feat: design a separate package for health check

internal/health/smtp.go

@@ -0,0 +1,106 @@
+package health
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	"net/smtp"
+	"time"
+)
+
+type SMTPConfig struct {
+	Host     string
+	Port     int
+	Username string
+	Password string
+	From     string
+}
+
+type SMTPChecker struct {
+	config SMTPConfig
+}
+
+func NewSMTPChecker(config SMTPConfig) *SMTPChecker {
+	return &SMTPChecker{
+		config: config,
+	}
+}
+
+func (c *SMTPChecker) Name() string {
+	return "smtp"
+}
+
+func (c *SMTPChecker) Check(ctx context.Context) Result {
+	start := time.Now()
+	address := fmt.Sprintf("%s:%d", c.config.Host, c.config.Port)
+
+	result := Result{
+		Status:    StatusHealthy,
+		Timestamp: time.Now().UTC(),
+		Details: map[string]any{
+			"host": address,
+		},
+	}
+
+	conn, err := net.Dial("tcp", address)
+	if err != nil {
+		result.Status = StatusDegraded
+		result.Message = fmt.Sprintf("Failed to connect to SMTP server: %v", err)
+		result.Latency = time.Since(start)
+		return result
+	}
+	defer conn.Close()
+
+	client, err := smtp.NewClient(conn, c.config.Host)
+	if err != nil {
+		result.Status = StatusDegraded
+		result.Message = fmt.Sprintf("Failed to create SMTP client: %v", err)
+		result.Latency = time.Since(start)
+		return result
+	}
+	defer client.Close()
+
+	err = client.Hello("goyco-health-check")
+	if err != nil {
+		result.Status = StatusDegraded
+		result.Message = fmt.Sprintf("EHLO failed: %v", err)
+		result.Latency = time.Since(start)
+		return result
+	}
+
+	if ok, _ := client.Extension("STARTTLS"); ok {
+		tlsConfig := &tls.Config{
+			ServerName: c.config.Host,
+		}
+		err = client.StartTLS(tlsConfig)
+		if err != nil {
+			result.Details["starttls"] = "failed"
+			result.Details["starttls_error"] = err.Error()
+		} else {
+			result.Details["starttls"] = "enabled"
+		}
+	} else {
+		result.Details["starttls"] = "not supported"
+	}
+
+	if c.config.Username != "" && c.config.Password != "" {
+		auth := smtp.PlainAuth("", c.config.Username, c.config.Password, c.config.Host)
+		err = client.Auth(auth)
+		if err != nil {
+			result.Details["auth"] = "failed"
+			result.Details["auth_error"] = err.Error()
+		} else {
+			result.Details["auth"] = "success"
+		}
+	} else {
+		result.Details["auth"] = "not configured"
+	}
+
+	client.Quit()
+
+	result.Latency = time.Since(start)
+	result.Details["handshake"] = "completed"
+
+	return result
+}