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fix(mcp): ensure proper environment variable override semantics

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Use a map to merge environment variables with guaranteed override
behavior. Config variables (cfg.Env) now properly override file
variables (envFile), which in turn override parent process environment.

Previously, simply appending to a slice could result in duplicate
variables, and while most systems use the last occurrence, this
behavior is not guaranteed and could lead to unexpected results.

Addresses Copilot code review feedback.
This commit is contained in:
yuchou87 2026-02-19 19:45:15 +08:00
parent f0ce26ff2b
commit 7577414761
1 changed files with 18 additions and 10 deletions
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28
pkg/mcp/manager.go
View file

@ -284,8 +284,16 @@ func (m *Manager) ConnectServer(ctx context.Context, name string, cfg config.MCP
// Create command with context
cmd := exec.CommandContext(ctx, cfg.Command, cfg.Args...)
// Set environment variables
env := cmd.Environ()
// Build environment variables with proper override semantics
// Use a map to ensure config variables override file variables
envMap := make(map[string]string)
// Start with parent process environment
for _, e := range cmd.Environ() {
if idx := strings.Index(e, "="); idx > 0 {
envMap[e[:idx]] = e[idx+1:]
}
}
// Load environment variables from file if specified
if cfg.EnvFile != "" {
@ -294,7 +302,7 @@ func (m *Manager) ConnectServer(ctx context.Context, name string, cfg config.MCP
return fmt.Errorf("failed to load env file %s: %w", cfg.EnvFile, err)
}
for k, v := range envVars {
env = append(env, fmt.Sprintf("%s=%s", k, v))
envMap[k] = v
}
logger.DebugCF("mcp", "Loaded environment variables from file",
map[string]interface{}{
@ -305,16 +313,16 @@ func (m *Manager) ConnectServer(ctx context.Context, name string, cfg config.MCP
}
// Environment variables from config override those from file
if len(cfg.Env) > 0 {
for k, v := range cfg.Env {
env = append(env, fmt.Sprintf("%s=%s", k, v))
}
for k, v := range cfg.Env {
envMap[k] = v
}
// Set environment if we added any variables
if len(env) > len(cmd.Environ()) {
cmd.Env = env
// Convert map to slice
env := make([]string, 0, len(envMap))
for k, v := range envMap {
env = append(env, fmt.Sprintf("%s=%s", k, v))
}
cmd.Env = env
transport = &mcp.CommandTransport{Command: cmd}
default: