lib/email: unexport the field ContentType in the field

The field ContentType will be set only when the field Name is
"Content-Type" so it's not always exist on each field.
To get the field ContentType, use Header.ContentType().

4 files changed, 15 insertions, 16 deletions

diff --git a/lib/email/doc.go b/lib/email/doc.go
index 934ea877..802b58a1 100644
--- a/lib/email/doc.go
+++ b/lib/email/doc.go
@@ -23,13 +23,13 @@
 //
 // A [Header] contains one or more [Field],
 //
-//	+-------------+---------------------+
-//	| Field                             |
-//	+-------------+------+-------+------+
-//	| ContentType | Name | Value | Type |
-//	+-------------+------+-------+------+
+//	+---------------------+
+//	| Field               |
+//	+------+-------+------+
+//	| Name | Value | Type |
+//	+------+-------+------+
 //
-// [Field] is parsed line that contains key and value separated by ": ".
+// [Field] is parsed line that contains Name and Value separated by ": ".
 //
 // A [ContentType] is special Field where Name is "Content-Type", and its
 // Value is parsed from string "top/sub; <param>; ...".
diff --git a/lib/email/field.go b/lib/email/field.go
index 8d757b52..cbd25530 100644
--- a/lib/email/field.go
+++ b/lib/email/field.go
@@ -17,9 +17,9 @@ import (
 
 // Field represent field name and value in header.
 type Field struct {
-	// ContentType contains unpacked value of field with Name
+	// contentType contains unpacked value of field with Name
 	// "Content-Type" or nil if still packed.
-	ContentType *ContentType
+	contentType *ContentType
 
 	date   *time.Time
 	mboxes []*Mailbox
@@ -508,12 +508,11 @@ func (field *Field) unpackContentType() (err error) {
 		return nil
 	}
 
-	ContentType, err := ParseContentType(field.Value)
+	field.contentType, err = ParseContentType(field.Value)
 	if err != nil {
 		return err
 	}
 
-	field.ContentType = ContentType
 	field.unpacked = true
 
 	return nil
diff --git a/lib/email/field_test.go b/lib/email/field_test.go
index ca0a898c..672cf181 100644
--- a/lib/email/field_test.go
+++ b/lib/email/field_test.go
@@ -333,7 +333,7 @@ func TestUnpackMailboxList(t *testing.T) {
 	}
 }
 
-func TestUnpackContentType(t *testing.T) {
+func TestField_unpackContentType(t *testing.T) {
 	cases := []struct {
 		expErr string
 		exp    string
@@ -361,7 +361,7 @@ func TestUnpackContentType(t *testing.T) {
 			continue
 		}
 
-		test.Assert(t, "Content-Type", c.exp, field.ContentType.String())
+		test.Assert(t, "Content-Type", c.exp, field.contentType.String())
 		test.Assert(t, "field.unpacked", true, field.unpacked)
 
 		err = field.unpack()
@@ -370,7 +370,7 @@ func TestUnpackContentType(t *testing.T) {
 			continue
 		}
 
-		test.Assert(t, "Content-Type", c.exp, field.ContentType.String())
+		test.Assert(t, "Content-Type", c.exp, field.contentType.String())
 		test.Assert(t, "field.unpacked", true, field.unpacked)
 	}
 }
diff --git a/lib/email/header.go b/lib/email/header.go
index 492ecebd..a8d6565a 100644
--- a/lib/email/header.go
+++ b/lib/email/header.go
@@ -108,14 +108,14 @@ func (hdr *Header) ContentType() *ContentType {
 		if f.Type != FieldTypeContentType {
 			continue
 		}
-		if f.ContentType == nil {
+		if f.contentType == nil {
 			err := f.unpack()
 			if err != nil {
 				log.Println("ContentType: ", err)
 				return nil
 			}
 		}
-		return f.ContentType
+		return f.contentType
 	}
 	return nil
 }
@@ -265,7 +265,7 @@ func (hdr *Header) WriteTo(w io.Writer) (n int, err error) {
 	)
 	for _, f = range hdr.fields {
 		if f.Type == FieldTypeContentType {
-			m, err = fmt.Fprintf(w, "%s: %s\r\n", f.Name, f.ContentType.String())
+			m, err = fmt.Fprintf(w, "%s: %s\r\n", f.Name, f.contentType.String())
 		} else if f.Type == FieldTypeMessageID {
 			m, err = fmt.Fprintf(w, "%s: <%s>\r\n", f.Name, f.oriValue)
 		} else {