MustGet sometimes panics even though Set was called in middleware

[tsirolnik]

Middleware -

func middleware() gin.HandlerFunc {
	return func(c *gin.Context) {
                //.....
                //.....
                //.....
                //.....
		c.Set("someKey", someValue)
		log.WithFields(log.Fields{
			"someKey": someValue,
		}).Infof("Middleware call")
		c.Next()
	}
}

Some handler that uses the middleware -

func someHandler(c *gin.Context) {
            //.....
           // Panic is being thrown sometimes
            c.MustGet("someKey")
            //.....
}

This results (Sometimes) in panic, for no apparent reason as I can clearly see the logging line with the expected values.
time="2017-03-15T08:08:05Z" level=info msg="Middleware call" someKey=someValue

[itsjamie]

Does middleware run on the same goroutine as someHandler?

[tsirolnik]

It does

[tsirolnik]

@itsjamie Here's a panic I've caught, seems like the context is shared until the last method -

Key "someKey" does not exist
/usr/lib/go/src/runtime/panic.go:426 (0x487fb9)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/context.go:180 (0x5ceb48)
/home/xxx/xxx/dev/xxx/yyy/src/zzz.go:211 (0x417217)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/context.go:97 (0x5ce44a)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/recovery.go:45 (0x5e1081)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/context.go:97 (0x5ce44a)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/logger.go:72 (0x5e02f2)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/context.go:97 (0x5ce44a)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/gin.go:284 (0x5d5582)
/home/xxx/xxx/dev/golang/src/github.com/gin-gonic/gin/gin.go:265 (0x5d51b7)
/usr/lib/go/src/net/http/server.go:2081 (0x54bdee)
/usr/lib/go/src/net/http/server.go:1472 (0x54869e)
/usr/lib/go/src/runtime/asm_amd64.s:1998 (0x4b8b11)

[maxatome]

@tsirolnik in your stack trace I do not see your middleware closure (in fact the call to c.Next() like the ones for recovery and logger). It means that in the case of this panic your middleware closure is not called, so the someKey key is not set, so MustGet("someKey") panics.

Note that it is not the same problem as in #702. Here the key is not found in the context instead of concurrent map read and map write for #702.

[thinkerou]

As @maxatome said, if still have problem please reopen, closing.