formsg-golang-sdk

Please note that this is an SDK for webhooks integration, and not the FormSG system.

FormSG Golang SDK

This SDK provides convenient utilities for verifying FormSG webhooks and decrypting submissions in golang.

Installation

Install the package with

go get github.com/afnexus/formsg-golang-sdk

Configuration

import (
    "github.com/afnexus/formsg-golang-sdk"
)

Usage

Webhook Authentication and Decrypting Submissions

⚠ If you are testing on localhost: Please remember to comment the check for X-FormSG-Signature as you will be using http protocol!

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/afnexus/formsg-golang-sdk/crypto"
	"github.com/afnexus/formsg-golang-sdk/webhooks"
)

const (
	// Set to true if you need to download and decrypt attachments from submissions
	has_attachments = true
)

// submissions is the handler for the /submissions endpoint.
func submissions(w http.ResponseWriter, r *http.Request) {
	// Set the Content-Type header to application/json
	w.Header().Set("Content-Type", "application/json")

	// Authenticate the request using the public key
	// Please comment the below codes if you are testing in localhost
	err := webhooks.Authenticate(r.Header.Get("X-FormSG-Signature"))
	if err != nil {
		http.Error(w, `{ "message": "Unauthorized" }`, http.StatusUnauthorized)
		return
	}

	var encryptedBody crypto.EncryptedBody
	// Decode the request body
	err = json.NewDecoder(r.Body).Decode(&encryptedBody)
	if err != nil {
		http.Error(w, `{ "message": "Invalid request" }`, http.StatusBadRequest)
		return
	}

	// Decrypt the submission content
	decryptedBody, err := crypto.Decrypt(encryptedBody)
	if err != nil {
		log.Println(err.Error())
		http.Error(w, `{ "message": "decryption fail"}`, http.StatusBadRequest)
		return
	}

	// save the decrypted submission to a file
	file, err := os.Create(fmt.Sprintf("./temp/%s.json", decryptedBody.Data.SubmissionID))
	if err != nil {
		http.Error(w, `{ "message": "file open fail"}`, http.StatusBadRequest)
		return
	}
	defer file.Close()

	err = json.NewEncoder(file).Encode(decryptedBody)
	if err != nil {
		http.Error(w, `{ "message": "file write fail"}`, http.StatusBadRequest)
		return
	}

	if has_attachments {
		for _, field := range decryptedBody.Data.DecryptedContent {
			if field.FieldType == "attachment" {
				if download_url, ok := encryptedBody.Data.AttachmentDownloadUrls[field.ID]; ok {
					decBytes, err := crypto.DownloadAttachment(download_url)
					if err != nil {
						log.Println(err.Error())
						http.Error(w, `{ "message": "download attachment fail"}`, http.StatusBadRequest)
						return
					}

					// save attachment to file
					file2, err := os.Create(fmt.Sprintf("./temp/%s.%s", field.ID, field.Answer))
					if err != nil {
						log.Panicln(err.Error())
						http.Error(w, `{ "message": "file open fail"}`, http.StatusBadRequest)
						return
					}
					defer file2.Close()

					_, err = file2.Write(decBytes)
					if err != nil {
						log.Panicln(err.Error())
						http.Error(w, `{ "message": "file write fail"}`, http.StatusBadRequest)
						return
					}
				}
			}
		}
	}

	w.Write([]byte("ok"))
}

func main() {
	if os.Getenv("FORM_PUBLIC_KEY") == "" {
		// set default public key
		os.Setenv("FORM_PUBLIC_KEY", "3Tt8VduXsjjd4IrpdCd7BAkdZl/vUCstu9UvTX84FWw=")
	}
	if os.Getenv("FORM_SECRET_KEY") == "" {
		// Your form's secret key downloaded from FormSG upon form creation
		os.Setenv("FORM_SECRET_KEY", "FORM_SECRET_KEY")
	}
	if os.Getenv("FORM_POST_URI") == "" {
		// This is where your domain is hosted, and should match
		// the URI supplied to FormSG in the form dashboard
		os.Setenv("FORM_POST_URI", "https://example.com/submissions")
	}

	// Create temp folder to house the content of the decrypted files from FormSG
	_, err := os.Stat("temp")

	if os.IsNotExist(err) {
		log.Println("Folder does not exist.")
		err := os.Mkdir("temp", 0755)
		if err != nil {
			log.Fatal(err)
		}
	} else {
		log.Println("Folder exist.")
	}
	
	http.Handle("/temp/", http.StripPrefix("/temp/", http.FileServer(http.Dir("./temp"))))
	http.HandleFunc("/submissions", submissions)
	http.ListenAndServe(":8080", nil)
}

Contributing

We welcome all contributions, bug reports, bug fixes, documentation improvements, enhancements, and ideas to improve the SDK. Please see our contributing guide.

License

Distributed under the GNU GPLv3 License. See LICENSE for more information.

Acknowledgements

Special thanks to the group of FormSG software engineers in Open Government Products who created the javascript version of the SDK.