worker: move shared code to lib

Avoid importing code from worker/lib into lib. It should only be the
other way around. Move the message parsing code used by maildir,
notmuch, mbox and the eml viewer into a lib/rfc822 package.

Adapt imports accordingly.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Reviewed-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Moritz Poldrack <moritz@poldrack.dev>
Tested-by: Inwit <inwit@sindominio.net>

1 files changed, 29 insertions, 0 deletions

diff --git a/worker/lib/headers.go b/worker/lib/headers.go
new file mode 100644
index 00000000..391d1d2a
--- /dev/null
+++ b/worker/lib/headers.go
@@ -0,0 +1,29 @@
+package lib
+
+import (
+	"strings"
+
+	"github.com/emersion/go-message/mail"
+)
+
+// LimitHeaders returns a new Header with the specified headers included or
+// excluded
+func LimitHeaders(hdr *mail.Header, fields []string, exclude bool) *mail.Header {
+	fieldMap := make(map[string]struct{}, len(fields))
+	for _, f := range fields {
+		fieldMap[strings.ToLower(f)] = struct{}{}
+	}
+	nh := &mail.Header{}
+	curFields := hdr.Fields()
+	for curFields.Next() {
+		key := strings.ToLower(curFields.Key())
+		_, present := fieldMap[key]
+		// XOR exclude and present. When they are equal, it means we
+		// should not add the header to the new header struct
+		if exclude == present {
+			continue
+		}
+		nh.Add(key, curFields.Value())
+	}
+	return nh
+}