Fix fallback for unsupported encodings

go.mod

@@ -1,8 +1,8 @@
 module github.com/on2itsecurity/parsemail
 
-go 1.12
+go 1.21
 
 require (
-	golang.org/x/net v0.0.0-20200927032502-5d4f70055728
-	golang.org/x/text v0.3.0
+	golang.org/x/net v0.15.0
+	golang.org/x/text v0.13.0
 )

go.sum

@@ -3,8 +3,12 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20200927032502-5d4f70055728 h1:5wtQIAulKU5AbLQOkjxl32UufnIOqgBX72pS0AV14H0=
 golang.org/x/net v0.0.0-20200927032502-5d4f70055728/go.mod h1:/O7V0waA8r7cgGh81Ro3o1hOxt32SMVPicZroKQ2sZA=
+golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
+golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.13.0 h1:ablQoSUd0tRdKxZewP80B+BaqeKJuVhuRxj/dkrun3k=
+golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=

parsemail.go

@@ -335,6 +335,8 @@ func decodeMimeSentence(s string) string {
 	ss := strings.Split(s, " ")
 
 	for _, word := range ss {
+		word = removeUnsupportedEncoding(word)
+
 		w, err := mimeWordDecoder.Decode(word)
 		if err != nil {
 			if len(result) == 0 {
@@ -350,6 +352,100 @@ func decodeMimeSentence(s string) string {
 	return strings.Join(result, "")
 }
 
+func removeUnsupportedEncodingForAddress(s string) string {
+	if s == "" {
+		return s
+	}
+
+	ss := strings.Split(s, " ")
+	result := []string{}
+
+	for _, word := range ss {
+		validWord := word
+
+		if !(strings.HasPrefix(word, "=?") && strings.HasSuffix(word, "?=")) {
+			result = append(result, validWord)
+
+			continue
+		}
+
+		word = word[2 : len(word)-2]
+
+		// split word "UTF-8?q?text" into "UTF-8", 'q', and "text"
+		charset, text, _ := strings.Cut(word, "?")
+		if charset == "" {
+			validWord = `"(removed text: non supported charset)"`
+		}
+
+		encoding, _, _ := strings.Cut(text, "?")
+		if len(encoding) != 1 {
+			validWord = `"(removed text: non supported encoding)"`
+		}
+
+		if charset != "" {
+			encoder, _ := ianaindex.MIME.Encoding(charset)
+
+			if encoder == nil {
+				validWord = `"(removed text: non supported encoder)"`
+			}
+		}
+
+		result = append(result, validWord)
+	}
+
+	return strings.Join(result, " ")
+}
+
+func removeUnsupportedEncodingForAddressList(s string) string {
+	if s == "" {
+		return s
+	}
+
+	addresses := s
+	result := []string{}
+
+	for _, address := range strings.Split(addresses, ",") {
+		result = append(result, removeUnsupportedEncodingForAddress(address))
+	}
+
+	return strings.Join(result, ",")
+}
+
+func removeUnsupportedEncoding(s string) string {
+	if s == "" {
+		return s
+	}
+
+	word := s
+
+	if !(strings.HasPrefix(word, "=?") && strings.HasSuffix(word, "?=")) {
+		return word
+	}
+
+	word = word[2 : len(word)-2]
+
+	// split word "UTF-8?q?text" into "UTF-8", 'q', and "text"
+	charset, text, _ := strings.Cut(word, "?")
+	if charset == "" {
+		return "(removed text: non supported charset)"
+	}
+
+	encoding, _, _ := strings.Cut(text, "?")
+	if len(encoding) != 1 {
+		return "(removed text: non supported encoding)"
+	}
+
+	if charset != "" {
+		encoder, _ := ianaindex.MIME.Encoding(charset)
+
+		if encoder == nil {
+			return "(removed text: non supported encoder)"
+		}
+	}
+
+	return s
+}
+
 func decodeHeaderMime(header mail.Header) (mail.Header, error) {
 	parsedHeader := map[string][]string{}
 
