Add support for custom configuration directory via CLAUDE_CONFIG_DIR environment variable

- Introduced environment variable handling in the MCP CLI for custom config paths.
- Updated config.yml to include CLAUDE_CONFIG_DIR in path checks.
- Implemented isPathValid function to validate paths with environment variables.
- Added tests for path validation and configuration updates with environment variables.

Author: jandroav

README.md

@@ -192,6 +192,26 @@ The MCP CLI uses several configuration files:
 Configuration files are typically stored in `~/.docker/mcp/`. This is in this directory that Docker Desktop's
 MCP Toolkit with store its configuration.
 
+### Environment Variables
+
+The MCP CLI respects the following environment variables for client configuration:
+
+- **`CLAUDE_CONFIG_DIR`**: Override the default Claude Code configuration directory (`~/.claude`). When set, Claude Code will use `$CLAUDE_CONFIG_DIR/.claude.json` instead of `~/.claude.json` for its MCP server configuration. This is useful for:
+  - Maintaining separate Claude Code installations for work and personal use
+  - Testing configuration changes in isolation
+  - Managing multiple Claude Code profiles
+
+Example usage:
+```bash
+# Set custom Claude Code configuration directory
+export CLAUDE_CONFIG_DIR=/path/to/custom/config
+
+# Connect MCP Gateway to Claude Code
+docker mcp client connect claude-code --global
+
+# Claude Code will now use /path/to/custom/config/.claude.json
+```
+
 ## Architecture
 
 The Docker MCP CLI implements a gateway pattern:

cmd/docker-mcp/client/config.yml

@@ -24,12 +24,16 @@ system:
     installCheckPaths:
       - $HOME/.claude
       - $USERPROFILE\.claude
+      - $CLAUDE_CONFIG_DIR
     paths:
       linux:
+        - $CLAUDE_CONFIG_DIR/.claude.json
         - $HOME/.claude.json
       darwin:
+        - $CLAUDE_CONFIG_DIR/.claude.json
         - $HOME/.claude.json
       windows:
+        - $CLAUDE_CONFIG_DIR\.claude.json
         - $USERPROFILE\.claude.json
     yq:
       list: '.mcpServers | to_entries | map(.value + {"name": .key})'

cmd/docker-mcp/client/global.go

@@ -4,13 +4,31 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"regexp"
 	"runtime"
 )
 
 const (
 	DockerMCPCatalog = "MCP_DOCKER"
 )
 
+var envVarRegex = regexp.MustCompile(`\$([A-Za-z_][A-Za-z0-9_]*)`)
+
+// isPathValid checks if all environment variables in a path are defined and non-empty
+func isPathValid(path string) bool {
+	matches := envVarRegex.FindAllStringSubmatch(path, -1)
+	for _, match := range matches {
+		if len(match) > 1 {
+			varName := match[1]
+			value, ok := os.LookupEnv(varName)
+			if !ok || value == "" {
+				return false
+			}
+		}
+	}
+	return true
+}
+
 type globalCfg struct {
 	DisplayName       string   `yaml:"displayName"`
 	Source            string   `yaml:"source"`
@@ -125,17 +143,29 @@ func (c *GlobalCfgProcessor) Update(key string, server *MCPServerSTDIO) error {
 		return fmt.Errorf("unknown config path for OS %s", runtime.GOOS)
 	}
 
-	// Use first existing path, or first path if none exist
-	var targetPath string
+	// Filter out paths with undefined environment variables
+	var validPaths []string
 	for _, path := range paths {
+		if isPathValid(path) {
+			validPaths = append(validPaths, path)
+		}
+	}
+
+	if len(validPaths) == 0 {
+		return fmt.Errorf("no valid config paths found (all paths contain undefined environment variables)")
+	}
+
+	// Use first existing path, or first valid path if none exist
+	var targetPath string
+	for _, path := range validPaths {
 		fullPath := os.ExpandEnv(path)
 		if _, err := os.Stat(fullPath); err == nil {
 			targetPath = fullPath
 			break
 		}
 	}
 	if targetPath == "" {
-		targetPath = os.ExpandEnv(paths[0])
+		targetPath = os.ExpandEnv(validPaths[0])
 	}
 
 	return updateConfig(targetPath, c.p.Add, c.p.Del, key, server)

