由于回應結構的微小變化，重復呼叫JSON解碼器

我已將 Github 和 Google 身份驗證系統添加到我的 Web 應用程式中。在這兩種情況下，我都希望獲得用戶電子郵件。我嘗試制作一個可以發出 API 請求并獲取電子郵件的函式。當Google 回傳一個 JSON 物件并在 Github 上回傳一個 JSON 陣列作為回應
時，我遇到了一個問題。 我無法弄清楚如何避免兩次呼叫 JSON 解碼器，因為我不能為它們兩個使用相同的型別變數。

// Sends a request to the API and
// authorizes it by setting HTTP header "Authorization" to authHeader value
func getUserEmail(endpoint, authHeader, provider string) (string, error) {
    var email string       // Store user email here
    var client http.Client // Create client so we can modify request headers

    // Create a GET request to the endpoint
    req, err := http.NewRequest("GET", endpoint, nil)
    if err != nil {
        return "", err
    }

    // Authorize the request by using the HTTP header
    req.Header.Add("Authorization", authHeader)

    // Give the data back as JSON
    req.Header.Add("accept", "application/json")

    // Send the request
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Internet connection or client policy error")
        return "", err
    }
    defer resp.Body.Close()

    if provider == "google" {
        var response map[string]interface{}

        err = json.NewDecoder(resp.Body).Decode(&response)
        if err != nil {
            fmt.Println("Error occured during decoding access token response")
            return "", err
        }

        email = response["email"].(string)

    } else if provider == "github" {
        var response []map[string]interface{}

        err = json.NewDecoder(resp.Body).Decode(&response)
        if err != nil {
            fmt.Println("Error occured during decoding access token response")
            return "", err
        }

        email = response[0]["email"].(string)
    } else {
        return "", errors.New("invalid provider")

    }

    return email, nil
}

uj5u.com熱心網友回復：

您可以解組為var response interface{}. 一旦 json 被解組，你可以在type assertion上做一個response檢查它是否是[]interface{}或map[string]interface{}從那里去。

var email string
var response interface{}
if err := json.NewDecoder(r.Body).Decode(&response); err != nil {
    return err
}

// If you are sure that the structure of the content of the response,
// given its type, is always what you expect it to be, you can use a
// quick-and-dirty type switch/assertion.
switch v := response.(type) {
case []interface{}:
    email = v[0].(map[string]interface{})["email"].(string)
case map[string]interface{}:
    email = v["email"].(string)
}

// But! If you're not sure, if the APIs don't provide a guarantee,
// then you should guard against panics using the comma-ok idiom
// at every step.
if s, ok := response.([]interface{}); ok && len(s) > 0 {
    if m, ok := s[0].(map[string]interface{}); ok && len(m) > 0 {
        email, _ = m["email"].(string)
    }
} else if m, ok := response.(map[string]interface{}); ok && len(m) > 0 {
    email, _ = m["email"].(string)
}

您還可以根據提供者值預先分配一個指向預期型別的??指標，并將請求正文解組到其中，這將減少必要的型別斷言的數量，但需要指標解參考。

var email string
var response interface{}
if provider == "google" {
    response = new(map[string]interface{})
} else if provider == "github" {
    response = new([]map[string]interface{})
}
if err := json.NewDecoder(r.Body).Decode(response); err != nil {
    return err
}

switch v := response.(type) {
case *[]map[string]interface{}:
    email = (*v)[0]["email"].(string) // no need to assert the slice element's type
case *map[string]interface{}:
    email = (*v)["email"].(string)
}

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