array from form-data in golang return as a string instead of array

I am passing an array from form data in postman, before the json.Marsal I get [0558485290,0209739442] after the json.Marshal when I print using (bytes.NewBuffer(jsonpayload)) I get ["0558485290,0209739442"]

Before JSON Marshal
[05583485362290,02097343639442]
After json.Marshal
"Recipient":["0558485290,0209739442"]
Below Here is my code

type QuickBulkVoiceCall struct {
Campaign      string                `form:"campaign"`
Recipient     []string              `form:"recipient"`
FileHeader    *multipart.FileHeader `form:"file_header"`
File          string                `form:"file"`
VoiceID       string                `form:"voice_id"`
Is_Schedule   bool                  `form:"is_schedule"`
Schedule_Date string                `form:"schedule_date"`
}
func (mnfyCmpgn *MnotifyCampaignService) CreateBulkVoiceCall(blkVcall *models.QuickBulkVoiceCall) (*mnotify.SMSData, error) {
api_key, base_url, err := mnotify.LoadAPIKeys()
if err != nil {
return nil, fmt.Errorf("error: %v", err.Error())
}
fmt.Println("Before JSON Marshal", blkVcall.Recipient)
jsonPayload, err := json.Marshal(blkVcall)
if err != nil {
return nil, fmt.Errorf("error: %v", err.Error())
}
fmt.Println("JSON Payload: ", bytes.NewBuffer(jsonPayload))
url := (*base_url + "voice/quick/" + "?key=" + *api_key)
req, err := http.NewRequest("POST", url, bytes.NewBuffer(jsonPayload))
if err != nil {
return nil, fmt.Errorf("error: %v", err.Error())
}
// req.Header.Set("Content-Type", "application/json")
// Make the HTTP Request
client := &http.Client{}
resp, err := client.Do(req)
if err != nil {
return nil, fmt.Errorf("error: %v", err.Error())
}
defer resp.Body.Close()
body, err := io.ReadAll(resp.Body)
if err != nil {
return nil, fmt.Errorf("error: %v", err)
}
responseBody := string(body)
data, err := mnotify.BulkCampaignFilterFilter(responseBody)
if err != nil {
return nil, fmt.Errorf("error: %v", err)
}
return &data, nil
}
func (mnfyCmpgn *MnotifyCampaignController) QuickBulkVoiceCallController(ctx *gin.Context) {
var blkVcCall *models.QuickBulkVoiceCall
err := ctx.ShouldBind(&blkVcCall)
if err != nil {
ctx.JSON(http.StatusBadRequest, gin.H{
"error": err.Error(),
})
return
}
file, err := ctx.FormFile("file_header")
if err != nil {
// Handle the error if the file is not found
ctx.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
return
}
// Save file to the Uploads directory
filePath := filepath.Join("./uploads", blkVcCall.FileHeader.Filename)
if err := ctx.SaveUploadedFile(file, filePath); err != nil {
ctx.JSON(http.StatusInternalServerError, gin.H{
"error": err.Error(),
})
}
//
fmt.Println("Recipient", blkVcCall.Recipient)
// Lets assign the file path to the struct file
blkVcCall.File = filePath
resp, err := mnfyCmpgn.Mnfycntrl.CreateBulkVoiceCall(blkVcCall)
if err != nil {
ctx.JSON(http.StatusBadRequest, gin.H{
"error": err.Error(),
})
return
}
ctx.JSON(http.StatusOK, gin.H{
"response": resp,
})
}

About the Print Output

> before the json.Marsal I get [0558485290,0209739442] after the json.Marshal when I print using (bytes.NewBuffer(jsonpayload)) I get ["0558485290,0209739442"]

Please note that the value is

[]string{"0558485290,0209739442"}

instead of

[]string{"0558485290", "0209739442"}.

See this simple demo:

package main

import "fmt"

func main() {
	recipients := []string{"0558485290,0209739442"}
	fmt.Println(recipients) // [0558485290,0209739442]

	recipients = []string{"0558485290", "0209739442"}
	fmt.Println(recipients) // [0558485290 0209739442]
}

Send Array in multipart/form-data Request

To send an array to the server in a multipart/form-data request, you can do it like this:

curl 'https://httpbin.org/anything' \
--form 'recipient="0558485290"' \
--form 'recipient="0209739442"' \
--form 'file_header=@"test.data"'

The corresponding request in postman is:

Send Array as JSON value in multipart/form-data Request

gin does not support JSON in multipart/form-data request very well. As of now, gin tries to unmarshal a JSON value in a multipart/form-data field only when the target field is a struct or a map (see this answer: https://stackoverflow.com/a/75989469/1369400). In the OP's case, the target field is a slice, so it does not work. BTW, 05583485362290,02097343639442 is not a valid JSON array (it's even not a valid JSON value). The valid JSON array should be: ["05583485362290","02097343639442"].

If you want to pass it as a JSON value, you have to unmarshal the value yourself. See the demo below:

package main

import (
	"encoding/json"
	"fmt"
	"mime/multipart"
	"net/http"

	"github.com/gin-gonic/gin"
)

type QuickBulkVoiceCall struct {
	Recipient  []string
	FileHeader *multipart.FileHeader `form:"file_header"`
}

func main() {
	r := gin.Default()
	r.POST("/create", func(ctx *gin.Context) {
		type temp struct {
			QuickBulkVoiceCall
			Recipient string `form:"recipient"`
		}
		var data temp
		err := ctx.ShouldBind(&data)
		if err != nil {
			ctx.JSON(http.StatusBadRequest, gin.H{
				"error": err.Error(),
			})
			return
		}

		blkVcCall := data.QuickBulkVoiceCall

		err = json.Unmarshal([]byte(data.Recipient), &blkVcCall.Recipient)
		if err != nil {
			ctx.JSON(http.StatusBadRequest, gin.H{
				"error": err.Error(),
			})
			return
		}

		fmt.Printf("%+v\n", blkVcCall)
	})
	r.Run()
}

Here is the request to send the JSON value in a multipart/form-data field:

curl 'http://localhost:8080/create' \
--form 'recipient="[\"0558485290\",\"0209739442\"]"' \
--form 'file_header=@"test.data"'

And here is the corresponding postman request: