parse msg-id lists more liberally

Some user agents deliberately generate non-standard
message identifier lists in In-Reply-To and References headers.

Instead of failing silently, aerc now falls back to a desperate parser
scavaging whatever looking like <id-left@id-right>.

As the more liberal parser being substituted with, References header
are now stored for IMAP not only when there's a parsing error.

Fixes: 31d2f5be3cec ("message-info: add explicit References field")
Signed-off-by: Nguyễn Gia Phong <mcsinyx@disroot.org>
Acked-by: Robin Jarry <robin@jarry.cc>

1 files changed, 42 insertions, 0 deletions

diff --git a/lib/parse/header.go b/lib/parse/header.go
new file mode 100644
index 00000000..361b3af0
--- /dev/null
+++ b/lib/parse/header.go
@@ -0,0 +1,42 @@
+package parse
+
+import (
+	"strings"
+
+	"git.sr.ht/~rjarry/aerc/log"
+	"github.com/emersion/go-message/mail"
+)
+
+// MsgIDList parses a list of message identifiers.  It returns message
+// identifiers without angle brackets.  If the header field is missing,
+// it returns nil.
+//
+// This can be used on In-Reply-To and References header fields.
+// If the field does not conform to RFC 5322, fall back
+// to greedily parsing a subsequence of the original field.
+func MsgIDList(h *mail.Header, key string) []string {
+	l, err := h.MsgIDList(key)
+	if err == nil {
+		return l
+	}
+	log.Errorf("%s: %s", err, h.Get(key))
+
+	// Expensive, fix your peer's MUA instead!
+	var list []string
+	header := &mail.Header{Header: h.Header.Copy()}
+	value := header.Get(key)
+	for err != nil && len(value) > 0 {
+		// Skip parsed IDs
+		if len(l) > 0 {
+			last := "<" + l[len(l)-1] + ">"
+			value = value[strings.Index(value, last)+len(last):]
+			list = append(list, l...)
+		}
+
+		// Skip a character until some IDs can be parsed
+		value = value[1:]
+		header.Set(key, value)
+		l, err = header.MsgIDList(key)
+	}
+	return append(list, l...)
+}