From 3986ec7a412bb13ffd017bdd4ce6c2ef97c8b9db Mon Sep 17 00:00:00 2001
From: Ralph Slooten <axllent@gmail.com>
Date: Thu, 29 Aug 2024 17:14:49 +1200
Subject: [PATCH 1/2] feat: add option to disable character detection

Resolves #340
---
 options.go                           | 12 ++++++++++++
 parser.go                            |  1 +
 part.go                              |  3 ++-
 part_test.go                         | 23 +++++++++++++++++++++++
 testdata/parts/chardet-detection.raw |  8 ++++++++
 5 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 testdata/parts/chardet-detection.raw

diff --git a/options.go b/options.go
index b7e6fd2..8b3104a 100644
--- a/options.go
+++ b/options.go
@@ -100,3 +100,15 @@ func (o disableTextConversionOption) apply(p *Parser) {
 func DisableTextConversion(disableTextConversion bool) Option {
 	return disableTextConversionOption(disableTextConversion)
 }
+
+type disableCharacterDetectionOption bool
+
+func (o disableCharacterDetectionOption) apply(p *Parser) {
+	p.disableCharacterDetection = bool(o)
+}
+
+// DisableCharacterDetection sets the disableCharacterDetection option. When true, the parser will use the
+// defined character set if it is defined in the message part.
+func DisableCharacterDetection(disableCharacterDetection bool) Option {
+	return disableCharacterDetectionOption(disableCharacterDetection)
+}
diff --git a/parser.go b/parser.go
index 2ca6939..9e57124 100644
--- a/parser.go
+++ b/parser.go
@@ -27,6 +27,7 @@ type Parser struct {
 	customParseMediaType            CustomParseMediaType
 	stripMediaTypeInvalidCharacters bool
 	disableTextConversion           bool
+	disableCharacterDetection       bool
 }
 
 // defaultParser is a Parser with default configuration.
diff --git a/part.go b/part.go
index 5aa9e37..579f015 100644
--- a/part.go
+++ b/part.go
@@ -210,7 +210,8 @@ func (p *Part) convertFromDetectedCharset(r io.Reader, readPartErrorPolicy ReadP
 	// Restore r.
 	r = bytes.NewReader(buf)
 
-	if cs == nil || cs.Confidence < minCharsetConfidence || len(bytes.Runes(buf)) < minCharsetRuneLength {
+	if (p.parser.disableCharacterDetection && p.Charset != "") ||
+		(cs == nil || cs.Confidence < minCharsetConfidence || len(bytes.Runes(buf)) < minCharsetRuneLength) {
 		// Low confidence or not enough characters, use declared character set.
 		return p.convertFromStatedCharset(r), nil
 	}
diff --git a/part_test.go b/part_test.go
index 8a7774e..a098e50 100644
--- a/part_test.go
+++ b/part_test.go
@@ -1318,3 +1318,26 @@ func TestCtypeInvalidCharacters(t *testing.T) {
 
 	test.ComparePart(t, p, wantp)
 }
+
+func TestDisableCharacterDetectionPart(t *testing.T) {
+	var wantp *enmime.Part
+	r := test.OpenTestData("parts", "chardet-detection.raw")
+	parser := enmime.NewParser(enmime.DisableCharacterDetection(true))
+	p, err := parser.ReadParts(r)
+
+	// Examine root
+	if err != nil {
+		t.Fatalf("Unexpected parse error: %+v", err)
+	}
+	if p == nil {
+		t.Fatal("Root node should not be nil")
+	}
+
+	wantp = &enmime.Part{
+		ContentType: "text/plain",
+		PartID:      "0",
+		Charset:     "utf-8",
+	}
+
+	test.ComparePart(t, p, wantp)
+}
diff --git a/testdata/parts/chardet-detection.raw b/testdata/parts/chardet-detection.raw
new file mode 100644
index 0000000..351d9af
--- /dev/null
+++ b/testdata/parts/chardet-detection.raw
@@ -0,0 +1,8 @@
+Content-Type: text/plain; charset=utf-8
+Content-Transfer-Encoding: quoted-printable
+
+Loggen Sie sich ein, um die Einladung zu akzeptieren oder geben Sie den fol=
+gen1233
+
+Nachricht:
+=C3=B6o=C3=B6o

From fc26e5e2e31836ab3e0de10cea288a8d59abda85 Mon Sep 17 00:00:00 2001
From: James Hillyerd <james@hillyerd.com>
Date: Sat, 31 Aug 2024 12:23:13 -0700
Subject: [PATCH 2/2] add test comment

Signed-off-by: James Hillyerd <james@hillyerd.com>
---
 part_test.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/part_test.go b/part_test.go
index a098e50..4be0d59 100644
--- a/part_test.go
+++ b/part_test.go
@@ -1321,6 +1321,8 @@ func TestCtypeInvalidCharacters(t *testing.T) {
 
 func TestDisableCharacterDetectionPart(t *testing.T) {
 	var wantp *enmime.Part
+
+	// chardet considers this test file to be ISO-8859-1.
 	r := test.OpenTestData("parts", "chardet-detection.raw")
 	parser := enmime.NewParser(enmime.DisableCharacterDetection(true))
 	p, err := parser.ReadParts(r)