HTTP gzip multipart form data client

main.go

package main

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"log"
	"mime/multipart"
	"net/http"
	"strings"
)

func main() {
	// URL and credentials
	url := "https://api.mailgun.net/v3/%s/messages"
	username := "api"
	password := "<snip>"
	domain := "example.com"
	to := "[email protected]"

	// Create a buffer to write our multipart form
	var formBuffer bytes.Buffer
	formWriter := multipart.NewWriter(&formBuffer)

	// Add form fields
	if err := formWriter.WriteField("from", fmt.Sprintf("Your Mom <root@%s>", domain)); err != nil {
		log.Fatal(err)
	}
	if err := formWriter.WriteField("to", fmt.Sprintf("admin@%s", domain)); err != nil {
		log.Fatal(err)
	}
	if err := formWriter.WriteField("to", to); err != nil {
		log.Fatal(err)
	}
	if err := formWriter.WriteField("subject", "My emotional state"); err != nil {
		log.Fatal(err)
	}
	if err := formWriter.WriteField("text", "I like people like I like my tea, in a bag and underwater"); err != nil {
		log.Fatal(err)
	}

	// Close the multipart writer
	if err := formWriter.Close(); err != nil {
		log.Fatal(err)
	}

	// Gzip compress the form data
	var gzipBuffer bytes.Buffer
	gzipWriter := gzip.NewWriter(&gzipBuffer)
	if _, err := gzipWriter.Write(formBuffer.Bytes()); err != nil {
		log.Fatal(err)
	}
	if err := gzipWriter.Close(); err != nil {
		log.Fatal(err)
	}

	// Create the HTTP request
	req, err := http.NewRequest("POST", fmt.Sprintf(url, domain), &gzipBuffer)
	if err != nil {
		log.Fatal(err)
	}

	// Set headers and basic authentication
	req.Header.Set("Content-Type", formWriter.FormDataContentType())
	req.Header.Set("Content-Encoding", "gzip")
	req.Header.Set("Accept-Encoding", "gzip")
	req.SetBasicAuth(username, password)

	// Create HTTP client and execute the request
	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()

	// Read and print the response
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Response:", strings.TrimSpace(string(body)))
}

response.txt

Response: {"message":"malformed multipart/form-data request"}