feat(backend): Go 服务骨架（配置、日志、数据库、中间件、Wire）

- config: Viper YAML 配置 + 环境变量覆盖
- logs: zap 结构化日志 + trace_id 链路追踪 + 敏感信息脱敏
- db: PostgreSQL (GORM) + Redis (go-redis) 连接管理
- middleware: Trace/Logger/CORS/Recovery 四层中间件
- provider: Wire 编译时依赖注入
- main.go: 优雅启动/关闭 HTTP 服务

Made-with: Cursor

backend/go-service/pkg/middleware/cors.go

@@ -0,0 +1,26 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// CORS 跨域中间件
+// 允许前端跨域访问后端 API
+func CORS() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Header("Access-Control-Allow-Origin", "*")
+		c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS, PATCH")
+		c.Header("Access-Control-Allow-Headers", "Origin, Content-Type, Authorization, X-Request-ID")
+		c.Header("Access-Control-Expose-Headers", "X-Request-ID")
+		c.Header("Access-Control-Max-Age", "86400")
+
+		if c.Request.Method == http.MethodOptions {
+			c.AbortWithStatus(http.StatusNoContent)
+			return
+		}
+
+		c.Next()
+	}
+}

backend/go-service/pkg/middleware/logger.go

@@ -0,0 +1,46 @@
+package middleware
+
+import (
+	"time"
+
+	"github.com/echochat/backend/pkg/logs"
+	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
+)
+
+// Logger 请求日志中间件
+// 记录每个请求的完整信息：方法、路径、状态码、耗时、IP、User-Agent
+// 自动携带 trace_id，慢请求（>500ms）记录 WARN
+func Logger() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+
+		c.Next()
+
+		latency := time.Since(start)
+		ctx := c.Request.Context()
+		funcName := "middleware.Logger"
+
+		fields := []zap.Field{
+			zap.String("method", c.Request.Method),
+			zap.String("path", c.Request.URL.Path),
+			zap.Int("status", c.Writer.Status()),
+			zap.Duration("latency", latency),
+			zap.String("ip", c.ClientIP()),
+			zap.String("user_agent", c.Request.UserAgent()),
+		}
+
+		if len(c.Errors) > 0 {
+			fields = append(fields, zap.String("error", c.Errors.String()))
+			logs.Error(ctx, funcName, "请求处理异常", fields...)
+			return
+		}
+
+		if latency > 500*time.Millisecond {
+			logs.Warn(ctx, funcName, "慢请求告警", fields...)
+			return
+		}
+
+		logs.Info(ctx, funcName, "请求完成", fields...)
+	}
+}

backend/go-service/pkg/middleware/recovery.go

@@ -0,0 +1,36 @@
+package middleware
+
+import (
+	"net/http"
+	"runtime/debug"
+
+	"github.com/echochat/backend/pkg/logs"
+	"github.com/echochat/backend/pkg/utils"
+	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
+)
+
+// Recovery Panic 恢复中间件
+// 捕获 panic 后记录 ERROR 日志含堆栈信息，返回 500 响应
+func Recovery() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		defer func() {
+			if r := recover(); r != nil {
+				ctx := c.Request.Context()
+				logs.Error(ctx, "middleware.Recovery", "服务发生 panic",
+					zap.Any("error", r),
+					zap.String("stack", string(debug.Stack())),
+					zap.String("path", c.Request.URL.Path),
+					zap.String("method", c.Request.Method),
+				)
+
+				c.AbortWithStatusJSON(http.StatusInternalServerError, utils.Response{
+					Code:    500,
+					Message: "服务内部错误",
+					TraceID: logs.GetTraceID(ctx),
+				})
+			}
+		}()
+		c.Next()
+	}
+}

backend/go-service/pkg/middleware/trace.go

@@ -0,0 +1,26 @@
+// Package middleware 提供 Gin HTTP 中间件
+package middleware
+
+import (
+	"github.com/echochat/backend/pkg/logs"
+	"github.com/gin-gonic/gin"
+)
+
+// Trace 链路追踪中间件
+// 从请求头提取 X-Request-ID，不存在则自动生成
+// 注入 context，后续所有日志自动携带 trace_id
+// 在响应头中返回 X-Request-ID
+func Trace() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		traceID := c.GetHeader("X-Request-ID")
+		if traceID == "" {
+			traceID = logs.GenerateTraceID()
+		}
+
+		ctx := logs.WithTraceID(c.Request.Context(), traceID)
+		c.Request = c.Request.WithContext(ctx)
+		c.Header("X-Request-ID", traceID)
+
+		c.Next()
+	}
+}