如何通过Struct字段名称获取Gmail API错误代码？

Question

The Gmail API err response struct includes a Code field according to Examiner

_, err := gmailService.Users.Messages.Send("me", &gMsg).Do()
t := reflect.TypeOf(err)
examiner(t,0)

Response

Type is  and kind is ptr
 Contained type:
 Type is Error and kind is struct
     Field 1 name is Code type is int and kind is int
...

I can successfully get the error code using the field index, but that is more obscure (and therefore more difficult to maintain) and feels more fragile:

errReflectElem := reflect.ValueOf(err).Elem() 
fmt.Printf("err.Code %v
",errReflectElem.Field(0).Interface())

It appears that I should also be able to get the error code as follows based on this sample:

fmt.Println("Code: %v",err.Code)

However that gives a build error:

err.Code undefined (type error has no field or method Code)

What am I missing?

Answer 1

According to the documentation it returns a *googleapi.Error. Simply assert to this type and you have full access to everything it contains. This is a prime example of the power of interfaces and proper error handling via an exported type. If such an error type is exported, there is no reflection necessary to access it.

if gapiErr, ok := err.(*googleapi.Error); ok {
    // use gapiErr.WhateverField
}