From a2108dded185176bc5ec16c8c0420e8bd2555ecc Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Mon, 20 Nov 2023 12:58:24 +0100
Subject: [PATCH] dkim: fix headerPicker.Pick with non-canonical header keys

Closes: https://github.com/emersion/go-msgauth/issues/58
---
 dkim/header.go      |  2 ++
 dkim/header_test.go | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/dkim/header.go b/dkim/header.go
index 39a2628..14c0729 100644
--- a/dkim/header.go
+++ b/dkim/header.go
@@ -149,6 +149,8 @@ func newHeaderPicker(h header) *headerPicker {
 }
 
 func (p *headerPicker) Pick(key string) string {
+	key = strings.ToLower(key)
+
 	at := p.picked[key]
 	for i := len(p.h) - 1; i >= 0; i-- {
 		kv := p.h[i]
diff --git a/dkim/header_test.go b/dkim/header_test.go
index 16379b5..5cc0aaf 100644
--- a/dkim/header_test.go
+++ b/dkim/header_test.go
@@ -133,7 +133,18 @@ func TestHeaderPicker_Pick(t *testing.T) {
 				t.Errorf("Parameter %s not found in headers %s", k, headers)
 			}
 		}
-
+	})
+	t.Run("non-canonical header fields", func(t *testing.T) {
+		headers := header{
+			"Message-ID: asdf",
+		}
+		picker := newHeaderPicker(headers)
+		if v := picker.Pick("Message-Id"); v != headers[0] {
+			t.Errorf("Pick() = %q, want %q", v, headers[0])
+		}
+		if v := picker.Pick("Message-ID"); v != "" {
+			t.Errorf("Pick() = %q, want %q", v, "")
+		}
 	})
 }