升级alexedwards/scs/v2后，如何结合Gorilla Websockets实现http.Hijacker

方案一：让sessionResponseWriter实现http.Hijacker接口 #

scs的sessionResponseWriter是对原始http.ResponseWriter的包装，只需扩展它并代理底层的Hijack方法即可：

import (
    "bufio"
    "net"
    "net/http"
    "github.com/alexedwards/scs/v2"
)

// 自定义ResponseWriter，嵌入scs的sessionResponseWriter
type hijackableResponseWriter struct {
    *scs.sessionResponseWriter
    hijacker http.Hijacker
}

// 实现http.Hijacker接口，直接调用底层ResponseWriter的Hijack
func (w *hijackableResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
    return w.hijacker.Hijack()
}

// 包装中间件，替换可劫持的ResponseWriter
func wrapHijack(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if hj, ok := w.(http.Hijacker); ok {
            if scsRW, ok := w.(*scs.sessionResponseWriter); ok {
                wrapped := &hijackableResponseWriter{
                    sessionResponseWriter: scsRW,
                    hijacker: hj,
                }
                next.ServeHTTP(wrapped, r)
                return
            }
        }
        next.ServeHTTP(w, r)
    })
}

然后调整中间件注册顺序，将这个包装中间件放在scs中间件之后、Websocket路由之前：

sessionManager := scs.New()
// ...配置sessionManager

mux := http.NewServeMux()
mux.HandleFunc("/ws", wsHandler)

// 中间件链：scs -> wrapHijack -> 路由
http.ListenAndServe(":8080", sessionManager.LoadAndSave(wrapHijack(mux)))

方案二：为Websocket路由绕过scs中间件 #

如果你的Websocket连接不需要会话支持，可直接将Websocket路由挂载在scs中间件之外，避免被sessionResponseWriter包装：

mux := http.NewServeMux()
// 受会话保护的路由
protectedMux := http.NewServeMux()
protectedMux.HandleFunc("/upload", uploadHandler)

// Websocket路由直接挂载，不经过scs中间件
mux.Handle("/ws", http.HandlerFunc(wsHandler))
mux.Handle("/", sessionManager.LoadAndSave(protectedMux))

http.ListenAndServe(":8080", mux)

方案三：修改scs库的sessionResponseWriter（不推荐） #

直接修改scs源码中的sessionResponseWriter，让它实现http.Hijacker接口：

// 在scs的response_writer.go文件中修改
type sessionResponseWriter struct {
    http.ResponseWriter
    // ...原有字段
}

func (w *sessionResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
    hj, ok := w.ResponseWriter.(http.Hijacker)
    if !ok {
        return nil, nil, fmt.Errorf("underlying response writer does not support hijack")
    }
    return hj.Hijack()
}

此方法需要fork scs库并维护自定义分支，后续升级scs时需手动合并代码，仅在其他方案不可行时使用。

内容的提问来源于stack exchange，提问作者RetroRocker