feat: don't auto detect charset when using raw content parser option (#…

…310)

* feat: don't auto detect charset when using raw content parser option
* tests: add comment on RawContent test cases

encode_test.go

@@ -365,8 +365,9 @@ func TestEncodePartContentNonAsciiText(t *testing.T) {
 	}
 }
 
-func TestParseRawContentOptionTrue(t *testing.T) {
-	r := test.OpenTestData("encode", "parser-raw-content-option.raw")
+// TestParseRawContentHTMLOptionTrue tests the RawContent Parser option with an HTML part only if the content isn't changed.
+func TestParseRawContentHTMLOptionTrue(t *testing.T) {
+	r := test.OpenTestData("encode", "parser-raw-content-html-option.raw")
 	p := enmime.NewParser(enmime.RawContent(true))
 	e, err := p.ReadEnvelope(r)
 	if err != nil {
@@ -376,11 +377,12 @@ func TestParseRawContentOptionTrue(t *testing.T) {
 	if err := e.Root.Encode(b); err != nil {
 		t.Fatal(err)
 	}
-	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-option-true.raw.golden")
+	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-html-option-true.raw.golden")
 }
 
-func TestParseRawContentOptionFalse(t *testing.T) {
-	r := test.OpenTestData("encode", "parser-raw-content-option.raw")
+// TestParseRawContentHTMLOptionFalse tests without the RawContent Parser option and an HTML part only if the content is normally parsed.
+func TestParseRawContentHTMLOptionFalse(t *testing.T) {
+	r := test.OpenTestData("encode", "parser-raw-content-html-option.raw")
 	p := enmime.NewParser()
 	e, err := p.ReadEnvelope(r)
 	if err != nil {
@@ -390,5 +392,36 @@ func TestParseRawContentOptionFalse(t *testing.T) {
 	if err := e.Root.Encode(b); err != nil {
 		t.Fatal(err)
 	}
-	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-option-false.raw.golden")
+	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-html-option-false.raw.golden")
+}
+
+// TestParseRawContentTextOptionTrue tests the RawContent Parser option with a TEXT part only if the content isn't changed.
+// This test uses Japanese characters to also ensure that the charset isn't altered.
+func TestParseRawContentTextOptionTrue(t *testing.T) {
+	r := test.OpenTestData("encode", "parser-raw-content-text-option.raw")
+	p := enmime.NewParser(enmime.RawContent(true))
+	e, err := p.ReadEnvelope(r)
+	if err != nil {
+		t.Fatal("Failed to parse MIME:", err)
+	}
+	b := &bytes.Buffer{}
+	if err := e.Root.Encode(b); err != nil {
+		t.Fatal(err)
+	}
+	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-text-option-true.raw.golden")
+}
+
+// TestParseRawContentTextOptionFalse tests without the RawContent Parser option and a TEXT part only if the content is normally parsed.
+func TestParseRawContentTextOptionFalse(t *testing.T) {
+	r := test.OpenTestData("encode", "parser-raw-content-text-option.raw")
+	p := enmime.NewParser()
+	e, err := p.ReadEnvelope(r)
+	if err != nil {
+		t.Fatal("Failed to parse MIME:", err)
+	}
+	b := &bytes.Buffer{}
+	if err := e.Root.Encode(b); err != nil {
+		t.Fatal(err)
+	}
+	test.DiffGolden(t, b.Bytes(), "testdata", "encode", "parser-raw-content-text-option-false.raw.golden")
 }

part.go

@@ -298,7 +298,7 @@ func (p *Part) decodeContent(r io.Reader, readPartErrorPolicy ReadPartErrorPolic
 			encoding)
 	}
 	// Build charset decoding reader.
-	if validEncoding && strings.HasPrefix(p.ContentType, "text/") {
+	if validEncoding && strings.HasPrefix(p.ContentType, "text/") && !p.parser.rawContent {
 		var err error
 		contentReader, err = p.convertFromDetectedCharset(contentReader, readPartErrorPolicy)
 		if err != nil {

testdata/encode/parser-raw-content-text-option-false.raw.golden

@@ -0,0 +1,8 @@
+Content-Transfer-Encoding: base64
+Content-Type: text/plain; charset=utf-8
+From: me@me.com
+Mime-Version: 1.0
+Subject: Test subject
+To: you@you.com
+
+Cgrmt7vku5jjg5XjgqHjgqTjg6vlkI3jg4bjgrnjg4gNCg==

testdata/encode/parser-raw-content-text-option-true.raw.golden

@@ -0,0 +1,9 @@
+Content-Transfer-Encoding: quoted-printable
+Content-Type: text/plain; charset=utf-8
+From: me@me.com
+Mime-Version: 1.0
+Subject: Test subject
+To: you@you.com
+
+=0A=0A=E6=B7=BB=E4=BB=98=E3=83=95=E3=82=A1=E3=
+=82=A4=E3=83=AB=E5=90=8D=E3=83=86=E3=82=B9=E3=83=88

testdata/encode/parser-raw-content-text-option.raw

@@ -0,0 +1,9 @@
+Content-Transfer-Encoding: quoted-printable
+Content-Type: text/plain; charset=utf-8
+From: me@me.com
+Mime-Version: 1.0
+Subject: Test subject
+To: you@you.com
+
+=0A=0A=E6=B7=BB=E4=BB=98=E3=83=95=E3=82=A1=E3=
+=82=A4=E3=83=AB=E5=90=8D=E3=83=86=E3=82=B9=E3=83=88