fix: add TLS credentials support to gRPC server (#20)

Why: gRPC TLS tests were timing out because gRPC servers require TLS
credentials configured via grpc.Creds(), not just a TLS listener
Approach:
- Added variadic grpc.ServerOption to NewGrpcServer signature
- Updated NewServer to accept optional *tls.Config and convert to grpc.Creds()
- Modified test harness to pass TLS config to gRPC servers, use plain listeners
- HTTP servers continue using TLS listeners (different architecture)
Learned: gRPC and HTTP handle TLS differently - gRPC needs server credentials,
HTTP uses TLS at listener level
Next: Create PR, merge, then rebase logs branch

Fixes #17

Co-authored-by: Claude <[email protected]>

Author: tobert

main_test.go

@@ -414,10 +414,20 @@ func runOtelCli(t *testing.T, fixture Fixture) (string, Results) {
 		return results.SpanCount >= fixture.Expect.SpanCount
 	}
 
+	// prepare TLS configuration if needed
+	var tlsConf *tls.Config
+	if fixture.Config.ServerTLSEnabled {
+		tlsConf = fixture.TlsData.serverTLSConf.Clone()
+		if fixture.Config.ServerTLSAuthEnabled {
+			tlsConf.ClientAuth = tls.RequireAndVerifyClientCert
+		}
+	}
+
+	// create server with TLS config if needed (gRPC requires it, HTTP uses TLS listener)
 	var cs otlpserver.OtlpServer
 	switch fixture.Config.ServerProtocol {
 	case grpcProtocol:
-		cs = otlpserver.NewServer("grpc", cb, func(otlpserver.OtlpServer) {})
+		cs = otlpserver.NewServer("grpc", cb, func(otlpserver.OtlpServer) {}, tlsConf)
 	case httpProtocol:
 		cs = otlpserver.NewServer("http", cb, func(otlpserver.OtlpServer) {})
 	}
@@ -443,11 +453,8 @@ func runOtelCli(t *testing.T, fixture Fixture) (string, Results) {
 	// port :0 means randomly assigned port, which we copy into {{endpoint}}
 	var listener net.Listener
 	var err error
-	if fixture.Config.ServerTLSEnabled {
-		tlsConf := fixture.TlsData.serverTLSConf.Clone()
-		if fixture.Config.ServerTLSAuthEnabled {
-			tlsConf.ClientAuth = tls.RequireAndVerifyClientCert
-		}
+	if fixture.Config.ServerTLSEnabled && fixture.Config.ServerProtocol == httpProtocol {
+		// HTTP needs a TLS listener; gRPC uses credentials passed to server
 		listener, err = tls.Listen("tcp", "localhost:0", tlsConf)
 	} else {
 		listener, err = net.Listen("tcp", "localhost:0")

otlpserver/grpcserver.go

@@ -26,10 +26,11 @@ type GrpcServer struct {
 }
 
 // NewGrpcServer takes a callback and stop function and returns a Server ready
-// to run with .Serve().
-func NewGrpcServer(cb Callback, stop Stopper) *GrpcServer {
+// to run with .Serve(). Optional grpc.ServerOption arguments can be provided
+// for TLS configuration and other server options.
+func NewGrpcServer(cb Callback, stop Stopper, opts ...grpc.ServerOption) *GrpcServer {
 	s := GrpcServer{
-		server:   grpc.NewServer(),
+		server:   grpc.NewServer(opts...),
 		callback: cb,
 		stopper:  make(chan struct{}),
 		stopdone: make(chan struct{}, 1),

otlpserver/server.go

@@ -6,10 +6,13 @@ package otlpserver
 
 import (
 	"context"
+	"crypto/tls"
 	"net"
 
 	colv1 "go.opentelemetry.io/proto/otlp/collector/trace/v1"
 	tracepb "go.opentelemetry.io/proto/otlp/trace/v1"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials"
 )
 
 // Callback is a type for the function passed to newServer that is
@@ -30,11 +33,17 @@ type OtlpServer interface {
 }
 
 // NewServer will start the requested server protocol, one of grpc, http/protobuf,
-// and http/json.
-func NewServer(protocol string, cb Callback, stop Stopper) OtlpServer {
+// and http/json. Optional TLS configuration can be provided for gRPC servers.
+func NewServer(protocol string, cb Callback, stop Stopper, tlsConf ...*tls.Config) OtlpServer {
 	switch protocol {
 	case "grpc":
-		return NewGrpcServer(cb, stop)
+		// if TLS config is provided, convert to gRPC credentials
+		var opts []grpc.ServerOption
+		if len(tlsConf) > 0 && tlsConf[0] != nil {
+			creds := credentials.NewTLS(tlsConf[0])
+			opts = append(opts, grpc.Creds(creds))
+		}
+		return NewGrpcServer(cb, stop, opts...)
 	case "http":
 		return NewHttpServer(cb, stop)
 	}