From 5596b578f46f0c48bdb2c143b807c79cae31bc6e Mon Sep 17 00:00:00 2001
From: Niko Abeler <niko@rerere.org>
Date: Tue, 6 Sep 2022 21:17:25 +0200
Subject: [PATCH] improved header parsing

---
 webmention.go      | 28 +++++++++++++++++++---------
 webmention_test.go | 17 +++++++++++++++++
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/webmention.go b/webmention.go
index c6992db..3602ffb 100644
--- a/webmention.go
+++ b/webmention.go
@@ -151,16 +151,26 @@ func (OwlHtmlParser) GetWebmentionEndpoint(resp *http.Response) (string, error)
 	requestUrl := resp.Request.URL
 
 	// Check link headers
-	for _, link := range resp.Header["Link"] {
-		if strings.Contains(link, "rel=\"webmention\"") || strings.Contains(link, "rel=webmention") {
-			link := strings.Split(link, ";")[0]
-			link = strings.Trim(link, "<>")
-			linkUrl, err := url.Parse(link)
-			if err != nil {
-				return "", err
+	for _, linkHeader := range resp.Header["Link"] {
+		linkHeaderParts := strings.Split(linkHeader, ",")
+		for _, linkHeaderPart := range linkHeaderParts {
+			linkHeaderPart = strings.TrimSpace(linkHeaderPart)
+			params := strings.Split(linkHeaderPart, ";")
+			if len(params) != 2 {
+				continue
+			}
+			for _, param := range params[1:] {
+				param = strings.TrimSpace(param)
+				if strings.Contains(param, "webmention") {
+					link := strings.Split(params[0], ";")[0]
+					link = strings.Trim(link, "<>")
+					linkUrl, err := url.Parse(link)
+					if err != nil {
+						return "", err
+					}
+					return requestUrl.ResolveReference(linkUrl).String(), nil
+				}
 			}
-			return requestUrl.ResolveReference(linkUrl).String(), nil
-
 		}
 	}
 
diff --git a/webmention_test.go b/webmention_test.go
index a96588e..4086ace 100644
--- a/webmention_test.go
+++ b/webmention_test.go
@@ -103,6 +103,23 @@ func TestGetWebmentionEndpointLinkHeader(t *testing.T) {
 	}
 }
 
+func TestGetWebmentionEndpointLinkHeaderCommas(t *testing.T) {
+	html := []byte("")
+	parser := &owl.OwlHtmlParser{}
+	resp := constructResponse(html)
+	resp.Header = http.Header{
+		"Link": []string{"<https://webmention.rocks/test/19/webmention/error>; rel=\"other\", <https://webmention.rocks/test/19/webmention>; rel=\"webmention\""},
+	}
+	endpoint, err := parser.GetWebmentionEndpoint(resp)
+
+	if err != nil {
+		t.Errorf("Unable to parse feed: %v", err)
+	}
+	if endpoint != "https://webmention.rocks/test/19/webmention" {
+		t.Errorf("Wrong endpoint. Expected %v, got %v", "https://webmention.rocks/test/19/webmention", endpoint)
+	}
+}
+
 func TestGetWebmentionEndpointRelativeLink(t *testing.T) {
 	html := []byte("<link rel=\"webmention\" href=\"/webmention\" />")
 	parser := &owl.OwlHtmlParser{}