cmd/docker-mcp/client/global_test.go

@@ -211,3 +211,159 @@ func TestGlobalCfgProcessor_SinglePath(t *testing.T) {
 	assert.True(t, result.IsOsSupported)
 	assert.Nil(t, result.Err)
 }
+
+func TestIsPathValid(t *testing.T) {
+	tests := []struct {
+		name     string
+		path     string
+		envVars  map[string]string
+		expected bool
+	}{
+		{
+			name:     "no_env_vars",
+			path:     "/absolute/path/config.json",
+			envVars:  map[string]string{},
+			expected: true,
+		},
+		{
+			name:     "defined_env_var",
+			path:     "$HOME/.config/app/config.json",
+			envVars:  map[string]string{"HOME": "/home/user"},
+			expected: true,
+		},
+		{
+			name:     "undefined_env_var",
+			path:     "$UNDEFINED_VAR/.config/app/config.json",
+			envVars:  map[string]string{},
+			expected: false,
+		},
+		{
+			name:     "empty_env_var",
+			path:     "$EMPTY_VAR/.config/app/config.json",
+			envVars:  map[string]string{"EMPTY_VAR": ""},
+			expected: false,
+		},
+		{
+			name:     "multiple_defined_env_vars",
+			path:     "$HOME/$CONFIG_DIR/config.json",
+			envVars:  map[string]string{"HOME": "/home/user", "CONFIG_DIR": ".config"},
+			expected: true,
+		},
+		{
+			name:     "multiple_mixed_env_vars",
+			path:     "$HOME/$UNDEFINED_VAR/config.json",
+			envVars:  map[string]string{"HOME": "/home/user"},
+			expected: false,
+		},
+		{
+			name:     "windows_style_defined",
+			path:     "$USERPROFILE\\.config\\app\\config.json",
+			envVars:  map[string]string{"USERPROFILE": "C:\\Users\\user"},
+			expected: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// Set up environment variables
+			for k, v := range tc.envVars {
+				t.Setenv(k, v)
+			}
+
+			result := isPathValid(tc.path)
+			assert.Equal(t, tc.expected, result)
+		})
+	}
+}
+
+func TestGlobalCfgProcessor_Update_WithEnvVarPaths(t *testing.T) {
+	tempDir := t.TempDir()
+
+	// Set up a custom config dir
+	customConfigDir := filepath.Join(tempDir, "custom-config")
+	require.NoError(t, os.MkdirAll(customConfigDir, 0o755))
+
+	// Create existing config in custom dir
+	customConfigPath := filepath.Join(customConfigDir, ".claude.json")
+	require.NoError(t, os.WriteFile(customConfigPath, []byte(`{"mcpServers": {"existing": {"command": "test"}}}`), 0o644))
+
+	// Set CLAUDE_CONFIG_DIR environment variable
+	t.Setenv("CLAUDE_CONFIG_DIR", customConfigDir)
+
+	// Create home config path (should be ignored when CLAUDE_CONFIG_DIR is set)
+	homeDir := filepath.Join(tempDir, "home")
+	require.NoError(t, os.MkdirAll(homeDir, 0o755))
+	homeConfigPath := filepath.Join(homeDir, ".claude.json")
+	t.Setenv("HOME", homeDir)
+
+	cfg := newTestGlobalCfg()
+	paths := []string{"$CLAUDE_CONFIG_DIR/.claude.json", "$HOME/.claude.json"}
+	setPathsForCurrentOS(&cfg, paths)
+
+	processor, err := NewGlobalCfgProcessor(cfg)
+	require.NoError(t, err)
+
+	err = processor.Update("new-server", &MCPServerSTDIO{
+		Name:    "new-server",
+		Command: "docker",
+		Args:    []string{"mcp", "gateway", "run"},
+	})
+	require.NoError(t, err)
+
+	// Verify update went to the custom config dir
+	content, err := os.ReadFile(customConfigPath)
+	require.NoError(t, err)
+	assert.Contains(t, string(content), "new-server")
+
+	// Verify home config was not created
+	_, err = os.ReadFile(homeConfigPath)
+	assert.True(t, os.IsNotExist(err), "home config should not be created when CLAUDE_CONFIG_DIR is set")
+}
+
+func TestGlobalCfgProcessor_Update_FallbackWhenEnvVarUndefined(t *testing.T) {
+	tempDir := t.TempDir()
+
+	// Set CLAUDE_CONFIG_DIR to empty - it should fall back to HOME
+	t.Setenv("CLAUDE_CONFIG_DIR", "")
+
+	homeDir := filepath.Join(tempDir, "home")
+	homeConfigPath := filepath.Join(homeDir, ".claude.json")
+	t.Setenv("HOME", homeDir)
+
+	cfg := newTestGlobalCfg()
+	paths := []string{"$CLAUDE_CONFIG_DIR/.claude.json", "$HOME/.claude.json"}
+	setPathsForCurrentOS(&cfg, paths)
+
+	processor, err := NewGlobalCfgProcessor(cfg)
+	require.NoError(t, err)
+
+	err = processor.Update("new-server", &MCPServerSTDIO{
+		Name:    "new-server",
+		Command: "docker",
+		Args:    []string{"mcp", "gateway", "run"},
+	})
+	require.NoError(t, err)
+
+	// Verify update went to the home config dir
+	content, err := os.ReadFile(homeConfigPath)
+	require.NoError(t, err)
+	assert.Contains(t, string(content), "new-server")
+}
+
+func TestGlobalCfgProcessor_Update_AllPathsInvalid(t *testing.T) {
+	cfg := newTestGlobalCfg()
+	// Only provide paths with undefined environment variables
+	paths := []string{"$UNDEFINED_VAR1/.config.json", "$UNDEFINED_VAR2/.config.json"}
+	setPathsForCurrentOS(&cfg, paths)
+
+	processor, err := NewGlobalCfgProcessor(cfg)
+	require.NoError(t, err)
+
+	err = processor.Update("new-server", &MCPServerSTDIO{
+		Name:    "new-server",
+		Command: "docker",
+		Args:    []string{"mcp", "gateway", "run"},
+	})
+	require.Error(t, err)
+	assert.ErrorContains(t, err, "no valid config paths found")
+}