genpb/cerbos/effect/v1"
+ enginev1 "github.com/cerbos/cerbos/api/genpb/cerbos/engine/v1"
+ requestv1 "github.com/cerbos/cerbos/api/genpb/cerbos/request/v1"
+ svcv1 "github.com/cerbos/cerbos/api/genpb/cerbos/svc/v1"
 
  "github.com/cerbos/cerbos-sdk-go/internal"
 )
@@ -42,6 +44,7 @@ type config struct {
  maxRetries uint
  plaintext bool
  tlsInsecure bool
+ statsHandler stats.Handler
 }
 
 type Opt func(*config)
@@ -133,6 +136,13 @@ func WithUnaryInterceptors(interceptors ...grpc.UnaryClientInterceptor) Opt {
  }
 }
 
+// WithStatsHandler sets the gRPC stats handler for the connection.
+func WithStatsHandler(handler stats.Handler) Opt {
+ return func(c *config) {
+ c.statsHandler = handler
+ }
+}
+
 // New creates a new Cerbos client.
 func New(address string, opts ...Opt) (*GRPCClient, error) {
  grpcConn, _, err := mkConn(address, opts...)
@@ -172,6 +182,10 @@ func mkConn(address string, opts ...Opt) (*grpc.ClientConn, *config, error) {
 func mkDialOpts(conf *config) ([]grpc.DialOption, error) {
  dialOpts := []grpc.DialOption{grpc.WithUserAgent(conf.userAgent)}
 
+ if conf.statsHandler != nil {
+ dialOpts = append(dialOpts, grpc.WithStatsHandler(conf.statsHandler))
+ }
+
  if conf.connectTimeout > 0 {
  dialOpts = append(dialOpts, grpc.WithConnectParams(grpc.ConnectParams{MinConnectTimeout: conf.connectTimeout}))
  }