How to Upload Files to Telegram with POST Requests in Golang?

Upload a File with POST Request in Go

Uploading a file via HTTP POST request can be a complex task, especially when dealing with third-party APIs like Telegram. To address this, let's explore a custom function written in Golang that handles file uploads efficiently.

Issue:

You've encountered an error from Telegram indicating a missing photo in the request, even after following unsuccessful online solutions.

Code Snippet:

The provided code snippet attempts to upload a file using the os.Open() function, but it fails due to Telegram's specific API requirements.

Solution:

To resolve this issue, we'll create a custom sendPostRequest function that utilizes a multipart/form-data request to handle file uploads. This method is widely supported by web servers and APIs. Here's the updated code:

<code class="go">import (
    "bytes"
    "io"
    "mime/multipart"
    "net/http"
    "path/filepath"
)

// content is a struct which contains a file's name, its type and its data.
type content struct {
    fname string
    ftype string
    fdata []byte
}

func sendPostRequest(url string, files ...content) ([]byte, error) {
    var (
        buf = new(bytes.Buffer)
        w   = multipart.NewWriter(buf)
    )

    for _, f := range files {
        part, err := w.CreateFormFile(f.ftype, filepath.Base(f.fname))
        if err != nil {
            return []byte{}, err
        }

        _, err = part.Write(f.fdata)
        if err != nil {
            return []byte{}, err
        }
    }

    err := w.Close()
    if err != nil {
        return []byte{}, err
    }

    req, err := http.NewRequest("POST", url, buf)
    if err != nil {
        return []byte{}, err
    }
    req.Header.Add("Content-Type", w.FormDataContentType())

    client := &http.Client{}
    res, err := client.Do(req)
    if err != nil {
        return []byte{}, err
    }
    defer res.Body.Close()

    cnt, err := io.ReadAll(res.Body)
    if err != nil {
        return []byte{}, err
    }
    return cnt, nil
}</code>

Understanding the Solution:

The sendPostRequest function accepts a URL and a variable number of content structs, each representing a file to be uploaded. It constructs a multipart HTTP request, where each file is included with its metadata (name, type, and data). This format ensures compatibility with Telegram's API.

Usage:

You can call the sendPostRequest function with your file information and receive the server's response in the cnt variable. For example:

<code class="go">resp, err := sendPostRequest("https://your-url.com", content{fname: "photo.jpg", ftype: "image/jpeg", fdata: []byte{your_file_data}})
if err != nil {
    // Handle error
}</code>

Conclusion:

This custom sendPostRequest function resolves the issue of uploading files via POST requests in Golang, specifically addressing Telegram's file upload requirements. By using multipart/form-data, it ensures compatibility and makes it easier to upload files to remote servers.

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