[GitHub] [apisix-dashboard] starsz commented on pull request #1812: fix: can not configure upstream with no nodes

[GitBox <gi...@apache.org>]

starsz commented on pull request #1812:
URL: https://github.com/apache/apisix-dashboard/pull/1812#issuecomment-825347305


   > > @liuxiran
   > > How about we make it in the backend? Please see https://github.com/apache/apisix-dashboard/blob/master/api/internal/core/entity/format.go#L49, we can initialize the `nodes` as an empty slice instead of a nil one. Just change `var nodes []*Node` to `nodes := make([]*Node, 0)` .
   > > Looking forward to your insights.
   > 
   > @imjoey Thanks for your advice, and it really make sense for me.
   > 
   > before this change, when get info about an upstream with no nodes
   > fe will get
   > <img alt="WechatIMG5" width="834" src="https://user-images.githubusercontent.com/2561857/115748640-ee326980-a3c8-11eb-809a-e09e63cd6955.png">
   > 
   > actually `nodes:null` causes the problem
   > 
   > after this change, fe will get
   > <img alt="WechatIMG4" width="969" src="https://user-images.githubusercontent.com/2561857/115748817-1ae68100-a3c9-11eb-87c6-89c5c9dcd18f.png">
   > 
   > which is matches expectation.
   > 
   > BTW, I have a question in the process of debugging:
   > there are some logs I added to watch the changes of `upstream.Nodes` before the advice
   > <img alt="WechatIMG7" width="740" src="https://user-images.githubusercontent.com/2561857/115749803-11a9e400-a3ca-11eb-96cc-a6621465ab08.png">
   > I found even if I did not do this change, the `upstram.Nodes` will always be `[]`, but what Fe got is different, I haven't thought about it for a long time.
   > 
   > Also @nic-chen @Jaycean @starsz to take a look, thanks a lot
   
   Hi, @liuxiran 
   In golang, you should distinguish `nil slice` and `empty slice`
   
   ```
   var x []*entity.Node
   ```
   is a nil slice.
   
   ```
   y := make([]*entity.Node, 0)
   ```
   is an empty slice. The length and value are 0.
   If you use printf or println to print them, the result is both "[]".
   
   In this situation, because the upstream.Nodes' type is interface{}.So it's a little more complex.
   You can use 
   ```
   reflect.ValueOf(upstream.Nodes).IsNil()
   ```
   to see the true value.
   
   
   
   


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