MM-48089 Fix relative email urls

utils/markdown.go

@@ -36,10 +36,17 @@ func StripMarkdown(markdown string) (string, error) {
 }
 
 // MarkdownToHTML takes a string containing Markdown and returns a string with HTML tagged version
-func MarkdownToHTML(markdown string) (string, error) {
+func MarkdownToHTML(markdown, siteURL string) (string, error) {
+	// Turn relative links into absolute links
+	relLinkRe := regexp.MustCompile(`\[(.*)]\((/.*)\)`)
+	absLinkMarkdown := relLinkRe.ReplaceAllFunc([]byte(markdown), func(s []byte) []byte {
+		out := relLinkRe.ReplaceAllString(string(s), "[$1]("+siteURL+"$2)")
+		return []byte(out)
+	})
+
 	// Unescape any blockquote text to be parsed by the markdown parser.
 	re := regexp.MustCompile(`^|\n(>)`)
-	markdownClean := re.ReplaceAllFunc([]byte(markdown), func(s []byte) []byte {
+	markdownClean := re.ReplaceAllFunc([]byte(absLinkMarkdown), func(s []byte) []byte {
 		out := html.UnescapeString(string(s))
 		return []byte(out)
 	})

utils/markdown_test.go

@@ -280,3 +280,37 @@ func TestStripMarkdown(t *testing.T) {
 		})
 	}
 }
+
+func TestMarkdownToHTML(t *testing.T) {
+	siteURL := "https://example.com"
+	tests := []struct {
+		name     string
+		markdown string
+		want     string
+	}{
+		{
+			name:     "absolute url not changed",
+			markdown: "[Link](https://example.com)",
+			want:     "<p><a href=\"https://example.com\">Link</a></p>\n",
+		},
+		{
+			name:     "relative url changed to absolute url",
+			markdown: "[Link](/foo)",
+			want:     "<p><a href=\"https://example.com/foo\">Link</a></p>\n",
+		},
+		{
+			name:     "relative url with query params changed to absolute url",
+			markdown: "[Link](/foo?bar=true)",
+			want:     "<p><a href=\"https://example.com/foo?bar=true\">Link</a></p>\n",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := MarkdownToHTML(tt.markdown, siteURL)
+			if err != nil {
+				t.Fatalf("error: %v", err)
+			}
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}