feat(nats): WithConfigFile - pass a configuration file to nats server

docs/modules/nats.md

@@ -75,6 +75,13 @@ These arguments are passed to the NATS server when it starts, as part of the com
 [Passing arguments](../../modules/nats/examples_test.go) inside_block:withArguments
 <!--/codeinclude-->
 
+#### Custom configuration file
+
+It's possible to pass a custom config file to NATS container using `nats.WithConfigFile(strings.NewReader(config))`. The `io.Reader` is passed as a `-config /etc/nats.conf` arguments to an entrypoint. 
+
+!!! note
+    Changing a connectivity (listen address or ports) can break the container setup. So configuration must be done with a care.
+
 ### Container Methods
 
 The NATS container exposes the following methods:
@@ -102,4 +109,4 @@ Exactly like `ConnectionString`, but it panics if an error occurs, returning jus
 
 <!--codeinclude-->
 [NATS Cluster](../../modules/nats/examples_test.go) inside_block:cluster
-<!--/codeinclude-->
+<!--/codeinclude-->

modules/nats/nats_test.go

@@ -1,7 +1,9 @@
 package nats_test
 
 import (
+	"bufio"
 	"context"
+	"strings"
 	"testing"
 
 	"github.com/nats-io/nats.go"
@@ -57,3 +59,52 @@ func TestNATS(t *testing.T) {
 
 	require.Equal(t, "hello", string(msg.Data))
 }
+
+func TestNATSWithConfigFile(t *testing.T) {
+	const natsConf = `
+listen: 0.0.0.0:4222
+authorization {
+    token: "s3cr3t"
+}
+`
+	ctx := context.Background()
+
+	//  createNATSContainer {
+	ctr, err := tcnats.Run(ctx, "nats:2.9", tcnats.WithConfigFile(strings.NewReader(natsConf)))
+	//  }
+	testcontainers.CleanupContainer(t, ctr)
+	require.NoError(t, err)
+
+	// connectionString {
+	uri, err := ctr.ConnectionString(ctx)
+	// }
+	require.NoError(t, err)
+
+	// connect without token {
+	mallory, err := nats.Connect(uri, nats.Name("Mallory"), nats.Token("secret"))
+	// }
+	require.Error(t, err)
+	require.ErrorIs(t, err, nats.ErrAuthorization)
+	t.Cleanup(mallory.Close)
+
+	// connect via token {
+	nc, err := nats.Connect(uri, nats.Name("API Token Test"), nats.Token("s3cr3t"))
+	// }
+	require.NoError(t, err)
+	t.Cleanup(nc.Close)
+
+	// validate /etc/nats.conf mentioned in logs {
+	const expected = "Using configuration file: /etc/nats.conf"
+	logs, err := ctr.Logs(ctx)
+	require.NoError(t, err)
+	sc := bufio.NewScanner(logs)
+	found := false
+	for sc.Scan() {
+		if strings.Contains(sc.Text(), expected) {
+			found = true
+			break
+		}
+	}
+	// }
+	require.Truef(t, found, "expected log line not found: %s", expected)
+}

modules/nats/options.go

@@ -1,6 +1,7 @@
 package nats
 
 import (
+	"io"
 	"strings"
 
 	"github.com/testcontainers/testcontainers-go"
@@ -16,7 +17,7 @@ func defaultOptions() options {
 	}
 }
 
-// Compiler check to ensure that Option implements the testcontainers.ContainerCustomizer interface.
+// Compiler check to ensure that CmdOption implements the testcontainers.ContainerCustomizer interface.
 var _ testcontainers.ContainerCustomizer = (*CmdOption)(nil)
 
 // CmdOption is an option for the NATS container.
@@ -49,3 +50,22 @@ func WithArgument(flag string, value string) CmdOption {
 		o.CmdArgs[flag] = value
 	}
 }
+
+// WithConfigFile pass io.Reader to the NATS container as /etc/nats.conf
+// Changes of a connectivity (listen address, or ports) may break a testcontainer
+func WithConfigFile(config io.Reader) testcontainers.CustomizeRequestOption {
+	return func(req *testcontainers.GenericContainerRequest) error {
+		if config != nil {
+			req.Cmd = append(req.Cmd, "-config", "/etc/nats.conf")
+			req.Files = append(
+				req.Files,
+				testcontainers.ContainerFile{
+					Reader:            config,
+					ContainerFilePath: "/etc/nats.conf",
+					FileMode:          0o644,
+				},
+			)
+		}
+		return nil
+	}
+}