core: Add functions to sanitize nicknames and messages

core/contactlist.go

@@ -84,12 +84,16 @@ func (this *ContactList) AddContactRequest(address, name, fromName, text string)
 	if !IsAddressValid(address) {
 		return nil, errors.New("Invalid ricochet address")
 	}
+	if len(fromName) > 0 && !IsNicknameAcceptable(fromName) {
+		return nil, errors.New("Invalid nickname")
+	}
+	if len(text) > 0 && !IsMessageAcceptable(text) {
+		return nil, errors.New("Invalid message")
+	}
 
 	this.mutex.Lock()
 	defer this.mutex.Unlock()
 
-	// XXX validity checks on name/text also useful
-
 	for _, contact := range this.contacts {
 		if contact.Address() == address {
 			return nil, errors.New("Contact already exists with this address")

core/sanitize.go

@@ -0,0 +1,56 @@
+package core
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// IsNicknameAcceptable returns true for strings that are usable as contact nicknames.
+// A nickname is acceptable if it:
+//   - Is composed of only valid UTF-8 sequences
+//   - Has between 1 and MaxNicknameLength unicode characters
+//   - Doesn't contain any characters from unicode Cf or Cc
+//   - Doesn't contain any of these HTML-sensitive characters: "<>&\
+//   - XXX This could use more thought on valid codepoints; note that Go
+//     has a good set of built-in range tables in `unicode`
+func IsNicknameAcceptable(nickname string) bool {
+	length := 0
+
+	blacklist := []rune{'"', '<', '>', '&', '\\'}
+
+	for len(nickname) > 0 {
+		r, sz := utf8.DecodeRuneInString(nickname)
+		if r == utf8.RuneError {
+			return false
+		}
+
+		if unicode.In(r, unicode.Cf, unicode.Cc) {
+			return false
+		}
+
+		for _, br := range blacklist {
+			if r == br {
+				return false
+			}
+		}
+
+		length++
+		if length > MaxNicknameLength {
+			return false
+		}
+		nickname = nickname[sz:]
+	}
+
+	return length > 0
+}
+
+// IsMessageAcceptable returns true for strings that are usable as chat messages.
+// A message is acceptable if it:
+//   - Is composed of only valid UTF-8 sequences
+//   - Encodes to between 1 and MaxMessageLength bytes in UTF-8
+//   - XXX This also needs more thought on valid unicode characters
+func IsMessageAcceptable(message string) bool {
+	return len(message) > 0 &&
+		len(message) <= MaxMessageLength &&
+		utf8.ValidString(message)
+}