Golang のマルチパート パッケージを使用してマルチパート POST リクエストを生成するにはどうすればよいですか?

<code class="go">import (
    "bytes"
    "mime/multipart"
    "net/http"
    "text/template"
)

// Declare a variable to represent the JSON string.
var jsonStr = []byte(`{"hello": "world"}`)

func generateMultipartRequest() (*http.Request, error) {
    // Create a buffer to store the request body.
    body := &bytes.Buffer{}
    
    // Create a multipart writer using the buffer.
    writer := multipart.NewWriter(body)
    
    // Create a part for the JSON data and specify its content type.
    part, err := writer.CreatePart(http.Header{
        "Content-Type": []string{"application/json"},
    })
    if err != nil {
        return nil, err
    }
    
    // Write the JSON data into the part.
    if _, err := part.Write(jsonStr); err != nil {
        return nil, err
    }
    
    // Close the writer to finalize the request body.
    if err := writer.Close(); err != nil {
        return nil, err
    }
    
    // Create a new HTTP request.
    req, err := http.NewRequest(http.MethodPost, "/blabla", body)
    if err != nil {
        return nil, err
    }
    
    // Set the Content-Type header with the specified boundary.
    req.Header.Set("Content-Type", writer.FormDataContentType())
    
    // Return the request.
    return req, nil
}</code>