Go语言Multipart表单文件上传：如何指定字段Content-Type

package main

import (
    "bytes"
    "fmt"
    "io"
    "mime/multipart"
    "net/http"
    "net/textproto"
    "os"
)

// CreateFormFileWithContentType 创建一个multipart表单文件字段，并允许自定义Content-Type
// w: multipart.Writer 实例
// fieldname: 表单字段的名称 (例如 "file")
// filename: 文件的原始名称 (例如 "helloWorld.wav")
// contentType: 自定义的Content-Type (例如 "audio/wav;rate=8000")
func CreateFormFileWithContentType(w *multipart.Writer, fieldname, filename, contentType string) (io.Writer, error) {
    h := make(textproto.MIMEHeader)
    // 设置Content-Disposition头部，指定字段名和文件名
    // 注意：这里的filename需要进行适当的MIME编码，尤其当文件名包含非ASCII字符时。
    // 为简化示例，此处直接使用字符串格式化，实际生产环境应考虑更健壮的编码。
    h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="%s"; filename="%s"`, fieldname, filename))
    // 设置自定义的Content-Type头部
    h.Set("Content-Type", contentType)
    return w.CreatePart(h)
}

func main() {
    // 1. 创建一个模拟文件
    fileContent := []byte("This is a test audio file content.")
    err := os.WriteFile("helloWorld.wav", fileContent, 0644)
    if err != nil {
        fmt.Printf("Error creating dummy file: %v\n", err)
        return
    }
    defer os.Remove("helloWorld.wav") // 清理文件

    // 2. 打开文件准备读取
    file, err := os.Open("helloWorld.wav")
    if err != nil {
        fmt.Printf("Error opening file: %v\n", err)
        return
    }
    defer file.Close()

    // 3. 创建一个bytes.Buffer来存储multipart请求体
    var requestBody bytes.Buffer
    writer := multipart.NewWriter(&requestBody)

    // 4. 使用自定义函数创建文件字段并指定Content-Type
    // 假设我们需要上传一个音频文件，并指定其Content-Type为 "audio/wav;rate=8000"
    filePartWriter, err := CreateFormFileWithContentType(
        writer,
        "file", // 表单字段名
        "helloWorld.wav", // 文件名
        "audio/wav;rate=8000", // 自定义Content-Type
    )
    if err != nil {
        fmt.Printf("Error creating form file part: %v\n", err)
        return
    }

    // 5. 将文件内容拷贝到表单字段写入器中
    _, err = io.Copy(filePartWriter, file)
    if err != nil {
        fmt.Printf("Error copying file content: %v\n", err)
        return
    }

    // 6. 添加其他普通文本字段（可选）
    _ = writer.WriteField("description", "This is an audio file upload example.")

    // 7. 关闭writer，完成multipart请求体的构建
    writer.Close()

    // 8. 打印生成的multipart请求体和Content-Type头部
    fmt.Println("Generated Multipart Request Body:")
    fmt.Println("---------------------------------")
    fmt.Println(requestBody.String())
    fmt.Println("---------------------------------")
    fmt.Printf("Content-Type Header for HTTP Request: %s\n", writer.FormDataContentType())

    // 9. (可选) 构建并发送HTTP请求
    // req, err := http.NewRequest("POST", "http://your-upload-endpoint.com", &requestBody)
    // if err != nil {
    //  fmt.Printf("Error creating HTTP request: %v\n", err)
    //  return
    // }
    // req.Header.Set("Content-Type", writer.FormDataContentType())
    //
    // client := &http.Client{}
    // resp, err := client.Do(req)
    // if err != nil {
    //  fmt.Printf("Error sending HTTP request: %v\n", err)
    //  return
    // }
    // defer resp.Body.Close()
    //
    // fmt.Printf("HTTP Response Status: %s\n", resp.Status)
    // responseBody, _ := io.ReadAll(resp.Body)
    // fmt.Printf("HTTP Response Body: %s\n", string(responseBody))
}

Generated Multipart Request Body:
---------------------------------
--0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732
Content-Disposition: form-data; name="file"; filename="helloWorld.wav"
Content-Type: audio/wav;rate=8000

This is a test audio file content.
--0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732
Content-Disposition: form-data; name="description"

This is an audio file upload example.
--0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732--

---------------------------------
Content-Type Header for HTTP Request: multipart/form-data; boundary=0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732