fix: Fixing email sending broken when attempting to send emails from different goroutines due to a data race

[andrew-pavlov-ua]

Fixes

When trying to send several emails at the same time, the emails are not sent because the client uses a shared built-in field rest.Request, which is overwritten by different goroutines.

// Client is the Twilio SendGrid Go client
type Client struct {
	rest.Request
}

// SendWithContext sends an email through Twilio SendGrid with context.Context
func (cl *Client) SendWithContext(ctx context.Context, email *mail.SGMailV3) (*rest.Response, error) {
	cl.Request.Body = mail.GetRequestBody(email)

	// ...
}

Here is a test I wrote to show this:

func Test_test_client_send_is_thread_safe(t *testing.T) {
	apiKey := "SENDGIRD_APIKEY"
	const numRequests = 5
	var wg sync.WaitGroup
	client := NewSendClient(apiKey)

	// Launch multiple goroutines to send concurrent requests
	for i := 0; i < numRequests; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			from := &mail.Email{
				Name:    "Name",
				Address: "[email protected]",
			}

			to := &mail.Email{
				Name:    "Recipient",
				Address: "[email protected]",
			}

			email := &mail.SGMailV3{
				From: from,
				Personalizations: []*mail.Personalization{
					{
						To:      []*mail.Email{to},
						Subject: "Subject",
					},
				},
				Content: []*mail.Content{
					{
						Type:  "text/plain",
						Value: "Value",
					},
				},
			}

			client.Send(email)
		}(i)
	}
	wg.Wait()
}

Started the test using the following command:

go test ./... -v -run=Test_test_client_send_is_thread_safe -race

Here is the console output after running the test before applying my fixes:

testing.go:1399: race detected during execution of test
--- FAIL: Test_test_client_send_is_thread_safe (0.83s)

After my fixes, the test passes, emails are successfully sent, and the client is now thread-safe.

I replaced the embedded Request in Client with two private fields: apiKey and emailOptions. When creating a client, either apiKey or Username and Password are required.

New Implementation:

// Client is the Twilio SendGrid Go client
type Client struct {
	apiKey       string
	emailOptions TwilioEmailOptions
}

I also created the SendWithHeaders method to support additional headers (used in testing). Additionally, I refactored the client creation methods (NewSendClient and NewTwilioEmailSendClient) accordingly.

NewApiKeySendClient:

// NewSendClient constructs a new Twilio SendGrid client given an API key
func NewSendClient(key string) *Client {
	return &Client{apiKey: key}
}

NewEmailSendClient:

// NewTwilioEmailSendClient constructs a new Twilio Email client given a username and password
func NewTwilioEmailSendClient(username, password string) *Client {
	emailOptions := &TwilioEmailOptions{Username: username, Password: password, Endpoint: "/v3/mail/send"}
	return &Client{emailOptions: *emailOptions}
}

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

[YaroslavPodorvanov]

This PR will fix #474