@@ -503,9 +599,15 @@ var mimeWordDecoder = &mime.WordDecoder{
 		if err != nil {
 			return nil, err
 		}
+
+		if enc == nil {
+			return nil, fmt.Errorf("invalid encoding for charset %s", charset)
+		}
+
 		return transform.NewReader(input, enc.NewDecoder()), nil
 	},
 }
+
 var addressParser = mail.AddressParser{
 	WordDecoder: mimeWordDecoder,
 }
@@ -516,7 +618,7 @@ func (hp headerParser) parseAddress(s string) (ma *mail.Address) {
 	}
 
 	if strings.Trim(s, " \n") != "" {
-		ma, hp.err = addressParser.Parse(s)
+		ma, hp.err = addressParser.Parse(removeUnsupportedEncodingForAddress(s))
 
 		return ma
 	}
@@ -530,7 +632,7 @@ func (hp headerParser) parseAddressList(s string) (ma []*mail.Address) {
 	}
 
 	if strings.Trim(s, " \n") != "" {
-		ma, hp.err = addressParser.ParseList(s)
+		ma, hp.err = addressParser.ParseList(removeUnsupportedEncodingForAddressList(s))
 		return
 	}
 

parsemail_on2it_test.go

@@ -63,6 +63,20 @@ func Test_decodeMimeSentence(t *testing.T) {
 			},
 			`John Do€`,
 		},
+		{
+			"utf-7",
+			args{
+				`=?utf-7?B?Sm9obiBEbytJS3ct?=`,
+			},
+			`(removed text: non supported encoder)`,
+		},
+		{
+			"gb2312",
+			args{
+				`=?gb2312?B?Sm9obiBEb2U=?=`,
+			},
+			`(removed text: non supported encoder)`,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -141,6 +155,26 @@ func Test_headerParser_parseAddress(t *testing.T) {
 				Address: `john.doe@example.com`,
 			},
 		},
+		{
+			"utf-7",
+			args{
+				`=?utf-7?B?Sm9obiBEbytJS3ct?= <john.doe@example.com>`,
+			},
+			&mail.Address{
+				Name:    `(removed text: non supported encoder)`,
+				Address: `john.doe@example.com`,
+			},
+		},
+		{
+			"gb2312",
+			args{
+				`=?gb2312?B?Sm9obiBEb2U=?= <john.doe@example.com>`,
+			},
+			&mail.Address{
+				Name:    `(removed text: non supported encoder)`,
+				Address: `john.doe@example.com`,
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -232,6 +266,49 @@ func Test_headerParser_parseAddressList(t *testing.T) {
 				},
 			},
 		},
+		{
+			"utf-7",
+			args{
+				`=?utf-7?B?Sm9obiBEbytJS3ct?= <john.doe@example.com>`,
+			},
+			[]*mail.Address{
+				{
+					Name:    `(removed text: non supported encoder)`,
+					Address: `john.doe@example.com`,
+				},
+			},
+		},
+		{
+			"gb2312",
+			args{
+				`=?gb2312?B?Sm9obiBEb2U=?= <john.doe@example.com>`,
+			},
+			[]*mail.Address{
+				{
+					Name:    `(removed text: non supported encoder)`,
+					Address: `john.doe@example.com`,
+				},
+			},
+		},
+		{
+			"multiple_charsets with unsupported encoders",
+			args{
+				`test@example.com,=?utf-8?Q?John_D=C3=B8e?= <john.doe@example.com>,=?gb2312?B?Sm9obiBEb2U=?= <john.doe@example.com>`,
+			},
+			[]*mail.Address{
+				{
+					Address: `test@example.com`,
+				},
+				{
+					Name:    `John Døe`,
+					Address: `john.doe@example.com`,
+				},
+				{
+					Name:    `(removed text: non supported encoder)`,
+					Address: `john.doe@example.com`,
+				},
+			},
+		},
 		{
 			"multiple_charsets",
 			args{