Implementation which does not depend on successive function calls (#121)

* Refactor rfc2047AttributeName to handle n-number of occurrences and appropriately manage quoting the final parameter value

* Check for missing token after slash, apply defaults if true

header.go

@@ -20,11 +20,13 @@ const (
 	cdInline     = "inline"
 
 	// Standard MIME content types
+	ctAppPrefix        = "application/"
 	ctAppOctetStream   = "application/octet-stream"
 	ctMultipartAltern  = "multipart/alternative"
 	ctMultipartMixed   = "multipart/mixed"
 	ctMultipartPrefix  = "multipart/"
 	ctMultipartRelated = "multipart/related"
+	ctTextPrefix       = "text/"
 	ctTextPlain        = "text/plain"
 	ctTextHTML         = "text/html"
 
@@ -269,6 +271,20 @@ func fixMangledMediaType(mtype, sep string) string {
 				// The content type is completely missing. Put in a placeholder.
 				p = ctPlaceholder
 			}
+			// Check for missing token after slash
+			if strings.HasSuffix(p, "/") {
+				switch p {
+				case ctTextPrefix:
+					p = ctTextPlain
+				case ctAppPrefix:
+					p = ctAppOctetStream
+				case ctMultipartPrefix:
+					p = ctMultipartMixed
+				default:
+					// Safe default
+					p = ctAppOctetStream
+				}
+			}
 		default:
 			if !strings.Contains(p, "=") {
 				p = p + "=" + pvPlaceholder
@@ -277,8 +293,8 @@ func fixMangledMediaType(mtype, sep string) string {
 			// RFC-2047 encoded attribute name
 			p = rfc2047AttributeName(p)
 
-			pair := strings.Split(p, "=")
-			if strings.Contains(mtype, pair[0]+"=") {
+			pair := strings.SplitAfter(p, "=")
+			if strings.Contains(mtype, pair[0]) {
 				// Ignore repeated parameters.
 				continue
 			}
@@ -505,20 +521,51 @@ func whiteSpaceRune(r rune) bool {
 // rfc2047AttributeName checks if the attribute name is encoded in RFC2047 format
 // RFC2047 Example:
 //     `=?UTF-8?B?bmFtZT0iw7DCn8KUwoo=?=`
-func rfc2047AttributeName(s string) string {
-	if !strings.Contains(s, "?=") {
-		return s
+func rfc2047AttributeName(name string) string {
+	if !strings.Contains(name, "?=") {
+		return name
 	}
-	pair := strings.SplitAfter(s, "?=")
-	// lets assume that the attribute was encoded because of unicode characters being present
-	// then the attribute value should be quoted
-	keyValuePair := strings.SplitAfter(decodeHeader(pair[0]), "=")
-	// only quote the parameter value if it isn't already quoted
-	if len(keyValuePair) > 1 {
-		if !strings.HasPrefix(keyValuePair[1], "\"") {
-			keyValuePair[1] = fmt.Sprintf("\"%s", keyValuePair[1])
+	// copy the string so we can return the original if we encounter any issues
+	s := name
+
+	// handle n-number of RFC2047 chunk occurrences
+	count := strings.Count(name, "?=")
+	result := &strings.Builder{}
+	var beginning, ending int
+	for i := 0; i < count; i++ {
+		beginning = strings.Index(s, "=?")
+		ending = strings.Index(s, "?=")
+
+		if beginning == -1 || ending == -1 {
+			// the RFC2047 chunk is either malformed or is not an RFC2047 chunk
+			return name
+		}
+
+		_, err := result.WriteString(s[:beginning])
+		if err != nil {
+			return name
+		}
+		_, err = result.WriteString(decodeHeader(s[beginning : ending+2]))
+		if err != nil {
+			return name
 		}
+
+		s = s[ending+2:]
+	}
+	_, err := result.WriteString(s)
+	if err != nil {
+		return name
+	}
+	keyValuePair := strings.SplitAfter(result.String(), "=")
+	if len(keyValuePair) < 2 {
+		return result.String()
+	}
+	// Add quotes as needed
+	if !strings.HasPrefix(keyValuePair[1], "\"") {
+		keyValuePair[1] = fmt.Sprintf("\"%s", keyValuePair[1])
+	}
+	if !strings.HasSuffix(keyValuePair[1], "\"") {
+		keyValuePair[1] = fmt.Sprintf("%s\"", keyValuePair[1])
 	}
-	pair[0] = strings.Join(keyValuePair, "")
-	return strings.Join(pair, "")
+	return strings.Join(keyValuePair, "")
 }

header_test.go

@@ -182,7 +182,12 @@ func TestFixMangledMediaType(t *testing.T) {
 		{
 			input: "application/octet-stream;=?UTF-8?B?bmFtZT0iw7DCn8KUwoo=?=You've got a new voice miss call.msg",
 			sep:   ";",
-			want:  "application/octet-stream;name=\"ð\u009f\u0094\u008aYou've got a new voice miss call.msg",
+			want:  "application/octet-stream;name=\"ð\u009f\u0094\u008aYou've got a new voice miss call.msg\"",
+		},
+		{
+			input: "application/; name=\"Voice message from =?UTF-8?B?4piOICsxIDI1MS0yNDUtODA0NC5tc2c=?=\";",
+			sep:   ";",
+			want:  "application/octet-stream; name=\"Voice message from ☎ +1 251-245-8044.msg\"",
 		},
 		{
 			input: "application/pdf name=\"file.pdf\"",
@@ -197,7 +202,7 @@ func TestFixMangledMediaType(t *testing.T) {
 		{
 			input: "application/octet-stream; =?UTF-8?B?bmFtZT3DsMKfwpTCii5tc2c=?=",
 			sep:   " ",
-			want:  "application/octet-stream;name=\"🔊.msg",
+			want:  "application/octet-stream;name=\"🔊.msg\"",
 		},
 		{
 			input: "one/two name=\"file.two\" name=\"file.two\"",