Enforce IPv4 for localhost

Signed-off-by: Radoslav Dimitrov <[email protected]>

Author: rdimitrov

cmd/thv/app/config.go

@@ -13,6 +13,7 @@ import (
 	"github.com/stacklok/toolhive/pkg/labels"
 	"github.com/stacklok/toolhive/pkg/logger"
 	"github.com/stacklok/toolhive/pkg/secrets"
+	"github.com/stacklok/toolhive/pkg/transport"
 )
 
 var configCmd = &cobra.Command{
@@ -262,7 +263,7 @@ func addRunningMCPsToClient(ctx context.Context, clientName string) error {
 		}
 
 		// Generate URL for the MCP server
-		url := client.GenerateMCPServerURL("localhost", port, name)
+		url := client.GenerateMCPServerURL(transport.LocalhostIPv4, port, name)
 
 		// Update each configuration file
 		for _, clientConfig := range clientConfigs {

cmd/thv/app/list.go

@@ -13,6 +13,7 @@ import (
 	"github.com/stacklok/toolhive/pkg/labels"
 	"github.com/stacklok/toolhive/pkg/lifecycle"
 	"github.com/stacklok/toolhive/pkg/logger"
+	"github.com/stacklok/toolhive/pkg/transport"
 )
 
 var listCmd = &cobra.Command{
@@ -28,10 +29,7 @@ var (
 )
 
 // Constants for list command
-const (
-	defaultHost      = "localhost"
-	unknownTransport = "unknown"
-)
+const unknownTransport = "unknown"
 
 // ContainerOutput represents container information for JSON output
 type ContainerOutput struct {
@@ -101,9 +99,9 @@ func printJSONOutput(containers []rt.ContainerInfo) error {
 		}
 
 		// Get transport type from labels
-		transport := labels.GetTransportType(c.Labels)
-		if transport == "" {
-			transport = unknownTransport
+		t := labels.GetTransportType(c.Labels)
+		if t == "" {
+			t = unknownTransport
 		}
 
 		// Get tool type from labels
@@ -118,15 +116,15 @@ func printJSONOutput(containers []rt.ContainerInfo) error {
 		// Generate URL for the MCP server
 		url := ""
 		if port > 0 {
-			url = client.GenerateMCPServerURL(defaultHost, port, name)
+			url = client.GenerateMCPServerURL(transport.LocalhostIPv4, port, name)
 		}
 
 		output = append(output, ContainerOutput{
 			ID:        truncatedID,
 			Name:      name,
 			Image:     c.Image,
 			State:     c.State,
-			Transport: transport,
+			Transport: t,
 			ToolType:  toolType,
 			Port:      port,
 			URL:       url,
@@ -174,7 +172,7 @@ func printMCPServersOutput(containers []rt.ContainerInfo) error {
 		// Generate URL for the MCP server
 		url := ""
 		if port > 0 {
-			url = client.GenerateMCPServerURL(defaultHost, port, name)
+			url = client.GenerateMCPServerURL(transport.LocalhostIPv4, port, name)
 		}
 
 		// Add the MCP server to the map
@@ -217,9 +215,9 @@ func printTextOutput(containers []rt.ContainerInfo) {
 		}
 
 		// Get transport type from labels
-		transport := labels.GetTransportType(c.Labels)
-		if transport == "" {
-			transport = unknownTransport
+		t := labels.GetTransportType(c.Labels)
+		if t == "" {
+			t = unknownTransport
 		}
 
 		// Get port from labels
@@ -231,7 +229,7 @@ func printTextOutput(containers []rt.ContainerInfo) {
 		// Generate URL for the MCP server
 		url := ""
 		if port > 0 {
-			url = client.GenerateMCPServerURL(defaultHost, port, name)
+			url = client.GenerateMCPServerURL(transport.LocalhostIPv4, port, name)
 		}
 
 		// Print container information
@@ -240,7 +238,7 @@ func printTextOutput(containers []rt.ContainerInfo) {
 			name,
 			c.Image,
 			c.State,
-			transport,
+			t,
 			port,
 			url,
 		)

cmd/thv/app/proxy.go

@@ -32,7 +32,7 @@ var (
 )
 
 func init() {
-	proxyCmd.Flags().StringVar(&proxyHost, "host", transport.LocalhostName, "Host for the HTTP proxy to listen on (IP or hostname)")
+	proxyCmd.Flags().StringVar(&proxyHost, "host", transport.LocalhostIPv4, "Host for the HTTP proxy to listen on (IP or hostname)")
 	proxyCmd.Flags().IntVar(&proxyPort, "port", 0, "Port for the HTTP proxy to listen on (host port)")
 	proxyCmd.Flags().StringVar(
 		&proxyTargetURI,

cmd/thv/app/run.go

@@ -75,13 +75,13 @@ var (
 func init() {
 	runCmd.Flags().StringVar(&runTransport, "transport", "stdio", "Transport mode (sse or stdio)")
 	runCmd.Flags().StringVar(&runName, "name", "", "Name of the MCP server (auto-generated from image if not provided)")
-	runCmd.Flags().StringVar(&runHost, "host", transport.LocalhostName, "Host for the HTTP proxy to listen on (IP or hostname)")
+	runCmd.Flags().StringVar(&runHost, "host", transport.LocalhostIPv4, "Host for the HTTP proxy to listen on (IP or hostname)")
 	runCmd.Flags().IntVar(&runPort, "port", 0, "Port for the HTTP proxy to listen on (host port)")
 	runCmd.Flags().IntVar(&runTargetPort, "target-port", 0, "Port for the container to expose (only applicable to SSE transport)")
 	runCmd.Flags().StringVar(
 		&runTargetHost,
 		"target-host",
-		"localhost",
+		transport.LocalhostIPv4,
 		"Host to forward traffic to (only applicable to SSE transport)")
 	runCmd.Flags().StringVar(
 		&runPermissionProfile,

pkg/transport/sse.go

@@ -17,6 +17,8 @@ import (
 const (
 	// LocalhostName is the standard hostname for localhost
 	LocalhostName = "localhost"
+	// LocalhostIPv4 is the standard IPv4 address for localhost
+	LocalhostIPv4 = "127.0.0.1"
 )
 
 // SSETransport implements the Transport interface using Server-Sent Events.
@@ -56,12 +58,12 @@ func NewSSETransport(
 	middlewares ...types.Middleware,
 ) *SSETransport {
 	if host == "" {
-		host = LocalhostName
+		host = LocalhostIPv4
 	}
 
 	// If targetHost is not specified, default to localhost
 	if targetHost == "" {
-		targetHost = LocalhostName
+		targetHost = LocalhostIPv4
 	}
 
 	return &SSETransport{