How to Properly Handle File Uploads in Multipart/Form-Data POST Requests with Go?

Troubleshooting Multipart/Form-Data POST in Go

In the context of sending a multipart form using Go's mime/multipart and http packages, you may encounter certain issues that require troubleshooting. Let's delve into a specific case related to creating a file field.

The Issue

You have the following code and are trying to send a multipart form with both text fields and a file:

func main() {
    // ...

    // Create a file field
    fw, err := w.CreateFormFile("file", "filename.dat")
    if err != nil {
        return err
    }

    // ...

    // Send the request
    resp, err := http.Post(url, w.FormDataContentType(), &buffer)
    if err != nil {
        return err
    }

    // ...
}

However, you're struggling with how to obtain a Reader to read the file into the file field writer fw.

The Solution

To solve this issue, you need to open the file using os.Open and pass the returned *os.File as the io.Writer to the CreateFormFile function. Here's the corrected code:

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

func main() {
    // ...

    // Open the file
    fd, err := os.Open("filename.dat")
    if err != nil {
        return err
    }

    // Create a file field
    fw, err := w.CreateFormFile("file", "filename.dat")
    if err != nil {
        return err
    }

    // Copy the file contents into the file field writer
    _, err = io.Copy(fw, fd)
    if err != nil {
        return err
    }

    // ...

    // Send the request
    resp, err := http.Post(url, w.FormDataContentType(), &buffer)
    if err != nil {
        return err
    }

    // ...
}

With this modification, the file's contents will be correctly written into the multipart form, allowing you to send both text fields and a file successfully.

The above is the detailed content of How to Properly Handle File Uploads in Multipart/Form-Data POST Requests with Go?. For more information, please follow other related articles on the PHP Chinese website!