Add image sending

receiving.go

@@ -56,5 +56,5 @@ type Attachment struct {
 // Payload is the information on where an attachment is.
 type Payload struct {
 	// URL is where the attachment resides on the internet.
-	URL string `json:"url"`
+	URL string `json:"url,omitempty"`
 }

response.go

@@ -3,6 +3,11 @@ package messenger
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
+	"image"
+	"image/jpeg"
+	"io"
+	"mime/multipart"
 	"net/http"
 )
 
@@ -47,6 +52,51 @@ func (r *Response) Text(message string) error {
 	return err
 }
 
+// Image sends an image.
+func (r *Response) Image(im image.Image) error {
+	var b bytes.Buffer
+	w := multipart.NewWriter(&b)
+
+	data, err := w.CreateFormFile("fielddata", "meme.jpg")
+	if err != nil {
+		return err
+	}
+
+	imageBytes := new(bytes.Buffer)
+	err = jpeg.Encode(imageBytes, im, nil)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(data, imageBytes)
+	if err != nil {
+		return err
+	}
+
+	w.WriteField("recipient", fmt.Sprintf(`{"id":"%v"}`, r.to.ID))
+	w.WriteField("message", `{"attachment":{"type":"image", "payload":{}}}`)
+
+	req, err := http.NewRequest("POST", SendMessageURL, &b)
+	if err != nil {
+		return err
+	}
+
+	req.URL.RawQuery = "access_token=" + r.token
+
+	req.Header.Set("Content-Type", w.FormDataContentType())
+
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+
+	var res bytes.Buffer
+	res.ReadFrom(resp.Body)
+	fmt.Println(res.String(), "DONE!")
+	return nil
+}
+
 // SendMessage is the information sent in an API request to Facebook.
 type SendMessage struct {
 	Recipient Recipient   `json:"recipient"`