Add passthrough for gRPC connection when using a proxy

internal/grpc/grpc.go

@@ -73,18 +73,15 @@ var (
 func NewGrpcConnection(ctx context.Context, agentConfig *config.Config,
 	commandConfig *config.Command,
 ) (*GrpcConnection, error) {
-	if commandConfig == nil || commandConfig.Server.Type != config.Grpc {
+	if commandConfig == nil || commandConfig.Server == nil || commandConfig.Server.Type != config.Grpc {
 		return nil, errors.New("invalid command server settings")
 	}
 
 	grpcConnection := &GrpcConnection{
 		commandConfig: commandConfig,
 	}
 
-	serverAddr := net.JoinHostPort(
-		commandConfig.Server.Host,
-		strconv.Itoa(commandConfig.Server.Port),
-	)
+	serverAddr := serverAddress(ctx, commandConfig)
 
 	slog.InfoContext(ctx, "Dialing grpc server", "server_addr", serverAddr)
 
@@ -406,3 +403,21 @@ func tlsConfigForCredentials(c *config.TLSConfig) (*tls.Config, error) {
 
 	return tlsConfig, nil
 }
+
+func serverAddress(ctx context.Context, commandConfig *config.Command) string {
+	serverAddr := net.JoinHostPort(
+		commandConfig.Server.Host,
+		strconv.Itoa(commandConfig.Server.Port),
+	)
+
+	// If using proxy, modify the server address to use passthrough resolver
+	// This prevents gRPC from trying to resolve DNS before calling our dialer
+	if commandConfig.Server.Proxy != nil &&
+		commandConfig.Server.Proxy.URL != "" &&
+		!strings.HasPrefix(serverAddr, "passthrough:///") {
+		serverAddr = "passthrough:///" + serverAddr
+		slog.InfoContext(ctx, "Using passthrough resolver for proxy", "updated_server_address", serverAddr)
+	}
+
+	return serverAddr
+}

internal/grpc/grpc_test.go

@@ -490,3 +490,151 @@ func Test_tlsConfig(t *testing.T) {
 		})
 	}
 }
+
+func Test_serverAddress(t *testing.T) {
+	ctx := context.Background()
+
+	tests := []struct {
+		commandConfig *config.Command
+		name          string
+		expectedAddr  string
+		logMessage    string
+		expectLog     bool
+	}{
+		{
+			name: "Test 1: No proxy configuration",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "example.com",
+					Port: 443,
+					Type: config.Grpc,
+				},
+			},
+			expectedAddr: "example.com:443",
+		},
+		{
+			name: "Test 2: Proxy with nil proxy config",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host:  "example.com",
+					Port:  443,
+					Type:  config.Grpc,
+					Proxy: nil,
+				},
+			},
+			expectedAddr: "example.com:443",
+		},
+		{
+			name: "Test 3: Proxy with empty URL",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "example.com",
+					Port: 443,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL: "",
+					},
+				},
+			},
+			expectedAddr: "example.com:443",
+		},
+		{
+			name: "Test 4: Proxy with valid URL",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "agent.connect.nginxlab.net",
+					Port: 443,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL: "http://squid-container:3128",
+					},
+				},
+			},
+			expectedAddr: "passthrough:///agent.connect.nginxlab.net:443",
+		},
+		{
+			name: "Test 5: IPv6 address with proxy",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "2001:db8::1",
+					Port: 443,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL: "http://proxy.example.com:8080",
+					},
+				},
+			},
+			expectedAddr: "passthrough:///[2001:db8::1]:443",
+		},
+		{
+			name: "Test 6: Already has passthrough prefix - no double prefix",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "example.com",
+					Port: 443,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL: "http://proxy.example.com:8080",
+					},
+				},
+			},
+			expectedAddr: "passthrough:///example.com:443",
+		},
+		{
+			name: "Test 7: Localhost with proxy",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "localhost",
+					Port: 8080,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL:        "http://proxy.local:3128",
+						AuthMethod: "basic",
+						Username:   "user",
+						Password:   "pass",
+					},
+				},
+			},
+			expectedAddr: "passthrough:///localhost:8080",
+		},
+		{
+			name: "Test 8: Custom port with proxy",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "api.example.com",
+					Port: 9090,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL:     "https://secure-proxy.example.com:8443",
+						Timeout: 30000000000, // 30 seconds in nanoseconds
+					},
+				},
+			},
+			expectedAddr: "passthrough:///api.example.com:9090",
+		},
+		{
+			name: "Test 9: Edge case - hostname that looks like passthrough but isn't",
+			commandConfig: &config.Command{
+				Server: &config.ServerConfig{
+					Host: "passthrough.example.com", // hostname that contains "passthrough" but isn't a passthrough URL
+					Port: 443,
+					Type: config.Grpc,
+					Proxy: &config.Proxy{
+						URL: "http://proxy.example.com:8080",
+					},
+				},
+			},
+			expectedAddr: "passthrough:///passthrough.example.com:443",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Call the function
+			result := serverAddress(ctx, tt.commandConfig)
+
+			// Verify the result
+			assert.Equal(t, tt.expectedAddr, result, "serverAddress() should return expected address")
+		})
+	}
+}