Golang gin-gonic 反向代理导致恐慌“接口转换：*http.timeoutWriter is not http.CloseNotifier：缺少方法CloseNotify”

Question

我正在使用Gin Gonic 框架创建一个反向代理端点，使用下面给出的代码使用grpc Gateway 为目标端点提供服务。这类似于为 gin here 和 here 建议的反向代理方法

ep1 := v1.Group("/ep1")
{
    ep1.GET("/ep2", reverseProxy("http://localhost:50000"))
}

func reverseProxy(target string) gin.HandlerFunc {
    url, err := url.Parse(target)
    if err != nil {
        log.Println("Reverse Proxy target url could not be parsed:", err)
        return nil
    }
    proxy := httputil.NewSingleHostReverseProxy(url)
    return func(c *gin.Context) {
        proxy.ServeHTTP(c.Writer, c.Request)
    }
}

但是，当实际向此 gin 端点 (/ep1/ep2) 发送请求时，会出现 go panic：

interface conversion: *http.timeoutWriter is not http.CloseNotifier: missing method CloseNotify
/usr/local/Cellar/go/1.8/libexec/src/runtime/panic.go:489 (0x10288df)
    gopanic: reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
/usr/local/Cellar/go/1.8/libexec/src/runtime/iface.go:131 (0x100c3af)
    additab: panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), iname})
/usr/local/Cellar/go/1.8/libexec/src/runtime/iface.go:79 (0x100bc34)
    getitab: additab(m, true, canfail)
/usr/local/Cellar/go/1.8/libexec/src/runtime/iface.go:256 (0x100cbb8)
    assertI2I: r.tab = getitab(inter, tab._type, false)
/path/to/vendor/github.com/gin-gonic/gin/response_writer.go:110 (0x14de6f3)
    (*responseWriter).CloseNotify: return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
/usr/local/Cellar/go/1.8/libexec/src/net/http/httputil/reverseproxy.go:142 (0x14d4d12)
    (*ReverseProxy).ServeHTTP: notifyChan := cn.CloseNotify()
/path/to/main.go:379 (0x16d2ead)
    reverseProxy.func1: proxy.ServeHTTP(c.Writer, c.Request)
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/locale.go:12 (0x15737d9)
    getLocaleMiddleware.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/session_cookie.go:27 (0x1574e7c)
    getSessionCookieMiddleware.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/affiliate_api.go:27 (0x15729a1)
    getAffiliateAPIMiddleware.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/metrics.go:17 (0x157465b)
    getMetricsMiddleware.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/input_validations.go:75 (0x1572dcb)
    getInputValidationMiddleware.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/logger.go:68 (0x1573aea)
    LoggerWithWriter.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/middlewares/request_tracer.go:13 (0x1574d6c)
    getTracerContext.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/vendor/github.com/gin-gonic/gin/recovery.go:45 (0x14e4b6a)
    RecoveryWithWriter.func1: c.Next()
/path/to/vendor/github.com/gin-gonic/gin/context.go:97 (0x14d657a)
    (*Context).Next: c.handlers[c.index](c)
/path/to/vendor/github.com/gin-gonic/gin/gin.go:284 (0x14dc710)
    (*Engine).handleHTTPRequest: context.Next()
/path/to/vendor/github.com/gin-gonic/gin/gin.go:265 (0x14dc02b)
    (*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/local/Cellar/go/1.8/libexec/src/net/http/server.go:2967 (0x140fa53)
    (*timeoutHandler).ServeHTTP.func1: h.handler.ServeHTTP(tw, r)
/usr/local/Cellar/go/1.8/libexec/src/runtime/asm_amd64.s:2197 (0x1054851)

关于为什么会发生这种情况或代码中有什么问题的任何想法？

Answer 1

发现问题是因为代码库没有直接使用来自gin-gonic的Run()方法。相反，它在启动 http 服务器时使用了超时，如下所示（在此处使用部分相关代码）：

type H struct {
    sync.Mutex
    Engine   *gin.Engine
    listener net.Listener
    running  bool
}
.
.
.
var h H
s := &http.Server{
    Addr:         address,
    Handler:      http.TimeoutHandler(h.Engine, time.Duration(100000)*time.Millisecond, ""),
    ReadTimeout:  time.Duration(100000) * time.Millisecond,
    WriteTimeout: time.Duration(100000) * time.Millisecond,
}


h.listener, err := net.Listen("tcp", s.Addr)
if err != nil {
    return err
}

h.running = true
s.Serve(h.listener)

但是，http.TimeoutHandler 没有实现http://grokbase.com/t/gg/golang-dev/13796p5h1n/net-http-timeouthandler-vs-closenotify 中提到的http.CloseNotifer 接口，这导致panic 带有错误消息interface conversion: *http.timeoutWriter is not http.CloseNotifier: missing method CloseNotify

因此，作为此问题的解决方法，将服务器处理程序修改为直接作为 gin 引擎，同时使用 http.Server 的 WriteTimeout 值用于超时目的。

修改后的代码不再恐慌，并导致成功的反向代理：

type H struct {
    sync.Mutex
    Engine   *gin.Engine
    listener net.Listener
    running  bool
}
.
.
.
var h H
s := &http.Server{
    Addr:         address,
    Handler:      h.Engine,
    ReadTimeout:  time.Duration(100000) * time.Millisecond,
    WriteTimeout: time.Duration(100000) * time.Millisecond,
}

h.listener, err := net.Listen("tcp", s.Addr)
if err != nil {
    return err
}

h.running = true
s.Serve(h.listener)

请注意，这里只需要修改&http.Server 的Handler。此外，不需要修改问题中的原始反向代理代码。