How to use SendGrid from Google App Engine Golang?

Question

The example code at: https://sendgrid.com/blog/send-email-go-google-app-engine/

My guess this is very old sample code to use sendgrid-go on Google App Engine.

I've attempted 4 permutations and failed each time with:

https://api.sendgrid.com/v3/mail/send: http.DefaultTransport and http.DefaultClient are not available in App Engine. See https://cloud.google.com/appengine/docs/go/urlfetch/

Here is a minimum hardcoded attempt with some logging:

package sendgridgo


import(
    "github.com/sendgrid/sendgrid-go"
    "fmt"
    _"google.golang.org/appengine"
    "net/http"
    "google.golang.org/appengine/log"
    "google.golang.org/appengine"
    "google.golang.org/appengine/urlfetch"
     _ "github.com/sendgrid/sendgrid-go/helpers/mail"
)

func init(){
    http.HandleFunc("/", IndexHandler)
    appengine.Main()
}

func IndexHandler (w http.ResponseWriter, r *http.Request){
    ctx := appengine.NewContext(r)

    log.Infof(ctx, "IndexHandler")
    sg := sendgrid.NewSendClient("SENDGRID_API_KEY")
    log.Infof(ctx, "%v", sg)
    bob := urlfetch.Client(ctx)

    log.Infof(ctx, "UrlFetchClient %v", bob)
    //resp, err := sg.Send(m)
    request := sendgrid.GetRequest("SENDGRID_API_KEY", "/v3/mail/send", "https://api.sendgrid.com")
    request.Method = "POST"

    request.Body = []byte(` {
    "personalizations": [
        {
            "to": [
                {
                    "email": "darian.hickman@gmail.com"
                }
            ],
            "subject": "Sending with SendGrid is Fun"
        }
    ],
    "from": {
        "email": "darian.hickman@villagethegame.com"
    },
    "content": [
        {
            "type": "text/plain",
            "value": "and easy to do anywhere, even with Go"
        }
    ]
}`)
    resp, err := sendgrid.API(request)

    if err != nil{
        log.Errorf(ctx, "Failed %v", err)
    }

    fmt.Fprint(w, resp)


}

Answer 1

After 8 different attempts, including trying an example published in Google Cloud docs for using Sendgrid, an example from Sendgrid blog, and trying to use deprecated versions of Sendgrid api, I found Sendgrid curl examples at:

https://sendgrid.com/docs/Classroom/Send/v3_Mail_Send/curl_examples.html

curl --request POST \
  --url https://api.sendgrid.com/v3/mail/send \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{"personalizations": [{"to": [{"email": "recipient@example.com"}]}],"from": {"email": "sendeexampexample@example.com"},"subject": "Hello, World!","content": [{"type": "text/plain", "value": "Heya!"}]}'

I then translated the HelloWorld example to into URLFetch usage

client := urlfetch.Client(ctx)

request, err := http.NewRequest("POST", "https://api.sendgrid.com/v3/mail/send", buf)
    if err != nil {
        log.Errorf(ctx, "Failed Request %v", request)
    }
    request.Header.Set("Authorization", "Bearer SENDGRID_API_KEY")
    request.Header.Set("Content-Type", "application/json")
    resp, err := client.Do(request)

One Easter weekend, later, it works!