Golang set http response code based on struct field

Question

Within an api I'm writing I have an error struct which marshals to json. When the api has an error it returns the struct and I set the http response code to be the appropriate value.

type PodsError struct {
    ErrorCode       int     `json:"error_code"`
    CallingFunction string  `json:"calling_function"`
    Message         string  `json:"error_message"`
}

type PodsErrorWrapper struct {
    Error   PodsError   `json:"error"`
}

Right now every time I write the struct I also write a header, but I don't like the amount of duplicate code I am seeing.

error := PodsError{http.StatusNotFound, "Calling Func", "Message"}
response.WriteHeader(error.ErrorCode)
response.WriteEntity(PodsErrorWrapper{error})

Is it possible to move the WriteHeader call to something that gets called whenever I pass the error to WriteEntity()? I figure there has to be a function I could implement for a PodsErrorWapper where I could just set the http status to be whatever the ErrorCode field is.

Edit: Sorry I forgot to mention, I am using the go-restful package (github.com/emicklei/go-restful)

what packages are you using? I don't know what is providing WriteEntity — Mr_Pink
– Mr_Pink, Commented May 1, 2015 at 19:08
whoops sorry I forgot to mention that, I am using github.com/emicklei/go-restful — Colin Murphy
– Colin Murphy, Commented May 1, 2015 at 19:27

Caleb · Accepted Answer · 2015-05-01 22:29:39Z

1

You can make your own function:

func writeEntity(r *restful.Response, value interface{}) error {
    // if value is an error
    if perr, ok := value.(PodsError); ok {
        r.WriteHeader(perr.ErrorCode)
        // reassign value so it gets wrapped: `{"error": value}`
        value = struct {
            Error PodsError `json:"error"`
        }{perr}
    }
    return r.WriteEntity(value)
}

Then just always call that instead of response.WriteEntity:

writeEntity(response, PodsError{http.StatusNotFound, "Calling Func", "Message"})

answered May 1, 2015 at 22:29

Caleb

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