Why Does My Go HTTP Response Return an Empty JSON with Text/Plain Content Type?

HTTP Responses with JSON

When creating HTTP responses with JSON in Go, it's necessary to ensure that the data is formatted correctly. One issue that can arise is an empty response with a text/plain content type. This often indicates a problem with the JSON encoding or the struct used to represent the data.

In the case described in the question, the code provided tries to send a JSON response using the following struct:

<code class="go">type ResponseCommands struct {
    key   string
    value bool
}</code>

However, as the answer correctly points out, the variables in this struct are not exported, which means they start with lowercase letters. This can cause issues with JSON encoding because JSON keys are expected to be exported (start with uppercase letters).

To fix the issue, the struct should be modified to export the variables:

<code class="go">type ResponseCommands struct {
    Key   string
    Value bool
}</code>

Additionally, it's essential to ensure that the Content-Type header is set to application/json before writing the response data. The following code updates the handler function to include this fix:

<code class="go">func handler(rw http.ResponseWriter, req *http.Request) {
    responseBody := ResponseCommands{"BackOff", false}

    data, err := json.Marshal(responseBody)
    if err != nil {
        http.Error(rw, err.Error(), http.StatusInternalServerError)
        return
    }
    rw.WriteHeader(200)
    rw.Header().Set("Content-Type", "application/json")
    rw.Write(data)
}</code>

By making these changes, the code should correctly generate a JSON response with the appropriate content type.

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