Redirect to StaticFIle endpoint panics at first attempt

[Jarema]

• go version: go1.11.4
• gin version (or commit ref): 29a145c (master)
• operating system: osx

Description

When redirect to StaticFile endpoint is made, when called for first time, it panics (after successful redirect)

router:

router := gin.New()
	router.Use(gin.LoggerWithFormatter(config.GinJSONLogger))
	router.Use(gin.Recovery())
	router.GET("/", RedirectRootToAPI(router))

	v1 := router.Group("/v1")
	{
		v1.StaticFile("/", "./api/index.html")
	}

	return router
}

// RedirectRootToAPI redirects all calls from root endpoint to current API documentation endpoint
func RedirectRootToAPI(r *gin.Engine) gin.HandlerFunc {
	return func(c *gin.Context) {
		c.Request.URL.Path = "/v1"
		r.HandleContext(c)
	}
}

customLogger (just in case)

// GinJSONLogger is a custom function that satisfies gin Logger.
// It does not use any Marshaler or encoder to not sacrifice performance
func GinJSONLogger(param gin.LogFormatterParams) string {
	return fmt.Sprintf("{\"timestamp\": \"%s\",\"statusCode\": %d,\"latency\": %d,\"clientIP\": \"%s\",\"method\": \"%s\",\"path\": \"%s\",\"errorMessage\": \"%s\"}\n",
		param.TimeStamp.Format("2006/01/02 - 15:04:05"), param.StatusCode, param.Latency, param.ClientIP, param.Method, param.Path, param.ErrorMessage)
}

panic:

2019/01/16 11:15:47 [Recovery] 2019/01/16 - 11:15:47 panic recovered:
GET / HTTP/1.1
Host: localhost:8080
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate, br
Accept-Language: en,pl;q=0.9,en-US;q=0.8
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36


runtime error: index out of range
/usr/local/go/src/runtime/panic.go:513 (0x102bdd8)
	gopanic: reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
/usr/local/go/src/runtime/panic.go:44 (0x102ac19)
	panicindex: panic(indexError)
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/context.go:109 (0x15f181f)
	(*Context).Next: c.handlers[c.index](c)
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/recovery.go:76 (0x1603cb9)
	RecoveryWithWriter.func1: c.Next()
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/context.go:109 (0x15f17e2)
	(*Context).Next: c.handlers[c.index](c)
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/logger.go:170 (0x1603090)
	LoggerWithConfig.func1: c.Next()
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/context.go:109 (0x15f17e2)
	(*Context).Next: c.handlers[c.index](c)
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/gin.go:383 (0x15fa92a)
	(*Engine).handleHTTPRequest: c.Next()
/Users/tomek/go/pkg/mod/github.com/gin-gonic/gin@v1.3.1-0.20190109013244-29a145c85dc0/gin.go:349 (0x15fa181)
	(*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/local/go/src/net/http/server.go:2741 (0x12cd7fa)
	serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/local/go/src/net/http/server.go:1847 (0x12c9a45)
	(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/local/go/src/runtime/asm_amd64.s:1333 (0x1059320)
	goexit: BYTE	$0x90	// NOP

[GIN-debug] [WARNING] Headers were already written. Wanted to override status code 301 with 500

how to reproduce

1. start a new server with such redirect
2. call / path (curl localhost:8080/)
3. check stack trace

note: redirect is successful, as the panic happens after redirect

[vkd]

In your case you can fix this by correct URL.Path in your redirect handler:

// RedirectRootToAPI redirects all calls from root endpoint to current API documentation endpoint
func RedirectRootToAPI(r *gin.Engine) gin.HandlerFunc {
	return func(c *gin.Context) {
		c.Request.URL.Path = "/v1/"  // <- this line
		r.HandleContext(c)
	}
}

By the way, I think this is a bug.

[Jarema]

The path fix help, so my problem is fixed (thanks for that @vkd ) but still, the behaviour is weird.

Also, before fix, debug stated: [GIN-debug] [WARNING] Headers were already written. Wanted to override status code 301 with 500

Which explains successful redirect, yet a panic afterwards.

[thinkerou]

@vkd welcome to commit one fix pull request, thanks!