feat: implements host-style bucket addressing in the gateway.

Closes #803

Implements host-style bucket addressing in the gateway. This feature can be enabled by running the gateway with the `--virtual-domain` flag and specifying a virtual domain name.
Example:

```bash
    ./versitygw -a user -s secret --virtual-domain localhost:7070 posix /tmp/vgw
```

The implementation follows this approach: it introduces a middleware (`HostStyleParser`) that parses the bucket name from the `Host` header and appends it to the URL path. This effectively transforms the request into a path-style bucket addressing format, which the gateway already supports. With this design, the gateway can handle both path-style and host-style requests when running in host-style mode.

For local testing, one can either set up a local DNS server to wildcard-match all subdomains of a specified domain and resolve them to the local IP address, or manually add entries to `/etc/hosts` to resolve bucket-prefixed hosts to the server IP (e.g., `127.0.0.1`).

cmd/versitygw/main.go

@@ -50,6 +50,7 @@ var (
 	logWebhookURL, accessLog                 string
 	adminLogFile                             string
 	healthPath                               string
+	virtualDomain                            string
 	debug                                    bool
 	pprof                                    string
 	quiet                                    bool
@@ -227,6 +228,13 @@ func initFlags() []cli.Flag {
 			Destination: &quiet,
 			Aliases:     []string{"q"},
 		},
+		&cli.StringFlag{
+			Name:        "virtual-domain",
+			Usage:       "enables the host-style bucket addressing with the specified virtual domain as base.",
+			EnvVars:     []string{"VGW_VIRTUAL_DOMAIN"},
+			Destination: &virtualDomain,
+			Aliases:     []string{"vd"},
+		},
 		&cli.StringFlag{
 			Name:        "access-log",
 			Usage:       "enable server access logging to specified file",
@@ -603,6 +611,9 @@ func runGateway(ctx context.Context, be backend.Backend) error {
 	if readonly {
 		opts = append(opts, s3api.WithReadOnly())
 	}
+	if virtualDomain != "" {
+		opts = append(opts, s3api.WithHostStyle(virtualDomain))
+	}
 
 	admApp := fiber.New(fiber.Config{
 		AppName:               "versitygw",

cmd/versitygw/test.go

@@ -34,7 +34,7 @@ var (
 	totalReqs         int
 	upload            bool
 	download          bool
-	pathStyle         bool
+	hostStyle         bool
 	checksumDisable   bool
 	versioningEnabled bool
 	azureTests        bool
@@ -74,6 +74,12 @@ func initTestFlags() []cli.Flag {
 			Destination: &endpoint,
 			Aliases:     []string{"e"},
 		},
+		&cli.BoolFlag{
+			Name:        "host-style",
+			Usage:       "Use host-style bucket addressing",
+			Value:       false,
+			Destination: &hostStyle,
+		},
 		&cli.BoolFlag{
 			Name:        "debug",
 			Usage:       "enable debug mode",
@@ -191,12 +197,6 @@ func initTestCommands() []*cli.Command {
 					Value:       1,
 					Destination: &concurrency,
 				},
-				&cli.BoolFlag{
-					Name:        "pathStyle",
-					Usage:       "Use Pathstyle bucket addressing",
-					Value:       false,
-					Destination: &pathStyle,
-				},
 				&cli.BoolFlag{
 					Name:        "checksumDis",
 					Usage:       "Disable server checksum",
@@ -228,8 +228,8 @@ func initTestCommands() []*cli.Command {
 				if debug {
 					opts = append(opts, integration.WithDebug())
 				}
-				if pathStyle {
-					opts = append(opts, integration.WithPathStyle())
+				if hostStyle {
+					opts = append(opts, integration.WithHostStyle())
 				}
 				if checksumDisable {
 					opts = append(opts, integration.WithDisableChecksum())
@@ -292,6 +292,9 @@ func initTestCommands() []*cli.Command {
 				if checksumDisable {
 					opts = append(opts, integration.WithDisableChecksum())
 				}
+				if hostStyle {
+					opts = append(opts, integration.WithHostStyle())
+				}
 
 				s3conf := integration.NewS3Conf(opts...)
 
@@ -321,6 +324,9 @@ func getAction(tf testFunc) func(*cli.Context) error {
 		if azureTests {
 			opts = append(opts, integration.WithAzureMode())
 		}
+		if hostStyle {
+			opts = append(opts, integration.WithHostStyle())
+		}
 
 		s := integration.NewS3Conf(opts...)
 		tf(s)
@@ -356,6 +362,9 @@ func extractIntTests() (commands []*cli.Command) {
 				if versioningEnabled {
 					opts = append(opts, integration.WithVersioningEnabled())
 				}
+				if hostStyle {
+					opts = append(opts, integration.WithHostStyle())
+				}
 
 				s := integration.NewS3Conf(opts...)
 				err := testFunc(s)