Posting to an API with Content-Type: multipart/form-data

When attempting to POST to an API requiring Content-Type: multipart/form-data, you may encounter issues if you are using []byte parameters and string arguments. The provided error message indicates a redirection issue, which is unrelated to the issue at hand.

The solution lies in constructing the multipart/form-data request body using the multipart package. Here's an example:

package main

import (
    "bytes"
    "fmt"
    "io"
    "io/ioutil"
    "mime/multipart"
    "net/http"

    "github.com/ganshane/typeregistry"
)

type FileItem struct {
    Key      string //image_content
    FileName string //test.jpg
    Content  []byte //[]byte
}

func NewPostFile(url string, paramTexts map[string]interface{}, paramFile FileItem) ([]byte, error) {
    // Construct the multipart request body

    bodyBuf := &bytes.Buffer{}
    bodyWriter := multipart.NewWriter(bodyBuf)

    for k, v := range paramTexts {
        bodyWriter.WriteField(k, v.(string))
    }
    fileWriter, err := bodyWriter.CreateFormFile(paramFile.Key, paramFile.FileName)
    if err != nil {
        fmt.Println(err)
        //fmt.Println("Create form file error: ", error)
        return nil, err
    }
    fileWriter.Write(paramFile.Content)
    contentType := bodyWriter.FormDataContentType()
    bodyWriter.Close()
    fmt.Println(bodyBuf.String())

    // Perform the POST request

    resp, err := http.Post(url, contentType, bodyBuf)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    fmt.Println(resp)

    // Handle the response

    if resp.StatusCode = 300 {
        b, _ := ioutil.ReadAll(resp.Body)
        return nil, fmt.Errorf("[%d %s]%s", resp.StatusCode, resp.Status, string(b))
    }
    respData, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        return nil, err
    }
    fmt.Println(string(respData))
    return respData, nil
}

func main() {
    m := make(map[string]interface{}, 0)
    m["fileName"] = "good"
    m["name"] = typeregistry.Base64ToByte("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 Tl5ufo6erx8vP09fb3 Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAwQFBgcICQoL/8QAtREAAgECBAQDBAcFBAQAAQJ3AAECAxEEBSExBhJBUQdhcRMiMoEIFEKRobHBCSMzUvAVYnLRChYkNOEl8RcYGRomJygpKjU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eHl6goOEhYaHiImKkpOUlZaXmJmaoqOkpaanqKmqsrO0tba3uLm6wsPExcbHyMnK0tPU1dbX2Nna4uPk5ebn6Onq8vP09fb3 Pn6/9oADAMBAAIRAxEAPwDHooor wD Zz//2Q==")

    paramFile := FileItem{
        Key:      "image_content",
        FileName: "test.jpg",
        Content:  m["name"].([]byte),
    }

    respData, err := NewPostFile("API_URL", m, paramFile)
    if err != nil {
        // Handle error
    }

    fmt.Println(string(respData))
}

In this example, we used the NewPostFile function to construct a POST request with multipart/form-data, including both regular form fields and a file. The function takes the URL, a map of string arguments, and a file item as input.

The response from the API can be retrieved from the respData variable and processed as needed. The error handling and response handling code is left to the developer to implement according to their specific requirements.

This solution should address the issue you were experiencing with POSTing to the API using Content-Type: multipart/form-data with []byte parameters and string arguments.