Add support for gRPC checks

Adds the glue necessary for the agent to start accepting and executing
gRPC checks.

internal/prober/prober.go

@@ -7,6 +7,7 @@ import (
 	"github.com/grafana/synthetic-monitoring-agent/internal/k6runner"
 	"github.com/grafana/synthetic-monitoring-agent/internal/model"
 	"github.com/grafana/synthetic-monitoring-agent/internal/prober/dns"
+	"github.com/grafana/synthetic-monitoring-agent/internal/prober/grpc"
 	"github.com/grafana/synthetic-monitoring-agent/internal/prober/http"
 	"github.com/grafana/synthetic-monitoring-agent/internal/prober/icmp"
 	"github.com/grafana/synthetic-monitoring-agent/internal/prober/k6"
@@ -86,6 +87,10 @@ func (f proberFactory) New(ctx context.Context, logger zerolog.Logger, check mod
 			err = fmt.Errorf("k6 checks are not enabled")
 		}
 
+	case sm.CheckTypeGrpc:
+		p, err = grpc.NewProber(ctx, check.Check, logger)
+		target = check.Target
+
 	default:
 		return nil, "", fmt.Errorf("unsupported check type")
 	}

pkg/accounting/accounting.go

@@ -61,6 +61,11 @@ func GetCheckAccountingClass(check synthetic_monitoring.Check) (string, error) {
 
 	case synthetic_monitoring.CheckTypeTraceroute:
 
+	case synthetic_monitoring.CheckTypeGrpc:
+		if check.Settings.Grpc.Tls {
+			key += "_ssl"
+		}
+
 	default:
 		return "", ErrUnhandledCheck
 	}

pkg/pb/synthetic_monitoring/checks_extra.go

@@ -158,6 +158,7 @@ const (
 	CheckTypeTraceroute CheckType = 4
 	CheckTypeK6         CheckType = 5
 	CheckTypeMultiHttp  CheckType = 6
+	CheckTypeGrpc       CheckType = 7
 )
 
 type CheckClass int32
@@ -199,6 +200,9 @@ func (c Check) Type() CheckType {
 	case c.Settings.Multihttp != nil:
 		return CheckTypeMultiHttp
 
+	case c.Settings.Grpc != nil:
+		return CheckTypeGrpc
+
 	default:
 		panic("unhandled check type")
 	}
@@ -210,7 +214,7 @@ func (c Check) Class() CheckClass {
 
 func (c CheckType) Class() CheckClass {
 	switch c {
-	case CheckTypeDns, CheckTypeHttp, CheckTypePing, CheckTypeTcp, CheckTypeTraceroute:
+	case CheckTypeDns, CheckTypeHttp, CheckTypePing, CheckTypeTcp, CheckTypeTraceroute, CheckTypeGrpc:
 		return CheckClassProtocol
 
 	case CheckTypeK6, CheckTypeMultiHttp:
@@ -289,6 +293,10 @@ func (c Check) validateTarget() error {
 		// not true that the target must be a valid URL.
 		// validation of URLs is the responsibility of the MultihttpEntryRequest
 		return nil
+
+	case CheckTypeGrpc:
+		return validateHostPort(c.Target)
+
 	default:
 		panic("unhandled check type")
 	}
@@ -400,6 +408,9 @@ func (c AdHocCheck) Type() CheckType {
 	case c.Settings.Multihttp != nil:
 		return CheckTypeMultiHttp
 
+	case c.Settings.Grpc != nil:
+		return CheckTypeGrpc
+
 	default:
 		panic("unhandled check type")
 	}
@@ -486,6 +497,9 @@ func (c AdHocCheck) validateTarget() error {
 	case CheckTypeMultiHttp:
 		return nil
 
+	case CheckTypeGrpc:
+		return validateHostPort(c.Target)
+
 	default:
 		panic("unhandled check type")
 	}
@@ -533,6 +547,11 @@ func (s CheckSettings) Validate() error {
 		validateFn = s.Multihttp.Validate
 	}
 
+	if s.Grpc != nil {
+		settingsCount++
+		validateFn = s.Grpc.Validate
+	}
+
 	if settingsCount != 1 {
 		return ErrInvalidCheckSettings
 	}
@@ -651,6 +670,10 @@ func (s *MultiHttpSettings) Validate() error {
 	return nil
 }
 
+func (s *GrpcSettings) Validate() error {
+	return nil
+}
+
 func hasUniqueValues[U any, V comparable](slice []U, fn func(U) V) bool {
 	set := make(map[V]struct{})