Add NewImageAttachment func

activitystreams/attachment.go

@@ -1,5 +1,10 @@
 package activitystreams
 
+import (
+	"mime"
+	"strings"
+)
+
 type Attachment struct {
 	Type      AttachmentType `json:"type"`
 	URL       string         `json:"url"`
@@ -10,3 +15,19 @@ type Attachment struct {
 type AttachmentType string
 
 const AttachImage AttachmentType = "Image"
+
+// NewImageAttachment creates a new Attachment from the given URL, setting the
+// correct type and automatically detecting the MediaType based on the file
+// extension.
+func NewImageAttachment(url string) *Attachment {
+	var imgType string
+	extIdx := strings.LastIndexByte(url, '.')
+	if extIdx > -1 {
+		imgType = mime.TypeByExtension(url[extIdx:])
+	}
+	return &Attachment{
+		Type:      AttachImage,
+		URL:       url,
+		MediaType: imgType,
+	}
+}