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fix panic risk in func Middleware #6

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fix panic risk in func Middleware #6

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YueHonghui
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In func Middleware, c.Next would be panic, then span.Finish will not be executed.

//...
	return func(c *gin.Context) {
		carrier := opentracing.HTTPHeadersCarrier(c.Request.Header)
		ctx, _ := tr.Extract(opentracing.HTTPHeaders, carrier)
		op := opts.opNameFunc(c.Request)
		sp := tr.StartSpan(op, ext.RPCServerOption(ctx))
		ext.HTTPMethod.Set(sp, c.Request.Method)
		ext.HTTPUrl.Set(sp, opts.urlTagFunc(c.Request.URL))
		opts.spanObserver(sp, c.Request)

		// set component name, use "net/http" if caller does not specify
		componentName := opts.componentName
		if componentName == "" {
			componentName = defaultComponentName
		}
		ext.Component.Set(sp, componentName)
		c.Request = c.Request.WithContext(
			opentracing.ContextWithSpan(c.Request.Context(), sp))

		c.Next()

		ext.HTTPStatusCode.Set(sp, uint16(c.Writer.Status()))
		sp.Finish()
	}
//...

stuart-mclaren
stuart-mclaren requested changes Apr 11, 2019
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@stuart-mclaren stuart-mclaren left a comment

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Thanks for your patch YueHonghui.

I'd like to see if we can keep this library and opentracing-contrib/go-stdlib consistent.

ginhttp/server.go
c.Next()
defer func() {
ext.HTTPStatusCode.Set(sp, uint16(c.Writer.Status()))
sp.Finish()
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When there is is a panic "c.Writer.Status" will be equal to 200.

This change means we will successfully complete the trace (sp.Finish()), but the response code will be 200 -- indicating the operation was successful. I wonder if that could be a little misleading?

Looking at https://github.com/opentracing-contrib/go-stdlib (which this library is derived from), our current behaviour matches theirs. When there is a panic the span is not finished (sp.Finish() is not called).

How would you feel about proposing a change similar to this to opentracing-contrib/go-stdlib:

       defer func() {                                                          
            if recover() != nil {                                                                            
                ext.HTTPStatusCode.Set(                                         
                    sp, uint16(http.StatusInternalServerError))                 
            } else {                                                                                            
                ext.HTTPStatusCode.Set(sp, uint16(sct.status))           
            }                                                                                                       
            sp.Finish()                                                         
        }()

That would mean that they would complete the span with an error if there is a panic. If that (or something similar) was acceptable we could then "backport" the change here.

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Just noticed https://github.com/opentracing-contrib/go-stdlib !

stuart-mclaren
stuart-mclaren reviewed Apr 11, 2019
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ginhttp/server_test.go
tr := &mocktracer.MockTracer{}
mw := Middleware(tr)
r := gin.New()
r.Use(gin.Recovery(), mw)
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If you reverse this to be
r.Use(mw, gin.Recover())

you can check for a status code of 500 in the panic case and 200 in the non-panic case.

See https://github.com/gin-gonic/gin/blob/master/recovery.go#L68

@YueHonghui
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@stuart-mclaren
It seems much more difficult to fix panic risk with gin comparing to stdlib(opentracing-contrib/go-stdlib#38). As you pointed out, gin's Writer.Status() will be 200 other than 500 when inner handler panicked. This is misleading, and not the same as golang's http implementation. Maybe I need to create an issue to gin's project first.

@polyrabbit
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Dears, any progress on the status code?

Just FYI, my current fix is just to leave the status code as it is:
polyrabbit@e7a5191

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@stuart-mclaren stuart-mclaren stuart-mclaren requested changes

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@YueHonghui @polyrabbit @stuart-mclaren @HonghuiYue